mcpls-core 0.8.0

//! LSP server lifecycle management.
//!
//! This module handles the complete lifecycle of an LSP server:
//! 1. Spawn server process
//! 2. Initialize → initialized handshake
//! 3. Capability negotiation
//! 4. Active request handling
//! 5. Graceful shutdown sequence

use std::path::{Path, PathBuf};
use std::process::Stdio;
use std::sync::Arc;

use lsp_types::{
    ClientCapabilities, ClientInfo, DidChangeConfigurationNotification,
    DidChangeConfigurationParams, ExitNotification, GeneralClientCapabilities, InitializeParams,
    InitializeRequest, InitializeResult, InitializedNotification, InitializedParams,
    PositionEncodingKind, Request, ServerCapabilities, ShutdownRequest, StaleRequestSupportOptions,
    SymbolKind, WorkspaceFolder,
};
use tokio::process::Command;
use tokio::sync::mpsc;
use tokio::time::{Duration, Instant, timeout, timeout_at};
use tracing::{debug, info, warn};

use crate::bridge::{WorkspaceRoots, try_path_to_uri};
use crate::config::{LspServerConfig, LspSettings, PositionEncodings, ServerCommand};
use crate::error::{
    BackgroundTask, Error, InitFailureHint, InitPhase, Result, ServerSpawnFailure, StartupFailure,
    StdioStream, UntrustedRefusal,
};
use crate::lsp::client::{LspClient, SHUTDOWN_TIMEOUT};
#[cfg(unix)]
use crate::lsp::process::Binding;
use crate::lsp::process::{MarkOutcome, ServerProcess};
use crate::lsp::stderr::{EofWait, StderrCapture};
use crate::lsp::transport::LspTransport;
use crate::lsp::types::LspNotification;
use crate::lsp::vetting::UntrustedVetting;
use crate::lsp::{
    CONTENT_MODIFIED_RETRY_METHODS, ManagedEnvVar, NotificationInbox, NotificationSink, ParentEnv,
    process_env, tsserver_pin,
};
use crate::redaction::Redactions;

/// Environment variables passed through to a spawned LSP server even though
/// its environment is otherwise cleared.
///
/// `PATH` lets the server resolve its own toolchain (e.g. rustup shims, venv
/// binaries); `HOME`/`USERPROFILE` and `TMPDIR`/`TEMP`/`TMP` let it find user
/// config/cache and scratch directories.
///
/// This list is not exhaustive: session-specific values that cannot be
/// hardcoded into a static [`LspServerConfig::env`] table (e.g.
/// `SSH_AUTH_SOCK`, which changes every login session) have no way through
/// today. See [`LspServerConfig::env`] for the config-level override/addition
/// mechanism this list feeds into.
const ENV_PASSTHROUGH: &[&str] = &[
    ManagedEnvVar::Path.name(),
    ManagedEnvVar::Home.name(),
    ManagedEnvVar::UserProfile.name(),
    "TMPDIR",
    "TEMP",
    "TMP",
];

/// Upper bound [`LspServer::shutdown`] waits for the child process to exit on
/// its own after sending the LSP `exit` notification, before falling back to
/// killing its process tree. Only the leader is awaited here.
const CHILD_EXIT_GRACE: Duration = Duration::from_secs(3);

/// Least time the final process-tree sweep may take even when the shutdown
/// deadline is already spent, so a whole shutdown stays within
/// `SHUTDOWN_TIMEOUT` plus this.
const MIN_SWEEP_BUDGET: Duration = Duration::from_secs(3);

/// How long [`LspServer::terminate`] lets the leader process exit on its own
/// after the `shutdown` handshake, before the process tree is killed.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ExitGrace {
    /// Up to the rest of the handshake budget, at most [`CHILD_EXIT_GRACE`]
    /// (normal shutdown).
    WithinBudget,
    /// A server that answered `shutdown` may take this long to exit, since a
    /// healthy server can be slow to flush; one that did not answer is killed
    /// at once.
    IfAnswered(Duration),
}

/// Whether the LSP `exit` notification reached the server on shutdown.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum ExitNotice {
    /// The `shutdown` handshake completed and `exit` was sent.
    Sent,
    /// The handshake failed or was cut short, or `exit` was withheld because
    /// escaping descendants could not be marked.
    NotSent,
}

impl ExitNotice {
    /// Judged from the handshake's own result, before it is merged with the
    /// message loop's stop.
    const fn of(handshake: &Result<MarkOutcome>) -> Self {
        match handshake {
            Ok(MarkOutcome::Confirmed) => Self::Sent,
            _ => Self::NotSent,
        }
    }
}

/// How long the leader process is given to exit on its own after the
/// handshake, with `remaining` of the shutdown budget left. `answered` is the
/// merged result of the handshake and the message loop's stop.
fn child_exit_wait(
    grace: ExitGrace,
    mark: MarkOutcome,
    answered: &Result<()>,
    remaining: Duration,
) -> Duration {
    match grace {
        _ if mark != MarkOutcome::Confirmed => Duration::ZERO,
        ExitGrace::WithinBudget => remaining.min(CHILD_EXIT_GRACE),
        ExitGrace::IfAnswered(grace) if answered.is_ok() => grace,
        ExitGrace::IfAnswered(_) => Duration::ZERO,
    }
}

/// How long a failed `initialize` waits for the child to be reaped before
/// concluding it is still running and keeping the original error.
const EARLY_EXIT_PROBE: Duration = Duration::from_millis(500);

/// Capacity of the diagnostics/log/showMessage notification channel (P3).
///
/// Raised from the pre-#422 value of 64: P1 makes mcpls advertise
/// `window.workDoneProgress`, so a server may now attach progress reporting
/// to ordinary request capabilities too, raising overall notification
/// volume generally even though progress itself moved to its own
/// [`LIFECYCLE_CHANNEL_CAPACITY`] lane.
const NOTIFICATION_CHANNEL_CAPACITY: usize = 256;

/// Capacity of the lifecycle channel (P3): `$/progress` `begin`/`end`
/// frames plus `Other` (rust-analyzer's `experimental/serverStatus`).
///
/// O(phases), not O(reports): a `$/progress` `report` frame is filtered out
/// before it ever reaches this channel (see
/// `lsp::client::LspClient::message_loop_inner`), so this only needs to hold
/// a handful of `begin`/`end` transitions even for a server with several
/// concurrent operations, not a `report`-per-package stream like gopls can
/// produce.
const LIFECYCLE_CHANNEL_CAPACITY: usize = 128;

/// Every symbol kind defined by LSP 3.17 and understood by mcpls, with the
/// lowercase name a `workspace/symbol` `kind_filter` accepts for it.
///
/// Single source of truth for both the `initialize` request's `value_set`
/// and the `kind_filter` validation in [`crate::bridge::translator::symbols`].
pub const SUPPORTED_SYMBOL_KINDS: [(SymbolKind, &str); 26] = [
    (SymbolKind::File, "file"),
    (SymbolKind::Module, "module"),
    (SymbolKind::Namespace, "namespace"),
    (SymbolKind::Package, "package"),
    (SymbolKind::Class, "class"),
    (SymbolKind::Method, "method"),
    (SymbolKind::Property, "property"),
    (SymbolKind::Field, "field"),
    (SymbolKind::Constructor, "constructor"),
    (SymbolKind::Enum, "enum"),
    (SymbolKind::Interface, "interface"),
    (SymbolKind::Function, "function"),
    (SymbolKind::Variable, "variable"),
    (SymbolKind::Constant, "constant"),
    (SymbolKind::String, "string"),
    (SymbolKind::Number, "number"),
    (SymbolKind::Boolean, "boolean"),
    (SymbolKind::Array, "array"),
    (SymbolKind::Object, "object"),
    (SymbolKind::Key, "key"),
    (SymbolKind::Null, "null"),
    (SymbolKind::EnumMember, "enummember"),
    (SymbolKind::Struct, "struct"),
    (SymbolKind::Event, "event"),
    (SymbolKind::Operator, "operator"),
    (SymbolKind::TypeParameter, "typeparameter"),
];

/// The kinds of [`SUPPORTED_SYMBOL_KINDS`] as the `initialize` request lists them.
fn advertised_symbol_kinds() -> Vec<SymbolKind> {
    SUPPORTED_SYMBOL_KINDS
        .iter()
        .map(|&(kind, _)| kind)
        .collect()
}

/// Windows-only additions to [`ENV_PASSTHROUGH`].
///
/// `SystemRoot`/`SystemDrive`/`windir` are required by the Windows process
/// loader itself; `APPDATA`/`LOCALAPPDATA` are read by the Node-based default
/// servers (pyright, typescript-language-server) for global config and
/// cache; the rest are conventionally expected by Windows child processes.
/// `NoDefaultCurrentDirectoryInExePath` passes through so a user who set it to
/// keep the current directory out of executable lookups is not overridden by
/// the environment clearing.
#[cfg(windows)]
const ENV_PASSTHROUGH_WINDOWS: &[&str] = &[
    ManagedEnvVar::NoDefaultCurrentDirectoryInExePath.name(),
    "SystemRoot",
    "SystemDrive",
    "windir",
    "APPDATA",
    "LOCALAPPDATA",
    "ProgramData",
    "ProgramFiles",
    "COMSPEC",
    "PATHEXT",
    "NUMBER_OF_PROCESSORS",
    "USERNAME",
];

/// State of an LSP server connection.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ServerState {
    /// Server has not been initialized.
    Uninitialized,
    /// Server is currently initializing.
    Initializing,
    /// Server is ready to handle requests.
    Ready,
    /// Server is shutting down.
    ShuttingDown,
    /// Server has been shut down.
    Shutdown,
}

impl ServerState {
    /// Check if the server is ready to handle requests.
    #[must_use]
    pub const fn is_ready(&self) -> bool {
        matches!(self, Self::Ready)
    }
}

/// Where a spawned server's working directory is.
///
/// A closed type so a spawn never silently depends on the working directory
/// mcpls itself happens to have.
///
/// # Examples
///
/// ```
/// use std::path::PathBuf;
///
/// use mcpls_core::lsp::ChildWorkingDir;
///
/// assert_eq!(ChildWorkingDir::default(), ChildWorkingDir::Inherit);
/// let fixed = ChildWorkingDir::Fixed(PathBuf::from("project"));
/// assert_ne!(fixed, ChildWorkingDir::Inherit);
/// ```
#[derive(Debug, Clone, PartialEq, Eq, Default)]
pub enum ChildWorkingDir {
    /// The server inherits mcpls's working directory.
    #[default]
    Inherit,
    /// The server starts in this directory.
    Fixed(PathBuf),
}

/// Whether a server belongs to an untrusted workspace, and if so what it was
/// vetted against.
#[derive(Debug, Clone)]
pub enum SpawnTrust {
    /// The server runs as configured.
    Trusted,
    /// The boundary the argument backstop and the tsserver pin are evaluated
    /// against again before every spawn, and the command as configured.
    Untrusted(UntrustedVetting),
}

impl SpawnTrust {
    /// What an untrusted server is vetted against; `None` for a trusted one.
    pub const fn vetting(&self) -> Option<&UntrustedVetting> {
        match self {
            Self::Trusted => None,
            Self::Untrusted(vetting) => Some(vetting),
        }
    }
}

/// A [`ServerInitConfig`] that [`ServerInitConfig::for_respawn`] vetted, so a
/// respawn spawns exactly what was checked. The spawn still re-runs the
/// argument backstop on purpose (#736): a workspace file can become
/// executable between vetting and spawn.
#[derive(Debug, Clone)]
pub struct VettedInitConfig(ServerInitConfig);

impl VettedInitConfig {
    /// The vetted config.
    pub(crate) fn into_inner(self) -> ServerInitConfig {
        self.0
    }
}

impl std::ops::Deref for VettedInitConfig {
    type Target = ServerInitConfig;

    fn deref(&self) -> &ServerInitConfig {
        &self.0
    }
}

/// Configuration for LSP server initialization.
///
/// Built by [`Self::new`]; the fields are private so the effective
/// `initialization_options` live in exactly one place, the
/// [`LspServerConfig`] this was built from.
#[derive(Debug, Clone)]
pub struct ServerInitConfig {
    server_config: LspServerConfig,
    workspace_roots: WorkspaceRoots,
    position_encodings: PositionEncodings,
    redactions: Arc<Redactions>,
    child_working_dir: ChildWorkingDir,
    /// The tsserver pin mcpls chose, as opposed to one the user configured, so
    /// a respawn can tell a pin that went stale (the install moved) from the
    /// user's own `tsserver.path`, which is never second-guessed.
    auto_pin: Option<PathBuf>,
    trust: SpawnTrust,
}

impl ServerInitConfig {
    /// Builds the config a server is spawned from.
    ///
    /// `server_config` must already carry the *effective* initialization
    /// options (for example with the tsserver pin applied): they are sent as
    /// they are and are the only copy.
    ///
    /// `position_encodings` is the preference order from
    /// [`crate::config::WorkspaceConfig::position_encodings`], sent as
    /// `capabilities.general.positionEncodings` during [`LspServer::spawn`]'s
    /// `initialize` handshake. `redactions` holds the secrets of every
    /// configured server, hidden in this server's output;
    /// [`LspServer::spawn`] adds the secrets of this server's own
    /// configuration and current environment, so an empty set still hides
    /// them, and `serve` fills it with the secrets of every configured server
    /// so a server that echoes another's secret has it hidden too.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::sync::Arc;
    ///
    /// use mcpls_core::bridge::WorkspaceRoots;
    /// use mcpls_core::config::{LspServerConfig, PositionEncodings};
    /// use mcpls_core::lsp::{ChildWorkingDir, ServerInitConfig};
    ///
    /// let config = ServerInitConfig::new(
    ///     LspServerConfig::rust_analyzer(),
    ///     WorkspaceRoots::default(),
    ///     PositionEncodings::DEFAULT,
    ///     Arc::default(),
    /// );
    /// assert_eq!(config.child_working_dir(), &ChildWorkingDir::Inherit);
    /// ```
    #[must_use]
    pub const fn new(
        server_config: LspServerConfig,
        workspace_roots: WorkspaceRoots,
        position_encodings: PositionEncodings,
        redactions: Arc<Redactions>,
    ) -> Self {
        Self {
            server_config,
            workspace_roots,
            position_encodings,
            redactions,
            child_working_dir: ChildWorkingDir::Inherit,
            auto_pin: None,
            trust: SpawnTrust::Trusted,
        }
    }

    /// This config with the given trust; an untrusted server's arguments must
    /// keep clear of the boundary its vetting holds (see [`Self::vet_arguments`]).
    #[must_use]
    pub(crate) fn with_trust(mut self, trust: SpawnTrust) -> Self {
        self.trust = trust;
        self
    }

    /// Re-runs the untrusted argument backstop on the arguments the server
    /// would be spawned with; trusted configs are never vetted.
    ///
    /// A workspace file can become executable after the plan admitted the
    /// server, so every spawn (startup, respawn, restart) checks again.
    /// Walks the file system, so async callers use
    /// [`Self::vet_arguments_off_runtime`].
    ///
    /// # Errors
    ///
    /// [`Error::ServerFailedToStart`] with the untrusted-mode refusal when an
    /// argument now names an executable inside the workspace.
    pub(crate) fn vet_arguments(&self) -> Result<()> {
        let Some(vetting) = self.trust.vetting() else {
            return Ok(());
        };
        vetting
            .boundary()
            .refuse_arguments(
                &self.server_config.args,
                &self.child_working_dir,
                self.server_config.env.host(),
            )
            .map_err(|refusal| self.refusal(refusal))
    }

    /// [`Self::vet_arguments`] on the blocking pool, skipped for a trusted
    /// config.
    pub(crate) async fn vet_arguments_off_runtime(&self) -> Result<()> {
        if self.trust.vetting().is_none() {
            return Ok(());
        }
        self.on_planning_pool(Self::vet_arguments).await
    }

    /// Runs the blocking `plan` on a clone of this config on the blocking pool.
    async fn on_planning_pool<T: Send + 'static>(
        &self,
        plan: impl FnOnce(&Self) -> Result<T> + Send + 'static,
    ) -> Result<T> {
        let config = self.clone();
        crate::on_blocking_pool(move || plan(&config))
            .await
            .map_err(|source| Error::TaskFailed {
                task: crate::error::BackgroundTask::ServerPlanning,
                source,
            })?
    }

    /// This config with `tsserver` recorded as the pin mcpls chose.
    #[must_use]
    pub(crate) fn with_auto_pin(mut self, tsserver: PathBuf) -> Self {
        self.auto_pin = Some(tsserver);
        self
    }

    /// This config with the child started in `dir`.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::path::PathBuf;
    /// use std::sync::Arc;
    ///
    /// use mcpls_core::bridge::WorkspaceRoots;
    /// use mcpls_core::config::{LspServerConfig, PositionEncodings};
    /// use mcpls_core::lsp::{ChildWorkingDir, ServerInitConfig};
    ///
    /// let dir = ChildWorkingDir::Fixed(PathBuf::from("project"));
    /// let config = ServerInitConfig::new(
    ///     LspServerConfig::rust_analyzer(),
    ///     WorkspaceRoots::default(),
    ///     PositionEncodings::DEFAULT,
    ///     Arc::default(),
    /// )
    /// .with_child_working_dir(dir.clone());
    /// assert_eq!(config.child_working_dir(), &dir);
    /// ```
    #[must_use]
    pub fn with_child_working_dir(mut self, dir: ChildWorkingDir) -> Self {
        self.child_working_dir = dir;
        self
    }

    /// The server's configuration, carrying the effective initialization options.
    #[must_use]
    pub const fn server_config(&self) -> &LspServerConfig {
        &self.server_config
    }

    /// The workspace roots sent as `workspaceFolders`.
    #[must_use]
    pub const fn workspace_roots(&self) -> &WorkspaceRoots {
        &self.workspace_roots
    }

    /// The position encoding preference order offered to the server.
    #[must_use]
    pub const fn position_encodings(&self) -> &PositionEncodings {
        &self.position_encodings
    }

    /// The secrets hidden in this server's output.
    #[must_use]
    pub const fn redactions(&self) -> &Arc<Redactions> {
        &self.redactions
    }

    /// Where the child process starts.
    #[must_use]
    pub const fn child_working_dir(&self) -> &ChildWorkingDir {
        &self.child_working_dir
    }

    /// Mutable access to the server config, for tests that adjust a fixture.
    #[cfg(test)]
    pub(crate) const fn server_config_mut(&mut self) -> &mut LspServerConfig {
        &mut self.server_config
    }

    /// The tsserver this config pins through `initialization_options.tsserver.path`.
    #[must_use]
    pub fn pinned_tsserver(&self) -> Option<PathBuf> {
        tsserver_pin::configured_tsserver_path(self.server_config.initialization_options.as_ref())
    }

    /// The config a respawn of this server spawns from.
    ///
    /// Called by a restart before it stops the running server and by every
    /// other respawn right before it spawns; the filesystem work runs on the
    /// blocking pool and only for an auto-pinned or untrusted server. The
    /// result is what the respawn spawns; the spawn re-runs the argument
    /// backstop on purpose (#736).
    ///
    /// In untrusted mode the argument backstop runs again
    /// ([`Self::vet_arguments`]). A tsserver pin mcpls chose whose canonical
    /// path changed (the install was upgraded, moved or retargeted through a
    /// symlink) is resolved again and, in untrusted mode, checked against the
    /// boundary it was first vetted against. A pin the user configured is kept
    /// as is.
    ///
    /// # Errors
    ///
    /// [`Error::ServerFailedToStart`] with an untrusted-mode refusal when the
    /// tsserver now resolves inside the workspace, the server is now
    /// launched in a way no tsserver can be pinned for (the same two checks
    /// startup makes), or an argument now names an executable inside the
    /// workspace.
    pub(crate) async fn for_respawn(&self) -> Result<VettedInitConfig> {
        if self.auto_pin.is_none() && self.trust.vetting().is_none() {
            return Ok(VettedInitConfig(self.clone()));
        }
        self.on_planning_pool(Self::plan_respawn).await
    }

    /// The blocking half of [`Self::for_respawn`]: canonicalizes the pin and
    /// re-plans the tsserver, so it runs on the blocking pool.
    pub(crate) fn plan_respawn(&self) -> Result<VettedInitConfig> {
        self.vet_arguments()?;
        let pin_is_current = self
            .auto_pin
            .as_ref()
            .is_none_or(|pin| dunce::canonicalize(pin).ok().as_ref() == Some(pin));
        if pin_is_current {
            return Ok(VettedInitConfig(self.clone()));
        }
        let mut unpinned = self.server_config.clone();
        unpinned.initialization_options = None;
        let plan = tsserver_pin::plan_typescript(unpinned, process_env);
        if let Some(vetting) = self.trust.vetting() {
            plan.vet_untrusted(vetting)
                .map_err(|refusal| self.refusal(refusal))?;
        }
        let (server_config, auto_pin) = plan.apply(&self.workspace_roots);
        Ok(VettedInitConfig(Self {
            server_config,
            auto_pin,
            ..self.clone()
        }))
    }

    fn refusal(&self, refusal: UntrustedRefusal) -> Error {
        Error::ServerFailedToStart(Box::new(ServerSpawnFailure {
            server_id: self.server_config.id(),
            language_id: self.server_config.language_id.clone(),
            command: self.server_config.command.server_command().clone(),
            reason: StartupFailure::RefusedUntrustedWorkspace(refusal),
        }))
    }
}

/// The terminal outcome of starting one configured server.
///
/// A closed type so a settled server is either running or has a recorded
/// failure, never both and never neither.
#[derive(Debug)]
pub enum ServerStartOutcome {
    /// The server initialized and is ready to register.
    Started(Box<SpawnedServer>),
    /// The server failed to start.
    Failed(ServerSpawnFailure),
}

/// The two inbound notification lanes of a spawned server.
///
/// Handed out once, together with the server, by [`LspServer::spawn`]: a pump
/// owns them from then on, so a lane cannot be taken twice or left behind.
#[derive(Debug)]
pub struct ServerLanes {
    /// Diagnostics mailbox plus the log and `showMessage` frames
    /// ([`crate::lsp::ServerMessage`]). `textDocument/publishDiagnostics` is coalesced per
    /// file and a publish the mailbox cannot hold is reported as lost instead
    /// of being dropped (see [`crate::lsp::PublishReader`]).
    pub notifications: NotificationInbox,
    /// The lifecycle lane: `$/progress` `begin`/`end` frames and unrecognized
    /// notifications (which carry e.g. rust-analyzer's
    /// `experimental/serverStatus`), kept separate from the notification lane
    /// so a high-volume diagnostics publisher can never starve out a
    /// workspace-readiness signal, or vice versa.
    pub lifecycle: mpsc::Receiver<LspNotification>,
}

/// A freshly initialized server together with its inbound lanes.
#[derive(Debug)]
pub struct SpawnedServer {
    /// The running server.
    pub server: LspServer,
    /// Its notification lanes, to be drained by a pump.
    pub lanes: ServerLanes,
}

/// Managed LSP server instance with capabilities and encoding.
pub struct LspServer {
    client: LspClient,
    capabilities: ServerCapabilities,
    position_encoding: PositionEncodingKind,
    /// Child process handle. Kept alive for process lifetime management and
    /// queried by [`Self::has_exited`] to detect a crash. [`LspServer::shutdown`]
    /// waits for it to exit after sending `exit`; otherwise, or if that wait
    /// times out, dropping it terminates the process via SIGKILL
    /// (`kill_on_drop`). The process is also bound to the mcpls process
    /// lifetime (see [`ServerProcess`]), so it dies with mcpls on any exit.
    ///
    /// `None` only for test fixtures that never spawn a real server process
    /// (see `crate::test_lsp`, `Self::new_for_test_with_encoding`) --
    /// [`Self::spawn`] always populates this with `Some`.
    child: Option<ServerProcess>,
    /// Config this server was spawned from; the single source of its routing
    /// identity, respawn config and indexing policy.
    init_config: ServerInitConfig,
}

impl std::fmt::Debug for LspServer {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("LspServer")
            .field("client", &self.client)
            .field("capabilities", &self.capabilities)
            .field("position_encoding", &self.position_encoding)
            .field("child", &"<process>")
            .field("id", &self.init_config.server_config.id())
            .finish()
    }
}

/// Resolve one environment variable as the spawned server would see it:
/// the server config's `env` override wins, otherwise the parent value.
///
/// `parent_env` is injected so callers and tests need not touch the real
/// process environment.
pub fn child_env_var(
    config: &LspServerConfig,
    key: &str,
    parent_env: impl ParentEnv,
) -> Option<std::ffi::OsString> {
    config
        .env
        .get(key)
        .map(std::ffi::OsString::from)
        .or_else(|| parent_env(key))
}

impl LspServer {
    /// The config this server was spawned from.
    pub(crate) const fn init_config(&self) -> &ServerInitConfig {
        &self.init_config
    }

    /// Replace the config a respawn of this server would use.
    #[cfg(test)]
    pub(crate) fn set_init_config(&mut self, config: ServerInitConfig) {
        self.init_config = config;
    }

    /// Spawn and initialize LSP server, returning it with its notification
    /// lanes.
    ///
    /// This performs the complete initialization sequence:
    /// 1. Spawns the LSP server as a child process
    /// 2. Sends initialize request with client capabilities
    /// 3. Receives server capabilities from initialize response
    /// 4. Sends initialized notification
    /// 5. Sends `workspace/didChangeConfiguration` with the configured
    ///    settings (null when unset), which servers that wait for a
    ///    configuration push (pyright) need before they answer requests
    ///
    /// # Errors
    ///
    /// Returns an error if:
    /// - Server process fails to spawn
    /// - Initialize request fails or times out
    /// - Server returns error during initialization
    /// - The `initialized` or `workspace/didChangeConfiguration` notification
    ///   cannot be written ([`Error::LspInitFailed`])
    pub async fn spawn(config: ServerInitConfig) -> Result<SpawnedServer> {
        // Repeated on purpose: a workspace file can become executable between plan and spawn (#736).
        config.vet_arguments_off_runtime().await?;
        let own = Redactions::for_server(config.server_config(), current_environment());
        let redactions = Arc::new(Redactions::union([config.redactions().as_ref(), &own]));
        Self::log_spawn(config.server_config(), &redactions);

        let command = Self::build_command(
            config.server_config(),
            config.child_working_dir(),
            process_env,
        );

        // Log allowlist presence and an override count only — never the
        // configured keys themselves, since `config.server_config.env` may
        // hold secret-bearing names (e.g. `AWS_SECRET_ACCESS_KEY`) whose
        // mere presence in a debug log would be its own disclosure.
        let passthrough_present = {
            let base = ENV_PASSTHROUGH
                .iter()
                .filter(|key| std::env::var_os(key).is_some())
                .count();
            #[cfg(windows)]
            let windows = ENV_PASSTHROUGH_WINDOWS
                .iter()
                .filter(|key| std::env::var_os(key).is_some())
                .count();
            #[cfg(not(windows))]
            let windows = 0;
            base.saturating_add(windows)
        };
        debug!(
            "Effective LSP server env: {passthrough_present} allowlisted key(s) present, \
             {} configured override(s) applied",
            config.server_config.env.len()
        );

        let mut child = ServerProcess::spawn(command)
            .map_err(|e| spawn_error(config.server_config.command.server_command().clone(), e))?;

        let stdin = child
            .take_stdin()
            .ok_or(Error::StdioCapture(StdioStream::Stdin))?;
        let stdout = child
            .take_stdout()
            .ok_or(Error::StdioCapture(StdioStream::Stdout))?;

        let stderr = child
            .take_stderr()
            .ok_or(Error::StdioCapture(StdioStream::Stderr))?;
        let stderr_capture = StderrCapture::start(stderr);

        let transport = LspTransport::with_redactions(stdin, stdout, Arc::clone(&redactions));
        let (notification_tx, notification_rx) = mpsc::channel(NOTIFICATION_CHANNEL_CAPACITY);
        let (notification_sink, publish_rx) = NotificationSink::new(notification_tx);
        let (lifecycle_tx, lifecycle_rx) = mpsc::channel(LIFECYCLE_CHANNEL_CAPACITY);
        let client = LspClient::from_transport_with_notifications(
            config.server_config.clone(),
            transport,
            notification_sink,
            lifecycle_tx,
            Arc::clone(&redactions),
        );
        #[cfg(unix)]
        let process_id = initialize_process_id(child.binding());
        #[cfg(windows)]
        let process_id = Some(mcpls_process_id());
        let (capabilities, position_encoding) =
            match Self::initialize_as(&client, &config, process_id).await {
                Ok(negotiated) => negotiated,
                Err(init_error) if is_connection_loss(&init_error) => {
                    return Err(Self::connection_loss_error(
                        &config,
                        &mut child,
                        stderr_capture,
                        &redactions,
                        init_error,
                    )
                    .await);
                }
                Err(Error::LspInitFailed { phase, cause, .. }) => {
                    // The server may be about to exit after printing its reason,
                    // so wait the (bounded) end-of-file grace whether or not it
                    // has exited yet.
                    let stderr = stderr_capture.finish(EofWait::Grace, &redactions).await;
                    let hint = Self::init_failure_hint(&config).await;
                    return Err(Error::LspInitFailed {
                        phase,
                        cause: Box::new(redactions.sanitize_error(*cause)),
                        hint,
                        stderr,
                    });
                }
                Err(init_error) => return Err(redactions.sanitize_error(init_error)),
            };

        info!("LSP server initialized successfully");

        Ok(SpawnedServer {
            server: Self {
                client,
                capabilities,
                position_encoding,
                child: Some(child),
                init_config: config,
            },
            lanes: ServerLanes {
                notifications: NotificationInbox::new(notification_rx, publish_rx),
                lifecycle: lifecycle_rx,
            },
        })
    }

    /// The error for an `initialize` that ended in a lost connection: the
    /// server exited (with its exit status) or the pipe closed first.
    async fn connection_loss_error(
        config: &ServerInitConfig,
        child: &mut ServerProcess,
        stderr_capture: StderrCapture,
        redactions: &Redactions,
        init_error: Error,
    ) -> Error {
        let exit_status = early_exit_status(child).await;
        let eof_wait = if exit_status.is_some() {
            EofWait::Grace
        } else {
            EofWait::Skip
        };
        let stderr = stderr_capture.finish(eof_wait, redactions).await;
        let hint = Self::init_failure_hint(config).await;
        match exit_status {
            Some(status) => Error::ServerExitedDuringInit {
                command: config.server_config.command.server_command().clone(),
                exit_code: status.code(),
                hint,
                stderr,
            },
            None => Error::LspInitFailed {
                phase: InitPhase::Initialize,
                cause: Box::new(redactions.sanitize_error(init_error)),
                hint,
                stderr,
            },
        }
    }

    /// The guidance for a failed `initialize` of `config`, if its cause is known.
    ///
    /// Runs on the failure path only. It walks `PATH` and reads package
    /// manifests, so it runs on the blocking pool; the hint is dropped when the
    /// pool is shutting down.
    async fn init_failure_hint(config: &ServerInitConfig) -> Option<InitFailureHint> {
        let config = config.clone();
        let hint = crate::on_blocking_pool(move || {
            tsserver_pin::init_failure_hint(
                config.server_config(),
                config.workspace_roots(),
                process_env,
            )
        })
        .await;
        hint.unwrap_or_else(|error| {
            debug!("Dropped the init failure hint: {error}");
            None
        })
    }

    /// Logs the command and argument count at `info`, and the argument values
    /// (redacted) only at `debug`.
    fn log_spawn(server_config: &LspServerConfig, redactions: &Redactions) {
        info!(
            "Spawning LSP server: {} ({} arg(s))",
            server_config.command,
            server_config.args.len()
        );
        debug!(
            "LSP server args: {:?}",
            server_config
                .args
                .iter()
                .map(|arg| redactions.apply(arg))
                .collect::<Vec<_>>()
        );
    }

    /// Build the child `Command` for a spawned LSP server, without spawning it.
    ///
    /// The child's environment is cleared, then [`ENV_PASSTHROUGH`] (plus
    /// [`ENV_PASSTHROUGH_WINDOWS`] under `cfg(windows)`) is copied in from
    /// `parent_env` for whichever of those keys it returns `Some` for, then
    /// `config.env` is applied last so it can override any passthrough
    /// value. `parent_env` is injected (production passes
    /// `std::env::var_os`) so tests can supply a fixed environment without
    /// racing on real process-global state.
    fn build_command(
        config: &LspServerConfig,
        working_dir: &ChildWorkingDir,
        parent_env: impl ParentEnv,
    ) -> Command {
        let mut command = Command::new(&config.command);
        command.args(&config.args).env_clear();
        if let ChildWorkingDir::Fixed(dir) = working_dir {
            command.current_dir(dir);
        }

        for key in ENV_PASSTHROUGH {
            if let Some(value) = child_env_var(config, key, &parent_env) {
                command.env(key, value);
            }
        }
        #[cfg(windows)]
        for key in ENV_PASSTHROUGH_WINDOWS {
            if let Some(value) = child_env_var(config, key, &parent_env) {
                command.env(key, value);
            }
        }

        command
            .envs(config.env.iter())
            .stdin(Stdio::piped())
            .stdout(Stdio::piped())
            .stderr(Stdio::piped());

        command
    }

    /// Folding ranges with columns (`lineFoldingOnly: false`), the three
    /// standard kinds, and collapsed text.
    fn folding_range_capabilities() -> lsp_types::FoldingRangeClientCapabilities {
        lsp_types::FoldingRangeClientCapabilities {
            dynamic_registration: Some(false),
            line_folding_only: Some(false),
            folding_range_kind: Some(lsp_types::ClientFoldingRangeKindOptions {
                value_set: Some(vec![
                    lsp_types::FoldingRangeKind::Comment,
                    lsp_types::FoldingRangeKind::Imports,
                    lsp_types::FoldingRangeKind::Region,
                ]),
            }),
            folding_range: Some(lsp_types::ClientFoldingRangeOptions {
                collapsed_text: Some(true),
            }),
            ..Default::default()
        }
    }

    /// Build the `capabilities` mcpls advertises in the `initialize`
    /// request, given the configured position-encoding preference order.
    ///
    /// Extracted from [`Self::initialize`] (S2) so a unit test can assert
    /// directly on the returned value -- in particular that
    /// `window.work_done_progress == Some(true)` (P1), without which no
    /// spec-compliant LSP server may ever initiate `$/progress` at all (see
    /// the matching `window/workDoneProgress/create` allowlist entry in
    /// [`crate::lsp::client::LspClient::server_request_result`]). Before
    /// this existed, deleting those capability lines would silently no-op
    /// the whole feature with an otherwise-green test suite.
    ///
    /// `workspace.configuration` is advertised only when `settings` are
    /// configured: without them mcpls has nothing to answer with.
    fn client_capabilities(
        position_encodings: &PositionEncodings,
        settings: Option<&LspSettings>,
    ) -> ClientCapabilities {
        ClientCapabilities {
            general: Some(GeneralClientCapabilities {
                position_encodings: Some(
                    position_encodings
                        .as_slice()
                        .iter()
                        .map(|encoding| encoding.to_kind())
                        .collect(),
                ),
                stale_request_support: Some(StaleRequestSupportOptions {
                    // mcpls does not implement active in-flight request
                    // cancellation.
                    cancel: false,
                    retry_on_content_modified: CONTENT_MODIFIED_RETRY_METHODS
                        .iter()
                        .map(ToString::to_string)
                        .collect(),
                }),
                ..Default::default()
            }),
            text_document: Some(lsp_types::TextDocumentClientCapabilities {
                synchronization: Some(lsp_types::TextDocumentSyncClientCapabilities {
                    dynamic_registration: Some(false),
                    did_save: Some(true),
                    ..Default::default()
                }),
                document_symbol: Some(lsp_types::DocumentSymbolClientCapabilities {
                    dynamic_registration: Some(false),
                    symbol_kind: Some(lsp_types::ClientSymbolKindOptions {
                        value_set: Some(advertised_symbol_kinds()),
                    }),
                    hierarchical_document_symbol_support: Some(true),
                    ..Default::default()
                }),
                hover: Some(lsp_types::HoverClientCapabilities {
                    dynamic_registration: Some(false),
                    content_format: Some(vec![
                        lsp_types::MarkupKind::Markdown,
                        lsp_types::MarkupKind::PlainText,
                    ]),
                }),
                definition: Some(lsp_types::DefinitionClientCapabilities {
                    dynamic_registration: Some(false),
                    link_support: Some(true),
                }),
                declaration: Some(lsp_types::DeclarationClientCapabilities {
                    dynamic_registration: Some(false),
                    link_support: Some(true),
                }),
                references: Some(lsp_types::ReferenceClientCapabilities {
                    dynamic_registration: Some(false),
                }),
                // clangd and typescript-language-server answer `prepareProvider` only
                // when the client advertises `prepareSupport`.
                rename: Some(lsp_types::RenameClientCapabilities {
                    dynamic_registration: Some(false),
                    prepare_support: Some(true),
                    prepare_support_default_behavior: Some(
                        lsp_types::PrepareSupportDefaultBehavior::Identifier,
                    ),
                    ..Default::default()
                }),
                folding_range: Some(Self::folding_range_capabilities()),
                // typescript-language-server publishes nothing unless this object is present;
                // only `versionSupport`, the one field the diagnostics cache retains.
                publish_diagnostics: Some(lsp_types::PublishDiagnosticsClientCapabilities {
                    version_support: Some(true),
                    ..Default::default()
                }),
                selection_range: Some(lsp_types::SelectionRangeClientCapabilities {
                    dynamic_registration: Some(false),
                }),
                code_action: Some(lsp_types::CodeActionClientCapabilities {
                    dynamic_registration: Some(false),
                    data_support: Some(true),
                    resolve_support: Some(lsp_types::ClientCodeActionResolveOptions {
                        properties: vec!["edit".to_string()],
                    }),
                    // Declare supported action kinds so the server returns
                    // CodeAction objects (not just legacy Command objects).
                    code_action_literal_support: Some(lsp_types::ClientCodeActionLiteralOptions {
                        code_action_kind: lsp_types::ClientCodeActionKindOptions {
                            value_set: std::iter::once(lsp_types::CodeActionKind::Empty)
                                .chain(
                                    crate::bridge::CodeActionKindFilter::ALL
                                        .map(lsp_types::CodeActionKind::from),
                                )
                                .collect(),
                        },
                    }),
                    ..Default::default()
                }),
                ..Default::default()
            }),
            workspace: Some(lsp_types::WorkspaceClientCapabilities {
                workspace_folders: Some(true),
                configuration: settings.map(|_| true),
                ..Default::default()
            }),
            // Required per LSP 3.17 before a server may send $/progress at all -- see this fn's doc.
            window: Some(lsp_types::WindowClientCapabilities {
                work_done_progress: Some(true),
                ..Default::default()
            }),
            // Required for rust-analyzer to ever emit experimental/serverStatus; other servers ignore this unrecognized key.
            experimental: Some(serde_json::json!({ "serverStatusNotification": true })),
            ..Default::default()
        }
    }

    /// Perform LSP initialization handshake.
    ///
    /// Sends initialize request and waits for response, then sends the
    /// initialized and `workspace/didChangeConfiguration` notifications.
    ///
    /// The pushed settings are the configured per-server settings. Without
    /// any they are null rather than `{}`: some servers rebuild their
    /// preferences from an empty settings map and so drop their
    /// `initialization_options`, while a non-map value is ignored. Because
    /// configured settings are never empty (see [`LspSettings`]), servers
    /// such as jdtls may replace their `initialization_options`-derived
    /// preferences with them.
    #[cfg(test)]
    async fn initialize(
        client: &LspClient,
        config: &ServerInitConfig,
    ) -> Result<(ServerCapabilities, PositionEncodingKind)> {
        Self::initialize_as(client, config, Some(mcpls_process_id())).await
    }

    /// As [`Self::initialize`], reporting `process_id` as the parent process
    /// the server may watch (`None` is allowed by LSP and sent while a
    /// lifeline watchdog is bound: a server that exits when mcpls vanishes
    /// would otherwise race the watchdog's freeze of its descendants).
    async fn initialize_as(
        client: &LspClient,
        config: &ServerInitConfig,
        process_id: Option<i32>,
    ) -> Result<(ServerCapabilities, PositionEncodingKind)> {
        debug!("Sending initialize request");
        if config.server_config().initialization_options.is_some()
            && config.server_config().settings.is_some()
        {
            warn!(
                "server `{}` has both initialization_options and settings: servers that pull \
                 workspace/configuration (rust-analyzer, jdtls) may replace the options with \
                 the settings",
                config.server_config.command
            );
        }

        let workspace_folders: Vec<WorkspaceFolder> = config
            .workspace_roots()
            .canonical()
            .iter()
            .map(|root| workspace_folder(root))
            .collect::<Result<Vec<_>>>()?;

        let params = InitializeParams {
            process_id,
            #[allow(
                deprecated,
                reason = "`root_uri` is deprecated but the struct literal must still set it"
            )]
            root_uri: None,
            initialization_options: config.server_config().initialization_options.clone(),
            capabilities: Self::client_capabilities(
                &config.position_encodings,
                config.server_config.settings.as_ref(),
            ),
            client_info: Some(ClientInfo {
                name: "mcpls".to_string(),
                version: Some(env!("CARGO_PKG_VERSION").to_string()),
            }),
            workspace_folders_initialize_params: lsp_types::WorkspaceFoldersInitializeParams {
                workspace_folders: Some(lsp_types::WorkspaceFolders::WorkspaceFolderList(
                    workspace_folders,
                )),
            },
            ..Default::default()
        };

        // Use the server's configured timeout for the initialize handshake too,
        // not a hardcoded 30s: large solutions (e.g. a 130-project Unity .sln via
        // OmniSharp) take minutes to respond to `initialize`.
        let result: InitializeResult = client
            .request_typed::<InitializeRequest>(
                params,
                config.server_config.timeout_seconds.as_duration(),
            )
            .await
            .map_err(|e| {
                if is_connection_loss(&e) {
                    e
                } else {
                    Error::LspInitFailed {
                        phase: InitPhase::Initialize,
                        cause: Box::new(e),
                        hint: None,
                        stderr: None,
                    }
                }
            })?;

        let position_encoding = result
            .capabilities
            .position_encoding
            .clone()
            .unwrap_or(PositionEncodingKind::UTF16);

        debug!(
            "Server capabilities received, encoding: {:?}",
            position_encoding
        );

        notify_handshake::<InitializedNotification>(
            client,
            InitPhase::Initialized,
            InitializedParams {},
        )
        .await?;
        notify_handshake::<DidChangeConfigurationNotification>(
            client,
            InitPhase::DidChangeConfiguration,
            DidChangeConfigurationParams {
                settings: config
                    .server_config
                    .settings
                    .as_ref()
                    .map_or(serde_json::Value::Null, LspSettings::to_value),
            },
        )
        .await?;

        Ok((result.capabilities, position_encoding))
    }

    /// Get server capabilities.
    #[must_use]
    pub const fn capabilities(&self) -> &ServerCapabilities {
        &self.capabilities
    }

    /// Get negotiated position encoding.
    #[must_use]
    pub fn position_encoding(&self) -> PositionEncodingKind {
        self.position_encoding.clone()
    }

    /// Get client for making requests.
    #[must_use]
    pub const fn client(&self) -> &LspClient {
        &self.client
    }

    /// Non-blocking check for whether the child process has already exited.
    ///
    /// Uses [`tokio::process::Child::try_wait`] on the leader process, which never blocks waiting
    /// for the process: `true` means it is gone (crashed, killed, or exited
    /// on its own), and any [`LspClient`] obtained from [`Self::client`] is
    /// now permanently disconnected -- new requests through it fail with
    /// [`crate::error::Error::ServerTerminated`]. Callers that want to
    /// recover substitute a freshly [`Self::spawn`]ed replacement.
    ///
    /// Always returns `Ok(false)` for a test fixture with no real backing
    /// process (`self.child` is `None`) -- there is nothing to have exited.
    /// [`Self::spawn`] always populates `child`, so production code never
    /// observes this case.
    ///
    /// # Errors
    ///
    /// Returns an error if the OS fails to report the process's status.
    pub fn has_exited(&mut self) -> Result<bool> {
        match &mut self.child {
            Some(child) => Ok(child.try_wait()?.is_some()),
            None => Ok(false),
        }
    }

    /// Whether this server can no longer serve requests: its child process
    /// has exited, or its message loop has stopped (e.g. it panicked) while
    /// the child is still running.
    ///
    /// Unlike [`Self::has_exited`], this catches a live child whose connection
    /// is already dead, which nothing else would ever respawn. Test fixtures
    /// with no child process are never reported dead.
    ///
    /// # Errors
    ///
    /// Returns an error if the OS fails to report the process's status.
    pub(crate) fn is_dead(&mut self) -> Result<bool> {
        if self.has_exited()? {
            return Ok(true);
        }
        Ok(self.child.is_some() && self.client.is_message_loop_finished())
    }

    /// Shutdown server gracefully, with an overall deadline of [`SHUTDOWN_TIMEOUT`].
    ///
    /// Sends the LSP `shutdown` request, waits for the response, has the
    /// lifeline watchdog freeze and record descendants that escaped the
    /// server's process group (Unix), sends the `exit` notification, stops the
    /// message loop, then waits up to a grace period (never past the overall
    /// deadline) for the leader process to exit on its own. Whatever is left,
    /// including escapees that left the group through `setsid`/`setpgid` and
    /// shared daemons such as Gradle or Bloop, is then killed and waited for,
    /// up to [`crate::lsp::LIFELINE_SWEEP_BUDGET`] beyond the deadline, so
    /// when this returns the server's whole tree is gone. If the escapee mark
    /// fails the `exit` notification is skipped and the tree is killed right
    /// away. A test fixture with no real backing process skips the process
    /// steps.
    ///
    /// # Errors
    ///
    /// Returns the first error of the handshake or the message-loop stop,
    /// including [`Error::ShutdownTimeout`] when the deadline elapsed. The
    /// process tree is still torn down regardless of whether this returns
    /// `Ok` or `Err`.
    pub async fn shutdown(mut self) -> Result<()> {
        self.terminate(SHUTDOWN_TIMEOUT, ExitGrace::WithinBudget)
            .await
    }

    /// Stop the server and its whole process tree, leaving `self` usable as a
    /// dead server (`is_dead()` is `true` for a real process).
    ///
    /// Sends the LSP `shutdown` request, waits for the response, sends the
    /// `exit` notification and stops the message loop, all within `budget`.
    /// It then lets the leader process exit on its own for as long as `grace`
    /// allows, which is the only path that lets the server reap its own
    /// children. Whatever is left in the server's process group is then killed
    /// (on Unix this includes shared daemons such as Gradle or Bloop started
    /// by the server). A test fixture with no real backing process (`child`
    /// is `None`) skips the process steps.
    ///
    /// # Errors
    ///
    /// Returns the first error of the handshake or the message-loop stop,
    /// including [`Error::ShutdownTimeout`] when `budget` elapsed. The
    /// process tree is still torn down regardless of whether this returns
    /// `Ok` or `Err`.
    #[allow(
        clippy::arithmetic_side_effects,
        reason = "SHUTDOWN_TIMEOUT and CHILD_EXIT_GRACE are small constants"
    )]
    pub(crate) async fn terminate(&mut self, budget: Duration, grace: ExitGrace) -> Result<()> {
        debug!("Shutting down LSP server");

        let deadline = Instant::now() + budget;
        let client = &mut self.client;
        let shutdown_request_timeout = Duration::from_secs(5).min(budget);

        let handshake: Result<MarkOutcome> = timeout_at(deadline, async {
            client.suppress_cancels();
            let _: serde_json::Value = client
                .request(
                    ShutdownRequest::METHOD.as_str(),
                    (),
                    shutdown_request_timeout,
                )
                .await?;
            #[cfg(unix)]
            let mark = match self.child.as_mut() {
                Some(child) => child.mark_escapees().await,
                None => MarkOutcome::Confirmed,
            };
            #[cfg(windows)]
            let mark = MarkOutcome::Confirmed;
            if mark == MarkOutcome::Confirmed {
                client.notify_typed::<ExitNotification>(()).await?;
            }
            Ok(mark)
        })
        .await
        .unwrap_or(Err(Error::ShutdownTimeout));
        let mark = handshake
            .as_ref()
            .map_or(MarkOutcome::Confirmed, |mark| *mark);
        let notice = ExitNotice::of(&handshake);
        let handshake = handshake.map(drop);
        let handshake = match client.shutdown_until(deadline).await {
            Ok(()) => handshake,
            Err(e) => handshake.and(Err(e)),
        };

        if let Some(child) = &mut self.child {
            let wait = child_exit_wait(
                grace,
                mark,
                &handshake,
                deadline.saturating_duration_since(Instant::now()),
            );
            match timeout(wait, child.wait()).await {
                Ok(Ok(status)) => match notice {
                    ExitNotice::Sent => {
                        debug!(
                            ?status,
                            "LSP server process exited after `exit` notification"
                        );
                    }
                    ExitNotice::NotSent => {
                        debug!(
                            ?status,
                            "LSP server process exited without an `exit` notification"
                        );
                    }
                },
                Ok(Err(e)) => warn!(error = %e, "failed to wait for LSP server process exit"),
                Err(_) => match notice {
                    ExitNotice::Sent => warn!(
                        waited = ?wait,
                        exit = ?notice,
                        "LSP server process did not exit within the wait after `exit` \
                         notification, killing it"
                    ),
                    ExitNotice::NotSent => warn!(
                        waited = ?wait,
                        exit = ?notice,
                        "LSP server process killed without an `exit` notification"
                    ),
                },
            }
            let sweep_budget = deadline
                .saturating_duration_since(Instant::now())
                .clamp(MIN_SWEEP_BUDGET, crate::lsp::LIFELINE_SWEEP_BUDGET);
            child.terminate_tree(sweep_budget).await;
        }

        handshake?;
        info!("LSP server shut down successfully");
        Ok(())
    }

    /// Spawns and initializes one server, turning an error or a panic into
    /// that server's [`ServerStartOutcome::Failed`] so it can never affect a
    /// sibling. Logs the outcome with the id and elapsed time.
    ///
    /// Runs on the caller's task: dropping the future drops the child
    /// process it owns.
    pub(crate) async fn start_contained(config: &ServerInitConfig) -> ServerStartOutcome {
        Box::pin(contain(config, Self::spawn(config.clone()))).await
    }
}

/// Drives `start` (one server's spawn and handshake) and classifies how it
/// ended; see [`LspServer::start_contained`].
async fn contain(
    config: &ServerInitConfig,
    start: impl std::future::Future<Output = Result<SpawnedServer>>,
) -> ServerStartOutcome {
    let server_id = config.server_config.id();
    let language_id = config.server_config.language_id.clone();
    let command = config.server_config.command.server_command().clone();
    let started = Instant::now();

    let reason = match crate::util::catch_panic(start).await {
        Ok(Ok(spawned)) => {
            info!(
                "Successfully spawned LSP server: {} ({}) in {:?}",
                server_id,
                command,
                started.elapsed()
            );
            return ServerStartOutcome::Started(Box::new(spawned));
        }
        Ok(Err(e)) => {
            tracing::error!(
                "Failed to spawn LSP server: {} ({}) after {:?}: {}",
                server_id,
                command,
                started.elapsed(),
                e
            );
            StartupFailure::Spawn(Arc::new(e))
        }
        Err(panicked) => {
            tracing::error!(
                "Starting LSP server {} ({}) panicked after {:?}: {}",
                server_id,
                command,
                started.elapsed(),
                panicked.message()
            );
            StartupFailure::InitTaskPanicked
        }
    };
    ServerStartOutcome::Failed(ServerSpawnFailure {
        server_id,
        language_id,
        command,
        reason,
    })
}

fn mcpls_process_id() -> i32 {
    i32::try_from(std::process::id()).unwrap_or(i32::MAX)
}

/// The `processId` to send: none while a lifeline watchdog is bound, the real
/// mcpls pid otherwise.
#[cfg(unix)]
fn initialize_process_id(binding: Binding) -> Option<i32> {
    match binding {
        Binding::Bound => None,
        Binding::Unbound => Some(mcpls_process_id()),
    }
}

/// Sends one handshake notification, mapping a failed write to
/// [`Error::LspInitFailed`] naming the notification's method.
async fn notify_handshake<N>(client: &LspClient, phase: InitPhase, params: N::Params) -> Result<()>
where
    N: lsp_types::Notification,
{
    client
        .notify_typed::<N>(params)
        .await
        .map_err(|e| Error::LspInitFailed {
            phase,
            cause: Box::new(e),
            hint: None,
            stderr: None,
        })
}

/// Whether `error` means the connection to the server is gone, as opposed to
/// the server answering with a failure of its own.
const fn is_connection_loss(error: &Error) -> bool {
    matches!(
        error,
        Error::ServerTerminated
            | Error::TaskFailed {
                task: BackgroundTask::LspReceiver,
                ..
            }
    )
}

/// Exit status of `child` if it has exited (or does so within
/// [`EARLY_EXIT_PROBE`]), `None` if it is still running.
async fn early_exit_status(child: &mut ServerProcess) -> Option<std::process::ExitStatus> {
    timeout(EARLY_EXIT_PROBE, child.wait()).await.ok()?.ok()
}

/// Classify a spawn failure: a missing executable gets its own variant so the
/// message can carry PATH and install guidance.
fn spawn_error(command: ServerCommand, source: std::io::Error) -> Error {
    if source.kind() == std::io::ErrorKind::NotFound {
        Error::ServerNotFound {
            command,
            io: source,
        }
    } else {
        Error::ServerSpawnFailed { command, source }
    }
}

/// The process environment as `(name, value)` pairs, skipping non-UTF-8 entries.
pub fn current_environment() -> Vec<(String, String)> {
    std::env::vars_os()
        .filter_map(|(name, value)| Some((name.into_string().ok()?, value.into_string().ok()?)))
        .collect()
}

/// Build the `workspace/workspaceFolders` entry for one configured root.
///
/// Reserved characters have to be percent-encoded here: an unencoded `#`
/// would truncate the path into a URI fragment, and `[` / `]` are rejected
/// outright by `Uri`.
fn workspace_folder(root: &Path) -> Result<WorkspaceFolder> {
    let uri = try_path_to_uri(root).ok_or_else(|| Error::PathToUri(root.to_path_buf()))?;
    Ok(WorkspaceFolder {
        uri,
        name: root
            .file_name()
            .and_then(|n| n.to_str())
            .unwrap_or("workspace")
            .to_string(),
    })
}

/// Builds an `LspServer` that can be registered without a real language
/// server: an inert, in-memory transport (see `crate::test_lsp`) and no
/// backing child process (`child: None`) -- neither is ever read from or
/// written to.
///
/// `pub` rather than private to this module's own `tests` (`lifecycle` is a
/// private module, so this stays crate-scoped in practice, per the
/// `redundant_pub_crate` clippy lint): it constructs `LspServer` via a
/// struct literal, which only code inside this module can do (all its
/// fields are private), so this is the one place other modules'
/// shutdown-path tests (`bridge::translator`, `lib.rs`) can get a real,
/// registerable `LspServer` from.
#[cfg(test)]
pub fn fake_lsp_server() -> LspServer {
    fake_lsp_server_with_config(LspServerConfig::pyright())
}

/// As [`fake_lsp_server`], with a caller-chosen config, which is also what
/// the returned server reports as its `init_config`.
#[cfg(test)]
pub fn fake_lsp_server_with_config(server_config: LspServerConfig) -> LspServer {
    let transport = crate::test_lsp::inert_transport();
    let client = LspClient::from_transport(server_config.clone(), transport);
    LspServer {
        client,
        capabilities: lsp_types::ServerCapabilities::default(),
        position_encoding: PositionEncodingKind::UTF8,
        child: None,
        init_config: crate::test_lsp::init_config_for(server_config),
    }
}

/// [`fake_lsp_server_with_config`] with inert lanes, as [`LspServer::spawn`]
/// returns it.
#[cfg(test)]
pub fn fake_spawned_server_with_config(server_config: LspServerConfig) -> SpawnedServer {
    let (_, messages) = mpsc::channel(1);
    let (_, lifecycle) = mpsc::channel(1);
    SpawnedServer {
        server: fake_lsp_server_with_config(server_config),
        lanes: ServerLanes {
            notifications: NotificationInbox::new(messages, crate::lsp::PublishReader::closed()),
            lifecycle,
        },
    }
}

/// A server whose child process (`sleep`) is alive but whose message loop
/// dies at once on its inert transport -- the shape of a panicked loop.
#[cfg(test)]
#[cfg(unix)]
pub fn fake_lsp_server_with_dead_loop_and_live_child() -> LspServer {
    let child = tokio::process::Command::new("sleep")
        .arg("30")
        .kill_on_drop(true)
        .spawn()
        .unwrap_or_else(|e| panic!("failed to spawn sleep: {e}"));
    let mut server = fake_lsp_server();
    server.child = Some(ServerProcess::from_unbound(child));
    server
}

#[cfg(test)]
impl LspServer {
    /// Construct an `LspServer` fixture carrying the given capabilities, for
    /// tests elsewhere in the crate that need to drive capability-gated
    /// dispatch paths in `Translator` without spawning a real language server.
    ///
    /// The underlying client and child process (`child: None`) are inert
    /// placeholders — only `capabilities()` is meaningful on the returned
    /// value.
    ///
    /// Uses `LspClient::new` (uninitialized, no background task) rather than
    /// `LspClient::from_transport`, so this does not depend on the Tokio
    /// message loop or a real process at all.
    pub(crate) fn new_for_test(capabilities: ServerCapabilities) -> Self {
        Self::new_for_test_with_encoding(capabilities, PositionEncodingKind::UTF16)
    }

    /// As [`Self::new_for_test`], but with a caller-chosen negotiated
    /// encoding -- for tests exercising a non-UTF-16 conversion path (e.g.
    /// `EncodingCtx`-driven range conversion) without spawning a real
    /// process.
    pub(crate) fn new_for_test_with_encoding(
        capabilities: ServerCapabilities,
        position_encoding: PositionEncodingKind,
    ) -> Self {
        Self::new_for_test_with_client(
            capabilities,
            position_encoding,
            LspClient::new(LspServerConfig::rust_analyzer()),
        )
    }

    /// As [`Self::new_for_test_with_encoding`], but around a caller-built
    /// client -- for tests that drive the client over a scripted transport
    /// (see `crate::test_lsp`).
    pub(crate) fn new_for_test_with_client(
        capabilities: ServerCapabilities,
        position_encoding: PositionEncodingKind,
        client: LspClient,
    ) -> Self {
        Self {
            client,
            capabilities,
            position_encoding,
            child: None,
            init_config: crate::test_lsp::init_config_for(LspServerConfig::rust_analyzer()),
        }
    }
}

#[cfg(test)]
mod tests {
    use std::assert_matches;
    use std::collections::HashMap;

    use super::*;
    use crate::bridge::PositionEncoding;
    use crate::config::{FilePattern, HostOs, LanguageId, TimeoutSecs, ToolSet};
    use crate::lsp::JsonRpcError;

    #[test]
    fn test_child_exit_wait_follows_the_grace_policy() {
        let remaining = Duration::from_secs(10);
        let grace = Duration::from_secs(7);
        let answered = Ok(());
        let unanswered = Err(Error::ShutdownTimeout);
        let wait = |policy, mark, answered: &Result<()>| {
            child_exit_wait(policy, mark, answered, remaining)
        };

        assert_eq!(
            wait(ExitGrace::WithinBudget, MarkOutcome::Confirmed, &answered),
            CHILD_EXIT_GRACE
        );
        assert_eq!(
            child_exit_wait(
                ExitGrace::WithinBudget,
                MarkOutcome::Confirmed,
                &answered,
                Duration::from_secs(1)
            ),
            Duration::from_secs(1)
        );
        assert_eq!(
            wait(
                ExitGrace::IfAnswered(grace),
                MarkOutcome::Confirmed,
                &answered
            ),
            grace
        );
        assert_eq!(
            wait(
                ExitGrace::IfAnswered(grace),
                MarkOutcome::Confirmed,
                &unanswered
            ),
            Duration::ZERO
        );
    }

    #[test]
    fn test_exit_notice_is_sent_only_after_a_confirmed_handshake() {
        assert_eq!(
            ExitNotice::of(&Ok(MarkOutcome::Confirmed)),
            ExitNotice::Sent
        );
        assert_eq!(
            ExitNotice::of(&Err(Error::ShutdownTimeout)),
            ExitNotice::NotSent
        );
        #[cfg(unix)]
        assert_eq!(
            ExitNotice::of(&Ok(MarkOutcome::Failed(
                crate::lsp::process::MarkFailure::NoConfirmation
            ))),
            ExitNotice::NotSent,
            "a withheld `exit` is not a sent one"
        );
    }

    #[test]
    fn test_client_capabilities_offer_configured_encodings_in_order() {
        let encodings =
            PositionEncodings::new(vec![PositionEncoding::Utf32, PositionEncoding::Utf8]).unwrap();
        let general = LspServer::client_capabilities(&encodings, None)
            .general
            .unwrap();
        assert_eq!(
            general.position_encodings,
            Some(vec![
                PositionEncodingKind::UTF32,
                PositionEncodingKind::UTF8
            ])
        );
    }

    /// P1/S2: without `window.work_done_progress == Some(true)`, no
    /// spec-compliant LSP server may ever initiate `$/progress` at all.
    /// Regression guard: deleting the capability lines in
    /// `client_capabilities` must fail this test, not silently no-op the
    /// whole feature with an otherwise-green suite.
    #[test]
    fn test_client_capabilities_advertises_work_done_progress() {
        let capabilities = LspServer::client_capabilities(&PositionEncodings::DEFAULT, None);

        assert_eq!(
            capabilities.window.and_then(|w| w.work_done_progress),
            Some(true)
        );
    }

    /// Without `prepareSupport`, clangd and typescript-language-server never
    /// advertise `prepareProvider`, which would make `prepare_rename`
    /// unreachable on them.
    #[test]
    fn test_client_capabilities_advertises_prepare_rename_support() {
        let rename = LspServer::client_capabilities(&PositionEncodings::DEFAULT, None)
            .text_document
            .and_then(|t| t.rename)
            .unwrap();

        assert_eq!(rename.prepare_support, Some(true));
        assert_eq!(
            rename.prepare_support_default_behavior,
            Some(lsp_types::PrepareSupportDefaultBehavior::Identifier)
        );
    }

    #[test]
    fn test_client_capabilities_advertises_folding_range_with_columns_and_collapsed_text() {
        let folding = LspServer::client_capabilities(&PositionEncodings::DEFAULT, None)
            .text_document
            .and_then(|t| t.folding_range)
            .unwrap();

        assert_eq!(folding.line_folding_only, Some(false));
        assert_eq!(
            folding
                .folding_range
                .and_then(|options| options.collapsed_text),
            Some(true)
        );
    }

    #[test]
    fn test_client_capabilities_advertises_selection_range() {
        let capabilities = LspServer::client_capabilities(&PositionEncodings::DEFAULT, None)
            .text_document
            .and_then(|t| t.selection_range)
            .unwrap();

        assert_eq!(capabilities.dynamic_registration, Some(false));
    }

    #[test]
    fn test_client_capabilities_advertise_did_save_without_dynamic_registration() {
        let synchronization = LspServer::client_capabilities(&PositionEncodings::DEFAULT, None)
            .text_document
            .and_then(|t| t.synchronization)
            .unwrap();

        assert_eq!(
            synchronization,
            lsp_types::TextDocumentSyncClientCapabilities {
                dynamic_registration: Some(false),
                did_save: Some(true),
                ..Default::default()
            }
        );
    }

    #[test]
    fn test_client_capabilities_advertises_publish_diagnostics_with_version_support_only() {
        let capabilities = LspServer::client_capabilities(&PositionEncodings::DEFAULT, None)
            .text_document
            .and_then(|t| t.publish_diagnostics)
            .unwrap();

        assert_eq!(
            capabilities,
            lsp_types::PublishDiagnosticsClientCapabilities {
                version_support: Some(true),
                ..Default::default()
            }
        );
    }

    #[test]
    fn test_client_capabilities_do_not_advertise_pull_diagnostics() {
        let text_document = LspServer::client_capabilities(&PositionEncodings::DEFAULT, None)
            .text_document
            .unwrap();

        assert!(text_document.diagnostic.is_none());
    }

    #[test]
    fn test_server_state_ready() {
        assert!(ServerState::Ready.is_ready());
    }

    #[test]
    fn test_server_state_uninitialized() {
        assert!(!ServerState::Uninitialized.is_ready());
    }

    #[test]
    fn test_server_state_initializing() {
        assert!(!ServerState::Initializing.is_ready());
    }

    #[test]
    fn test_workspace_folder_encodes_fragment_char() {
        // An unencoded `#` parses as a fragment, silently handing the server
        // the parent directory as its root.
        #[cfg(windows)]
        let (root, expected) = (
            Path::new(r"C:\home\me\dev\#work"),
            "file:///C:/home/me/dev/%23work",
        );
        #[cfg(not(windows))]
        let (root, expected) = (
            Path::new("/home/me/dev/#work"),
            "file:///home/me/dev/%23work",
        );

        let folder = workspace_folder(root).unwrap();

        assert_eq!(folder.uri.as_ref(), expected);
        assert_eq!(folder.name, "#work");
    }

    #[test]
    fn test_workspace_folder_encodes_bracket_chars() {
        #[cfg(windows)]
        let (root, expected) = (
            Path::new(r"C:\home\me\dev\[env]"),
            "file:///C:/home/me/dev/%5Benv%5D",
        );
        #[cfg(not(windows))]
        let (root, expected) = (
            Path::new("/home/me/dev/[env]"),
            "file:///home/me/dev/%5Benv%5D",
        );

        let folder = workspace_folder(root).unwrap();

        assert_eq!(folder.uri.as_ref(), expected);
        assert_eq!(folder.name, "[env]");
    }

    #[test]
    fn test_workspace_folder_rejects_relative_root() {
        let err = workspace_folder(Path::new("relative/root")).unwrap_err();
        assert_matches!(err, Error::PathToUri(_), "got {err:?}");
    }

    #[test]
    fn test_server_state_shutting_down() {
        assert!(!ServerState::ShuttingDown.is_ready());
    }

    #[test]
    fn test_server_state_shutdown() {
        assert!(!ServerState::Shutdown.is_ready());
    }

    #[test]
    fn test_server_state_equality() {
        assert_eq!(ServerState::Ready, ServerState::Ready);
        assert_ne!(ServerState::Ready, ServerState::Uninitialized);
        assert_eq!(ServerState::Shutdown, ServerState::Shutdown);
    }

    #[test]
    fn test_server_state_clone() {
        let state = ServerState::Ready;
        let cloned = state;
        assert_eq!(state, cloned);
    }

    #[test]
    fn test_server_state_debug() {
        let state = ServerState::Ready;
        let debug_str = format!("{state:?}");
        assert!(debug_str.contains("Ready"));
    }

    #[test]
    fn test_server_init_config_clone() {
        let config = ServerInitConfig::new(
            {
                let mut c = LspServerConfig::rust_analyzer();
                c.initialization_options = Some(serde_json::json!({"key": "value"}));
                c
            },
            WorkspaceRoots::for_test(vec![PathBuf::from("/tmp/workspace")], vec![]),
            PositionEncodings::DEFAULT,
            std::sync::Arc::default(),
        );

        #[allow(clippy::redundant_clone, reason = "the test exercises `Clone` itself")]
        let cloned = config.clone();
        assert_eq!(cloned.server_config().language_id, "rust");
        assert_eq!(cloned.workspace_roots().canonical().len(), 1);
    }

    #[test]
    fn test_server_init_config_debug() {
        let config = ServerInitConfig::new(
            LspServerConfig::pyright(),
            WorkspaceRoots::default(),
            PositionEncodings::DEFAULT,
            std::sync::Arc::default(),
        );

        let debug_str = format!("{config:?}");
        assert!(debug_str.contains("python"));
        assert!(debug_str.contains("pyright"));
    }

    #[test]
    fn test_server_init_config_with_options() {
        let init_opts = serde_json::json!({
            "settings": {
                "python": {
                    "analysis": {
                        "typeCheckingMode": "strict"
                    }
                }
            }
        });

        let mut env = crate::config::ServerEnv::default();
        env.insert(
            crate::config::EnvKey::from_static("PYTHONPATH"),
            crate::config::EnvValue::from_static("/usr/lib"),
        )
        .unwrap();

        let config = ServerInitConfig::new(
            LspServerConfig {
                language_id: LanguageId::from_static("python"),
                command: ServerCommand::from_static("pyright-langserver").into(),
                args: crate::config::ServerArgs::try_from(vec!["--stdio".to_string()]).unwrap(),
                env,
                file_patterns: vec![FilePattern::from_static("**/*.py")],
                initialization_options: Some(init_opts),
                settings: None,
                timeout_seconds: TimeoutSecs::new(10).unwrap(),
                request_timeout_seconds: TimeoutSecs::new(10).unwrap(),
                heuristics: None,
                name: None,
                handles: None,
                indexing: crate::bridge::IndexingPolicy::Auto,
            },
            WorkspaceRoots::for_test(vec![PathBuf::from("/workspace")], vec![]),
            PositionEncodings::DEFAULT,
            std::sync::Arc::default(),
        );

        assert!(config.server_config().initialization_options.is_some());
        assert_eq!(config.workspace_roots().canonical().len(), 1);
    }

    #[test]
    fn test_server_init_config_empty_workspace() {
        let config = ServerInitConfig::new(
            LspServerConfig::typescript(),
            WorkspaceRoots::default(),
            PositionEncodings::DEFAULT,
            std::sync::Arc::default(),
        );

        assert_eq!(config.workspace_roots().canonical().len(), 0);
    }

    #[test]
    fn test_server_init_config_multiple_workspaces() {
        let config = ServerInitConfig::new(
            LspServerConfig::rust_analyzer(),
            WorkspaceRoots::for_test(
                vec![
                    PathBuf::from("/workspace1"),
                    PathBuf::from("/workspace2"),
                    PathBuf::from("/workspace3"),
                ],
                vec![],
            ),
            PositionEncodings::DEFAULT,
            std::sync::Arc::default(),
        );

        assert_eq!(config.workspace_roots().canonical().len(), 3);
    }

    /// #249: `has_exited` must distinguish a live child from one that has
    /// already exited, since this is the signal the respawn path relies on
    /// to detect a crashed LSP server.
    ///
    /// Unix-only: spawns a real `sleep` subprocess, which is unavailable on
    /// the Windows CI runner.
    #[cfg(unix)]
    #[tokio::test]
    async fn test_has_exited_reflects_child_process_state() {
        use lsp_types::ServerCapabilities;

        let mut mock_child = tokio::process::Command::new("sleep")
            .arg("2")
            .stdin(Stdio::piped())
            .stdout(Stdio::piped())
            .kill_on_drop(true)
            .spawn()
            .unwrap();

        let mock_stdin = mock_child.stdin.take().unwrap();
        let mock_stdout = mock_child.stdout.take().unwrap();

        let transport = LspTransport::new(mock_stdin, mock_stdout);
        let client = LspClient::from_transport(LspServerConfig::rust_analyzer(), transport);

        let mut server = LspServer {
            client,
            capabilities: ServerCapabilities::default(),
            position_encoding: PositionEncodingKind::UTF8,
            child: Some(ServerProcess::from_unbound(mock_child)),
            init_config: crate::test_lsp::init_config_for(LspServerConfig::rust_analyzer()),
        };

        assert!(
            !server.has_exited().unwrap(),
            "freshly spawned `sleep 2` should still be running"
        );

        server.child.as_mut().unwrap().kill().await.unwrap();
        // `kill().await` waits for the process to actually exit, so the
        // very next `try_wait` reliably observes it as gone.
        assert!(
            server.has_exited().unwrap(),
            "killed child must report as exited"
        );
    }

    /// A live child whose message loop has stopped must be reported dead.
    #[cfg(unix)]
    #[tokio::test]
    async fn test_is_dead_when_message_loop_finished_but_child_alive() {
        let mut server = fake_lsp_server_with_dead_loop_and_live_child();

        tokio::time::timeout(Duration::from_secs(2), async {
            while !server.client.is_message_loop_finished() {
                tokio::time::sleep(Duration::from_millis(10)).await;
            }
        })
        .await
        .unwrap();

        assert!(!server.has_exited().unwrap());
        assert!(server.is_dead().unwrap());
    }

    /// A server that never answers `shutdown` fails the handshake with the
    /// request timeout, well inside `SHUTDOWN_TIMEOUT`, and still stops its
    /// message loop.
    #[tokio::test(start_paused = true)]
    async fn test_shutdown_reports_handshake_timeout_within_deadline() {
        let (client, _fake_server) = crate::test_lsp::fake_lsp_client();
        let probe = client.clone();
        let server = LspServer {
            client,
            capabilities: lsp_types::ServerCapabilities::default(),
            position_encoding: PositionEncodingKind::UTF8,
            child: None,
            init_config: crate::test_lsp::init_config_for(LspServerConfig::rust_analyzer()),
        };

        let started = Instant::now();
        let result = server.shutdown().await;

        assert_matches!(result, Err(Error::Timeout(_)), "got {result:?}");
        assert!(started.elapsed() <= SHUTDOWN_TIMEOUT);
        assert_matches!(probe.state().await, ServerState::Shutdown);
    }

    #[tokio::test]
    async fn test_is_dead_false_for_childless_fixture() {
        let mut server = fake_lsp_server();
        tokio::time::sleep(Duration::from_millis(50)).await;
        assert!(!server.is_dead().unwrap());
    }

    #[tokio::test]
    async fn test_lsp_server_getters() {
        use lsp_types::ServerCapabilities;

        let transport = crate::test_lsp::inert_transport();
        let client = LspClient::from_transport(LspServerConfig::rust_analyzer(), transport);

        let server = LspServer {
            client,
            capabilities: ServerCapabilities::default(),
            position_encoding: PositionEncodingKind::UTF8,
            child: None,
            init_config: crate::test_lsp::init_config_for(LspServerConfig::rust_analyzer()),
        };

        assert_eq!(server.position_encoding(), PositionEncodingKind::UTF8);
        assert!(server.capabilities().text_document_sync.is_none());

        let debug_str = format!("{server:?}");
        assert!(debug_str.contains("LspServer"));
        assert!(debug_str.contains("<process>"));
    }

    #[test]
    fn test_spawn_error_classifies_not_found() {
        use std::io::{Error as IoError, ErrorKind};

        let missing = spawn_error(
            ServerCommand::from_static("x"),
            IoError::from(ErrorKind::NotFound),
        );
        assert_matches!(missing, Error::ServerNotFound { .. });
        let denied = spawn_error(
            ServerCommand::from_static("x"),
            IoError::from(ErrorKind::PermissionDenied),
        );
        assert_matches!(denied, Error::ServerSpawnFailed { .. });
    }

    #[tokio::test]
    async fn test_spawn_nonexistent_command_is_server_not_found() {
        let mut server_config = LspServerConfig::rust_analyzer();
        server_config.command = ServerCommand::from_static("nonexistent-lsp-cmd-xyz").into();
        let config = ServerInitConfig::new(
            server_config,
            WorkspaceRoots::default(),
            PositionEncodings::DEFAULT,
            std::sync::Arc::default(),
        );
        let err = LspServer::spawn(config).await.unwrap_err();
        assert_matches!(err, Error::ServerNotFound { .. }, "got {err:?}");
    }

    #[tokio::test]
    async fn test_is_connection_loss_excludes_server_replies() {
        let join_error = tokio::spawn(async { panic!("receiver died") })
            .await
            .unwrap_err();
        assert!(is_connection_loss(&Error::ServerTerminated));
        assert!(is_connection_loss(&Error::TaskFailed {
            task: BackgroundTask::LspReceiver,
            source: join_error,
        }));
        assert!(!is_connection_loss(&Error::StdioCapture(
            StdioStream::Stdin
        )));
        assert!(!is_connection_loss(&Error::LspServerError(JsonRpcError {
            code: -32603,
            message: "bad".to_string(),
            data: None,
        })));
    }

    /// A server that answers `initialize` with an error and then exits keeps
    /// its own error instead of being reported as an early exit.
    #[cfg(unix)]
    #[tokio::test]
    async fn test_spawn_keeps_servers_own_initialize_error_when_it_exits_afterwards() {
        let dir = tempfile::TempDir::new().unwrap();
        let config = crate::test_lsp::sh_script_init_config(
            dir.path(),
            &crate::test_lsp::with_read_preamble(
                r#"body='{"jsonrpc":"2.0","id":1,"error":{"code":-32603,"message":"rejected by server"}}'
printf 'Content-Length: %d\r\n\r\n%s' ${#body} "$body"
"#,
            ),
        );

        let err = LspServer::spawn(config).await.unwrap_err();

        assert_matches!(
            &err,
            Error::LspInitFailed { phase: InitPhase::Initialize, cause, .. }
                if matches!(**cause, Error::LspServerError(JsonRpcError { code: -32603, .. })),
            "got {err:?}"
        );
        assert!(err.to_string().contains("rejected by server"), "{err}");
    }

    /// Connection lost while the child is still running: the error keeps the
    /// "initialize failed" context rather than a bare transport error.
    #[cfg(unix)]
    #[tokio::test]
    async fn test_spawn_connection_loss_with_live_child_is_lsp_init_failed() {
        let dir = tempfile::TempDir::new().unwrap();
        let config = crate::test_lsp::sh_script_init_config(dir.path(), "exec 1>&-\nsleep 5\n");

        let err = LspServer::spawn(config).await.unwrap_err();

        assert_matches!(
            &err,
            Error::LspInitFailed {
                phase: InitPhase::Initialize,
                ..
            },
            "got {err:?}"
        );
        assert!(
            err.to_string().contains("Initialize request failed"),
            "{err}"
        );
    }

    #[cfg(unix)]
    #[tokio::test]
    async fn test_spawn_exiting_before_initialize_reply_is_server_exited_during_init() {
        let dir = tempfile::TempDir::new().unwrap();
        let config = crate::test_lsp::sh_script_init_config(dir.path(), "exit 1\n");

        let err = LspServer::spawn(config).await.unwrap_err();

        assert_matches!(
            err,
            Error::ServerExitedDuringInit {
                exit_code: Some(1),
                ..
            },
            "got {err:?}"
        );
    }

    #[cfg(unix)]
    #[test]
    fn test_unbound_server_gets_the_real_process_id() {
        assert_eq!(
            initialize_process_id(Binding::Unbound),
            Some(i32::try_from(std::process::id()).unwrap())
        );
    }

    #[cfg(unix)]
    #[test]
    fn test_bound_server_gets_no_process_id() {
        assert_eq!(initialize_process_id(Binding::Bound), None);
    }

    /// A server guarded by a lifeline watchdog must not be handed the mcpls
    /// pid to watch: it could exit before the watchdog has frozen its tree.
    #[cfg(unix)]
    #[tokio::test]
    async fn test_spawn_sends_null_process_id_while_a_lifeline_is_bound() {
        let dir = tempfile::TempDir::new().unwrap();
        let dump = dir.path().join("request");
        let script = format!(
            "read -r header\nread -r _\nhead -c \"$(printf %s \"$header\" | tr -dc 0-9)\" > '{}'\nexit 1\n",
            dump.display()
        );
        let config = crate::test_lsp::sh_script_init_config(dir.path(), &script);

        LspServer::spawn(config).await.unwrap_err();

        let request = std::fs::read_to_string(&dump).unwrap();
        assert!(request.contains(r#""processId":null"#), "got {request}");
    }

    /// #534: what the server printed before exiting reaches the error.
    #[cfg(unix)]
    #[tokio::test]
    async fn test_spawn_exit_during_init_carries_stderr() {
        let dir = tempfile::TempDir::new().unwrap();
        let config = crate::test_lsp::sh_script_init_config(
            dir.path(),
            "echo 'fatal: bad toolchain' >&2\nexit 1\n",
        );

        let err = LspServer::spawn(config).await.unwrap_err();

        let Error::ServerExitedDuringInit {
            stderr: Some(stderr),
            ..
        } = &err
        else {
            panic!("got {err:?}");
        };
        assert_eq!(stderr.head(), "fatal: bad toolchain");
        assert!(err.to_string().contains("stderr: fatal: bad toolchain"));
    }

    /// A server that rejects `initialize` and prints its reason just before
    /// exiting must not lose that last line.
    #[cfg(unix)]
    #[tokio::test]
    async fn test_spawn_rejection_keeps_stderr_written_just_before_exit() {
        let dir = tempfile::TempDir::new().unwrap();
        let config = crate::test_lsp::sh_script_init_config(
            dir.path(),
            &crate::test_lsp::with_read_preamble(
                r#"body='{"jsonrpc":"2.0","id":1,"error":{"code":-32603,"message":"rejected by server"}}'
printf 'Content-Length: %d\r\n\r\n%s' ${#body} "$body"
# Shell-only pause: an external `sleep` can take longer than the 100 ms EOF grace just to start on a loaded macOS runner.
i=0; while [ $i -lt 300 ]; do i=$((i+1)); done
echo 'fatal: bad toolchain' >&2
"#,
            ),
        );

        let err = LspServer::spawn(config).await.unwrap_err();

        let Error::LspInitFailed {
            stderr: Some(stderr),
            ..
        } = &err
        else {
            panic!("got {err:?}");
        };
        assert_eq!(stderr.head(), "fatal: bad toolchain");
    }

    /// #534: a server that hangs after writing to stderr times out with its
    /// output attached.
    #[cfg(unix)]
    #[tokio::test]
    async fn test_spawn_initialize_timeout_carries_stderr() {
        let dir = tempfile::TempDir::new().unwrap();
        let mut config = crate::test_lsp::sh_script_init_config(
            dir.path(),
            "echo 'indexing forever' >&2\nsleep 5\n",
        );
        config.server_config.timeout_seconds = TimeoutSecs::new(1).unwrap();

        let err = LspServer::spawn(config).await.unwrap_err();

        let Error::LspInitFailed {
            stderr: Some(stderr),
            ..
        } = &err
        else {
            panic!("got {err:?}");
        };
        assert_eq!(stderr.head(), "indexing forever");
    }

    /// #612: a secret of another configured server, handed in through the
    /// init config, is hidden from this server's output although its own
    /// configuration does not name it.
    #[cfg(unix)]
    #[tokio::test]
    async fn test_spawn_hides_another_servers_secret_from_stderr() {
        let dir = tempfile::TempDir::new().unwrap();
        let mut config = crate::test_lsp::sh_script_init_config(
            dir.path(),
            "echo \"seen=$OTHER_VALUE own=$API_TOKEN\" >&2\nexit 1\n",
        );
        config
            .server_config
            .env
            .insert(
                crate::config::EnvKey::from_static("OTHER_VALUE"),
                crate::config::EnvValue::from_static("bravo-secret-222"),
            )
            .unwrap();
        config
            .server_config
            .env
            .insert(
                crate::config::EnvKey::from_static("API_TOKEN"),
                crate::config::EnvValue::from_static("s3cr3t-value"),
            )
            .unwrap();
        config.redactions = std::sync::Arc::new(Redactions::new([(
            "B_TOKEN".to_owned(),
            "bravo-secret-222".to_owned(),
        )]));

        let err = LspServer::spawn(config).await.unwrap_err();

        let text = err.to_string();
        assert!(text.contains("seen=[redacted:B_TOKEN]"), "{text}");
        assert!(text.contains("own=[redacted:API_TOKEN]"), "{text}");
    }

    /// Values configured in `env` never reach the error text.
    #[cfg(unix)]
    #[tokio::test]
    async fn test_spawn_stderr_redacts_configured_env_values() {
        let dir = tempfile::TempDir::new().unwrap();
        let mut config = crate::test_lsp::sh_script_init_config(
            dir.path(),
            "echo \"token=$API_TOKEN toolchain=$RUSTUP_TOOLCHAIN\" >&2\nexit 1\n",
        );
        config
            .server_config
            .env
            .insert(
                crate::config::EnvKey::from_static("RUSTUP_TOOLCHAIN"),
                crate::config::EnvValue::from_static("nightly-2024-01-01"),
            )
            .unwrap();
        config
            .server_config
            .env
            .insert(
                crate::config::EnvKey::from_static("API_TOKEN"),
                crate::config::EnvValue::from_static("s3cr3t-value"),
            )
            .unwrap();

        let err = LspServer::spawn(config).await.unwrap_err();

        let text = err.to_string();
        assert!(text.contains("token=[redacted:API_TOKEN]"), "{text}");
        assert!(text.contains("toolchain=nightly-2024-01-01"), "{text}");
        assert!(!text.contains("s3cr3t-value"), "{text}");
    }

    #[test]
    fn test_log_spawn_hides_argument_values() {
        use tracing_subscriber::prelude::*;

        use crate::test_lsp::CapturedLogs;

        let mut config = LspServerConfig::rust_analyzer();
        config.args = crate::config::ServerArgs::new(["--api-key=SuperSecretArg456"]).unwrap();
        let redactions = Redactions::for_server(&config, std::iter::empty());
        let logs = CapturedLogs::default();
        let info_only = tracing_subscriber::registry()
            .with(tracing_subscriber::filter::LevelFilter::INFO)
            .with(logs.clone());

        tracing::subscriber::with_default(info_only, || {
            LspServer::log_spawn(&config, &redactions);
        });

        let output = logs.messages().join("\n");
        assert!(output.contains("(1 arg(s))"), "{output}");
        assert!(!output.contains("SuperSecretArg456"), "{output}");
    }

    /// FR-012: a panic while starting one server is that server's failure.
    #[tokio::test]
    async fn contain_attributes_a_panic_to_its_own_server() {
        let config = crate::test_lsp::init_config_for(LspServerConfig::rust_analyzer());

        let outcome = contain(&config, async { panic!("start boom") }).await;

        assert_matches!(
            outcome,
            ServerStartOutcome::Failed(failure)
                if failure.server_id == config.server_config.id()
                    && matches!(failure.reason, StartupFailure::InitTaskPanicked)
        );
    }

    #[tokio::test]
    async fn contain_reports_a_spawn_error_as_that_servers_failure() {
        let config = crate::test_lsp::init_config_for(LspServerConfig::rust_analyzer());

        let outcome = contain(&config, async { Err(Error::ServerTerminated) }).await;

        assert_matches!(
            outcome,
            ServerStartOutcome::Failed(failure) if matches!(failure.reason, StartupFailure::Spawn(_))
        );
    }

    /// `window/logMessage` and `window/showMessage` text echoing configured
    /// secrets is redacted before it reaches the notification lane (#554).
    #[cfg(unix)]
    #[tokio::test]
    async fn test_spawn_redacts_secrets_in_server_log_and_show_messages() {
        let dir = tempfile::TempDir::new().unwrap();
        let script = r#"body='{"jsonrpc":"2.0","id":1,"result":{"capabilities":{}}}'
printf 'Content-Length: %d\r\n\r\n%s' ${#body} "$body"
body="{\"jsonrpc\":\"2.0\",\"method\":\"window/logMessage\",\"params\":{\"type\":3,\"message\":\"env=$API_TOKEN arg=$1\"}}"
printf 'Content-Length: %d\r\n\r\n%s' ${#body} "$body"
body="{\"jsonrpc\":\"2.0\",\"method\":\"window/showMessage\",\"params\":{\"type\":3,\"message\":\"env=$API_TOKEN\"}}"
printf 'Content-Length: %d\r\n\r\n%s' ${#body} "$body"
sleep 5
"#;
        let mut config = crate::test_lsp::sh_script_init_config(
            dir.path(),
            &crate::test_lsp::with_read_preamble(script),
        );
        config.server_config.args = crate::config::ServerArgs::new(
            config
                .server_config
                .args
                .iter()
                .cloned()
                .chain(["--api-key=SuperSecretArg456".to_string()]),
        )
        .unwrap();
        config
            .server_config
            .env
            .insert(
                crate::config::EnvKey::from_static("API_TOKEN"),
                crate::config::EnvValue::from_static("SuperSecretValue123"),
            )
            .unwrap();

        let SpawnedServer {
            server: _server,
            lanes,
        } = LspServer::spawn(config).await.unwrap();
        let mut rx = lanes.notifications.messages;
        let mut texts = Vec::new();
        for _ in 0..2 {
            let notification = tokio::time::timeout(Duration::from_secs(5), rx.recv())
                .await
                .unwrap()
                .unwrap();
            texts.push(format!("{notification:?}"));
        }

        let joined = texts.join("\n");
        assert!(!joined.contains("SuperSecretValue123"), "{joined}");
        assert!(!joined.contains("SuperSecretArg456"), "{joined}");
        assert!(joined.contains("[redacted:API_TOKEN]"), "{joined}");
        assert!(joined.contains("[redacted:api-key]"), "{joined}");
    }

    /// A secret echoed into a mistyped `initialize` result reaches the serde
    /// error text, which is redacted too (#554).
    #[cfg(unix)]
    #[tokio::test]
    async fn test_spawn_redacts_secrets_in_initialize_decode_error() {
        let dir = tempfile::TempDir::new().unwrap();
        let script = r#"body='{"jsonrpc":"2.0","id":1,"result":{"capabilities":"SuperSecretValue123"}}'
printf 'Content-Length: %d\r\n\r\n%s' ${#body} "$body"
sleep 5
"#;
        let mut config = crate::test_lsp::sh_script_init_config(
            dir.path(),
            &crate::test_lsp::with_read_preamble(script),
        );
        config
            .server_config
            .env
            .insert(
                crate::config::EnvKey::from_static("API_TOKEN"),
                crate::config::EnvValue::from_static("SuperSecretValue123"),
            )
            .unwrap();

        let err = LspServer::spawn(config).await.unwrap_err();

        let text = err.to_string();
        assert!(!text.contains("SuperSecretValue123"), "{text}");
    }

    /// The server's own `initialize` error text is redacted (#554).
    #[cfg(unix)]
    #[tokio::test]
    async fn test_spawn_redacts_secrets_in_initialize_error_message() {
        let dir = tempfile::TempDir::new().unwrap();
        let script = r#"body="{\"jsonrpc\":\"2.0\",\"id\":1,\"error\":{\"code\":-32603,\"message\":\"bad token $API_TOKEN\"}}"
printf 'Content-Length: %d\r\n\r\n%s' ${#body} "$body"
sleep 5
"#;
        let mut config = crate::test_lsp::sh_script_init_config(
            dir.path(),
            &crate::test_lsp::with_read_preamble(script),
        );
        config
            .server_config
            .env
            .insert(
                crate::config::EnvKey::from_static("API_TOKEN"),
                crate::config::EnvValue::from_static("SuperSecretValue123"),
            )
            .unwrap();

        let err = LspServer::spawn(config).await.unwrap_err();

        let text = err.to_string();
        assert!(text.contains("[redacted:API_TOKEN]"), "{text}");
        assert!(!text.contains("SuperSecretValue123"), "{text}");
    }

    /// Regression guard for the drain: a server flooding stderr both before
    /// and after it answers `initialize` must never block or lose its pipe
    /// (`EPIPE`/`SIGPIPE`) once `spawn` has returned.
    #[cfg(unix)]
    #[tokio::test]
    async fn test_spawn_keeps_draining_stderr_after_initialize() {
        let dir = tempfile::TempDir::new().unwrap();
        let marker = dir.path().join("flooded");
        let script = format!(
            r#"head -c 200000 /dev/zero | tr '\0' 'e' >&2
body='{{"jsonrpc":"2.0","id":1,"result":{{"capabilities":{{}}}}}}'
printf 'Content-Length: %d\r\n\r\n%s' ${{#body}} "$body"
sleep 0.3
head -c 200000 /dev/zero | tr '\0' 'e' >&2 && echo done > '{}'
sleep 5
"#,
            marker.display()
        );
        let config = crate::test_lsp::sh_script_init_config(
            dir.path(),
            &crate::test_lsp::with_read_preamble(&script),
        );

        let mut server = LspServer::spawn(config).await.unwrap().server;

        let flooded = tokio::time::timeout(Duration::from_secs(5), async {
            while !marker.exists() {
                tokio::time::sleep(Duration::from_millis(20)).await;
            }
        })
        .await;
        assert!(
            flooded.is_ok(),
            "server's post-initialize stderr flood did not complete"
        );
        assert!(!server.has_exited().unwrap());
    }

    /// Wire-level regressions for the `initialize` request. The tests
    /// capture the real bytes `LspServer::initialize` writes over an
    /// in-memory duplex pipe standing in for the LSP server. Mirrors the
    /// `fake_lsp_client`/`FakeServer` pattern in
    /// `client.rs::tests::retry_behavior`.
    mod initialize_wire {

        use tempfile::TempDir;
        use tokio::io::BufReader;

        use super::*;
        use crate::test_lsp::{
            fake_lsp_client, read_framed_message, write_response as write_success_response,
        };

        #[tokio::test]
        async fn test_initialize_sends_configured_position_encodings() {
            let (client, mut server) = fake_lsp_client();

            let config = ServerInitConfig::new(
                LspServerConfig::rust_analyzer(),
                WorkspaceRoots::default(),
                PositionEncodings::new(vec![PositionEncoding::Utf32, PositionEncoding::Utf8])
                    .unwrap(),
                std::sync::Arc::default(),
            );

            let init_task =
                tokio::spawn(async move { LspServer::initialize(&client, &config).await });

            let mut reader = BufReader::new(&mut server.write_stdout);
            let request = read_framed_message(&mut reader).await;

            assert_eq!(request["method"], "initialize");
            assert_eq!(
                request["params"]["capabilities"]["general"]["positionEncodings"],
                serde_json::json!(["utf-32", "utf-8"]),
                "initialize request must carry the configured encoding order, not the \
                 hardcoded [UTF8, UTF16] default"
            );

            write_success_response(
                &mut server.read_half_stdin,
                &request["id"].clone(),
                serde_json::json!({ "capabilities": {} }),
            )
            .await;

            // The response written above must let `initialize` complete successfully.
            init_task.await.unwrap().unwrap();
        }

        /// The three client frames of a handshake: `initialize`, `initialized`
        /// and `workspace/didChangeConfiguration`.
        struct Handshake {
            initialize: serde_json::Value,
            initialized: serde_json::Value,
            configuration: serde_json::Value,
        }

        async fn handshake_with_settings(settings_json: Option<&str>) -> Handshake {
            let (client, mut server) = fake_lsp_client();
            let mut server_config = LspServerConfig::rust_analyzer();
            server_config.settings = settings_json.map(|json| serde_json::from_str(json).unwrap());
            let config = crate::test_lsp::init_config_for(server_config);
            let init_task =
                tokio::spawn(async move { LspServer::initialize(&client, &config).await });

            let mut reader = BufReader::new(&mut server.write_stdout);
            let initialize = read_framed_message(&mut reader).await;
            assert_eq!(initialize["method"], "initialize");
            write_success_response(
                &mut server.read_half_stdin,
                &initialize["id"].clone(),
                serde_json::json!({ "capabilities": {} }),
            )
            .await;
            let initialized = read_framed_message(&mut reader).await;
            let configuration = read_framed_message(&mut reader).await;
            init_task.await.unwrap().unwrap();
            Handshake {
                initialize,
                initialized,
                configuration,
            }
        }

        #[tokio::test]
        async fn test_initialize_pushes_null_settings_right_after_initialized() {
            let wire = handshake_with_settings(None).await;

            assert_eq!(wire.initialized["method"], "initialized");
            assert_eq!(
                wire.configuration["method"],
                "workspace/didChangeConfiguration"
            );
            assert_eq!(
                wire.configuration["params"],
                serde_json::json!({ "settings": null })
            );
        }

        #[tokio::test]
        async fn test_initialize_pushes_configured_settings_and_advertises_configuration() {
            let wire =
                handshake_with_settings(Some(r#"{"python.analysis.typeCheckingMode": "strict"}"#))
                    .await;

            assert_eq!(
                wire.initialize["params"]["capabilities"]["workspace"]["configuration"],
                serde_json::json!(true)
            );
            assert_eq!(
                wire.configuration["params"],
                serde_json::json!({
                    "settings": { "python": { "analysis": { "typeCheckingMode": "strict" } } }
                })
            );
        }

        #[tokio::test]
        async fn test_initialize_pushes_gopls_flat_and_yaml_url_keys_on_the_wire() {
            let wire = handshake_with_settings(Some(
                r#"{"gopls":{"ui.semanticTokens":true},
                    "yaml.schemas":{"https://json.schemastore.org/x.json":"*.yml"}}"#,
            ))
            .await;

            let settings =
                serde_json::to_string(&wire.configuration["params"]["settings"]).unwrap();
            assert!(
                settings.contains(r#""gopls":{"ui.semanticTokens":true}"#),
                "{settings}"
            );
            assert!(
                settings.contains(
                    r#""yaml":{"schemas":{"https://json.schemastore.org/x.json":"*.yml"}}"#
                ),
                "{settings}"
            );
        }

        #[test]
        fn test_workspace_configuration_not_advertised_without_settings() {
            let workspace = LspServer::client_capabilities(&PositionEncodings::DEFAULT, None)
                .workspace
                .unwrap();
            assert_eq!(workspace.configuration, None);
        }

        #[tokio::test]
        async fn test_initialize_advertises_stale_request_support() {
            let (client, mut server) = fake_lsp_client();

            let config = ServerInitConfig::new(
                LspServerConfig::rust_analyzer(),
                WorkspaceRoots::default(),
                PositionEncodings::DEFAULT,
                std::sync::Arc::default(),
            );

            let init_task =
                tokio::spawn(async move { LspServer::initialize(&client, &config).await });

            let mut reader = BufReader::new(&mut server.write_stdout);
            let request = read_framed_message(&mut reader).await;
            let params: InitializeParams =
                serde_json::from_value(request["params"].clone()).unwrap();
            let stale_request_support = params
                .capabilities
                .general
                .unwrap()
                .stale_request_support
                .unwrap();

            assert_eq!(request["method"], "initialize");
            assert!(
                !stale_request_support.cancel,
                "mcpls does not implement active in-flight request cancellation"
            );
            assert_eq!(
                stale_request_support.retry_on_content_modified,
                CONTENT_MODIFIED_RETRY_METHODS
                    .iter()
                    .map(ToString::to_string)
                    .collect::<Vec<_>>(),
                "the wire-advertised capability must match the methods LspClient::request \
                 actually retries -32801 for, not drift from it"
            );

            write_success_response(
                &mut server.read_half_stdin,
                &request["id"].clone(),
                serde_json::json!({ "capabilities": {} }),
            )
            .await;

            init_task.await.unwrap().unwrap();
        }

        #[tokio::test]
        async fn test_initialize_advertises_server_status_notification_support() {
            let (client, mut server) = fake_lsp_client();

            let config = ServerInitConfig::new(
                LspServerConfig::rust_analyzer(),
                WorkspaceRoots::default(),
                PositionEncodings::DEFAULT,
                std::sync::Arc::default(),
            );

            let init_task =
                tokio::spawn(async move { LspServer::initialize(&client, &config).await });

            let mut reader = BufReader::new(&mut server.write_stdout);
            let request = read_framed_message(&mut reader).await;

            assert_eq!(request["method"], "initialize");
            assert_eq!(
                request["params"]["capabilities"]["experimental"]["serverStatusNotification"],
                serde_json::json!(true),
                "without this, rust-analyzer never emits experimental/serverStatus and the \
                 indexing-readiness gate in Translator::wait_for_indexing_ready is a \
                 permanent no-op"
            );

            write_success_response(
                &mut server.read_half_stdin,
                &request["id"].clone(),
                serde_json::json!({ "capabilities": {} }),
            )
            .await;

            init_task.await.unwrap().unwrap();
        }

        #[tokio::test]
        async fn test_initialize_advertises_hierarchical_document_symbols() {
            let (client, mut server) = fake_lsp_client();

            let config = ServerInitConfig::new(
                LspServerConfig::rust_analyzer(),
                WorkspaceRoots::default(),
                PositionEncodings::DEFAULT,
                std::sync::Arc::default(),
            );

            let init_task =
                tokio::spawn(async move { LspServer::initialize(&client, &config).await });

            let mut reader = BufReader::new(&mut server.write_stdout);
            let request = read_framed_message(&mut reader).await;
            let params: InitializeParams =
                serde_json::from_value(request["params"].clone()).unwrap();
            let document_symbol = params
                .capabilities
                .text_document
                .unwrap()
                .document_symbol
                .unwrap();

            assert_eq!(request["method"], "initialize");
            assert_eq!(document_symbol.dynamic_registration, Some(false));
            assert_eq!(
                document_symbol.hierarchical_document_symbol_support,
                Some(true)
            );
            assert_eq!(
                document_symbol.symbol_kind.unwrap().value_set,
                Some(advertised_symbol_kinds())
            );

            write_success_response(
                &mut server.read_half_stdin,
                &request["id"].clone(),
                serde_json::json!({ "capabilities": {} }),
            )
            .await;

            init_task.await.unwrap().unwrap();
        }

        #[tokio::test]
        async fn test_initialize_accepts_resolved_dot_workspace_root() {
            let temp_dir = TempDir::new().unwrap();
            let base = dunce::canonicalize(temp_dir.path()).unwrap();
            let workspace_roots =
                crate::bridge::WorkspaceRoots::from_paths_with(&[PathBuf::from(".")], || {
                    Ok(crate::bridge::ProcessCwd::new(base.clone(), None))
                })
                .unwrap()
                .canonical()
                .to_vec();
            assert_eq!(workspace_roots, vec![base.clone()]);

            let (client, mut server) = fake_lsp_client();
            let config = ServerInitConfig::new(
                LspServerConfig::rust_analyzer(),
                WorkspaceRoots::for_test(workspace_roots, vec![]),
                PositionEncodings::DEFAULT,
                std::sync::Arc::default(),
            );

            let init_task =
                tokio::spawn(async move { LspServer::initialize(&client, &config).await });

            let mut reader = BufReader::new(&mut server.write_stdout);
            let request = read_framed_message(&mut reader).await;
            let expected_uri = try_path_to_uri(&base).unwrap();
            assert_eq!(
                request["params"]["workspaceFolders"][0]["uri"],
                expected_uri.as_ref()
            );

            write_success_response(
                &mut server.read_half_stdin,
                &request["id"].clone(),
                serde_json::json!({ "capabilities": {} }),
            )
            .await;

            init_task.await.unwrap().unwrap();
        }
    }

    /// #691: an override spelled `Path` is the `PATH` the child sees on Windows,
    /// so resolution must read it too; elsewhere it is another variable.
    #[test]
    fn child_env_var_compares_names_as_the_host_does() {
        let parent = |_: &str| Some(std::ffi::OsString::from("/parent"));
        let on = |host| {
            let mut config = bare_server_config(HashMap::new());
            config.env = crate::config::ServerEnv::from_entries(
                [(
                    crate::config::EnvKey::from_static("Path"),
                    crate::config::EnvValue::from_static("/over"),
                )],
                host,
            )
            .unwrap();
            child_env_var(&config, "PATH", parent)
        };

        assert_eq!(on(HostOs::Windows), Some(std::ffi::OsString::from("/over")));
        assert_eq!(on(HostOs::Other), Some(std::ffi::OsString::from("/parent")));
    }

    /// Minimal [`LspServerConfig`] for `build_command` tests, where only
    /// `command`/`args`/`env` matter.
    fn bare_server_config(
        env: HashMap<crate::config::EnvKey, crate::config::EnvValue>,
    ) -> LspServerConfig {
        LspServerConfig {
            language_id: LanguageId::from_static("test"),
            command: ServerCommand::from_static("irrelevant-for-build-command").into(),
            args: crate::config::ServerArgs::default(),
            env: crate::config::ServerEnv::from_entries(env, HostOs::CURRENT).unwrap(),
            file_patterns: vec![],
            initialization_options: None,
            settings: None,
            timeout_seconds: TimeoutSecs::new(5).unwrap(),
            request_timeout_seconds: TimeoutSecs::new(5).unwrap(),
            heuristics: None,
            name: None,
            handles: None,
            indexing: crate::bridge::IndexingPolicy::Auto,
        }
    }

    /// Collects the env vars a `Command` would set, resolving `env_clear`
    /// removals (`None` values from `get_envs`) away so the map reflects
    /// what the child process would actually see.
    fn effective_envs(command: &Command) -> HashMap<String, String> {
        command
            .as_std()
            .get_envs()
            .filter_map(|(k, v)| {
                v.map(|v| {
                    (
                        k.to_string_lossy().into_owned(),
                        v.to_string_lossy().into_owned(),
                    )
                })
            })
            .collect()
    }

    /// Regression test for #236/#246: a spawned LSP server used to inherit
    /// mcpls's entire environment. `build_command` must only pass through
    /// `ENV_PASSTHROUGH` keys from `parent_env`, not arbitrary ones.
    #[test]
    fn test_build_command_excludes_non_allowlisted_parent_env_vars() {
        let config = bare_server_config(HashMap::new());
        let command =
            LspServer::build_command(&config, &ChildWorkingDir::Inherit, |key| match key {
                "PATH" => Some("/parent/bin".into()),
                "MCPLS_TEST_LEAK_CANARY" => Some("should-not-reach-child".into()),
                _ => None,
            });

        let envs = effective_envs(&command);

        assert!(
            !envs.contains_key("MCPLS_TEST_LEAK_CANARY"),
            "non-allowlisted parent env var leaked into child command: {envs:?}"
        );

        // The assertion above is provably vacuous on its own:
        // `Command::get_envs()` only reports explicit `.env()`/`.envs()`
        // modifications and is blind to whether `.env_clear()` was called,
        // and `build_command`'s passthrough loop never even queries
        // `parent_env` for a key outside `ENV_PASSTHROUGH`, so it would
        // pass unchanged even if `.env_clear()` were deleted from
        // `build_command` entirely. `std::process::Command`'s `Debug` impl
        // does encode clearing, prefixing the formatted command with
        // `env -i ` on Unix once `.env_clear()` has run; assert on that to
        // actually guard against the clear being removed.
        #[cfg(unix)]
        assert!(
            format!("{:?}", command.as_std()).starts_with("env -i "),
            "build_command must call .env_clear() so the child doesn't inherit the full parent environment"
        );
    }

    /// Regression test for #236/#246: allowlisted vars present in the parent
    /// (e.g. `PATH`) must still reach the child.
    #[test]
    fn test_build_command_passes_through_allowlisted_env_vars() {
        let config = bare_server_config(HashMap::new());
        let command = LspServer::build_command(&config, &ChildWorkingDir::Inherit, |key| {
            (key == "PATH").then(|| "/parent/bin".into())
        });

        let envs = effective_envs(&command);

        assert_eq!(envs.get("PATH"), Some(&"/parent/bin".to_string()));
    }

    #[test]
    fn test_build_command_inherits_working_dir_unless_fixed() {
        let config = bare_server_config(HashMap::new());
        let inherited = LspServer::build_command(&config, &ChildWorkingDir::Inherit, |_| None);
        assert_eq!(inherited.as_std().get_current_dir(), None);

        let dir = PathBuf::from("/fixed/dir");
        let fixed =
            LspServer::build_command(&config, &ChildWorkingDir::Fixed(dir.clone()), |_| None);
        assert_eq!(fixed.as_std().get_current_dir(), Some(dir.as_path()));
    }

    #[test]
    fn test_server_init_config_defaults_to_inherited_working_dir() {
        let config = ServerInitConfig::new(
            LspServerConfig::rust_analyzer(),
            WorkspaceRoots::default(),
            PositionEncodings::DEFAULT,
            std::sync::Arc::default(),
        );
        assert_eq!(config.child_working_dir(), &ChildWorkingDir::Inherit);
        let fixed = config.with_child_working_dir(ChildWorkingDir::Fixed(PathBuf::from("/x")));
        assert_eq!(
            fixed.child_working_dir(),
            &ChildWorkingDir::Fixed(PathBuf::from("/x"))
        );
    }

    #[tokio::test]
    async fn test_for_respawn_keeps_the_config_and_pinned_tsserver() {
        let mut server_config = LspServerConfig::typescript();
        server_config.initialization_options =
            Some(serde_json::json!({"tsserver": {"path": "/pin/tsserver.js"}}));
        let config = ServerInitConfig::new(
            server_config,
            WorkspaceRoots::default(),
            PositionEncodings::DEFAULT,
            std::sync::Arc::default(),
        );
        assert_eq!(
            config.pinned_tsserver(),
            Some(PathBuf::from("/pin/tsserver.js"))
        );

        let respawn = config.for_respawn().await.unwrap();
        assert_eq!(
            respawn.server_config().initialization_options,
            config.server_config().initialization_options
        );
        assert_eq!(respawn.pinned_tsserver(), config.pinned_tsserver());
    }

    /// An auto-pinned server is re-planned on the blocking pool and the result
    /// keeps the entry's identity; a pin that no longer resolves is dropped.
    #[tokio::test]
    async fn test_for_respawn_replans_an_auto_pinned_server_off_the_runtime() {
        let mut server_config = LspServerConfig::typescript();
        server_config.initialization_options =
            Some(serde_json::json!({"tsserver": {"path": "/mcpls-test/stale/tsserver.js"}}));
        let config = ServerInitConfig::new(
            server_config,
            WorkspaceRoots::default(),
            PositionEncodings::DEFAULT,
            std::sync::Arc::default(),
        )
        .with_auto_pin(PathBuf::from("/mcpls-test/stale/tsserver.js"));

        let respawn = config.for_respawn().await.unwrap();

        assert_eq!(respawn.server_config().id(), config.server_config().id());
        assert_ne!(respawn.pinned_tsserver(), config.pinned_tsserver());
    }

    /// An untrusted server with `tool`, a file inside its boundary that is not
    /// executable yet, as its only argument.
    fn untrusted_init_naming_a_tool_argument() -> (tempfile::TempDir, PathBuf, ServerInitConfig) {
        let dir = tempfile::TempDir::new().unwrap();
        let workspace = dunce::canonicalize(dir.path()).unwrap();
        let tool = workspace.join("tool");
        std::fs::write(&tool, "").unwrap();
        let roots = WorkspaceRoots::from_paths(std::slice::from_ref(&workspace)).unwrap();
        let mut server_config = LspServerConfig::rust_analyzer();
        server_config.command = ServerCommand::from_static("mcpls-test-no-such-server").into();
        server_config.args =
            crate::config::ServerArgs::new([tool.to_string_lossy().into_owned()]).unwrap();
        let command = server_config.command.server_command().clone();
        let init = ServerInitConfig::new(
            server_config,
            roots.clone(),
            PositionEncodings::DEFAULT,
            std::sync::Arc::default(),
        )
        .with_trust(SpawnTrust::Untrusted(UntrustedVetting::new(roots, command)));
        (dir, tool, init)
    }

    /// Makes the file `tool` something the host would start.
    fn become_executable(tool: &Path) {
        #[cfg(unix)]
        {
            use std::os::unix::fs::PermissionsExt as _;
            std::fs::set_permissions(tool, std::fs::Permissions::from_mode(0o755)).unwrap();
        }
        #[cfg(windows)]
        std::fs::write(tool.with_added_extension("exe"), "").unwrap();
    }

    fn refused_argument(error: &Error) -> bool {
        matches!(
            error,
            Error::ServerFailedToStart(failure) if matches!(
                failure.reason,
                StartupFailure::RefusedUntrustedWorkspace(
                    UntrustedRefusal::WorkspaceExecutableArgument { index: 0, .. }
                )
            )
        )
    }

    /// Regression test for #736: the backstop runs again at spawn time.
    #[tokio::test]
    async fn test_spawn_refuses_an_argument_that_became_executable_after_planning() {
        let (_dir, tool, init) = untrusted_init_naming_a_tool_argument();
        init.vet_arguments().unwrap();

        become_executable(&tool);

        let Err(error) = LspServer::spawn(init).await else {
            panic!("the spawn must be refused");
        };
        assert!(refused_argument(&error), "{error:?}");
    }

    /// Regression test for #736: a respawn plan is a complete dry run.
    #[tokio::test]
    async fn test_for_respawn_refuses_an_argument_that_became_executable_after_planning() {
        let (_dir, tool, init) = untrusted_init_naming_a_tool_argument();
        let unchanged = init.for_respawn().await.unwrap();
        assert_eq!(unchanged.server_config().args, init.server_config().args);

        become_executable(&tool);

        let Err(error) = init.for_respawn().await else {
            panic!("the respawn plan must be refused");
        };
        assert!(refused_argument(&error), "{error:?}");
    }

    #[tokio::test]
    async fn test_a_trusted_config_is_never_vetted_at_spawn_time() {
        let (_dir, tool, init) = untrusted_init_naming_a_tool_argument();
        let trusted = ServerInitConfig::new(
            init.server_config().clone(),
            init.workspace_roots().clone(),
            PositionEncodings::DEFAULT,
            std::sync::Arc::default(),
        );
        become_executable(&tool);

        trusted.vet_arguments().unwrap();
        trusted.vet_arguments_off_runtime().await.unwrap();
        trusted.for_respawn().await.unwrap();
    }

    /// The `shutdown` result is `null` by the specification; a server that
    /// answers with another value still gets the `exit` that follows.
    #[tokio::test(start_paused = true)]
    async fn test_terminate_sends_exit_after_a_shutdown_answer_that_is_not_null() {
        use tokio::io::BufReader;

        use crate::test_lsp::{fake_lsp_client, read_framed_message, write_response};

        let (client, mut fake) = fake_lsp_client();
        let mut server = LspServer {
            client,
            capabilities: lsp_types::ServerCapabilities::default(),
            position_encoding: PositionEncodingKind::UTF8,
            child: None,
            init_config: crate::test_lsp::init_config_for(LspServerConfig::rust_analyzer()),
        };
        let terminating = tokio::spawn(async move {
            server
                .terminate(SHUTDOWN_TIMEOUT, ExitGrace::WithinBudget)
                .await
        });
        let mut wire = BufReader::new(&mut fake.write_stdout);

        let request = read_framed_message(&mut wire).await;
        assert_eq!(request["method"], "shutdown");
        write_response(
            &mut fake.read_half_stdin,
            &request["id"],
            serde_json::json!({}),
        )
        .await;
        let exit = read_framed_message(&mut wire).await;

        assert_eq!(exit["method"], "exit");
        assert_matches!(terminating.await.unwrap(), Ok(()));
    }

    /// Regression test for #247: `LspServerConfig::env` entries must reach
    /// the spawned child (previously dead configuration).
    #[test]
    fn test_build_command_includes_configured_env_vars() {
        let mut env = HashMap::new();
        env.insert(
            crate::config::EnvKey::from_static("MCPLS_TEST_CONFIGURED"),
            crate::config::EnvValue::from_static("from-server-config"),
        );
        let config = bare_server_config(env);
        let command = LspServer::build_command(&config, &ChildWorkingDir::Inherit, |_| None);

        let envs = effective_envs(&command);

        assert_eq!(
            envs.get("MCPLS_TEST_CONFIGURED"),
            Some(&"from-server-config".to_string())
        );
    }

    /// Regression test for #247: a `LspServerConfig::env` entry must be able
    /// to override an allowlisted passthrough value, since `config.env` is
    /// applied after the passthrough loop in `build_command`.
    #[test]
    fn test_build_command_configured_env_overrides_allowlisted_var() {
        let mut env = HashMap::new();
        env.insert(
            crate::config::EnvKey::from_static("PATH"),
            crate::config::EnvValue::from_static("/configured/override/path"),
        );
        let config = bare_server_config(env);
        let command = LspServer::build_command(&config, &ChildWorkingDir::Inherit, |key| {
            (key == "PATH").then(|| "/parent/bin".into())
        });

        let envs = effective_envs(&command);

        assert_eq!(
            envs.get("PATH"),
            Some(&"/configured/override/path".to_string())
        );
    }

    /// #174 section 8 regression: the diagnostics route must be read from the
    /// router as re-derived after the explicit diagnostics server failed, not
    /// from the configured one. A narrow "diagnostics-only" server
    /// (`pyright-diag`) fails to start, leaving only a catch-all (`pylsp`);
    /// resolving `Diagnostics` against the configured router would name the
    /// dead `pyright-diag` and silence diagnostics for `python`.
    #[tokio::test]
    async fn test_settling_dead_diagnostics_server_hands_the_route_to_the_catch_all() {
        use crate::bridge::Translator;
        use crate::config::{ServerId, ToolKind, ToolRouter};

        let pylsp_id = ServerId::from_static("pylsp");
        let configs = vec![
            LspServerConfig {
                language_id: LanguageId::from_static("python"),
                command: ServerCommand::from_static("pyright-langserver").into(),
                args: crate::config::ServerArgs::default(),
                env: crate::config::ServerEnv::default(),
                file_patterns: vec![],
                initialization_options: None,
                settings: None,
                timeout_seconds: TimeoutSecs::new(30).unwrap(),
                request_timeout_seconds: TimeoutSecs::new(30).unwrap(),
                heuristics: None,
                name: Some(ServerId::from_static("pyright-diag")),
                handles: Some(ToolSet::new(vec![ToolKind::Diagnostics]).unwrap()),
                indexing: crate::bridge::IndexingPolicy::Auto,
            },
            LspServerConfig {
                language_id: LanguageId::from_static("python"),
                command: ServerCommand::from_static("pylsp").into(),
                args: crate::config::ServerArgs::default(),
                env: crate::config::ServerEnv::default(),
                file_patterns: vec![],
                initialization_options: None,
                settings: None,
                timeout_seconds: TimeoutSecs::new(30).unwrap(),
                request_timeout_seconds: TimeoutSecs::new(30).unwrap(),
                heuristics: None,
                name: Some(ServerId::from_static("pylsp")),
                handles: None,
                indexing: crate::bridge::IndexingPolicy::Auto,
            },
        ];
        let router = ToolRouter::from_configs(&configs).unwrap();
        let translator = Translator::new().with_router(router);
        translator.set_expected_servers(
            [ServerId::from_static("pyright-diag"), pylsp_id.clone()]
                .into_iter()
                .collect(),
        );

        translator.settle_failed(&ServerSpawnFailure {
            server_id: ServerId::from_static("pyright-diag"),
            language_id: LanguageId::from_static("python"),
            command: ServerCommand::from_static("pyright-langserver"),
            reason: StartupFailure::InitTaskPanicked,
        });
        translator.settle_started(fake_lsp_server_with_config(configs[1].clone()));

        assert!(
            translator.is_diagnostics_route(&LanguageId::from_static("python"), &pylsp_id),
            "pylsp must inherit the diagnostics route once pyright-diag is known dead"
        );
    }
}