rch 2.1.13

//! Rust toolchain version detection.
//!
//! Resolves project toolchain declarations and active rustup identities.
//! Compiler commit dates are diagnostic metadata, never rustup archive dates.

#![allow(dead_code)]

use rch_common::ToolchainInfo;
use std::io::{Read, Seek};
use std::path::{Path, PathBuf};
use std::process::{Child, Command, Stdio};
use std::time::{Duration, Instant};

const TOOLCHAIN_PROBE_BUDGET: Duration = Duration::from_secs(2);
const MAX_TOOLCHAIN_PROBE_BYTES: u64 = 64 * 1024;

/// Errors that can occur during toolchain detection.
#[derive(Debug, thiserror::Error)]
pub enum ToolchainError {
    #[error("IO error: {0}")]
    Io(#[from] std::io::Error),
    #[error("Invalid toolchain file format")]
    InvalidFormat,
    #[error("Failed to parse rustc version: {0}")]
    ParseError(String),
    #[error("TOML parse error: {0}")]
    Toml(#[from] toml::de::Error),
    #[error("Toolchain resolution refused: {0}")]
    Resolution(String),
}

/// Detect the active Rust toolchain for a project.
///
/// Explicit command selectors are handled by the hook first; an explicit
/// environment identity can also be resolved without a locally installed rustc.
/// Otherwise Rustup, not a file-only approximation, resolves directory overrides
/// and toolchain files by proximity. Its private settings format is never read.
/// Only an absent Rustup executable permits the standalone file/rustc fallback;
/// a failed or malformed Rustup query must not select an unrelated compiler.
pub fn detect_toolchain(project_root: &Path) -> Result<ToolchainInfo, ToolchainError> {
    let ambient = match std::env::var("RUSTUP_TOOLCHAIN") {
        Ok(value) => Some(value),
        Err(std::env::VarError::NotPresent) => None,
        Err(std::env::VarError::NotUnicode(_)) => return Err(ToolchainError::InvalidFormat),
    };
    detect_resolved_toolchain_with(project_root, ambient.as_deref(), "rustup", "rustc")
}

/// Also used with explicit executable paths by subprocess-boundary tests.
fn detect_resolved_toolchain_with(
    project_root: &Path,
    ambient: Option<&str>,
    rustup: &str,
    rustc: &str,
) -> Result<ToolchainInfo, ToolchainError> {
    if let Some(name) = ambient.filter(|name| !name.is_empty()) {
        if name.contains(char::is_whitespace) || name.chars().any(char::is_control) {
            return Err(ToolchainError::InvalidFormat);
        }
        return parse_active_toolchain(name);
    }
    let until = Instant::now() + TOOLCHAIN_PROBE_BUDGET;
    if let Some(output) =
        run_toolchain_probe(toolchain_probe(rustup, &["show"], project_root), until)?
    {
        return resolved_rustup_identity(project_root, &rustup_show_identity(&output)?);
    }
    // Without Rustup, retain support for standalone installations and project
    // declarations. Do not make a second Rustup attempt or renew the budget.
    detect_toolchain_with(project_root, None, |root| {
        detect_rustc_toolchain(root, rustc, until)
    })
}

/// A fallback for hosts without Rustup, not an authority over its override DB.
fn detect_toolchain_with(
    project_root: &Path,
    ambient: Option<&str>,
    fallback: impl FnOnce(&Path) -> Result<ToolchainInfo, ToolchainError>,
) -> Result<ToolchainInfo, ToolchainError> {
    if let Some(name) = ambient.filter(|name| !name.is_empty()) {
        return parse_active_toolchain(name);
    }
    if let Some(path) = nearest_toolchain_file(project_root)? {
        let parsed = if path
            .file_name()
            .is_some_and(|name| name == "rust-toolchain")
        {
            parse_legacy_toolchain_file(&path)
        } else {
            parse_toolchain_file(&path)
        };
        match parsed {
            Ok(info) => return Ok(info),
            // Only a valid channel-less declaration may use the standalone
            // compiler. A broken pin must not silently select a different one.
            Err(ToolchainError::InvalidFormat) if file_has_implicit_channel(&path) => {}
            Err(error) => return Err(error),
        }
    }
    fallback(project_root)
}

/// Read the components explicitly declared by the project's rust-toolchain
/// file. Plain-text legacy files declare no components. Invalid or unreadable
/// files return an empty set so callers can still report connectivity without
/// inventing requirements.
pub fn detect_declared_components(project_root: &Path) -> Vec<String> {
    nearest_toolchain_file(project_root)
        .ok()
        .flatten()
        .and_then(|path| std::fs::read_to_string(path).ok())
        .map(|content| parse_declared_components(&content))
        .unwrap_or_default()
}

/// Match rustup's ancestor search and same-directory filename precedence.
/// A nearer declaration shadows the entire ancestor declaration, including
/// components; unreadable entries must not reveal a farther declaration.
fn nearest_toolchain_file(project_root: &Path) -> Result<Option<PathBuf>, ToolchainError> {
    let root = project_root.canonicalize()?;
    for directory in root.ancestors() {
        for name in ["rust-toolchain", "rust-toolchain.toml"] {
            let path = directory.join(name);
            match path.try_exists() {
                Ok(true) => return Ok(Some(path)),
                Ok(false) => {}
                Err(error) => return Err(error.into()),
            }
        }
    }
    Ok(None)
}

fn parse_declared_components(content: &str) -> Vec<String> {
    let Ok(value) = toml::from_str::<toml::Value>(content) else {
        return Vec::new();
    };
    let Some(values) = value
        .get("toolchain")
        .and_then(|toolchain| toolchain.get("components"))
        .and_then(toml::Value::as_array)
    else {
        return Vec::new();
    };

    let mut components = values
        .iter()
        .filter_map(toml::Value::as_str)
        .map(str::trim)
        .filter(|component| !component.is_empty())
        .map(str::to_string)
        .collect::<Vec<_>>();
    components.sort();
    components.dedup();
    components
}

/// Parse a rust-toolchain.toml file.
fn parse_toolchain_file(path: &Path) -> Result<ToolchainInfo, ToolchainError> {
    let content = std::fs::read_to_string(path)?;
    let toml: toml::Value = toml::from_str(&content)?;

    let channel = toml
        .get("toolchain")
        .and_then(|t| t.get("channel"))
        .and_then(|c| c.as_str())
        .ok_or(ToolchainError::InvalidFormat)?;

    parse_channel_string(channel)
}

/// Parse a legacy rust-toolchain file (plain text channel name or TOML).
fn parse_legacy_toolchain_file(path: &Path) -> Result<ToolchainInfo, ToolchainError> {
    let content = std::fs::read_to_string(path)?;

    // rustup allows `rust-toolchain` (no extension) to be either TOML or plain text.
    // Try TOML parsing first.
    if let Ok(toml) = toml::from_str::<toml::Value>(&content) {
        let channel = toml
            .get("toolchain")
            .and_then(|t| t.get("channel"))
            .and_then(|c| c.as_str())
            .ok_or(ToolchainError::InvalidFormat)?;
        return parse_channel_string(channel);
    }

    // Fallback: treat as plain text channel name (trim whitespace)
    let channel = content.trim();
    if channel.is_empty() || channel.contains(char::is_whitespace) {
        return Err(ToolchainError::InvalidFormat);
    }
    parse_channel_string(channel)
}

/// Parse a channel string like "nightly-2024-01-15" or "stable".
pub fn parse_channel_string(channel: &str) -> Result<ToolchainInfo, ToolchainError> {
    // Handle nightly-YYYY-MM-DD format
    if let Some(date) = channel.strip_prefix("nightly-")
        && is_valid_date(date)
    {
        return Ok(ToolchainInfo {
            channel: "nightly".to_string(),
            date: Some(date.to_string()),
            full_version: channel.to_string(),
        });
    }

    // Handle beta-YYYY-MM-DD format
    if let Some(date) = channel.strip_prefix("beta-")
        && is_valid_date(date)
    {
        return Ok(ToolchainInfo {
            channel: "beta".to_string(),
            date: Some(date.to_string()),
            full_version: channel.to_string(),
        });
    }

    // Handle simple channel names
    if channel == "stable" || channel == "beta" || channel == "nightly" {
        return Ok(ToolchainInfo {
            channel: channel.to_string(),
            date: None,
            full_version: channel.to_string(),
        });
    }

    // Handle specific version like "1.75.0"
    if is_version_number(channel) {
        return Ok(ToolchainInfo {
            channel: channel.to_string(),
            date: None,
            full_version: channel.to_string(),
        });
    }

    // Unknown format, treat as channel name
    Ok(ToolchainInfo {
        channel: channel.to_string(),
        date: None,
        full_version: channel.to_string(),
    })
}

/// Check if a string looks like a date (YYYY-MM-DD).
fn is_valid_date(s: &str) -> bool {
    if s.len() != 10 {
        return false;
    }
    let parts: Vec<&str> = s.split('-').collect();
    if parts.len() != 3 {
        return false;
    }
    // Check format: YYYY-MM-DD with all digits
    if !(parts[0].len() == 4
        && parts[1].len() == 2
        && parts[2].len() == 2
        && parts.iter().all(|p| p.chars().all(|c| c.is_ascii_digit())))
    {
        return false;
    }
    // Validate month and day ranges
    let month: u32 = parts[1].parse().unwrap_or(0);
    let day: u32 = parts[2].parse().unwrap_or(0);
    (1..=12).contains(&month) && (1..=31).contains(&day)
}

/// Check if a string looks like a version number (X.Y.Z).
fn is_version_number(s: &str) -> bool {
    let parts: Vec<&str> = s.split('.').collect();
    parts.len() >= 2
        && parts.len() <= 3
        && parts
            .iter()
            .all(|p| !p.is_empty() && p.chars().all(|c| c.is_ascii_digit()))
}

/// Keep rustup proxies from installing missing toolchains during detection.
fn toolchain_probe(program: &str, args: &[&str], project_root: &Path) -> Command {
    let mut command = Command::new(program);
    command
        .args(args)
        .current_dir(project_root)
        .env("RUSTUP_AUTO_INSTALL", "0")
        .env("RUSTUP_TERM_COLOR", "never")
        .stdin(Stdio::null());
    command
}

/// Own and reap the directly spawned query even when a deadline, size check or
/// read fails. This does not claim to sandbox a hostile executable's descendants.
struct ToolchainProbeChild(Child);

impl Drop for ToolchainProbeChild {
    fn drop(&mut self) {
        if !matches!(self.0.try_wait(), Ok(Some(_))) {
            let _ = self.0.kill();
            let _ = self.0.wait();
        }
    }
}

fn probe_remaining(until: Instant) -> std::io::Result<Duration> {
    until
        .checked_duration_since(Instant::now())
        .filter(|remaining| !remaining.is_zero())
        .ok_or_else(|| {
            std::io::Error::new(
                std::io::ErrorKind::TimedOut,
                "toolchain resolution deadline elapsed",
            )
        })
}

/// Bound the wait and parsed bytes without pipe-drainer threads. An inherited
/// stdout pipe must not keep a completed query alive. Private scratch receives
/// stdout; stderr is discarded rather than retained or used as selection data.
/// Filesystem and process-spawn syscalls themselves are not preemptible.
/// `None` means only that the requested executable could not be found at spawn.
fn run_toolchain_probe(
    mut command: Command,
    until: Instant,
) -> Result<Option<String>, ToolchainError> {
    probe_remaining(until)?;
    let mut output = tempfile::tempfile()?;
    command.stdout(output.try_clone()?).stderr(Stdio::null());
    let child = match command.spawn() {
        Ok(child) => child,
        Err(error) if error.kind() == std::io::ErrorKind::NotFound => return Ok(None),
        Err(error) => return Err(error.into()),
    };
    let mut child = ToolchainProbeChild(child);
    loop {
        let remaining = probe_remaining(until)?;
        if output.metadata()?.len() > MAX_TOOLCHAIN_PROBE_BYTES {
            return Err(ToolchainError::Resolution(
                "query output exceeds byte limit".into(),
            ));
        }
        if let Some(status) = child.0.try_wait()? {
            if !status.success() {
                return Err(ToolchainError::Resolution(format!(
                    "query exited with {status}"
                )));
            }
            break;
        }
        std::thread::sleep(remaining.min(Duration::from_millis(5)));
    }
    probe_remaining(until)?;
    output.rewind()?;
    let mut bytes = Vec::new();
    output
        .take(MAX_TOOLCHAIN_PROBE_BYTES + 1)
        .read_to_end(&mut bytes)?;
    if bytes.len() as u64 > MAX_TOOLCHAIN_PROBE_BYTES {
        return Err(ToolchainError::Resolution(
            "query output exceeds byte limit".into(),
        ));
    }
    probe_remaining(until)?;
    String::from_utf8(bytes)
        .map(Some)
        .map_err(|_| ToolchainError::InvalidFormat)
}

fn detect_rustc_toolchain(
    project_root: &Path,
    rustc: &str,
    until: Instant,
) -> Result<ToolchainInfo, ToolchainError> {
    let output = run_toolchain_probe(toolchain_probe(rustc, &["--version"], project_root), until)?
        .ok_or_else(|| {
            ToolchainError::Resolution("neither Rustup nor rustc is available".into())
        })?;
    parse_rustc_version(&output)
}

fn active_identity_parts(output: &str) -> Result<(&str, Option<&str>), ToolchainError> {
    let output = output.trim_end_matches(['\r', '\n']);
    if output.is_empty() || output.chars().any(char::is_control) {
        return Err(ToolchainError::InvalidFormat);
    }
    let (identity, source) = match output.split_once(" (") {
        Some((identity, source)) => (
            identity,
            Some(
                source
                    .strip_suffix(')')
                    .filter(|s| !s.is_empty())
                    .ok_or(ToolchainError::InvalidFormat)?,
            ),
        ),
        None => (output, None),
    };
    if identity.is_empty() || identity.contains(char::is_whitespace) {
        return Err(ToolchainError::InvalidFormat);
    }
    Ok((identity, source))
}

/// `show active-toolchain` requires an installed toolchain even with automatic
/// installation disabled. Plain `show` reports its selected name and source
/// BEFORE the installation check, so an offload-only dispatcher needs no local
/// compiler installation. Accept only its unambiguous active section, never an
/// installed/default entry or a name extracted from error text. Unknown layouts
/// and "no active toolchain" are resolution failures, not standalone fallbacks.
fn rustup_show_identity(output: &str) -> Result<String, ToolchainError> {
    if output
        .chars()
        .any(|c| c.is_control() && c != '\n' && c != '\r')
    {
        return Err(ToolchainError::InvalidFormat);
    }
    let lines: Vec<_> = output.lines().collect();
    let mut sections = lines
        .iter()
        .enumerate()
        .filter(|(_, line)| **line == "active toolchain");
    let (start, _) = sections.next().ok_or(ToolchainError::InvalidFormat)?;
    if sections.next().is_some() || lines.get(start + 1) != Some(&"----------------") {
        return Err(ToolchainError::InvalidFormat);
    }
    let name = lines
        .get(start + 2)
        .and_then(|line| line.strip_prefix("name: "))
        .ok_or(ToolchainError::InvalidFormat)?;
    if name.is_empty() || name.contains(char::is_whitespace) {
        return Err(ToolchainError::InvalidFormat);
    }
    let source = lines
        .get(start + 3)
        .and_then(|line| line.strip_prefix("active because: "))
        .filter(|source| !source.is_empty())
        .ok_or(ToolchainError::InvalidFormat)?;
    let tail = &lines[start + 4..];
    if !tail.is_empty()
        && (tail[0] != "installed targets:"
            || tail[1..]
                .iter()
                .any(|line| !line.starts_with("  ") || line.trim().is_empty()))
    {
        return Err(ToolchainError::InvalidFormat);
    }
    let identity = format!("{name} ({source})");
    active_identity_parts(&identity)?;
    Ok(identity)
}

/// Preserve an explicitly host-qualified FILE pin only when Rustup names that
/// exact file as the selected source. A nearer directory override wins even
/// over a malformed/foreign-host ancestor pin. Controller host suffixes added
/// by Rustup to ordinary identities still do not become worker host demands.
fn resolved_rustup_identity(
    project_root: &Path,
    output: &str,
) -> Result<ToolchainInfo, ToolchainError> {
    let (identity, source) = active_identity_parts(output)?;
    let resolved = parse_active_toolchain(output)?;
    let Some(source) = source.filter(|source| source.starts_with("overridden by '")) else {
        return Ok(resolved);
    };
    let Some(path) = nearest_toolchain_file(project_root)? else {
        return Err(ToolchainError::Resolution(
            "selected toolchain file disappeared".into(),
        ));
    };
    if source != format!("overridden by '{}'", path.display()) {
        return Err(ToolchainError::Resolution(
            "selected toolchain file changed".into(),
        ));
    }
    let declared = if path
        .file_name()
        .is_some_and(|name| name == "rust-toolchain")
    {
        parse_legacy_toolchain_file(&path)
    } else {
        parse_toolchain_file(&path)
    };
    match declared {
        Ok(pin)
            if pin.rustup_toolchain() == identity
                || pin.rustup_toolchain() == resolved.rustup_toolchain() =>
        {
            Ok(pin)
        }
        // A component-only file delegates its channel to Rustup's default.
        Err(ToolchainError::InvalidFormat) if file_has_implicit_channel(&path) => Ok(resolved),
        Err(error) => Err(error),
        Ok(_) => Err(ToolchainError::Resolution(
            "selected toolchain file changed after resolution".into(),
        )),
    }
}

fn file_has_implicit_channel(path: &Path) -> bool {
    let Ok(content) = std::fs::read_to_string(path) else {
        return false;
    };
    let Ok(value) = toml::from_str::<toml::Value>(&content) else {
        return false;
    };
    let Some(table) = value.get("toolchain").and_then(toml::Value::as_table) else {
        return false;
    };
    !table.contains_key("channel")
        && !table.contains_key("path")
        && ["components", "targets"].iter().any(|key| {
            table.get(*key).is_some_and(|values| {
                values
                    .as_array()
                    .is_some_and(|items| items.iter().all(toml::Value::is_str))
            })
        })
}

/// Rustup appends the controller host to official identities. A remote
/// worker must resolve the same release for its own host. Strip recognized
/// Linux/macOS/Windows controller hosts only; unknown/custom suffixes remain
/// opaque. Do not obtain the release date from a compiler version.
fn parse_active_toolchain(output: &str) -> Result<ToolchainInfo, ToolchainError> {
    let (identity, _) = active_identity_parts(output)?;
    let official = regex::Regex::new(
        r"^((?:stable|beta|nightly)(?:-\d{4}-\d{2}-\d{2})?|\d+\.\d+(?:\.\d+)?(?:-beta(?:\.\d+)?)?)-(?:x86_64|aarch64|i686)-(?:unknown-linux-(?:gnu|musl)|apple-darwin|pc-windows-(?:msvc|gnu|gnullvm))$",
    )
    .map_err(|error| ToolchainError::ParseError(error.to_string()))?;
    let release = official
        .captures(identity)
        .and_then(|captures| captures.get(1))
        .map_or(identity, |matched| matched.as_str());
    parse_channel_string(release)
}

/// Parse rustc --version output.
///
/// Examples:
/// - "rustc 1.76.0-nightly (abc123def 2024-01-15)"
/// - "rustc 1.75.0 (82e1608df 2023-12-21)"
pub fn parse_rustc_version(version_str: &str) -> Result<ToolchainInfo, ToolchainError> {
    // Pattern: rustc VERSION(-CHANNEL)? (HASH DATE)
    // VERSION = major.minor.patch
    // CHANNEL = nightly or beta
    // HASH = hex commit hash
    // DATE = YYYY-MM-DD

    let version_str = version_str.trim();

    // First try with regex for accurate parsing
    if let Ok(re) = regex::Regex::new(
        r"rustc (\d+\.\d+\.\d+)(-nightly|-beta)? \([a-f0-9]+ (\d{4}-\d{2}-\d{2})\)",
    ) && let Some(caps) = re.captures(version_str)
    {
        let _version = caps.get(1).unwrap().as_str();
        let channel_suffix = caps.get(2).map(|m| m.as_str());

        let channel = match channel_suffix {
            Some("-nightly") => "nightly".to_string(),
            Some("-beta") => "beta".to_string(),
            Some(other) => other.trim_start_matches('-').to_string(),
            None => "stable".to_string(),
        };

        // This is the compiler commit date, which can precede the archive
        // date even for nightly/beta. Only a declared or active rustup
        // identity can establish an archive date.
        return Ok(ToolchainInfo {
            channel,
            date: None,
            full_version: version_str.to_string(),
        });
    }

    // Fallback: simple parsing for edge cases
    if version_str.starts_with("rustc ") {
        let parts: Vec<&str> = version_str.split_whitespace().collect();
        if parts.len() >= 2 {
            let version_part = parts[1];
            if version_part.contains("-nightly") {
                return Ok(ToolchainInfo {
                    channel: "nightly".to_string(),
                    date: None,
                    full_version: version_str.to_string(),
                });
            } else if version_part.contains("-beta") {
                return Ok(ToolchainInfo {
                    channel: "beta".to_string(),
                    date: None,
                    full_version: version_str.to_string(),
                });
            } else {
                return Ok(ToolchainInfo {
                    channel: "stable".to_string(),
                    date: None,
                    full_version: version_str.to_string(),
                });
            }
        }
    }

    Err(ToolchainError::ParseError(version_str.to_string()))
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::io::Write;
    use tempfile::TempDir;

    fn declared_toolchain(root: &Path) -> Result<ToolchainInfo, ToolchainError> {
        detect_toolchain_with(root, None, |_| Err(ToolchainError::InvalidFormat))
    }

    #[test]
    fn test_parse_nightly_channel() {
        let info = parse_channel_string("nightly-2024-01-15").unwrap();
        assert_eq!(info.channel, "nightly");
        assert_eq!(info.date, Some("2024-01-15".to_string()));
        assert_eq!(info.rustup_toolchain(), "nightly-2024-01-15");
    }

    #[test]
    fn test_parse_beta_channel() {
        let info = parse_channel_string("beta-2024-02-01").unwrap();
        assert_eq!(info.channel, "beta");
        assert_eq!(info.date, Some("2024-02-01".to_string()));
        assert_eq!(info.rustup_toolchain(), "beta-2024-02-01");
    }

    #[test]
    fn test_parse_stable_channel() {
        let info = parse_channel_string("stable").unwrap();
        assert_eq!(info.channel, "stable");
        assert_eq!(info.date, None);
        assert_eq!(info.rustup_toolchain(), "stable");
    }

    #[test]
    fn test_parse_nightly_channel_no_date() {
        let info = parse_channel_string("nightly").unwrap();
        assert_eq!(info.channel, "nightly");
        assert_eq!(info.date, None);
        assert_eq!(info.rustup_toolchain(), "nightly");
    }

    #[test]
    fn test_parse_specific_version() {
        let info = parse_channel_string("1.75.0").unwrap();
        assert_eq!(info.channel, "1.75.0");
        assert_eq!(info.date, None);
        assert_eq!(info.rustup_toolchain(), "1.75.0");
    }

    #[test]
    fn test_parse_rustc_version_nightly() {
        let info = parse_rustc_version("rustc 1.76.0-nightly (abc123def 2024-01-15)").unwrap();
        assert_eq!(info.channel, "nightly");
        assert_eq!(info.date, None);
        assert_eq!(info.rustup_toolchain(), "nightly");
    }

    #[test]
    fn test_parse_rustc_version_stable() {
        let info = parse_rustc_version("rustc 1.75.0 (82e1608df 2023-12-21)").unwrap();
        assert_eq!(info.channel, "stable");
        // Commit date must NOT leak into the toolchain identity for stable:
        // `stable-2023-12-21` is not a rustup archive name and cannot be
        // installed. The identifier handed to `rustup run` must be `stable`.
        assert_eq!(info.date, None);
        assert_eq!(info.rustup_toolchain(), "stable");
    }

    #[test]
    fn test_parse_rustc_version_stable_fallback_resolvable_identifier() {
        // Regression for issue #43: the exact scenario from the report.
        let info = parse_rustc_version("rustc 1.97.1 (8bab26f4f 2026-07-14)").unwrap();
        assert_eq!(info.channel, "stable");
        assert_eq!(info.rustup_toolchain(), "stable");
        assert!(!info.rustup_toolchain().contains("2026-07-14"));
    }

    #[test]
    fn test_parse_rustc_version_beta() {
        let info = parse_rustc_version("rustc 1.76.0-beta (abcdef123 2024-01-20)").unwrap();
        assert_eq!(info.channel, "beta");
        assert_eq!(info.date, None);
        assert_eq!(info.rustup_toolchain(), "beta");
    }

    #[test]
    fn test_is_valid_date() {
        assert!(is_valid_date("2024-01-15"));
        assert!(is_valid_date("2023-12-31"));
        assert!(!is_valid_date("2024-1-15")); // Missing leading zero
        assert!(!is_valid_date("2024-01-1")); // Missing leading zero
        assert!(!is_valid_date("24-01-15")); // Year too short
        assert!(!is_valid_date("not-a-date"));
    }

    #[test]
    fn test_is_version_number() {
        assert!(is_version_number("1.75.0"));
        assert!(is_version_number("1.76"));
        assert!(is_version_number("2.0.0"));
        assert!(!is_version_number("stable"));
        assert!(!is_version_number("1.75.0-nightly"));
        assert!(!is_version_number(""));
    }

    #[test]
    fn test_toolchain_info_serialization() {
        let info = ToolchainInfo {
            channel: "nightly".to_string(),
            date: Some("2024-01-15".to_string()),
            full_version: "rustc 1.76.0-nightly".to_string(),
        };
        let json = serde_json::to_string(&info).unwrap();
        let parsed: ToolchainInfo = serde_json::from_str(&json).unwrap();
        assert_eq!(info, parsed);
    }

    #[test]
    fn test_detect_toolchain_from_toml() {
        let tmp = TempDir::new().unwrap();
        let toolchain_path = tmp.path().join("rust-toolchain.toml");
        let mut file = std::fs::File::create(&toolchain_path).unwrap();
        writeln!(file, "[toolchain]").unwrap();
        writeln!(file, "channel = \"nightly-2024-01-15\"").unwrap();

        let info = declared_toolchain(tmp.path()).unwrap();
        assert_eq!(info.channel, "nightly");
        assert_eq!(info.date, Some("2024-01-15".to_string()));
    }

    #[test]
    fn test_detect_toolchain_from_legacy() {
        let tmp = TempDir::new().unwrap();
        let toolchain_path = tmp.path().join("rust-toolchain");
        std::fs::write(&toolchain_path, "stable\n").unwrap();

        let info = declared_toolchain(tmp.path()).unwrap();
        assert_eq!(info.channel, "stable");
        assert_eq!(info.date, None);
    }

    #[test]
    fn test_detect_toolchain_legacy_priority() {
        // Rustup gives rust-toolchain priority, even when both files are TOML.
        let tmp = TempDir::new().unwrap();

        let toml_path = tmp.path().join("rust-toolchain.toml");
        let mut file = std::fs::File::create(&toml_path).unwrap();
        writeln!(file, "[toolchain]").unwrap();
        writeln!(file, "channel = \"nightly\"").unwrap();

        let legacy_path = tmp.path().join("rust-toolchain");
        std::fs::write(&legacy_path, "stable").unwrap();

        let info = declared_toolchain(tmp.path()).unwrap();
        assert_eq!(info.channel, "stable");
        assert!(detect_declared_components(tmp.path()).is_empty());

        std::fs::write(
            &legacy_path,
            "[toolchain]\nchannel = 'beta'\ncomponents = ['rustfmt']\n",
        )
        .unwrap();
        assert_eq!(declared_toolchain(tmp.path()).unwrap().channel, "beta");
        assert_eq!(detect_declared_components(tmp.path()), ["rustfmt"]);
    }

    #[test]
    fn test_unspecified_channel_fallback_uses_caller_directory() {
        let tmp = TempDir::new().unwrap();
        let caller = tmp.path().join("nested");
        std::fs::create_dir(&caller).unwrap();
        // TMPDIR can itself live beneath a repository pin. A nearest
        // component-only declaration shadows that pin without supplying a
        // channel, so this test must exercise the fallback on every host.
        std::fs::write(
            caller.join("rust-toolchain.toml"),
            "[toolchain]\ncomponents = ['rustfmt']\n",
        )
        .unwrap();
        let calls = std::cell::Cell::new(0);
        let info = detect_toolchain_with(&caller, None, |cwd| {
            calls.set(calls.get() + 1);
            assert_eq!(cwd, caller);
            parse_active_toolchain(
                "nightly-2026-08-31-x86_64-unknown-linux-gnu (directory override for '/project')",
            )
        })
        .unwrap();
        assert_eq!(calls.get(), 1);
        assert_eq!(info.rustup_toolchain(), "nightly-2026-08-31");
        assert!(
            detect_toolchain_with(&caller, None, |cwd| {
                calls.set(calls.get() + 1);
                assert_eq!(cwd, caller);
                Err(ToolchainError::InvalidFormat)
            })
            .is_err()
        );
        assert_eq!(calls.get(), 2);
    }

    #[test]
    fn test_inherited_pin_components_and_nearest_shadowing() {
        let tmp = TempDir::new().unwrap();
        let nested = tmp.path().join("tests/fixtures/hello_world");
        std::fs::create_dir_all(&nested).unwrap();
        std::fs::write(
            tmp.path().join("rust-toolchain.toml"),
            "[toolchain]\nchannel = 'nightly-2026-08-31'\ncomponents = ['rustfmt', 'clippy']\n",
        )
        .unwrap();
        assert_eq!(
            declared_toolchain(&nested).unwrap().rustup_toolchain(),
            "nightly-2026-08-31"
        );
        assert_eq!(detect_declared_components(&nested), ["clippy", "rustfmt"]);
        let compiler = parse_rustc_version("rustc 1.100.0-nightly (908501772 2026-08-30)").unwrap();
        assert_eq!(compiler.date, None);
        assert_eq!(compiler.rustup_toolchain(), "nightly");

        std::fs::write(nested.parent().unwrap().join("rust-toolchain"), "stable\n").unwrap();
        assert_eq!(declared_toolchain(&nested).unwrap().channel, "stable");
        assert!(detect_declared_components(&nested).is_empty());
        std::fs::write(
            nested.join("rust-toolchain.toml"),
            "[toolchain]\nchannel = 'beta'\ncomponents = ['clippy']\n",
        )
        .unwrap();
        assert_eq!(declared_toolchain(&nested).unwrap().channel, "beta");
        assert_eq!(detect_declared_components(&nested), ["clippy"]);
    }

    #[test]
    fn test_ambient_override_precedes_pin_without_installing() {
        let tmp = TempDir::new().unwrap();
        std::fs::write(tmp.path().join("rust-toolchain"), "stable").unwrap();
        let info = detect_toolchain_with(
            tmp.path(),
            Some("nightly-1999-01-01-x86_64-unknown-linux-gnu"),
            |_| panic!("an explicit identity must not require an installed toolchain"),
        )
        .unwrap();
        assert_eq!(info.rustup_toolchain(), "nightly-1999-01-01");
        assert_eq!(
            detect_toolchain_with(tmp.path(), Some(""), |_| {
                panic!("empty ambient override must preserve the file fast path")
            })
            .unwrap()
            .channel,
            "stable"
        );
    }

    #[test]
    fn test_active_identity_preserves_archive_and_custom_names() {
        for (active, expected) in [
            (
                "nightly-2026-08-31-x86_64-unknown-linux-gnu (default)",
                "nightly-2026-08-31",
            ),
            (
                "beta-2026-08-31-aarch64-apple-darwin (default)",
                "beta-2026-08-31",
            ),
            ("stable-x86_64-pc-windows-msvc (default)", "stable"),
            ("1.90.0-x86_64-unknown-linux-gnu (default)", "1.90.0"),
            (
                "custom-x86_64-unknown-linux-gnu (default)",
                "custom-x86_64-unknown-linux-gnu",
            ),
            (
                "nightly-optimized-with-assertions (default)",
                "nightly-optimized-with-assertions",
            ),
            (
                "beta-custom-with-checks (default)",
                "beta-custom-with-checks",
            ),
        ] {
            assert_eq!(
                parse_active_toolchain(active).unwrap().rustup_toolchain(),
                expected
            );
        }
        assert!(parse_active_toolchain("").is_err());
        assert!(parse_active_toolchain("no active toolchain").is_err());

        // An explicitly host-qualified project pin is intentional and does
        // not pass through active-output normalization.
        let tmp = TempDir::new().unwrap();
        std::fs::write(
            tmp.path().join("rust-toolchain.toml"),
            "[toolchain]\nchannel = 'nightly-2026-08-31-x86_64-pc-windows-msvc'\n",
        )
        .unwrap();
        assert_eq!(
            declared_toolchain(tmp.path()).unwrap().rustup_toolchain(),
            "nightly-2026-08-31-x86_64-pc-windows-msvc"
        );
    }

    #[cfg(unix)]
    #[test]
    fn test_read_only_probes_use_caller_directory() {
        use std::os::unix::fs::PermissionsExt;

        let tmp = TempDir::new().unwrap();
        let caller = tmp.path().join("caller");
        std::fs::create_dir(&caller).unwrap();
        let program = tmp.path().join("identity-probe");
        // A shell protocol fixture, not evidence of an installed toolchain.
        // Relative input paths prove the subprocess actually runs in caller.
        std::fs::write(
            &program,
            "#!/bin/sh\n[ \"$RUSTUP_AUTO_INSTALL\" = 0 ] && [ \"$RUSTUP_TERM_COLOR\" = never ] || exit 91\ncase \"$*\" in\nshow) cat active;;\n'--version') cat compiler;;\n*) exit 92;;\nesac\n",
        )
        .unwrap();
        std::fs::set_permissions(&program, std::fs::Permissions::from_mode(0o755)).unwrap();
        std::fs::write(
            caller.join("active"),
            show_report(
                "nightly-2026-08-31-x86_64-unknown-linux-gnu",
                "it's the default toolchain",
                true,
            ),
        )
        .unwrap();
        std::fs::write(
            caller.join("compiler"),
            "rustc 1.100.0-nightly (908501772 2026-08-30)\n",
        )
        .unwrap();
        let executable = program.to_str().unwrap();
        let info = detect_resolved_toolchain_with(&caller, None, executable, executable).unwrap();
        assert_eq!(info.rustup_toolchain(), "nightly-2026-08-31");

        // Only an unavailable Rustup permits a standalone compiler fallback.
        // Shadow any TMPDIR ancestor pin without choosing its channel.
        std::fs::write(
            caller.join("rust-toolchain.toml"),
            "[toolchain]\ncomponents = []\n",
        )
        .unwrap();
        let absent = tmp.path().join("not-installed");
        let info =
            detect_resolved_toolchain_with(&caller, None, absent.to_str().unwrap(), executable)
                .unwrap();
        assert_eq!(info.rustup_toolchain(), "nightly");
        std::fs::write(caller.join("active"), "no active toolchain\n").unwrap();
        assert!(detect_resolved_toolchain_with(&caller, None, executable, executable).is_err());
        std::fs::write(caller.join("compiler"), "not a compiler\n").unwrap();
        assert!(
            detect_resolved_toolchain_with(&caller, None, absent.to_str().unwrap(), executable)
                .is_err()
        );
    }

    // The public Rustup CLI boundary is scripted below. These tests exercise
    // RCH's real process launcher/parser and file handling, not an installed
    // Rustup distribution or a compiler. No user settings are modified.
    fn show_report(name: &str, source: &str, installed: bool) -> String {
        format!(
            "Default host: x86_64-unknown-linux-gnu\nrustup home: /unused\n\ninstalled toolchains\n--------------------\nstable-x86_64-unknown-linux-gnu (default)\n\nactive toolchain\n----------------\nname: {name}\nactive because: {source}\n{}",
            if installed {
                "installed targets:\n  x86_64-unknown-linux-gnu\n"
            } else {
                ""
            },
        )
    }

    #[cfg(unix)]
    fn script(path: &Path, body: &str) {
        use std::os::unix::fs::PermissionsExt;
        std::fs::write(path, body).unwrap();
        std::fs::set_permissions(path, std::fs::Permissions::from_mode(0o755)).unwrap();
    }

    #[cfg(unix)]
    #[test]
    fn directory_override_resolution_precedes_pins_without_installing_or_running_rustc() {
        let tmp = TempDir::new().unwrap();
        let root = tmp.path().canonicalize().unwrap();
        let child = root.join("nested");
        std::fs::create_dir(&child).unwrap();
        let rustup = root.join("rustup-query");
        let rustc = root.join("rustc-query");
        script(
            &rustup,
            "#!/bin/sh\n[ \"$*\" = show ] && [ \"$RUSTUP_AUTO_INSTALL\" = 0 ] && [ \"$RUSTUP_TERM_COLOR\" = never ] || exit 91\ncat active\n",
        );
        script(&rustc, "#!/bin/sh\ntouch compiler-ran\nexit 92\n");
        for pin in ["[toolchain]\nchannel='stable'\n", "malformed [[[\n"] {
            std::fs::write(root.join("rust-toolchain.toml"), pin).unwrap();
            for directory in [&root, &child] {
                for installed in [false, true] {
                    std::fs::write(
                        child.join("active"),
                        show_report(
                            "nightly-2026-08-31-x86_64-unknown-linux-gnu",
                            &format!("directory override for '{}'", directory.display()),
                            installed,
                        ),
                    )
                    .unwrap();
                    let info = detect_resolved_toolchain_with(
                        &child,
                        None,
                        rustup.to_str().unwrap(),
                        rustc.to_str().unwrap(),
                    )
                    .unwrap();
                    assert_eq!(info.rustup_toolchain(), "nightly-2026-08-31");
                    assert!(!child.join("compiler-ran").exists());
                }
            }
        }
    }

    #[test]
    fn selected_file_pins_preserve_host_intent_and_refuse_changed_source() {
        let tmp = TempDir::new().unwrap();
        let root = tmp.path().canonicalize().unwrap();
        let nested = root.join("nested");
        std::fs::create_dir(&nested).unwrap();
        let path = nested.join("rust-toolchain.toml");
        std::fs::write(root.join("rust-toolchain"), "stable").unwrap();
        let source = format!("overridden by '{}'", path.display());
        for pin in [
            "nightly-2026-08-31",
            "nightly-2026-08-31-x86_64-pc-windows-msvc",
            "custom-local",
        ] {
            std::fs::write(&path, format!("[toolchain]\nchannel='{pin}'\n")).unwrap();
            let identity = if pin == "nightly-2026-08-31" {
                "nightly-2026-08-31-x86_64-unknown-linux-gnu"
            } else {
                pin
            };
            let report = rustup_show_identity(&show_report(identity, &source, false)).unwrap();
            assert_eq!(
                resolved_rustup_identity(&nested, &report)
                    .unwrap()
                    .rustup_toolchain(),
                pin
            );
            std::fs::write(&path, "[toolchain]\nchannel='beta'\n").unwrap();
            assert!(resolved_rustup_identity(&nested, &report).is_err());
        }
        let wrong_source = format!(
            "nightly (overridden by '{}')",
            root.join("rust-toolchain").display()
        );
        assert!(resolved_rustup_identity(&nested, &wrong_source).is_err());
    }

    #[test]
    fn resolved_implicit_channel_is_not_confused_with_a_broken_pin() {
        let tmp = TempDir::new().unwrap();
        let root = tmp.path().canonicalize().unwrap();
        let path = root.join("rust-toolchain.toml");
        let active = format!(
            "stable-x86_64-unknown-linux-gnu (overridden by '{}')",
            path.display()
        );
        for contents in [
            "[toolchain]\ncomponents=[]\n",
            "[toolchain]\ntargets=['wasm32-unknown-unknown']\n",
        ] {
            std::fs::write(&path, contents).unwrap();
            assert_eq!(
                resolved_rustup_identity(&root, &active)
                    .unwrap()
                    .rustup_toolchain(),
                "stable"
            );
        }
        for contents in [
            "",
            "[toolchain]\n",
            "[toolchain]\nchannel=3\ncomponents=[]\n",
            "[toolchain]\npath='/local'\ncomponents=[]\n",
            "broken [[[",
        ] {
            std::fs::write(&path, contents).unwrap();
            assert!(
                resolved_rustup_identity(&root, &active).is_err(),
                "{contents}"
            );
        }
    }

    #[test]
    fn show_parser_requires_exactly_one_complete_active_identity() {
        let valid = show_report(
            "beta-x86_64-unknown-linux-gnu",
            "it's the default toolchain",
            true,
        );
        assert!(rustup_show_identity(&valid).unwrap().starts_with("beta-"));
        assert!(rustup_show_identity(&valid.replace('\n', "\r\n")).is_ok());
        for invalid in [
            "stable-x86_64-unknown-linux-gnu (default)\n".to_owned(),
            "active toolchain\n----------------\nno active toolchain\n".to_owned(),
            valid.replace("active because:", "reason:"),
            valid.replace("name: beta-", "name: wrong beta-"),
            valid.replace("name: beta-", "name: \0beta-"),
            valid.replace("active toolchain", "\x1b[1mactive toolchain"),
            format!("{valid}{valid}"),
            format!("{valid}name: stable\n"),
        ] {
            assert!(rustup_show_identity(&invalid).is_err(), "{invalid:?}");
        }
        for invalid in [
            "nightly (default)\nstable (default)",
            "nightly (default",
            " nightly",
            "nightly\0",
        ] {
            assert!(parse_active_toolchain(invalid).is_err());
        }
    }

    #[cfg(unix)]
    #[test]
    fn rustup_errors_and_non_utf8_cannot_fall_back_to_a_valid_pin_or_compiler() {
        let tmp = TempDir::new().unwrap();
        let root = tmp.path();
        let rustup = root.join("rustup-query");
        let rustc = root.join("compiler-query");
        std::fs::write(root.join("rust-toolchain"), "stable").unwrap();
        script(
            &rustc,
            "#!/bin/sh\ntouch compiler-ran\nprintf 'rustc 1.90.0 (abcdef 2025-09-01)\\n'\n",
        );
        for body in [
            "#!/bin/sh\ncat active\nexit 1\n",
            "#!/bin/sh\nprintf 'not a Rustup report\\n'\n",
            "#!/bin/sh\nprintf '\\377\\n'\n",
        ] {
            std::fs::write(
                root.join("active"),
                show_report("beta", "it's the default toolchain", false),
            )
            .unwrap();
            script(&rustup, body);
            assert!(
                detect_resolved_toolchain_with(
                    root,
                    None,
                    rustup.to_str().unwrap(),
                    rustc.to_str().unwrap(),
                )
                .is_err()
            );
            assert!(!root.join("compiler-ran").exists());
        }
    }

    #[test]
    fn explicit_environment_and_absent_rustup_keep_offline_declarations() {
        let tmp = TempDir::new().unwrap();
        let absent = tmp.path().join("not-installed");
        let absent = absent.to_str().unwrap();
        std::fs::write(tmp.path().join("rust-toolchain"), "beta").unwrap();
        assert_eq!(
            detect_resolved_toolchain_with(tmp.path(), Some("nightly-2026-08-31"), absent, absent)
                .unwrap()
                .rustup_toolchain(),
            "nightly-2026-08-31"
        );
        assert_eq!(
            detect_resolved_toolchain_with(tmp.path(), None, absent, absent)
                .unwrap()
                .rustup_toolchain(),
            "beta"
        );
        for invalid in ["nightly\0", "nightly (default)", " nightly"] {
            assert!(
                detect_resolved_toolchain_with(tmp.path(), Some(invalid), absent, absent).is_err()
            );
        }
        std::fs::write(tmp.path().join("rust-toolchain"), "").unwrap();
        assert!(
            detect_toolchain_with(tmp.path(), None, |_| {
                panic!("a broken pin must not invoke the standalone fallback")
            })
            .is_err()
        );
    }

    #[cfg(unix)]
    #[test]
    fn query_deadlines_cover_spawn_wait_and_do_not_renew_for_output() {
        let tmp = TempDir::new().unwrap();
        let marker = tmp.path().join("spawned");
        let mut command = Command::new("/bin/sh");
        command
            .args(["-c", "echo started > \"$1\"", "query"])
            .arg(&marker);
        assert!(matches!(
            run_toolchain_probe(command, Instant::now()),
            Err(ToolchainError::Io(error)) if error.kind() == std::io::ErrorKind::TimedOut
        ));
        assert!(!marker.exists());
        let mut command = Command::new("/bin/sh");
        command.args(["-c", "printf 'partial'; while :; do :; done"]);
        assert!(matches!(
            run_toolchain_probe(command, Instant::now() + Duration::from_millis(50)),
            Err(ToolchainError::Io(error)) if error.kind() == std::io::ErrorKind::TimedOut
        ));
        // A successful subprocess cannot grant a fresh budget to a later one.
        let until = Instant::now();
        assert!(detect_rustc_toolchain(tmp.path(), "/bin/false", until).is_err());
    }

    #[cfg(unix)]
    #[test]
    fn query_byte_limit_is_checked_before_parsing_and_stderr_is_not_identity() {
        for (count, accepted) in [
            (MAX_TOOLCHAIN_PROBE_BYTES, true),
            (MAX_TOOLCHAIN_PROBE_BYTES + 1, false),
        ] {
            let mut command = Command::new("/bin/sh");
            command
                .args(["-c", "head -c \"$1\" /dev/zero", "query"])
                .arg(count.to_string());
            let result = run_toolchain_probe(command, Instant::now() + TOOLCHAIN_PROBE_BUDGET);
            if accepted {
                assert_eq!(result.unwrap().unwrap().len() as u64, count);
            } else {
                assert!(result.is_err());
            }
        }
        let mut command = Command::new("/bin/sh");
        command.args(["-c", "echo stable >&2"]);
        assert_eq!(
            run_toolchain_probe(command, Instant::now() + TOOLCHAIN_PROBE_BUDGET).unwrap(),
            Some(String::new())
        );
    }

    // === Additional edge case tests for toolchain synchronization ===

    #[test]
    fn test_parse_channel_string_beta_no_date() {
        let info = parse_channel_string("beta").unwrap();
        assert_eq!(info.channel, "beta");
        assert_eq!(info.date, None);
        assert_eq!(info.rustup_toolchain(), "beta");
    }

    #[test]
    fn test_parse_channel_string_two_digit_version() {
        // Handle two-part versions like "1.75"
        let info = parse_channel_string("1.75").unwrap();
        assert_eq!(info.channel, "1.75");
        assert_eq!(info.date, None);
    }

    #[test]
    fn test_parse_channel_string_unknown_format() {
        // Unknown formats should still parse without error
        let info = parse_channel_string("custom-toolchain").unwrap();
        assert_eq!(info.channel, "custom-toolchain");
        assert_eq!(info.date, None);
    }

    #[test]
    fn test_parse_channel_string_nightly_with_invalid_date() {
        // "nightly-" prefix but not a valid date should treat as custom channel
        let info = parse_channel_string("nightly-not-a-date").unwrap();
        // Should not extract as date since it's not a valid date format
        assert_eq!(info.channel, "nightly-not-a-date");
        assert_eq!(info.date, None);
    }

    #[test]
    fn test_is_valid_date_edge_cases() {
        // Boundary dates
        assert!(is_valid_date("2000-01-01"));
        assert!(is_valid_date("2099-12-31"));

        // Invalid formats
        assert!(!is_valid_date(""));
        assert!(!is_valid_date("2024"));
        assert!(!is_valid_date("2024-01"));
        assert!(!is_valid_date("2024/01/15"));
        assert!(!is_valid_date("01-15-2024"));
        assert!(!is_valid_date("2024-13-01")); // Technically valid format, but invalid month
    }

    #[test]
    fn test_is_version_number_edge_cases() {
        // Valid versions
        assert!(is_version_number("0.0.1"));
        assert!(is_version_number("99.99.99"));
        assert!(is_version_number("1.0"));

        // Invalid versions
        assert!(!is_version_number("1"));
        assert!(!is_version_number("1."));
        assert!(!is_version_number(".1.0"));
        assert!(!is_version_number("1.2.3.4")); // Too many parts
        assert!(!is_version_number("a.b.c"));
    }

    #[test]
    fn test_parse_rustc_version_edge_cases() {
        // Minimal nightly format
        let info = parse_rustc_version("rustc 1.80.0-nightly (abcdef123 2025-01-01)").unwrap();
        assert_eq!(info.channel, "nightly");
        assert_eq!(info.date, None);

        // Minimal beta format
        let info = parse_rustc_version("rustc 1.80.0-beta.1 (abcdef123 2025-02-01)");
        // beta.1 format should fall back to simple parsing
        assert!(info.is_ok());

        // Fallback for unusual formats
        let info = parse_rustc_version("rustc 1.80.0-nightly");
        assert!(info.is_ok());
        let info = info.unwrap();
        assert_eq!(info.channel, "nightly");
    }

    #[test]
    fn test_parse_rustc_version_invalid_formats() {
        // Empty string
        let result = parse_rustc_version("");
        assert!(result.is_err());

        // Not rustc output
        let result = parse_rustc_version("cargo 1.75.0");
        assert!(result.is_err());
    }

    #[test]
    fn test_detect_toolchain_toml_with_components() {
        // TOML with additional fields like components and targets
        let tmp = TempDir::new().unwrap();
        let toolchain_path = tmp.path().join("rust-toolchain.toml");
        let mut file = std::fs::File::create(&toolchain_path).unwrap();
        writeln!(file, "[toolchain]").unwrap();
        writeln!(file, "channel = \"nightly-2024-06-01\"").unwrap();
        writeln!(file, "components = [\"rustfmt\", \"clippy\"]").unwrap();
        writeln!(file, "targets = [\"wasm32-unknown-unknown\"]").unwrap();

        let info = declared_toolchain(tmp.path()).unwrap();
        assert_eq!(info.channel, "nightly");
        assert_eq!(info.date, Some("2024-06-01".to_string()));
    }

    #[test]
    fn test_parse_declared_components_is_sorted_deduplicated_and_nonblank() {
        let components = parse_declared_components(
            r#"
                [toolchain]
                channel = "nightly-2026-07-05"
                components = ["rustfmt", "clippy", "rustfmt", ""]
            "#,
        );
        assert_eq!(components, vec!["clippy", "rustfmt"]);
        assert!(parse_declared_components("nightly-2026-07-05").is_empty());
    }

    #[test]
    fn test_detect_toolchain_toml_with_profile() {
        // TOML with profile field
        let tmp = TempDir::new().unwrap();
        let toolchain_path = tmp.path().join("rust-toolchain.toml");
        let mut file = std::fs::File::create(&toolchain_path).unwrap();
        writeln!(file, "[toolchain]").unwrap();
        writeln!(file, "channel = \"stable\"").unwrap();
        writeln!(file, "profile = \"minimal\"").unwrap();

        let info = declared_toolchain(tmp.path()).unwrap();
        assert_eq!(info.channel, "stable");
    }

    #[test]
    fn test_detect_toolchain_legacy_with_whitespace() {
        // Legacy file with extra whitespace
        let tmp = TempDir::new().unwrap();
        let toolchain_path = tmp.path().join("rust-toolchain");
        std::fs::write(&toolchain_path, "  nightly-2024-03-15  \n\n").unwrap();

        let info = declared_toolchain(tmp.path()).unwrap();
        assert_eq!(info.channel, "nightly");
        assert_eq!(info.date, Some("2024-03-15".to_string()));
    }

    #[test]
    fn test_detect_toolchain_legacy_empty_file() {
        // Empty legacy file should fail
        let tmp = TempDir::new().unwrap();
        let toolchain_path = tmp.path().join("rust-toolchain");
        std::fs::write(&toolchain_path, "").unwrap();

        assert!(matches!(
            declared_toolchain(tmp.path()),
            Err(ToolchainError::InvalidFormat)
        ));
        assert!(detect_declared_components(tmp.path()).is_empty());
    }

    #[test]
    fn test_detect_toolchain_invalid_toml() {
        // Invalid TOML must not silently select an unrelated ancestor pin.
        let tmp = TempDir::new().unwrap();
        let toolchain_path = tmp.path().join("rust-toolchain.toml");
        std::fs::write(&toolchain_path, "this is not valid toml [[[").unwrap();

        assert!(matches!(
            declared_toolchain(tmp.path()),
            Err(ToolchainError::Toml(_))
        ));
        assert!(detect_declared_components(tmp.path()).is_empty());
    }

    #[test]
    fn test_detect_toolchain_toml_missing_channel() {
        // TOML without channel field
        let tmp = TempDir::new().unwrap();
        let toolchain_path = tmp.path().join("rust-toolchain.toml");
        let mut file = std::fs::File::create(&toolchain_path).unwrap();
        writeln!(file, "[toolchain]").unwrap();
        writeln!(file, "components = [\"rustfmt\"]").unwrap();
        // No channel field

        let info = detect_toolchain_with(tmp.path(), None, |cwd| {
            assert_eq!(cwd, tmp.path());
            parse_active_toolchain("stable-x86_64-unknown-linux-gnu (default)")
        })
        .unwrap();
        assert_eq!(info.channel, "stable");
        assert_eq!(detect_declared_components(tmp.path()), ["rustfmt"]);
    }

    #[test]
    fn test_toolchain_info_display() {
        // Test Display trait implementation (via rustup_toolchain)
        let info = ToolchainInfo {
            channel: "nightly".to_string(),
            date: Some("2024-01-15".to_string()),
            full_version: "rustc 1.76.0-nightly".to_string(),
        };
        assert_eq!(format!("{}", info), "nightly-2024-01-15");

        let info = ToolchainInfo {
            channel: "stable".to_string(),
            date: None,
            full_version: "rustc 1.75.0".to_string(),
        };
        assert_eq!(format!("{}", info), "stable");
    }

    #[test]
    fn test_toolchain_info_equality() {
        let info1 = ToolchainInfo {
            channel: "nightly".to_string(),
            date: Some("2024-01-15".to_string()),
            full_version: "a".to_string(),
        };
        let info2 = ToolchainInfo {
            channel: "nightly".to_string(),
            date: Some("2024-01-15".to_string()),
            full_version: "b".to_string(),
        };
        // Different full_version means not equal
        assert_ne!(info1, info2);

        let info3 = info1.clone();
        assert_eq!(info1, info3);
    }

    #[test]
    fn test_toolchain_info_methods() {
        let nightly = ToolchainInfo::new("nightly", Some("2024-01-15".to_string()), "");
        assert!(nightly.is_nightly());
        assert!(!nightly.is_stable());
        assert!(!nightly.is_beta());

        let stable = ToolchainInfo::new("stable", None, "");
        assert!(stable.is_stable());
        assert!(!stable.is_nightly());
        assert!(!stable.is_beta());

        let beta = ToolchainInfo::new("beta", None, "");
        assert!(beta.is_beta());
        assert!(!beta.is_stable());
        assert!(!beta.is_nightly());

        // Custom channel
        let custom = ToolchainInfo::new("1.75.0", None, "");
        assert!(!custom.is_nightly());
        assert!(!custom.is_stable());
        assert!(!custom.is_beta());
    }
}