ktstr 0.23.0

//! `cargo ktstr affected` — which declared schedulers a `base..HEAD` diff
//! affects, as a flat JSON array of package names for a GitHub dynamic matrix
//! (`strategy.matrix.scheduler: ${{ fromJSON(...) }}` -> one job per
//! scheduler).
//!
//! ## Attribution (a union of two layers)
//!
//! A scheduler is affected if a changed path is reachable by EITHER layer:
//!
//! 1. **`.d` input set** ([`dep_info`]): the schedulers are built once (all in
//!    a single cargo invocation -- [`build_schedulers`]) and each cargo
//!    `<artifact>.d` dep-info is parsed into the exact set of source files that
//!    compiled into it -- the Rust sources, the generated BPF skeletons, and
//!    (via clang's `-M`) every `.bpf.c` / header it includes, including
//!    cross-scheduler text-includes (e.g. `scx_chaos` including `scx_p2dq`'s
//!    BPF) and shared headers under the `bpf_h -> scheds/include` symlink.
//!    File-precise, and always the fresh ground truth (uncached -- see
//!    [`scheduler_input_set_from_artifact`]).
//!
//! 2. **cargo dep-closure** (cargo_metadata): a changed path is attributed to
//!    its owning workspace crate; the scheduler is affected if that crate is
//!    in the scheduler's transitive dependency closure. Catches shared *Rust*
//!    library changes, which rustc's per-crate `.d` does NOT list.
//!
//! The `.d` build is skipped for a pure-Rust change (every changed path is a
//! `.rs` owned by a workspace crate): Rust has no text-include, so the
//! crate-closure alone is sound and no scheduler need be built. It runs only
//! when a native (`.c`/`.h`) source or a crate-orphan path changed.
//!
//! ## Fail-safe (a false-negative is the worst outcome)
//!
//! Every uncertainty widens to RunAll, never to a skip: an unresolvable base,
//! a diff failure, a workspace-root / infra change, or ANY changed non-docs
//! path attributed to neither a scheduler `.d` nor a workspace crate. A
//! per-scheduler build/read failure marks that scheduler affected. Only a
//! strictly docs-only change yields the empty set.
//!
//! ## `--relevant`
//!
//! The same engine powers [`relevant_test_filter`], which additionally folds
//! the working tree into the changed set and maps the outcome onto a nextest
//! filter over test NAMES (rather than a package matrix) so `cargo ktstr test
//! --relevant` runs only the tests a local change touches.

use std::collections::{BTreeMap, BTreeSet, VecDeque};
use std::path::{Path, PathBuf};
use std::process::{Command, Stdio};

use anyhow::{Context, Result, anyhow};

mod dep_info;
mod diff;

/// A declared scheduler discovered from the target repo's test binaries.
struct SchedulerInfo {
    /// The scheduler's declared name -- the key `--relevant` maps a test's
    /// `scheduler` field onto, to find its package.
    name: String,
    /// The cargo package to build; `Some` only for `Discover` schedulers
    /// (`Path`/`Eevdf`/`KernelBuiltin` have no target-repo package).
    package: Option<String>,
    /// Count of `#[ktstr_test]`s declared against this scheduler.
    test_count: usize,
}

/// Outcome of the affected computation.
#[derive(Debug, PartialEq)]
enum AffectedOutcome {
    /// Run every testable scheduler (a broad/infra change or any attribution
    /// failure -- over-run, never under-run).
    RunAll,
    /// Run nothing (a strictly docs-only change).
    Empty,
    /// Run exactly these scheduler packages.
    Subset(Vec<String>),
}

/// Entry point: print the flat JSON array of affected scheduler package names.
///
/// The array holds only cargo-PACKAGE (`Discover`) schedulers with >=1 test.
/// Package-less schedulers (`Eevdf` / `Path` / `KernelBuiltin`) have no cargo
/// package to key a matrix job on, so they are NOT in this array and cannot be
/// change-scoped -- CI must run their tests in a SEPARATE UNCONDITIONAL leg.
pub(crate) fn run(base: Option<&str>, base_ref: Option<&str>, default_branch: &str) -> Result<()> {
    let schedulers = enumerate_schedulers().context("enumerate declared schedulers")?;
    let (outcome, testable) = compute_outcome(base, base_ref, default_branch, false, &schedulers)?;
    let names = match outcome {
        AffectedOutcome::RunAll => testable,
        AffectedOutcome::Empty => Vec::new(),
        AffectedOutcome::Subset(pkgs) => pkgs,
    };
    println!(
        "{}",
        serde_json::to_string(&names).context("serialize affected JSON")?
    );
    Ok(())
}

/// Every Discover-package scheduler carrying >=1 test, sorted+deduped. The
/// pre-workspace-graph fallback set (used only if `cargo metadata` fails);
/// once the graph is built, [`compute_outcome`] narrows this to workspace members.
fn package_schedulers(schedulers: &[SchedulerInfo]) -> Vec<String> {
    let mut v: Vec<String> = schedulers
        .iter()
        .filter(|s| s.test_count > 0)
        .filter_map(|s| s.package.clone())
        .collect();
    v.sort();
    v.dedup();
    v
}

/// Enumerate declared schedulers by probing the target's built test binaries
/// with `--ktstr-list-schedulers`. Deduplicates by scheduler name, summing
/// `test_count` across binaries (a scheduler may be registered in more than
/// one test binary).
fn enumerate_schedulers() -> Result<Vec<SchedulerInfo>> {
    let per_binary: Vec<Vec<ktstr::test_support::SchedulerListEntry>> = crate::misc::probe_collect(
        None,
        false,
        |bin| {
            let mut c = Command::new(bin);
            c.arg("--ktstr-list-schedulers");
            c
        },
        |_bin, out| {
            serde_json::from_slice::<Vec<ktstr::test_support::SchedulerListEntry>>(&out.stdout)
                .map_err(|e| format!("parse --ktstr-list-schedulers output: {e}"))
        },
    )
    .map_err(|e| anyhow!("probe test binaries for declared schedulers: {e:?}"))?;

    let mut by_name: BTreeMap<String, SchedulerInfo> = BTreeMap::new();
    for entry in per_binary.into_iter().flatten() {
        let name = entry.scheduler.name.clone();
        let package = match entry.scheduler.binary_kind {
            ktstr::test_support::BinaryKindJson::Discover(pkg) => Some(pkg),
            _ => None,
        };
        by_name
            .entry(name.clone())
            .and_modify(|si| si.test_count += entry.test_count)
            .or_insert(SchedulerInfo {
                name,
                package,
                test_count: entry.test_count,
            });
    }
    Ok(by_name.into_values().collect())
}

/// Enumerate declared tests with their scheduler by probing the target's built
/// test binaries with `--ktstr-list-scheduler-tests`. Used by
/// [`relevant_test_filter`] to map each test onto its scheduler's package.
/// Deduplicates by test name (a test is registered in exactly one binary; the
/// probe visits each binary, so re-seen entries are idempotent).
fn enumerate_scheduler_tests() -> Result<Vec<ktstr::test_support::SchedulerTestJson>> {
    let per_binary: Vec<Vec<ktstr::test_support::SchedulerTestJson>> = crate::misc::probe_collect(
        None,
        false,
        |bin| {
            let mut c = Command::new(bin);
            c.arg("--ktstr-list-scheduler-tests");
            c
        },
        |_bin, out| {
            serde_json::from_slice::<Vec<ktstr::test_support::SchedulerTestJson>>(&out.stdout)
                .map_err(|e| format!("parse --ktstr-list-scheduler-tests output: {e}"))
        },
    )
    .map_err(|e| anyhow!("probe test binaries for declared tests: {e:?}"))?;

    let mut by_name: BTreeMap<String, ktstr::test_support::SchedulerTestJson> = BTreeMap::new();
    for entry in per_binary.into_iter().flatten() {
        by_name.entry(entry.test.clone()).or_insert(entry);
    }
    Ok(by_name.into_values().collect())
}

/// The core fallback + attribution engine. Resolves the changed-path set
/// (`base..HEAD`, plus the working tree when `include_worktree`), classifies
/// it, and returns the [`AffectedOutcome`] alongside the ws-filtered testable
/// scheduler-package universe (the set `RunAll` expands to). Separating the
/// outcome from the flattening lets [`run`] emit package names while
/// [`relevant_test_filter`] maps the SAME outcome onto test names.
fn compute_outcome(
    base: Option<&str>,
    base_ref: Option<&str>,
    default_branch: &str,
    include_worktree: bool,
    schedulers: &[SchedulerInfo],
) -> Result<(AffectedOutcome, Vec<String>)> {
    // Resolve cargo ONCE ($CARGO else "cargo") and use it for BOTH `cargo
    // metadata` and `build_schedulers`, so `PackageId.repr` (an opaque,
    // cargo-version-dependent string) is spelled identically across the two
    // invocations. A mismatch (e.g. $CARGO differs from PATH `cargo`) would make
    // every artifact->package lookup miss -> empty input sets -> all schedulers
    // conservatively affected: still fail-safe (over-run), but it would silently
    // defeat the precise `.d` attribution this layer exists for.
    let cargo = std::env::var_os("CARGO")
        .map(PathBuf::from)
        .unwrap_or_else(|| PathBuf::from("cargo"));

    // Build the workspace graph FIRST so the RunAll set and the Subset set draw
    // from the SAME ws-filtered testable universe. A `cargo metadata` failure
    // is the one case that falls back to the unfiltered enumeration set.
    let mut meta_cmd = cargo_metadata::MetadataCommand::new();
    meta_cmd.cargo_path(&cargo);
    let meta = match meta_cmd.exec() {
        Ok(m) => m,
        Err(_) => return Ok((AffectedOutcome::RunAll, package_schedulers(schedulers))),
    };
    let ws_root = PathBuf::from(meta.workspace_root.as_str());
    let repo_root = std::fs::canonicalize(&ws_root).unwrap_or(ws_root);
    let ws = WorkspaceGraph::build(&meta, &repo_root);

    // Testable = a Discover scheduler with >=1 test whose package is a
    // workspace member (buildable). A tested Discover package that is NOT a
    // member (a fixture, or a mis-declared scheduler) is DIAGNOSED to stderr,
    // never silently dropped.
    let mut testable_pkgs: Vec<String> = Vec::new();
    for s in schedulers {
        if s.test_count == 0 {
            continue;
        }
        let Some(pkg) = s.package.as_deref() else {
            continue; // package-less scheduler -- see run() doc.
        };
        if ws.is_member(pkg) {
            testable_pkgs.push(pkg.to_string());
        } else {
            eprintln!(
                "ktstr affected: declared scheduler package `{pkg}` (with tests) \
                 is not a workspace member; excluded from the matrix"
            );
        }
    }
    testable_pkgs.sort();
    testable_pkgs.dedup();

    // --- Base resolution + diff; any failure -> RunAll (over-run beats a CI
    // error or a silently-empty gate). The gix workdir MUST equal the cargo
    // workspace root, or the diff paths and the repo-relative .d/crate paths
    // live in different spaces (attribution unsafe) -> RunAll. ---
    let cwd = std::env::current_dir().context("resolve current dir")?;
    let repo = match gix::discover(&cwd) {
        Ok(r) => r,
        Err(_) => return Ok((AffectedOutcome::RunAll, testable_pkgs)),
    };
    let workdir_matches_root = repo
        .workdir()
        .and_then(|w| std::fs::canonicalize(w).ok())
        .is_some_and(|w| w == repo_root);
    if !workdir_matches_root {
        return Ok((AffectedOutcome::RunAll, testable_pkgs));
    }
    let sel = crate::perf_delta::select_base(
        base,
        base_ref,
        std::env::var("GITHUB_BASE_REF").ok().as_deref(),
        default_branch,
    );
    let base_oid = match crate::perf_delta::resolve_baseline(&repo, &sel) {
        Ok(o) => o,
        Err(_) => return Ok((AffectedOutcome::RunAll, testable_pkgs)),
    };
    let head_oid = match repo.head_id() {
        Ok(h) => h.detach(),
        Err(_) => return Ok((AffectedOutcome::RunAll, testable_pkgs)),
    };
    let mut changed = match diff::changed_paths_committed(&repo, base_oid, head_oid) {
        Ok(c) => c,
        Err(_) => return Ok((AffectedOutcome::RunAll, testable_pkgs)),
    };
    // --relevant additionally folds in uncommitted + untracked working-tree
    // edits, so the local dev loop scopes tests to changes not yet committed.
    // A clean tree contributes nothing (the union degrades to base..HEAD).
    if include_worktree {
        match diff::changed_paths_worktree(&repo) {
            Ok(w) => changed.extend(w),
            Err(_) => return Ok((AffectedOutcome::RunAll, testable_pkgs)),
        }
    }

    // --- Cheap whole-set verdicts. ---
    if changed.is_empty() {
        // base == HEAD with a clean (or worktree-excluded) tree: nothing changed.
        return Ok((AffectedOutcome::Empty, testable_pkgs));
    }
    if changed.iter().all(|p| is_docs_only(p)) {
        return Ok((AffectedOutcome::Empty, testable_pkgs));
    }
    if changed.iter().any(|p| is_infra_path(p)) {
        return Ok((AffectedOutcome::RunAll, testable_pkgs));
    }

    // --- Layer 1 (.d): built only when a native source or a crate-orphan path
    // changed (a pure-Rust change needs only the crate-closure). ---
    let need_dot_d = changed
        .iter()
        .any(|p| is_native_source(p) || ws.owning_crate(p).is_none());
    let mut input_sets: BTreeMap<String, Option<BTreeSet<String>>> = BTreeMap::new();
    if need_dot_d {
        // ONE cargo build for every testable scheduler (cargo resolves the graph
        // and compiles shared deps once). A package ABSENT from the result map
        // (its bin did not build) -> None -> conservatively affected, matching
        // the per-scheduler fail-safe.
        let id_to_name: BTreeMap<String, String> = meta
            .packages
            .iter()
            .map(|p| (p.id.repr.clone(), p.name.to_string()))
            .collect();
        let artifacts = build_schedulers(&cargo, &testable_pkgs, &id_to_name);
        for pkg in &testable_pkgs {
            let set = artifacts
                .get(pkg)
                .and_then(|a| scheduler_input_set_from_artifact(pkg, a, &repo_root, &ws).ok());
            input_sets.insert(pkg.clone(), set);
        }
    }

    let outcome = attribute(&changed, &testable_pkgs, &input_sets, &ws);
    Ok((outcome, testable_pkgs))
}

/// A nextest filter-expression narrowing a run to the tests affected by the
/// changes between `base` and the working tree (committed `base..HEAD` UNIONed
/// with uncommitted + untracked edits), or `None` to apply no narrowing.
///
/// - `RunAll` (broad/infra change or any attribution failure) -> `None`: run
///   whatever the user already selected, unnarrowed (the fail-safe).
/// - `Empty` (strictly docs-only, or nothing changed vs base) -> `Some("none()")`:
///   a valid nullary expression matching zero tests.
/// - `Subset(pkgs)` -> a `test(...)` union over every test whose scheduler maps
///   to an affected package, plus every package-less scheduler's tests
///   (`Eevdf`/`Path`/`KernelBuiltin` sit outside the package matrix, so on any
///   non-docs change they are conservatively kept). An empty union (no
///   enumerated test maps to an affected package) -> `None`, the fail-safe:
///   never silently narrow to nothing off a mapping we could not build.
///
/// The caller ANDs this with any user `-E` (nextest UNIONs multiple `-E`, so
/// narrowing requires a single composed `(relevant)&(user)` expression).
pub(crate) fn relevant_test_filter(
    base: Option<&str>,
    base_ref: Option<&str>,
    default_branch: &str,
) -> Result<Option<String>> {
    let schedulers = enumerate_schedulers().context("enumerate declared schedulers")?;
    let (outcome, _testable) = compute_outcome(base, base_ref, default_branch, true, &schedulers)?;

    // RunAll / Empty resolve without the per-test scheduler map, so skip the
    // (build+run) test-list probe on those paths; only Subset needs it.
    if !matches!(outcome, AffectedOutcome::Subset(_)) {
        return Ok(select_relevant_tests(&outcome, &BTreeMap::new(), &[]));
    }
    // scheduler name -> its package (None = package-less: outside the matrix).
    let pkg_of: BTreeMap<&str, Option<&str>> = schedulers
        .iter()
        .map(|s| (s.name.as_str(), s.package.as_deref()))
        .collect();
    let tests = enumerate_scheduler_tests().context("enumerate declared tests")?;
    Ok(select_relevant_tests(&outcome, &pkg_of, &tests))
}

/// Pure mapping of an [`AffectedOutcome`] onto a nextest filter over test NAMES,
/// given the scheduler-name -> package map and the declared tests. Extracted
/// from [`relevant_test_filter`] so the outcome -> test-name selection (the
/// actual `--relevant` payload) is unit-testable without git, a build, or a
/// probe.
///
/// - `RunAll` -> `None`: run everything, unnarrowed (the fail-safe).
/// - `Empty` -> `Some("none()")`: a nullary expression matching zero tests.
/// - `Subset` -> a `build_nextest_filter` union over every test whose scheduler
///   maps to an affected package, PLUS every package-less or unenumerable
///   scheduler's test (`Eevdf`/`Path`/`KernelBuiltin` sit outside the package
///   matrix, so on any non-docs change they are conservatively kept). An empty
///   selection -> `None` (fail-safe: never silently narrow to nothing off a
///   mapping we could not build) -- distinct from `Empty`'s deliberate
///   `none()`.
fn select_relevant_tests(
    outcome: &AffectedOutcome,
    pkg_of: &BTreeMap<&str, Option<&str>>,
    tests: &[ktstr::test_support::SchedulerTestJson],
) -> Option<String> {
    let affected: BTreeSet<&str> = match outcome {
        AffectedOutcome::RunAll => return None,
        AffectedOutcome::Empty => return Some("none()".to_string()),
        AffectedOutcome::Subset(pkgs) => pkgs.iter().map(String::as_str).collect(),
    };
    let selected: BTreeSet<&str> = tests
        .iter()
        .filter(|t| match pkg_of.get(t.scheduler.as_str()).copied() {
            // A Discover scheduler: keep the test iff its package is affected.
            Some(Some(pkg)) => affected.contains(pkg),
            // Package-less scheduler, or a scheduler we could not enumerate:
            // keep on any non-docs change (Subset) -- the fail-safe.
            _ => true,
        })
        .map(|t| t.test.as_str())
        .collect();

    if selected.is_empty() {
        None
    } else {
        Some(crate::replay::build_nextest_filter(&selected))
    }
}

/// Pure attribution: given the changed paths, the testable scheduler packages,
/// each scheduler's `.d` input set (`None` = could not compute -> conservatively
/// affected), and the workspace graph, decide the outcome. Extracted from
/// [`compute_outcome`] so the layer-1 ∪ layer-2 union and the fail-safe
/// (unattributed -> RunAll) are unit-testable without git or a build.
fn attribute(
    changed: &BTreeSet<String>,
    testable_pkgs: &[String],
    input_sets: &BTreeMap<String, Option<BTreeSet<String>>>,
    ws: &WorkspaceGraph,
) -> AffectedOutcome {
    let mut affected: BTreeSet<String> = BTreeSet::new();
    let mut unattributed = false;
    for path in changed {
        if is_docs_only(path) {
            continue;
        }
        let mut attributed = false;

        // Layer 2: owned by a workspace crate -> attributed; affected
        // schedulers are those whose dependency closure contains the owner.
        if let Some(owner) = ws.owning_crate(path) {
            attributed = true;
            for pkg in testable_pkgs {
                if ws.closure_contains(pkg, owner) {
                    affected.insert(pkg.clone());
                }
            }
        }

        // Layer 1: present in a scheduler's .d input set.
        for (pkg, set) in input_sets {
            if set.as_ref().is_some_and(|s| s.contains(path)) {
                attributed = true;
                affected.insert(pkg.clone());
            }
        }

        // A non-docs path attributed to neither a crate nor a .d has an
        // unknown blast radius.
        if !attributed {
            unattributed = true;
        }
    }

    // A scheduler whose .d could not be computed is conservatively affected --
    // never silently dropped.
    for (pkg, set) in input_sets {
        if set.is_none() {
            affected.insert(pkg.clone());
        }
    }

    if unattributed {
        return AffectedOutcome::RunAll;
    }
    let affected: Vec<String> = affected.into_iter().collect();
    if affected.is_empty() {
        AffectedOutcome::Empty
    } else {
        AffectedOutcome::Subset(affected)
    }
}

/// A scheduler's `.d` input set (canonicalized, repo-relative) from its
/// PRE-BUILT `[[bin]]` artifact: reads the dep-info alongside `artifact` and
/// folds in the scheduler's own manifest + build.rs paths (build inputs the
/// `.d` never lists, so a dep bump in its Cargo.toml still marks it affected).
/// The scheduler is built once, in a batch, by [`build_schedulers`].
///
/// Deliberately UNCACHED: the `.d` is the only ground truth for the input set,
/// and any cache keyed on a cheaper proxy (source-path set, Cargo.lock) risks a
/// stale set that silently under-runs when a shared header gains a new include
/// -- the worst outcome. Rebuilding every run is the accepted cost.
fn scheduler_input_set_from_artifact(
    pkg: &str,
    artifact: &Path,
    repo_root: &Path,
    ws: &WorkspaceGraph,
) -> Result<BTreeSet<String>> {
    let (manifest_rel, build_rs_rel) = ws.scheduler_manifest_inputs(pkg, repo_root)?;
    let dot_d = artifact.with_extension("d");
    let contents = std::fs::read_to_string(&dot_d)
        .with_context(|| format!("read dep-info {}", dot_d.display()))?;
    let mut set: BTreeSet<String> = dep_info::parse_dep_info(&contents)
        .iter()
        .filter_map(|p| dep_info::normalize_to_repo_relative(p, repo_root))
        .collect();
    // The manifest + build.rs are build inputs the .d never lists.
    set.insert(manifest_rel);
    if let Some(b) = build_rs_rel {
        set.insert(b);
    }
    Ok(set)
}

/// Build EVERY testable scheduler in ONE `cargo build -p A -p B ...` and map
/// each package NAME to its `[[bin]]` artifact path (its `.d` sits alongside).
/// One cargo invocation instead of one-per-scheduler: cargo resolves the graph
/// and compiles shared dependencies once.
///
/// A package that produced no bin artifact (its build failed, or cargo stopped
/// before reaching it) is ABSENT from the map, so
/// [`scheduler_input_set_from_artifact`] is never called for it and its input
/// set stays `None` -> conservatively affected (the per-scheduler fail-safe,
/// preserved). The exit status is therefore NOT checked: cargo still emits
/// artifacts for the packages that DID build even when a sibling fails, so
/// parse-what-was-emitted keeps the successful schedulers precise while the
/// failed ones fall through to the conservative `None`.
///
/// Deliberately NOT [`ktstr::build_and_find_binary`], which pins cargo's cwd to
/// ktstr's own manifest dir (baked via `env!("CARGO_MANIFEST_DIR")` at compile
/// time) -- wrong here, because `affected` runs INSIDE the target repo, whose
/// schedulers are what we build. Uses the SAME profile
/// (`ktstr::scheduler_profile_name`: `KTSTR_SCHEDULER_PROFILE` or the release
/// default) the scheduler-under-test is built with, so the `.d` lands in the
/// matching `target/<profile>/` and a warm build is reused.
///
/// `cargo` is the caller-resolved cargo binary (the SAME one `cargo metadata`
/// used), so the `PackageId.repr` in the emitted artifacts matches the metadata
/// reprs `id_to_name` is keyed on.
fn build_schedulers(
    cargo: &Path,
    pkgs: &[String],
    id_to_name: &BTreeMap<String, String>,
) -> BTreeMap<String, PathBuf> {
    if pkgs.is_empty() {
        return BTreeMap::new();
    }
    let profile = ktstr::scheduler_profile_name();
    let mut cmd = Command::new(cargo);
    cmd.args([
        "build",
        "--message-format=json",
        "--profile",
        profile.as_str(),
    ]);
    for pkg in pkgs {
        cmd.args(["-p", pkg]);
    }
    let output = match cmd.stdout(Stdio::piped()).stderr(Stdio::inherit()).output() {
        Ok(o) => o,
        // Spawn failure -> empty map -> every scheduler conservatively affected.
        Err(_) => return BTreeMap::new(),
    };
    map_artifacts_to_bins(std::io::Cursor::new(output.stdout), id_to_name)
}

/// Parse a `cargo build --message-format=json` stream into a package-NAME ->
/// `[[bin]]` artifact-path map. Extracted from [`build_schedulers`] so the
/// artifact filtering (a non-test `[[bin]]` target of a known package that has
/// an executable) is unit-testable without spawning cargo. `id_to_name` maps
/// `PackageId.repr` to the package name, so an artifact is attributed to its
/// package regardless of whether the `[[bin]]` name matches the package name;
/// an artifact whose `package_id` is not in the map (a dependency) is skipped.
///
/// Assumes ONE `[[bin]]` per scheduler package (true for every scx scheduler,
/// and the same assumption [`ktstr::build_and_find_binary`] makes). If a package
/// emits multiple bins the last wins and a diagnostic is logged to stderr; a
/// future multi-bin scheduler would want the per-bin `.d` sets unioned instead.
fn map_artifacts_to_bins<R: std::io::BufRead>(
    stream: R,
    id_to_name: &BTreeMap<String, String>,
) -> BTreeMap<String, PathBuf> {
    let mut map: BTreeMap<String, PathBuf> = BTreeMap::new();
    for msg in cargo_metadata::Message::parse_stream(stream).flatten() {
        let cargo_metadata::Message::CompilerArtifact(art) = msg else {
            continue;
        };
        if art.target.is_bin()
            && !art.profile.test
            && let Some(name) = id_to_name.get(&art.package_id.repr)
            && let Some(exe) = art.executable
        {
            let path = PathBuf::from(exe.as_str());
            if let Some(prev) = map.insert(name.clone(), path) {
                eprintln!(
                    "ktstr affected: scheduler package `{name}` emitted multiple \
                     [[bin]] artifacts; using the last, ignoring {} (its `.d` \
                     inputs are not considered)",
                    prev.display()
                );
            }
        }
    }
    map
}

/// Workspace crate graph: member manifest dirs (repo-relative) + dependency
/// closures, all derived once from `cargo metadata`.
struct WorkspaceGraph {
    /// crate name -> repo-relative manifest directory (with a trailing `/`).
    crate_dirs: BTreeMap<String, String>,
    /// crate name -> its transitive workspace dependency closure (crate names,
    /// including itself).
    closures: BTreeMap<String, BTreeSet<String>>,
    /// crate name -> absolute manifest path.
    manifest_paths: BTreeMap<String, PathBuf>,
    member_names: BTreeSet<String>,
}

impl WorkspaceGraph {
    fn build(meta: &cargo_metadata::Metadata, repo_root: &Path) -> Self {
        let member_ids: BTreeSet<&cargo_metadata::PackageId> =
            meta.workspace_members.iter().collect();
        let mut member_names = BTreeSet::new();
        let mut crate_dirs = BTreeMap::new();
        let mut manifest_paths = BTreeMap::new();
        // id -> name, for the resolve-graph walk.
        let mut id_to_name: BTreeMap<&cargo_metadata::PackageId, String> = BTreeMap::new();

        for p in &meta.packages {
            let name = p.name.to_string();
            if member_ids.contains(&p.id) {
                member_names.insert(name.clone());
                let manifest = PathBuf::from(p.manifest_path.as_str());
                if let Some(dir) = manifest.parent() {
                    // Canonicalize so the crate dir strips against the canonical
                    // repo root. ASSUMES crate dirs are not reached via an
                    // in-repo symlink: git reports the symlink path while
                    // canonicalize resolves it, so a symlinked crate dir would
                    // break owning_crate's prefix match (not reachable in scx;
                    // a future one would need the diff paths canonicalized too).
                    let canon = std::fs::canonicalize(dir).unwrap_or_else(|_| dir.to_path_buf());
                    if let Ok(rel) = canon.strip_prefix(repo_root) {
                        let rel = rel.to_string_lossy().into_owned();
                        // A root package strips to "" and would prefix-match
                        // EVERY path; skip it so a repo-root file falls through
                        // to unattributed -> RunAll rather than being wrongly
                        // owned by the root package.
                        if !rel.is_empty() {
                            crate_dirs.insert(name.clone(), format!("{rel}/"));
                        }
                    }
                }
                manifest_paths.insert(name.clone(), manifest);
            }
            id_to_name.insert(&p.id, name);
        }

        // Member->member dependency edges (Normal + Build; a pure dev-dep is
        // not linked into the scheduler binary). Empty dep_kinds (older cargo)
        // -> treat as Normal.
        let mut edges: BTreeMap<String, BTreeSet<String>> = BTreeMap::new();
        if let Some(resolve) = &meta.resolve {
            for node in &resolve.nodes {
                let Some(from) = id_to_name
                    .get(&node.id)
                    .filter(|n| member_names.contains(*n))
                else {
                    continue;
                };
                for dep in &node.deps {
                    let Some(to) = id_to_name
                        .get(&dep.pkg)
                        .filter(|n| member_names.contains(*n))
                    else {
                        continue;
                    };
                    let linked = dep.dep_kinds.is_empty()
                        || dep.dep_kinds.iter().any(|dk| {
                            matches!(
                                dk.kind,
                                cargo_metadata::DependencyKind::Normal
                                    | cargo_metadata::DependencyKind::Build
                            )
                        });
                    if linked {
                        edges
                            .entry((*from).clone())
                            .or_default()
                            .insert((*to).clone());
                    }
                }
            }
        }

        let closures = member_names
            .iter()
            .map(|name| (name.clone(), transitive_closure(name, &edges)))
            .collect();

        Self {
            crate_dirs,
            closures,
            manifest_paths,
            member_names,
        }
    }

    fn is_member(&self, pkg: &str) -> bool {
        self.member_names.contains(pkg)
    }

    /// The workspace crate that owns `path` (longest repo-relative
    /// manifest-dir prefix wins, so a crate nested under another is
    /// attributed to the inner one).
    fn owning_crate(&self, path: &str) -> Option<&str> {
        self.crate_dirs
            .iter()
            .filter(|(_, dir)| path.starts_with(dir.as_str()))
            .max_by_key(|(_, dir)| dir.len())
            .map(|(name, _)| name.as_str())
    }

    fn closure_contains(&self, scheduler: &str, crate_name: &str) -> bool {
        self.closures
            .get(scheduler)
            .is_some_and(|c| c.contains(crate_name))
    }

    /// (manifest repo-rel, build.rs repo-rel) for the scheduler -- build inputs
    /// the `.d` never lists, folded into the scheduler's input set so a change
    /// to its Cargo.toml / build.rs marks it affected.
    fn scheduler_manifest_inputs(
        &self,
        pkg: &str,
        repo_root: &Path,
    ) -> Result<(String, Option<String>)> {
        let manifest = self
            .manifest_paths
            .get(pkg)
            .ok_or_else(|| anyhow!("{pkg} not in workspace metadata"))?;
        let dir = manifest
            .parent()
            .ok_or_else(|| anyhow!("{pkg} manifest has no parent dir"))?;
        let build_rs_path = dir.join("build.rs");
        let manifest_rel = dep_info::normalize_to_repo_relative(manifest, repo_root)
            .ok_or_else(|| anyhow!("{pkg} manifest is outside the repo"))?;
        let build_rs_rel = if build_rs_path.exists() {
            dep_info::normalize_to_repo_relative(&build_rs_path, repo_root)
        } else {
            None
        };
        Ok((manifest_rel, build_rs_rel))
    }
}

/// Transitive closure of `start` over `edges` (includes `start`).
fn transitive_closure(start: &str, edges: &BTreeMap<String, BTreeSet<String>>) -> BTreeSet<String> {
    let mut seen = BTreeSet::new();
    let mut queue = VecDeque::new();
    queue.push_back(start.to_string());
    while let Some(n) = queue.pop_front() {
        if !seen.insert(n.clone()) {
            continue;
        }
        if let Some(next) = edges.get(&n) {
            for m in next {
                if !seen.contains(m) {
                    queue.push_back(m.clone());
                }
            }
        }
    }
    seen
}

/// A change confined to documentation: a `.md` file, or anything under a
/// top-level `doc`/`docs` directory. STRICT (matched with `.all()` over the
/// full changed set) -- `src/docs_render.rs` is NOT docs.
fn is_docs_only(path: &str) -> bool {
    path.ends_with(".md") || matches!(path.split('/').next(), Some("doc" | "docs"))
}

/// A change to workspace-root / build-graph infrastructure whose blast radius
/// spans every scheduler -> RunAll. The kernel tree (`../linux`) lives OUTSIDE
/// the target repo and cannot appear here; a kernel bump must force RunAll
/// out-of-band in CI. `ktstr.kconfig` (in-repo) IS detectable.
fn is_infra_path(path: &str) -> bool {
    matches!(
        path,
        "Cargo.toml" | "Cargo.lock" | "rust-toolchain.toml" | "rust-toolchain" | "ktstr.kconfig"
    ) || path.starts_with(".cargo/")
}

/// A native (C / BPF) source or header -- a change to one may be text-included
/// by a scheduler other than its owner, so the `.d` layer must run.
fn is_native_source(path: &str) -> bool {
    path.ends_with(".c") || path.ends_with(".h")
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn docs_only_classification() {
        assert!(is_docs_only("README.md"));
        assert!(is_docs_only("docs/guide/x.md"));
        assert!(is_docs_only("doc/notes.txt"));
        // Not docs: a source file whose name merely contains "docs".
        assert!(!is_docs_only("src/docs_render.rs"));
        assert!(!is_docs_only("scheds/rust/scx_x/src/main.rs"));
    }

    #[test]
    fn infra_classification() {
        assert!(is_infra_path("Cargo.lock"));
        assert!(is_infra_path("Cargo.toml"));
        assert!(is_infra_path("rust-toolchain.toml"));
        assert!(is_infra_path("ktstr.kconfig"));
        assert!(is_infra_path(".cargo/config.toml"));
        // A per-crate Cargo.toml is NOT the root infra file.
        assert!(!is_infra_path("scheds/rust/scx_x/Cargo.toml"));
    }

    #[test]
    fn native_source_classification() {
        assert!(is_native_source("scheds/rust/scx_x/src/bpf/main.bpf.c"));
        assert!(is_native_source("scheds/include/scx/common.bpf.h"));
        assert!(!is_native_source("scheds/rust/scx_x/src/main.rs"));
    }

    fn graph() -> WorkspaceGraph {
        let mut crate_dirs = BTreeMap::new();
        crate_dirs.insert("scx_a".to_string(), "scheds/rust/scx_a/".to_string());
        crate_dirs.insert("scx_b".to_string(), "scheds/rust/scx_b/".to_string());
        crate_dirs.insert("scx_common".to_string(), "rust/scx_common/".to_string());
        let mut closures = BTreeMap::new();
        closures.insert(
            "scx_a".to_string(),
            ["scx_a", "scx_common"]
                .iter()
                .map(|s| s.to_string())
                .collect(),
        );
        closures.insert(
            "scx_b".to_string(),
            ["scx_b"].iter().map(|s| s.to_string()).collect(),
        );
        closures.insert(
            "scx_common".to_string(),
            ["scx_common"].iter().map(|s| s.to_string()).collect(),
        );
        WorkspaceGraph {
            crate_dirs,
            closures,
            manifest_paths: BTreeMap::new(),
            member_names: ["scx_a", "scx_b", "scx_common"]
                .iter()
                .map(|s| s.to_string())
                .collect(),
        }
    }

    #[test]
    fn owning_crate_longest_prefix() {
        let g = graph();
        assert_eq!(
            g.owning_crate("scheds/rust/scx_a/src/main.rs"),
            Some("scx_a")
        );
        assert_eq!(
            g.owning_crate("rust/scx_common/src/lib.rs"),
            Some("scx_common")
        );
        // A shared header outside every crate dir has no owner (the .d layer
        // attributes it instead).
        assert_eq!(g.owning_crate("scheds/include/scx/common.bpf.h"), None);
    }

    #[test]
    fn closure_reflects_dependency_edges() {
        let g = graph();
        // scx_a depends on scx_common; scx_b does not.
        assert!(g.closure_contains("scx_a", "scx_common"));
        assert!(!g.closure_contains("scx_b", "scx_common"));
        assert!(g.closure_contains("scx_a", "scx_a"));
    }

    #[test]
    fn transitive_closure_follows_chain() {
        let mut edges: BTreeMap<String, BTreeSet<String>> = BTreeMap::new();
        edges.insert("a".into(), ["b"].iter().map(|s| s.to_string()).collect());
        edges.insert("b".into(), ["c"].iter().map(|s| s.to_string()).collect());
        let c = transitive_closure("a", &edges);
        assert_eq!(
            c,
            ["a", "b", "c"]
                .iter()
                .map(|s| s.to_string())
                .collect::<BTreeSet<_>>()
        );
    }

    fn changed(paths: &[&str]) -> BTreeSet<String> {
        paths.iter().map(|s| s.to_string()).collect()
    }

    #[test]
    fn attribute_docs_only_is_empty() {
        let g = graph();
        let pkgs = vec!["scx_a".to_string()];
        let out = attribute(
            &changed(&["README.md", "docs/x.md"]),
            &pkgs,
            &BTreeMap::new(),
            &g,
        );
        assert_eq!(out, AffectedOutcome::Empty);
    }

    #[test]
    fn attribute_layer2_closure_hit() {
        // A pure-Rust change to scx_common (no .d) affects scx_a (depends on
        // it) but not scx_b.
        let g = graph();
        let pkgs = vec!["scx_a".to_string(), "scx_b".to_string()];
        let out = attribute(
            &changed(&["rust/scx_common/src/lib.rs"]),
            &pkgs,
            &BTreeMap::new(),
            &g,
        );
        assert_eq!(out, AffectedOutcome::Subset(vec!["scx_a".to_string()]));
    }

    #[test]
    fn attribute_layer1_shared_header_via_dot_d() {
        // A shared BPF header owned by NO crate, but present in scx_a's .d,
        // affects scx_a alone -- attributed, no run_all.
        let g = graph();
        let pkgs = vec!["scx_a".to_string(), "scx_b".to_string()];
        let mut input_sets = BTreeMap::new();
        input_sets.insert(
            "scx_a".to_string(),
            Some(changed(&["scheds/include/scx/common.bpf.h"])),
        );
        input_sets.insert("scx_b".to_string(), Some(BTreeSet::new()));
        let out = attribute(
            &changed(&["scheds/include/scx/common.bpf.h"]),
            &pkgs,
            &input_sets,
            &g,
        );
        assert_eq!(out, AffectedOutcome::Subset(vec!["scx_a".to_string()]));
    }

    #[test]
    fn attribute_unattributed_non_docs_is_runall() {
        // A non-docs path owned by no crate and in no .d -> unknown blast
        // radius -> RunAll (the fail-safe).
        let g = graph();
        let pkgs = vec!["scx_a".to_string()];
        let mut input_sets = BTreeMap::new();
        input_sets.insert("scx_a".to_string(), Some(BTreeSet::new()));
        let out = attribute(
            &changed(&["tools/random_script.sh"]),
            &pkgs,
            &input_sets,
            &g,
        );
        assert_eq!(out, AffectedOutcome::RunAll);
    }

    #[test]
    fn attribute_uncomputable_dot_d_is_conservatively_affected() {
        // A scheduler whose .d could not be computed (None) is affected
        // regardless -- never silently dropped.
        let g = graph();
        let pkgs = vec!["scx_a".to_string(), "scx_b".to_string()];
        let mut input_sets = BTreeMap::new();
        input_sets.insert("scx_a".to_string(), None); // build/read failed
        input_sets.insert("scx_b".to_string(), Some(BTreeSet::new()));
        // A change owned by scx_b's crate keeps the path attributed.
        let out = attribute(
            &changed(&["scheds/rust/scx_b/src/bpf/main.bpf.c"]),
            &pkgs,
            &input_sets,
            &g,
        );
        assert_eq!(
            out,
            AffectedOutcome::Subset(vec!["scx_a".to_string(), "scx_b".to_string()])
        );
    }

    /// changed_paths_committed captures BOTH the source and destination of a
    /// rename (the location + source_location union) -- else a scheduler whose
    /// `.d` referenced the pre-rename path is wrongly judged unaffected. Shells
    /// `git` to build the fixture (same dependency perf-delta's tests use).
    #[test]
    fn changed_paths_committed_captures_rename_source_and_dest() {
        use std::process::Command;
        let dir = std::env::temp_dir().join(format!("ktstr-aff-gitfix-{}", std::process::id()));
        let _ = std::fs::remove_dir_all(&dir);
        std::fs::create_dir_all(&dir).expect("mk tempdir");
        let run = |args: &[&str]| {
            let ok = Command::new("git")
                .current_dir(&dir)
                .args([
                    "-c",
                    "user.email=t@example.invalid",
                    "-c",
                    "user.name=t",
                    "-c",
                    "commit.gpgsign=false",
                ])
                .args(args)
                .status()
                .map(|s| s.success())
                .unwrap_or(false);
            assert!(ok, "git {args:?} failed");
        };
        run(&["init", "-q"]);
        run(&["config", "diff.renames", "true"]);
        std::fs::write(dir.join("a.rs"), "fn a() {}\n").expect("write a.rs");
        run(&["add", "."]);
        run(&["commit", "-q", "-m", "first"]);
        run(&["mv", "a.rs", "b.rs"]);
        run(&["commit", "-q", "-am", "rename a.rs -> b.rs"]);

        let repo = gix::discover(&dir).expect("discover temp repo");
        let oid = |spec: &str| -> gix::ObjectId {
            match repo.rev_parse(spec).expect("rev-parse").detach() {
                gix::revision::plumbing::Spec::Include(id)
                | gix::revision::plumbing::Spec::ExcludeParents(id) => id,
                other => panic!("{spec} did not resolve to a commit: {other:?}"),
            }
        };
        let changed = diff::changed_paths_committed(&repo, oid("HEAD~1"), oid("HEAD"))
            .expect("changed paths");
        assert!(
            changed.contains("a.rs"),
            "rename source captured: {changed:?}"
        );
        assert!(
            changed.contains("b.rs"),
            "rename dest captured: {changed:?}"
        );
        std::fs::remove_dir_all(&dir).ok();
    }

    /// WorkspaceGraph::build derives crate dirs + dependency closures from real
    /// `cargo metadata`: a virtual root contributes no `""` crate_dir (so a
    /// top-level file is unowned), owning_crate maps member paths, and the
    /// closure reflects the `user -> dep` edge.
    #[test]
    fn workspace_graph_from_metadata() {
        let dir = std::env::temp_dir().join(format!("ktstr-aff-wsfix-{}", std::process::id()));
        let _ = std::fs::remove_dir_all(&dir);
        std::fs::create_dir_all(dir.join("dep/src")).unwrap();
        std::fs::create_dir_all(dir.join("user/src")).unwrap();
        std::fs::write(
            dir.join("Cargo.toml"),
            "[workspace]\nmembers = [\"dep\", \"user\"]\nresolver = \"2\"\n",
        )
        .unwrap();
        std::fs::write(
            dir.join("dep/Cargo.toml"),
            "[package]\nname = \"dep\"\nversion = \"0.1.0\"\nedition = \"2021\"\n",
        )
        .unwrap();
        std::fs::write(dir.join("dep/src/lib.rs"), "").unwrap();
        std::fs::write(
            dir.join("user/Cargo.toml"),
            "[package]\nname = \"user\"\nversion = \"0.1.0\"\nedition = \"2021\"\n\
             [dependencies]\ndep = { path = \"../dep\" }\n",
        )
        .unwrap();
        std::fs::write(dir.join("user/src/lib.rs"), "").unwrap();

        let repo_root = std::fs::canonicalize(&dir).unwrap();
        let meta = cargo_metadata::MetadataCommand::new()
            .manifest_path(dir.join("Cargo.toml"))
            .exec()
            .expect("cargo metadata");
        let ws = WorkspaceGraph::build(&meta, &repo_root);

        assert!(ws.is_member("dep") && ws.is_member("user"));
        assert_eq!(ws.owning_crate("dep/src/lib.rs"), Some("dep"));
        assert_eq!(ws.owning_crate("user/src/lib.rs"), Some("user"));
        // A virtual-workspace root contributes no "" crate_dir, so a top-level
        // file is UNOWNED (falls through to unattributed -> RunAll).
        assert_eq!(ws.owning_crate("README.md"), None);
        assert!(ws.closure_contains("user", "dep"));
        assert!(!ws.closure_contains("dep", "user"));
        std::fs::remove_dir_all(&dir).ok();
    }

    fn sched_test(test: &str, scheduler: &str) -> ktstr::test_support::SchedulerTestJson {
        ktstr::test_support::SchedulerTestJson {
            test: test.to_string(),
            scheduler: scheduler.to_string(),
        }
    }

    /// RunAll -> None (run everything, the fail-safe); no test map is consulted.
    #[test]
    fn select_relevant_runall_is_none() {
        assert_eq!(
            select_relevant_tests(&AffectedOutcome::RunAll, &BTreeMap::new(), &[]),
            None
        );
    }

    /// Empty (strictly docs-only) -> Some("none()"): a deliberate zero-match
    /// filterset, DISTINCT from the empty-selection fail-safe (which is None).
    #[test]
    fn select_relevant_empty_is_none_filterset() {
        assert_eq!(
            select_relevant_tests(&AffectedOutcome::Empty, &BTreeMap::new(), &[]),
            Some("none()".to_string())
        );
    }

    /// Subset maps each test onto its scheduler's package: an affected Discover
    /// package's test is kept, an unaffected one dropped; a package-less
    /// scheduler's test and an unenumerable (unknown-name) test are kept (the
    /// conservative inclusion).
    #[test]
    fn select_relevant_subset_maps_tests_to_affected_packages() {
        let mut pkg_of: BTreeMap<&str, Option<&str>> = BTreeMap::new();
        pkg_of.insert("scx_a_sched", Some("scx_a"));
        pkg_of.insert("scx_b_sched", Some("scx_b"));
        pkg_of.insert("builtin", None); // package-less scheduler
        let tests = vec![
            sched_test("t_a", "scx_a_sched"),   // affected pkg -> kept
            sched_test("t_b", "scx_b_sched"),   // unaffected pkg -> dropped
            sched_test("t_builtin", "builtin"), // package-less -> kept
            sched_test("t_unknown", "ghost"),   // not in pkg_of -> kept
        ];
        let outcome = AffectedOutcome::Subset(vec!["scx_a".to_string()]);
        let expr = select_relevant_tests(&outcome, &pkg_of, &tests).expect("Subset selects tests");
        // Match on the `NAME$` boundary `build_nextest_filter` emits, so a
        // dropped name is not falsely "found" as a prefix of a kept one
        // (e.g. `t_b` is a prefix of `t_builtin`).
        assert!(
            expr.contains("t_a$"),
            "affected Discover pkg test kept: {expr}"
        );
        assert!(
            expr.contains("t_builtin$"),
            "package-less test kept: {expr}"
        );
        assert!(
            expr.contains("t_unknown$"),
            "unenumerable-scheduler test kept: {expr}"
        );
        assert!(
            !expr.contains("t_b$"),
            "unaffected Discover pkg test dropped: {expr}"
        );
    }

    /// Subset whose every test maps to an unaffected Discover package -> the
    /// selection is empty -> None (run everything, the fail-safe), NOT
    /// Some("none()") (which would silently run zero tests).
    #[test]
    fn select_relevant_subset_empty_selection_is_none_failsafe() {
        let mut pkg_of: BTreeMap<&str, Option<&str>> = BTreeMap::new();
        pkg_of.insert("scx_b_sched", Some("scx_b"));
        let tests = vec![sched_test("t_b", "scx_b_sched")];
        let outcome = AffectedOutcome::Subset(vec!["scx_a".to_string()]);
        assert_eq!(select_relevant_tests(&outcome, &pkg_of, &tests), None);
    }

    /// map_artifacts_to_bins keeps ONLY a non-test `[[bin]]` artifact of a KNOWN
    /// package that has an executable, attributed by `package_id` -> its
    /// `executable`. Each of the four filter conjuncts is exercised in
    /// isolation: a lib (not a bin), a TEST-profile bin (dropped by `!test`, and
    /// ordered AFTER the real bin so a broken `!test` filter would overwrite and
    /// flip the asserted path), a bin with a null executable (dropped by
    /// `executable.is_some()`), and a bin of an unknown package (a dependency).
    /// Fixture is real `cargo build --message-format=json` output shape.
    #[test]
    fn map_artifacts_to_bins_filters_and_attributes() {
        let mut id_to_name: BTreeMap<String, String> = BTreeMap::new();
        id_to_name.insert(
            "scx_a 1.0.0 (path+file:///w/scx_a)".to_string(),
            "scx_a".to_string(),
        );
        id_to_name.insert(
            "scx_b 1.0.0 (path+file:///w/scx_b)".to_string(),
            "scx_b".to_string(),
        );
        let stream = concat!(
            // scx_a real bin (non-test, has executable) -> the sole mapped entry.
            r#"{"reason":"compiler-artifact","package_id":"scx_a 1.0.0 (path+file:///w/scx_a)","target":{"name":"scx_a","kind":["bin"],"src_path":"/w/scx_a/src/main.rs"},"profile":{"opt_level":"3","debug_assertions":false,"overflow_checks":false,"test":false},"features":[],"filenames":["/w/target/release/scx_a"],"executable":"/w/target/release/scx_a","fresh":false}"#,
            "\n",
            // scx_a lib -> dropped (not a bin).
            r#"{"reason":"compiler-artifact","package_id":"scx_a 1.0.0 (path+file:///w/scx_a)","target":{"name":"scx_a","kind":["lib"],"src_path":"/w/scx_a/src/lib.rs"},"profile":{"opt_level":"3","debug_assertions":false,"overflow_checks":false,"test":false},"features":[],"filenames":["/w/target/release/libscx_a.rlib"],"executable":null,"fresh":false}"#,
            "\n",
            // scx_a TEST-profile bin (after the real bin, different executable)
            // -> dropped by `!test`; a broken filter would overwrite scx_a.
            r#"{"reason":"compiler-artifact","package_id":"scx_a 1.0.0 (path+file:///w/scx_a)","target":{"name":"scx_a","kind":["bin"],"src_path":"/w/scx_a/src/main.rs"},"profile":{"opt_level":"3","debug_assertions":false,"overflow_checks":false,"test":true},"features":[],"filenames":["/w/target/release/deps/scx_a-abc123"],"executable":"/w/target/release/deps/scx_a-abc123","fresh":false}"#,
            "\n",
            // scx_b bin with a null executable -> dropped by `executable.is_some()`.
            r#"{"reason":"compiler-artifact","package_id":"scx_b 1.0.0 (path+file:///w/scx_b)","target":{"name":"scx_b","kind":["bin"],"src_path":"/w/scx_b/src/main.rs"},"profile":{"opt_level":"3","debug_assertions":false,"overflow_checks":false,"test":false},"features":[],"filenames":[],"executable":null,"fresh":false}"#,
            "\n",
            // Unknown package (a dependency) bin -> dropped (not in id_to_name).
            r#"{"reason":"compiler-artifact","package_id":"ghost 1.0.0 (path+file:///w/ghost)","target":{"name":"ghost","kind":["bin"],"src_path":"/w/ghost/src/main.rs"},"profile":{"opt_level":"3","debug_assertions":false,"overflow_checks":false,"test":false},"features":[],"filenames":["/w/target/release/ghost"],"executable":"/w/target/release/ghost","fresh":false}"#,
            "\n",
            r#"{"reason":"build-finished","success":true}"#,
            "\n",
        );
        let map = map_artifacts_to_bins(std::io::Cursor::new(stream), &id_to_name);
        assert_eq!(map.len(), 1, "only the known non-test bin maps: {map:?}");
        assert_eq!(
            map.get("scx_a").map(|p| p.to_string_lossy().into_owned()),
            Some("/w/target/release/scx_a".to_string()),
            "the real (non-test) bin is mapped, not the test-profile bin",
        );
        assert!(
            !map.contains_key("scx_b"),
            "a bin with a null executable is not mapped: {map:?}",
        );
    }
}