big_code_analysis/

langs.rs

// Per-language metric and AST modules deliberately consume the macro-
// generated tree-sitter token enums via `use crate::*` and `use Foo::*`
// inside match expressions — explicit imports would list dozens of
// variants per arm and obscure the per-language token sets that are the
// point of these files. Allowed at the module level rather than per
// function so the per-language impl blocks stay readable.
#![allow(clippy::wildcard_imports, clippy::enum_glob_use)]

use std::path::Path;
use std::sync::Arc;
use tree_sitter::Language;

// `get_language` is referenced from feature-gated arms inside the
// `mk_lang!` expansion; an `--no-default-features` build with no
// language features compiles every arm out, leaving the import
// nominally unused. The macro itself carries the same allow.
#[allow(unused_imports)]
use crate::macros::{
    get_language, mk_action, mk_code, mk_emacs_mode, mk_extensions, mk_lang, mk_langs,
};
use crate::preproc::PreprocResults;
use crate::*;

mk_langs!(
    // 1) Cargo feature name that enables this variant's grammar
    // 2) Name for enum
    // 3) Language description
    // 4) Display name
    // 5) Empty struct name to implement
    // 6) Parser name
    // 7) tree-sitter function to call to get a Language
    // 8) file extensions
    // 9) emacs modes
    // 10) pinned grammar crate version (mirrors the `=X.Y.Z` pin in the
    //     workspace `Cargo.toml`; a drift test below asserts they agree)
    //
    // Per #252, each variant carries a Cargo feature that gates the
    // grammar crate references in `mk_lang!` / `mk_action!`. The enum
    // surface (variants, file-extension lookup, emacs-mode lookup,
    // per-language `*Code` / `*Parser` tags) is always compiled in;
    // disabling a feature only strips the grammar crate from the dep
    // graph and turns every dispatcher into
    // `Err(MetricsError::LanguageDisabled(_))`.
    //
    // `Ccomment` and `Preproc` ride the internal `c-family-helpers`
    // feature because they are helpers for the C-family pipeline; that
    // feature pulls the `tree-sitter-ccomment` / `tree-sitter-preproc`
    // crates and is enabled by every C-family language feature (`cpp`,
    // `c`, and `mozcpp`), so the helpers are compiled in whenever any of
    // them is (#721). `Tsx` rides `typescript` because
    // both variants resolve to the `tree-sitter-typescript` crate
    // (TSX vs TypeScript is a per-grammar `LANGUAGE_*` constant
    // inside that one crate, see `get_language!` in `src/macros/mod.rs`).
    (
        "javascript",
        Javascript,
        "The `JavaScript` language (upstream `tree-sitter-javascript` \
         grammar; the default for `.js` / `.mjs` / `.cjs` / `.jsx`)",
        "javascript",
        JavascriptCode,
        JavascriptParser,
        tree_sitter_javascript,
        [js, mjs, cjs, jsx],
        ["js", "js2"],
        "0.25.0"
    ),
    (
        "mozjs",
        Mozjs,
        "The Mozilla/SpiderMonkey `JavaScript` dialect (vendored \
         `tree-sitter-mozjs` fork; opt-in, owns the `.jsm` module \
         extension)",
        "mozjs",
        MozjsCode,
        MozjsParser,
        tree_sitter_mozjs,
        [jsm],
        [],
        "2.0.0"
    ),
    (
        "java",
        Java,
        "The `Java` language",
        "java",
        JavaCode,
        JavaParser,
        tree_sitter_java,
        [java],
        ["java"],
        "0.23.5"
    ),
    (
        "go",
        Go,
        "The `Go` language",
        "go",
        GoCode,
        GoParser,
        tree_sitter_go,
        [go],
        ["go"],
        "0.25.0"
    ),
    (
        "kotlin",
        Kotlin,
        "The `Kotlin` language",
        "kotlin",
        KotlinCode,
        KotlinParser,
        tree_sitter_kotlin_ng,
        [kt, kts],
        ["kotlin"],
        "1.1.0"
    ),
    (
        "lua",
        Lua,
        "The `Lua` language",
        "lua",
        LuaCode,
        LuaParser,
        tree_sitter_lua,
        [lua],
        ["lua"],
        "0.5.0"
    ),
    (
        "rust",
        Rust,
        "The `Rust` language",
        "rust",
        RustCode,
        RustParser,
        tree_sitter_rust,
        [rs],
        ["rust"],
        "0.24.2"
    ),
    (
        "tcl",
        Tcl,
        "The `Tcl` language",
        "tcl",
        TclCode,
        TclParser,
        tree_sitter_tcl,
        [tcl, tk, tm],
        ["tcl"],
        "2.0.0"
    ),
    (
        "irules",
        Irules,
        "The `Irules` language",
        "irules",
        IrulesCode,
        IrulesParser,
        tree_sitter_irules,
        [irule, irules],
        ["irules"],
        "0.1.1"
    ),
    (
        "c",
        C,
        "The `C` language (upstream `tree-sitter-c` grammar). Owns `.c` \
         and the `c` emacs mode since #721. C++ headers stay on \
         `LANG::Cpp` (`.h` is asymmetric: a C++ header through the C \
         grammar ERROR-cascades on `class` / `template`, while a C \
         header through the C++ grammar only trips on C++-keyword \
         identifiers).",
        "c",
        CCode,
        CParser,
        tree_sitter_c,
        [c],
        ["c"],
        "0.24.2"
    ),
    (
        "cpp",
        Cpp,
        "The `C/C++` language (upstream `tree-sitter-cpp` grammar; the \
         default for `.cpp` / `.cc` / `.h` and the rest of the C-family \
         extensions). C moved to `LANG::C` (`.c`) in #721; the \
         Mozilla/Gecko dialect moved to opt-in `LANG::Mozcpp` in #720. \
         Objective-C (`.m`) moved to `LANG::Objc` in #724; `.mm` \
         Objective-C++ stays here because the C++ grammar handles the \
         C++ half (the ObjC glue still ERROR-cascades).",
        "cpp",
        CppCode,
        CppParser,
        tree_sitter_cpp,
        [cpp, cxx, cc, hxx, hpp, h, hh, inc, mm],
        ["c++", "objc++", "objective-c++"],
        "0.23.4"
    ),
    (
        "mozcpp",
        Mozcpp,
        "The Mozilla/Gecko `C++` dialect (vendored `tree-sitter-mozcpp` \
         fork: upstream `tree-sitter-cpp` plus the `MOZ_*` / `QM_TRY_*` / \
         alone-macro overlay; opt-in, owns no file extensions — select it \
         explicitly with `--language mozcpp`, a manifest, or the API).",
        "mozcpp",
        MozcppCode,
        MozcppParser,
        tree_sitter_mozcpp,
        [],
        [],
        "2.0.0"
    ),
    (
        "objc",
        Objc,
        "The `Objective-C` language (upstream `tree-sitter-objc` \
         grammar). Owns `.m` and the `objc` / `objective-c` emacs \
         modes since #724. Objective-C++ (`.mm`) stays on `LANG::Cpp`: \
         the ObjC grammar parses C but not the C++ half of a `.mm` \
         file, and C++ is the larger surface, so `Cpp` degrades more \
         gracefully there (the same trade-off #721 used for `.h`).",
        "objc",
        ObjcCode,
        ObjcParser,
        tree_sitter_objc,
        [m],
        ["objc", "objective-c"],
        "3.0.2"
    ),
    (
        "csharp",
        Csharp,
        "The `C#` language",
        "csharp",
        CsharpCode,
        CsharpParser,
        tree_sitter_c_sharp,
        [cs, csx, cake],
        ["csharp"],
        "0.23.5"
    ),
    (
        "elixir",
        Elixir,
        "The `Elixir` language",
        "elixir",
        ElixirCode,
        ElixirParser,
        tree_sitter_elixir,
        [ex, exs],
        ["elixir"],
        "0.3.5"
    ),
    (
        "python",
        Python,
        "The `Python` language",
        "python",
        PythonCode,
        PythonParser,
        tree_sitter_python,
        [py],
        ["python"],
        "0.25.0"
    ),
    (
        "typescript",
        Tsx,
        "The `Tsx` language incorporates the `JSX` syntax inside `TypeScript`",
        "tsx",
        TsxCode,
        TsxParser,
        tree_sitter_tsx,
        [tsx],
        [],
        "0.23.2"
    ),
    (
        "typescript",
        Typescript,
        "The `TypeScript` language",
        "typescript",
        TypescriptCode,
        TypescriptParser,
        tree_sitter_typescript,
        [ts, jsw, jsmw],
        ["typescript"],
        "0.23.2"
    ),
    (
        "bash",
        Bash,
        "The `Bash` language",
        "bash",
        BashCode,
        BashParser,
        tree_sitter_bash,
        [sh, bash],
        ["sh"],
        "0.25.1"
    ),
    (
        "c-family-helpers",
        Ccomment,
        "The `Ccomment` language is a variant of the `C` language focused on comments",
        "ccomment",
        CcommentCode,
        CcommentParser,
        tree_sitter_ccomment,
        [],
        [],
        "2.0.0"
    ),
    (
        "c-family-helpers",
        Preproc,
        "The `PreProc` language is a variant of the `C/C++` language focused on macros",
        "preproc",
        PreprocCode,
        PreprocParser,
        tree_sitter_preproc,
        [],
        [],
        "2.0.0"
    ),
    (
        "perl",
        Perl,
        "The `Perl` language",
        "perl",
        PerlCode,
        PerlParser,
        tree_sitter_perl,
        [pl, pm, t],
        ["perl", "cperl"],
        "1.1.2"
    ),
    (
        "php",
        Php,
        "The `Php` language",
        "php",
        PhpCode,
        PhpParser,
        tree_sitter_php,
        [php, phtml, php3, php4, php5, php7, phps],
        ["php"],
        "0.24.2"
    ),
    (
        "ruby",
        Ruby,
        "The `Ruby` language",
        "ruby",
        RubyCode,
        RubyParser,
        tree_sitter_ruby,
        [rb, rake, gemspec],
        ["ruby"],
        "0.23.1"
    ),
    (
        "groovy",
        Groovy,
        "The `Groovy` language",
        "groovy",
        GroovyCode,
        GroovyParser,
        dekobon_tree_sitter_groovy,
        [groovy, gradle, gvy, gy, gsh],
        ["groovy"],
        "0.2.2"
    )
);

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

    /// Drift guard: every [`LANG::grammar_version`] literal must match the
    /// `=X.Y.Z` pin in the workspace `Cargo.toml`. Bumping a grammar pin
    /// without updating the macro literal (or vice versa) fails here, so the
    /// runtime accessor and the actual dependency graph cannot silently
    /// disagree (#727). Feature-independent: the version literals and the
    /// manifest pins both exist regardless of the enabled language set.
    #[test]
    fn grammar_version_matches_cargo_toml_pin() {
        // CARGO_MANIFEST_DIR is the root crate's dir, which is the workspace
        // root, so this is the manifest that carries `[workspace.dependencies]`.
        let manifest = include_str!(concat!(env!("CARGO_MANIFEST_DIR"), "/Cargo.toml"));

        // LANG variant -> its `[workspace.dependencies]` key. Tsx and
        // Typescript share the one `tree-sitter-typescript` crate; the
        // C-family helpers and dialect forks each have their own vendored
        // `bca-tree-sitter-*` crate (aliased back to `tree-sitter-*`).
        let dep_key = |lang: LANG| -> &'static str {
            match lang {
                LANG::Javascript => "tree-sitter-javascript",
                LANG::Mozjs => "tree-sitter-mozjs",
                LANG::Java => "tree-sitter-java",
                LANG::Go => "tree-sitter-go",
                LANG::Kotlin => "tree-sitter-kotlin-ng",
                LANG::Lua => "tree-sitter-lua",
                LANG::Rust => "tree-sitter-rust",
                LANG::Tcl => "tree-sitter-tcl",
                LANG::Irules => "tree-sitter-irules",
                LANG::C => "tree-sitter-c",
                LANG::Cpp => "tree-sitter-cpp",
                LANG::Mozcpp => "tree-sitter-mozcpp",
                LANG::Objc => "tree-sitter-objc",
                LANG::Csharp => "tree-sitter-c-sharp",
                LANG::Elixir => "tree-sitter-elixir",
                LANG::Python => "tree-sitter-python",
                LANG::Tsx | LANG::Typescript => "tree-sitter-typescript",
                LANG::Bash => "tree-sitter-bash",
                LANG::Ccomment => "tree-sitter-ccomment",
                LANG::Preproc => "tree-sitter-preproc",
                LANG::Perl => "tree-sitter-perl",
                LANG::Php => "tree-sitter-php",
                LANG::Ruby => "tree-sitter-ruby",
                LANG::Groovy => "dekobon-tree-sitter-groovy",
            }
        };

        // Pull the pinned `=X.Y.Z` for `key` out of the manifest. Handles
        // both the bare-string form (`key = "=1.2.3"`) and the table form
        // (`key = { package = ..., version = "=1.1.0" }`): the `"=` token
        // appears only at the exact-version pin in either shape. The
        // trailing space in the prefix keeps `tree-sitter-c` from matching
        // `tree-sitter-c-sharp` / `tree-sitter-cpp`.
        let pinned = |key: &str| -> String {
            let prefix = format!("{key} = ");
            let line = manifest
                .lines()
                .map(str::trim)
                .find(|l| l.starts_with(&prefix))
                .unwrap_or_else(|| panic!("no `{key}` pin in workspace Cargo.toml"));
            let Some(quote_eq) = line.find("\"=") else {
                panic!("`{key}` pin is not an exact `=X.Y.Z` version: {line}")
            };
            let after_eq = &line[quote_eq + 2..];
            let end = after_eq
                .find('"')
                .expect("closing quote on the version pin");
            after_eq[..end].to_owned()
        };

        for lang in LANG::into_enum_iter() {
            assert_eq!(
                lang.grammar_version(),
                pinned(dep_key(lang)),
                "grammar_version() for {lang:?} drifted from its Cargo.toml pin",
            );
        }
    }

    // The test suite normally runs under the workspace default
    // feature set (`all-languages` is on, see `Cargo.toml`), so
    // every variant must report itself as enabled. A regression in
    // the cfg-gating of `is_enabled` would flip individual arms to
    // `false` even when the matching grammar crate is in the dep
    // graph; this test would catch that without needing a separate
    // `--no-default-features` build matrix entry. Gated on
    // `feature = "all-languages"` so the CI minimal-langs matrix
    // entry (`--no-default-features --features rust,typescript`)
    // still compiles cleanly without a runtime failure.
    #[cfg(feature = "all-languages")]
    #[test]
    fn every_lang_variant_is_enabled_under_all_languages() {
        for lang in LANG::into_enum_iter() {
            assert!(
                lang.is_enabled(),
                "{} should be enabled under the default `all-languages` feature set",
                lang.name(),
            );
        }
    }

    // Smoke test for the `LanguageDisabled` contract on a build
    // without the `javascript` feature: every dispatch entry point
    // (here, `tree_sitter_language`) must hand back
    // `Err(LanguageDisabled(LANG::Javascript))`. Gated on
    // `not(feature = "javascript")` so it only runs in a feature-
    // subset build where the language is actually disabled — the
    // `all-languages` default would have `is_enabled` return true
    // and `tree_sitter_language` succeed.
    #[cfg(not(feature = "javascript"))]
    #[test]
    fn disabled_language_dispatch_returns_language_disabled() {
        assert!(!LANG::Javascript.is_enabled());
        match LANG::Javascript.tree_sitter_language() {
            Err(MetricsError::LanguageDisabled(LANG::Javascript)) => {}
            other => panic!(
                "expected Err(LanguageDisabled(Javascript)) for disabled `javascript` feature, got {other:?}",
            ),
        }
    }

    // `is_enabled` and `tree_sitter_language` must agree: a
    // variant that reports itself enabled must hand back a usable
    // `Language`, never `Err(LanguageDisabled)`. The pairing exists
    // so callers that branch on `is_enabled` (rather than match on
    // the error) can rely on the language lookup succeeding.
    #[test]
    fn is_enabled_matches_get_tree_sitter_language() {
        for lang in LANG::into_enum_iter() {
            let lookup = lang.tree_sitter_language();
            assert_eq!(
                lang.is_enabled(),
                lookup.is_ok(),
                "{} disagrees: is_enabled={}, tree_sitter_language={:?}",
                lang.name(),
                lang.is_enabled(),
                lookup.map(|_| "Ok"),
            );
        }
    }

    // Regression guard for issue #262: the `MetricsError::EmptyRoot`
    // variant is documented as "Reserved — not produced today".
    // `metrics_with_options` pushes a synthetic top-level Unit
    // `FuncSpace` before walking, so every parse — including empty,
    // whitespace-only, and comment-only input — currently returns
    // `Ok(FuncSpace { kind: Unit, .. })`. If the walker is ever
    // changed to legitimately drain its state stack (e.g. by
    // dropping the synthetic root), this test will start failing
    // and the variant docs must be revisited.
    #[test]
    fn empty_and_comment_only_input_never_returns_empty_root() {
        use crate::{MetricsOptions, Source, SpaceKind, analyze};

        // Pair every enabled language with sources that would, by
        // the old (false) variant doc, surface `EmptyRoot`. The
        // comment syntaxes cover line and block forms across the
        // supported language families.
        let inputs: &[&[u8]] = &[b"", b"   \n\t\n", b"// just a comment\n", b"/* block */\n"];

        for lang in LANG::into_enum_iter() {
            if !lang.is_enabled() {
                continue;
            }
            for src in inputs {
                let space = analyze(Source::new(lang, src), MetricsOptions::default())
                    .unwrap_or_else(|err| {
                        panic!(
                            "{} on input {:?} unexpectedly returned {err:?}; \
                             EmptyRoot is documented as not produced today",
                            lang.name(),
                            String::from_utf8_lossy(src),
                        )
                    });
                assert_eq!(
                    space.kind,
                    SpaceKind::Unit,
                    "{} on input {:?} produced a non-Unit top-level FuncSpace",
                    lang.name(),
                    String::from_utf8_lossy(src),
                );
            }
        }
    }

    // `Display` must agree with `name` for every variant — the
    // impl delegates to it, so this pins that contract against future
    // refactors that might diverge the two.
    #[test]
    fn display_matches_name_for_every_variant() {
        for lang in LANG::into_enum_iter() {
            assert_eq!(lang.to_string(), lang.name());
        }
    }

    // `Display` -> `FromStr` round-trip over EVERY variant. Since #540
    // every variant has a distinct canonical slug, so the round-trip is
    // exact: `from_str(to_string(l)) == Ok(l)` for all `l`. This single
    // iterating assertion proves both round-trip fidelity AND injectivity
    // (a slug collision would make `from_str` resolve to the
    // first-declared sibling, failing the `Ok(l)` equality for the
    // later one). Test-via-revert: reintroducing the old "c/c++" display
    // for `Cpp` keeps the round-trip passing for `Cpp` (it still parses
    // back to `Cpp`), but reverting `Tsx` to "typescript" makes this
    // test fail on whichever of `Tsx`/`Typescript` is declared second.
    #[test]
    fn display_fromstr_round_trips_exactly_for_every_variant() {
        use std::str::FromStr;
        for lang in LANG::into_enum_iter() {
            assert_eq!(
                LANG::from_str(&lang.to_string()),
                Ok(lang),
                "{} did not round-trip exactly through Display/FromStr",
                lang.name(),
            );
        }
    }

    // No variant's canonical slug may contain `/` or `#` — the
    // punctuation that made the old "c/c++" / "c#" display forms
    // unusable as lookup tokens and leaked through the web `/metrics`
    // `language` field (#540). Guards against reintroducing a
    // human-pretty display form.
    #[test]
    fn no_variant_slug_contains_punctuation() {
        for lang in LANG::into_enum_iter() {
            let name = lang.name();
            assert!(
                !name.contains('/') && !name.contains('#'),
                "{name} contains punctuation that breaks FromStr lookup",
            );
        }
    }

    // The JavaScript pair has distinct display names since #507, so
    // `Display` is injective for it and the round-trip is exact —
    // "javascript" -> `Javascript` (upstream grammar, the default) and
    // "mozjs" -> `Mozjs` (the opt-in Mozilla fork). Pin both so a future
    // reorder or display-string change is deliberate and test-visible.
    #[test]
    fn javascript_pair_has_distinct_names() {
        use std::str::FromStr;
        assert_eq!(LANG::Javascript.name(), "javascript");
        assert_eq!(LANG::Mozjs.name(), "mozjs");
        assert_eq!(LANG::from_str("javascript"), Ok(LANG::Javascript));
        assert_eq!(LANG::from_str("mozjs"), Ok(LANG::Mozjs));
    }

    // The TypeScript pair has distinct slugs since #540 ("tsx" for
    // `Tsx`, "typescript" for `Typescript`), even though both ride the
    // upstream `tree-sitter-typescript` crate. Both round-trip to their
    // own variant — no aliasing collapse.
    #[test]
    fn typescript_pair_has_distinct_slugs() {
        use std::str::FromStr;
        assert_eq!(LANG::Tsx.name(), "tsx");
        assert_eq!(LANG::Typescript.name(), "typescript");
        assert_eq!(LANG::from_str("tsx"), Ok(LANG::Tsx));
        assert_eq!(LANG::from_str("typescript"), Ok(LANG::Typescript));
    }

    // Extension dispatch after the #507 default-grammar swap: the
    // standard JS extensions resolve to the upstream `Javascript`
    // grammar (including the newly-supported `.cjs`), while the Mozilla
    // fork owns only `.jsm`.
    #[test]
    fn javascript_extension_dispatch_defaults_to_upstream() {
        assert_eq!(get_from_ext("js"), Some(LANG::Javascript));
        assert_eq!(get_from_ext("mjs"), Some(LANG::Javascript));
        assert_eq!(get_from_ext("cjs"), Some(LANG::Javascript));
        assert_eq!(get_from_ext("jsx"), Some(LANG::Javascript));
        assert_eq!(get_from_ext("jsm"), Some(LANG::Mozjs));
    }

    // The `js` / `js2` emacs modes moved to the upstream `Javascript`
    // default alongside the extensions; pin them so a future `mk_langs!`
    // reorder cannot silently reroute emacs-mode dispatch to the fork.
    #[test]
    fn javascript_emacs_mode_dispatch_defaults_to_upstream() {
        assert_eq!(get_from_emacs_mode("js"), Some(LANG::Javascript));
        assert_eq!(get_from_emacs_mode("js2"), Some(LANG::Javascript));
    }

    // The `Cpp` and `Csharp` variants now expose punctuation-free
    // canonical slugs ("cpp", "csharp") since #540; `FromStr` round-trips
    // them and the former human-pretty "c/c++" / "c#" forms are no longer
    // accepted (the slug is the single canonical token everywhere).
    #[test]
    fn cpp_and_csharp_slugs_round_trip() {
        use std::str::FromStr;
        assert_eq!(LANG::Cpp.to_string(), "cpp");
        assert_eq!(LANG::from_str("cpp"), Ok(LANG::Cpp));
        assert_eq!(LANG::Csharp.to_string(), "csharp");
        assert_eq!(LANG::from_str("csharp"), Ok(LANG::Csharp));
        // The dropped pretty forms no longer parse.
        assert!(LANG::from_str("c/c++").is_err());
        assert!(LANG::from_str("c#").is_err());
    }

    // Since #720 the C++ pair is split like the JS pair: upstream
    // `Cpp` ("cpp", the default for the C-family extensions) and the
    // opt-in Mozilla fork `Mozcpp` ("mozcpp"). Distinct slugs, both
    // round-trip — no aliasing collapse (the #540 injectivity contract).
    #[test]
    fn cpp_pair_has_distinct_names() {
        use std::str::FromStr;
        assert_eq!(LANG::Cpp.name(), "cpp");
        assert_eq!(LANG::Mozcpp.name(), "mozcpp");
        assert_eq!(LANG::from_str("cpp"), Ok(LANG::Cpp));
        assert_eq!(LANG::from_str("mozcpp"), Ok(LANG::Mozcpp));
    }

    // Extension dispatch after the #720 default-grammar swap: the
    // C-family extensions resolve to the upstream `Cpp` grammar, while
    // the Mozilla fork `Mozcpp` owns *no* extension — it is reachable
    // only by explicit `--language mozcpp` / manifest / API selection.
    // Pin this so a future `mk_langs!` reorder cannot silently hand a
    // C-family extension to the fork (the failure mode #720 guards).
    #[test]
    fn cpp_extension_dispatch_defaults_to_upstream() {
        assert_eq!(get_from_ext("cpp"), Some(LANG::Cpp));
        assert_eq!(get_from_ext("cc"), Some(LANG::Cpp));
        assert_eq!(get_from_ext("hpp"), Some(LANG::Cpp));
        // `.h` stays on `Cpp` (decision-log #1: asymmetric failure modes).
        assert_eq!(get_from_ext("h"), Some(LANG::Cpp));
        // The fork claims zero extensions.
        assert!(LANG::Mozcpp.extensions().is_empty());
        assert!(
            !LANG::into_enum_iter().any(|l| l == LANG::Mozcpp && !l.extensions().is_empty()),
            "Mozcpp must own no file extension"
        );
    }

    // The dedicated C language (#721) owns `.c` and the `c` emacs mode,
    // both moved out of `Cpp`. `.h` stays on `Cpp` (decision-log #1:
    // asymmetric failure modes — a C++ header through the C grammar
    // ERROR-cascades, while a C header through C++ only trips on
    // C++-keyword identifiers). Pin the reroute so a `mk_langs!` reorder
    // cannot silently hand `.c` back to the C++ grammar.
    #[test]
    fn c_language_dispatch_owns_dot_c_and_h_stays_cpp() {
        use std::str::FromStr;
        assert_eq!(LANG::C.name(), "c");
        assert_eq!(LANG::from_str("c"), Ok(LANG::C));
        assert_eq!(get_from_ext("c"), Some(LANG::C));
        assert_eq!(get_from_emacs_mode("c"), Some(LANG::C));
        // `.h` and the C++ extensions remain on `Cpp`.
        assert_eq!(get_from_ext("h"), Some(LANG::Cpp));
        assert_eq!(get_from_ext("cpp"), Some(LANG::Cpp));
        // `.m` (Objective-C) now owns `LANG::Objc` (#724); `.mm`
        // Objective-C++ stays on `Cpp` by design (the ObjC grammar
        // can't parse the C++ half of a `.mm` file).
        assert_eq!(get_from_ext("m"), Some(LANG::Objc));
        assert_eq!(get_from_ext("mm"), Some(LANG::Cpp));
        assert_eq!(LANG::Objc.name(), "objc");
        assert_eq!(LANG::from_str("objc"), Ok(LANG::Objc));
        assert_eq!(get_from_emacs_mode("objc"), Some(LANG::Objc));
        assert_eq!(get_from_emacs_mode("objective-c"), Some(LANG::Objc));
        // The ObjC++ emacs modes remain mapped to `Cpp`.
        assert_eq!(get_from_emacs_mode("objc++"), Some(LANG::Cpp));
        assert_eq!(get_from_emacs_mode("objective-c++"), Some(LANG::Cpp));
    }

    // Unknown / mis-cased input is rejected; matching is case-sensitive,
    // mirroring `Metric`'s `FromStr`.
    #[test]
    fn fromstr_rejects_unknown_and_miscased() {
        use std::str::FromStr;
        assert!(LANG::from_str("Rust").is_err());
        assert!(LANG::from_str("klingon").is_err());
        assert!(LANG::from_str("").is_err());
        // The error carries the offending input verbatim, recoverable
        // both via `Display` and the additive `input()` accessor (#536).
        let err = LANG::from_str("klingon").unwrap_err();
        assert!(err.to_string().contains("klingon"));
        assert_eq!(err.input(), "klingon");
    }

    // `Hash` (+ `Eq`) lets `LANG` key a `HashMap` / populate a
    // `HashSet` — the headline use case from issue #508.
    #[test]
    fn lang_is_usable_as_hash_key() {
        use std::collections::{HashMap, HashSet};
        let mut set = HashSet::new();
        for lang in LANG::into_enum_iter() {
            assert!(set.insert(lang), "{} inserted twice", lang.name());
        }
        assert_eq!(set.len(), LANG::into_enum_iter().count());

        let mut map = HashMap::new();
        map.insert(LANG::Rust, "rs");
        map.insert(LANG::Python, "py");
        assert_eq!(map.get(&LANG::Rust), Some(&"rs"));
        assert_eq!(map.get(&LANG::Cpp), None);
    }

    // The error variant carries the originating `LANG` so callers
    // can distinguish "X is disabled" from "Y is disabled" in a
    // mixed batch. Verifies the `Display` impl mentions the
    // language name as documented in `src/error.rs`.
    #[test]
    fn language_disabled_display_includes_language_name() {
        let err = MetricsError::LanguageDisabled(LANG::Rust);
        let rendered = err.to_string();
        assert!(
            rendered.contains("rust"),
            "expected LanguageDisabled display to mention `rust`, got {rendered:?}",
        );
    }

    // Drift guard for the crate-level `## Supported Languages` rustdoc
    // list in `src/lib.rs` (#769): every LANG variant's canonical slug
    // — the single source of truth from `name()` — must appear in that
    // list as a backtick-delimited token. Without this guard, adding a
    // language (or renaming a slug) silently desyncs the docs.rs
    // landing page, which is exactly how Objective-C went missing for a
    // full release after #724 shipped it.
    //
    // The slug set is derived from `LANG::into_enum_iter()`, which is
    // compiled unconditionally (the enum surface is feature-independent;
    // only the grammar crates are gated), so this test is robust under
    // `--no-default-features` and any per-language feature subset — no
    // `all-languages` gate needed. Distinct slugs are deduplicated, so
    // shared-slug families do not require one bullet per variant.
    #[test]
    fn supported_languages_rustdoc_lists_every_slug() {
        // Bound the search to the `## Supported Languages` section so an
        // incidental backtick match elsewhere in the module docs (e.g.
        // a slug named in the metrics section) cannot mask a real
        // omission from the list itself.
        const SECTION_HEADER: &str = "## Supported Languages";
        const NEXT_HEADER: &str = "## Supported Metrics";

        let lib_rs = std::fs::read_to_string(concat!(env!("CARGO_MANIFEST_DIR"), "/src/lib.rs"))
            .expect("src/lib.rs is readable from CARGO_MANIFEST_DIR");

        let section_start = lib_rs
            .find(SECTION_HEADER)
            .expect("rustdoc must contain a `## Supported Languages` section");
        let section_end = lib_rs[section_start..]
            .find(NEXT_HEADER)
            .map(|offset| section_start + offset)
            .expect("`## Supported Languages` must be followed by `## Supported Metrics`");
        let section = &lib_rs[section_start..section_end];

        for lang in LANG::into_enum_iter() {
            let slug_token = format!("`{}`", lang.name());
            assert!(
                section.contains(&slug_token),
                "LANG::{lang:?} slug {slug_token} is missing from the \
                 `## Supported Languages` rustdoc list in src/lib.rs — \
                 add an entry there (see #769)",
            );
        }
    }
}