rustyfi-syntax 0.1.4

//! Target SATySFi language version.
//!
//! 0.0.6 and 0.1.x diverge at several points in the pipeline (lexing headers,
//! module resolution in the loader, elaboration in `rustyfi-lang`, ...).
//! Rather than let each divergence point grow its own ad-hoc flag, the target
//! version is threaded through the pipeline as a single [`RustyfiVersion`]
//! value (see [`crate`]'s consumers: `rustyfi-loader`'s `LoadOptions` and
//! `rustyfi`'s `--lang` flag), and each divergence point is expressed as a
//! method on it, rather than scattering `if opt_a && opt_b` checks across the
//! crate graph.
//!
//! ## Verification note on the 0.1 header syntax
//!
//! The exact SATySFi 0.1.0 `use` header grammar is **not independently
//! confirmed** from upstream sources here (the sandbox this was written in had
//! no network access), so the `sniff_version` heuristic below for 0.1
//! (`use `-prefixed header lines) is best-effort. The 0.0.6 side (`@require:` /
//! `@import:` / `@stage:`) *is* verified, directly against this port's own
//! [`crate::cst`]/[`crate::lexer`] implementation of the v0.0.6 grammar.

use std::fmt;
use std::str::FromStr;

/// Target SATySFi language version.
///
/// `#[non_exhaustive]` because more 0.1.z-era (and later) variants are
/// expected as the upstream module system design settles; treat any `match`
/// on this type as needing a wildcard arm.
#[non_exhaustive]
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum RustyfiVersion {
    /// SATySFi 0.0.6 (and, as far as this port is concerned, the rest of the
    /// 0.0.x series): `@require:` / `@import:` headers, the module-less
    /// surface syntax this port's `rustyfi-syntax` / `rustyfi-loader` /
    /// `rustyfi-lang` implement.
    V0_0,
    /// SATySFi 0.1.x: the `dev-0-1-0` language generation — an ML-style
    /// module system (F-ing Modules-based), row-polymorphic records and
    /// optional-argument encodings, and a reworked surface grammar — shared
    /// near-identically by `saphe-split` (confirmed by direct diff). This
    /// says nothing about *packaging*: `V0_1` documents may resolve
    /// dependencies via either today's `@require:`/`@import:` headers
    /// (`dev-0-1-0`'s own model, and this port's `LoadMode::Legacy`) or the
    /// `use`/manifest/lockfile model (`saphe-split`'s `LoadMode::Envelopes`,
    /// a later milestone) — see `rustyfi_loader::LoadMode`.
    V0_1,
}

impl RustyfiVersion {
    /// The version this port targets when none is specified.
    pub const DEFAULT: Self = Self::V0_0;

    /// Whether this version has an ML-style module system (`module M = struct
    /// ... end` bindings that erase to stamped-flat names, `val` bindings
    /// inside them, later: signatures/functors). `false` for `V0_0` (which
    /// has only its own non-parameterized, single-level `module`/`sig`
    /// surface — not a real module *system*); `true` for `V0_1`.
    ///
    /// Unlike every sibling capability probe, this one has no non-test
    /// caller — only this file's own `capability_probes` unit test —
    /// hence `cfg(test)` rather than a live `pub`/`pub(crate)` method.
    #[cfg(test)]
    fn has_module_system(&self) -> bool {
        matches!(self, Self::V0_1)
    }

    /// Whether this version's type system has row-polymorphic records and
    /// optional-argument rows (`?(l = e)` bundles, `?'r` row variables).
    /// `false` for `V0_0` (closed `Kind::Record` rows only); `true` for
    /// `V0_1`.
    pub fn has_row_polymorphism(&self) -> bool {
        matches!(self, Self::V0_1)
    }

    /// Whether `page-break`/`page-break-multicolumn`/`page-break-two-column`
    /// take the `page` ADT (`A4Paper`/`UserDefinedPaper`) as their paper-size
    /// argument, as opposed to `V0_1`'s plain `length * length`. Deliberately
    /// phrased as an assertion about `V0_0`'s surface (not "is it 0.0.6"),
    /// so a future third generation that also drops the ADT reads correctly
    /// without touching call sites.
    pub fn has_page_adt(&self) -> bool {
        matches!(self, Self::V0_0)
    }

    /// Whether the `math` type is split into `math-text` (unparsed `${...}`
    /// source) / `math-boxes` (evaluated tree) with a `read-math` primitive
    /// bridging them, as opposed to `V0_0`'s single unsplit `math` type.
    /// `false` for `V0_0`; `true` for `V0_1`.
    pub fn math_is_split(&self) -> bool {
        matches!(self, Self::V0_1)
    }

    /// Whether the `graphics` type is a **collection** (0.1's `GraphicD.t =
    /// 'a element list`, with `Clip`/`Group` container elements — a
    /// graphics-producing callback returns ONE `graphics` value) as opposed
    /// to `V0_0`'s single drawing element (a callback returns `list
    /// graphics`). `false` for `V0_0`; `true` for `V0_1`. Backs the
    /// graphics-collection sweep: every fork in the shared
    /// `place_graphics`/`coerce_graphics_result` machinery keys on this one
    /// method, so the env and type-env agree by construction (mirrors
    /// `math_is_split`'s role for the math slice).
    pub fn graphics_is_collection(&self) -> bool {
        matches!(self, Self::V0_1)
    }

    /// Whether a single BINDING may carry its own stage qualifier — 0.1's
    /// `val ~x = e` / `val persistent ~x = e` (`dev-0-1-0`
    /// `parser.mly:416-421`, `UTBindValue(Stage0 | Persistent0, _)`). `false`
    /// for `V0_0`, which declares one stage per FILE with a `@stage:` header
    /// and has no binding-level spelling at all: 0.0.6's `EXACT_TILDE` occurs
    /// only as a splice operand prefix (`v0.0.6 parser.mly:797`) and as macro
    /// syntax (`:608`, `:1199`).
    ///
    /// The two generations share one `cst::TopLet`/`TopBinding` (the 0.1
    /// lowering builds them), so the `~` prefix is *parseable* under both and
    /// this is what makes it an ERROR under 0.0.6 rather than a silent accept
    /// — see `elaborate.rs`'s `binding_stage`.
    pub fn has_per_binding_stage(&self) -> bool {
        matches!(self, Self::V0_1)
    }

    /// Whether the `code` TYPE has a surface spelling — 0.1's `code τ`, a
    /// one-argument prefix type application decoded alongside `list`/`ref`
    /// (`dev-0-1-0 src/frontend/manualTypeDecoder.ml:31-36`). `false` for
    /// `V0_0`, whose own manual-type decoder (`v0.0.6
    /// src/frontend/typeenv.ml:527-530`) special-cases `list` and `ref` and
    /// nothing else, so `CodeType` there is inference-only.
    pub fn has_code_type_syntax(&self) -> bool {
        matches!(self, Self::V0_1)
    }

    /// Whether this port actually implements this version end-to-end
    /// (lexer through PDF rendering). True for both generations.
    pub fn is_implemented(&self) -> bool {
        matches!(self, Self::V0_0 | Self::V0_1)
    }

    /// Every version this enum currently distinguishes (implemented or
    /// not), in a stable order, for building help/error text.
    ///
    /// `cfg(test)`-gated: only this file's own round-trip unit test calls
    /// it; `Self::supported`, the method callers outside this module
    /// actually want, does not go through it.
    #[cfg(test)]
    fn all() -> &'static [RustyfiVersion] {
        &[Self::V0_0, Self::V0_1]
    }

    /// The subset of `RustyfiVersion::all` this port can actually load.
    pub fn supported() -> &'static [RustyfiVersion] {
        &[Self::V0_0, Self::V0_1]
    }
}

impl Default for RustyfiVersion {
    fn default() -> Self {
        Self::DEFAULT
    }
}

impl fmt::Display for RustyfiVersion {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::V0_0 => write!(f, "0.0"),
            Self::V0_1 => write!(f, "0.1"),
        }
    }
}

/// Error returned by `RustyfiVersion`'s [`FromStr`] impl for a string that
/// does not name a recognized version.
#[derive(Debug, Clone, PartialEq, Eq, thiserror::Error)]
#[error(
    "unrecognized SATySFi version {input:?}; supported values: \
     0.0 (alias: v0.0), 0.1 (aliases: 0.1.x, v0.1, v0.1.0; not yet implemented)"
)]
pub struct ParseVersionError {
    /// The string that failed to parse.
    pub input: String,
}

impl FromStr for RustyfiVersion {
    type Err = ParseVersionError;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let normalized = s.trim();
        let normalized = normalized
            .strip_prefix('v')
            .or_else(|| normalized.strip_prefix('V'))
            .unwrap_or(normalized);
        match normalized {
            "0.0" => Ok(Self::V0_0),
            "0.1" | "0.1.x" | "0.1.0" => Ok(Self::V0_1),
            _ => Err(ParseVersionError {
                input: s.to_string(),
            }),
        }
    }
}

/// Best-effort detection of a document's target version from its source
/// text, by inspecting the header-like lines at the top of the file (before
/// any prelude bindings), and, failing that, the first content line.
///
/// - A `@stage:` header line is a real, direct signal: 0.1's lexer rejects it
///   outright, so seeing it at all yields `Some(V0_0)`.
/// - `@require:` / `@import:` header lines are *transparent*: byte-identical
///   in both v0.0.6 and dev-0-1-0, so their presence pins neither axis — they
///   are skipped just like a blank/comment line.
/// - A `use`-shaped header line — 0.1/Saphe's module-header syntax, see
///   `is_use_header` — yields `Some(V0_1)`. **This half of the heuristic is
///   best-effort**: the exact grammar could not be confirmed against
///   upstream from this sandbox (no network access to GitHub / zenn.dev at
///   the time this was written).
/// - Blank lines and `%`-comments (SATySFi's line-comment syntax, both
///   versions) are skipped while looking for the first header-shaped line.
/// - Once a non-blank, non-comment, non-header line is reached (headers are
///   only valid at the top of a file), that single line is inspected for a
///   content-level signal (see `sniff_content_line`) and the result —
///   including `None` — is returned regardless.
/// - Returns `None` if no signal is found at all (e.g. a bare `let ... in
///   ...` document with no headers, which is valid and version-ambiguous in
///   0.0.x).
pub fn sniff_version(src: &str) -> Option<RustyfiVersion> {
    sniff_headers(src).version
}

/// What [`sniff_headers`] learned from the header block. `version` is exactly
/// [`sniff_version`]'s result (Axis A); `envelope_headers` is the Axis-B
/// signal the CLI's detection ladder needs — a `use`-shaped header pins Axis
/// B = `LoadMode::Envelopes`, and sets BOTH fields.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
pub struct HeaderSniff {
    /// The detected target version, if any (`None` = ambiguous/no signal).
    pub version: Option<RustyfiVersion>,
    /// Whether a `use`-shaped (Envelopes/Saphe) header was seen. When `true`,
    /// `version` is also `Some(V0_1)` (a `use` header is a 0.1-only construct).
    pub envelope_headers: bool,
}

/// Best-effort detection of a document's target version AND packaging axis
/// from its source text — see [`sniff_version`]'s doc comment for the
/// version-detection rules. The one addition: a `use`-shaped header line
/// (`is_use_header`) sets both `version = Some(V0_1)` and
/// `envelope_headers = true`, so the CLI's detection ladder can pin
/// `LoadMode::Envelopes` off it.
pub fn sniff_headers(src: &str) -> HeaderSniff {
    for raw_line in src.lines() {
        let line = match raw_line.find('%') {
            Some(idx) => &raw_line[..idx],
            None => raw_line,
        };
        let line = line.trim();

        if line.is_empty() {
            continue;
        }

        // `@stage:` is a real signal: 0.1's lexer rejects it outright (the
        // header-lexing rule dropped the `"stage" -> HEADER_STAGE*` arm
        // between v0.0.6 and dev-0-1-0), so seeing it at all means 0.0.6.
        if line.starts_with("@stage:") {
            return HeaderSniff {
                version: Some(RustyfiVersion::V0_0),
                envelope_headers: false,
            };
        }

        // `@require:`/`@import:` are *transparent*: byte-identical in both
        // v0.0.6 and dev-0-1-0 (same citation), so their presence pins
        // neither axis. Skip past them exactly like a blank/comment line —
        // do NOT return here: returning `Some(V0_0)` on the very first
        // `@require:` misclassifies every 0.1-syntax-body-with-legacy-headers
        // document, which is a legitimate document shape this loader must
        // support.
        if line.starts_with("@require:") || line.starts_with("@import:") {
            continue;
        }

        if is_use_header(line) {
            return HeaderSniff {
                version: Some(RustyfiVersion::V0_1),
                envelope_headers: true,
            };
        }

        // First non-blank, non-comment, non-header line: headers are only
        // valid at the top of a file, so inspect this one line for a
        // content-level signal, then stop looking regardless of the result.
        return HeaderSniff {
            version: sniff_content_line(line),
            envelope_headers: false,
        };
    }
    HeaderSniff::default()
}

/// Recognize a `use`-shaped 0.1/Saphe header line: bare `use Ident[.Ident]*`,
/// `use package ...`, `use open ...`, or `use #[attr] ...`. Best-effort
/// (Saphe's exact grammar is `saphe-split`-only and not yet ported), but
/// deliberately broader than "bare `use Ident`" — narrow enough that
/// no 0.0.6 keyword or identifier can start a line with `use ` (0.0.6 has no
/// `use` keyword at all), so widening this can only ever gain true positives,
/// never introduce a false positive against the 0.0.6 corpus.
fn is_use_header(line: &str) -> bool {
    let Some(rest) = line.strip_prefix("use") else {
        return false;
    };
    let Some(rest) = rest.strip_prefix(|c: char| c.is_whitespace()) else {
        return false; // `used`, `user`, ... — not the `use` keyword
    };
    let rest = rest.trim_start();
    if rest.is_empty() {
        return false;
    }
    if rest.starts_with('#') {
        return true; // `use #[attr] ...`
    }
    let first_word = rest.split_whitespace().next().unwrap_or("");
    if first_word == "package" || first_word == "open" {
        return true; // `use package ...` / `use open ...`
    }
    // bare `use Ident[.Ident]*` (possibly followed by `as .../of ...`, which
    // this only requires the *first* word to look like a module path for).
    first_word
        .chars()
        .next()
        .map(|c| c.is_ascii_uppercase())
        .unwrap_or(false)
        && first_word
            .chars()
            .all(|c| c.is_ascii_alphanumeric() || c == '_' || c == '.')
}

/// Inspect the first non-header content line for a version signal.
/// `module <Upper> ... = struct` is deliberately **not** checked here:
/// 0.0.6's `TopBinding::Module` makes the sig annotation optional and all
/// 29 shipped 0.0.6 packages open with a `module` head after their
/// headers, so a `module` head is no signal in either direction and
/// correctly falls through to `None` below.
fn sniff_content_line(line: &str) -> Option<RustyfiVersion> {
    if starts_with_word(line, "val") {
        return Some(RustyfiVersion::V0_1);
    }
    for kw in ["let-rec", "let-inline", "let-block", "let-math", "let-mutable"] {
        if starts_with_word(line, kw) {
            return Some(RustyfiVersion::V0_0);
        }
    }
    None
}

/// True if `line` starts with `word` followed by a word boundary (end of
/// string or non-identifier character) — so `"val"` matches `"val f = .."`
/// but not an identifier like `"values"` or `"val-like"`.
fn starts_with_word(line: &str, word: &str) -> bool {
    match line.strip_prefix(word) {
        Some(rest) => rest
            .chars()
            .next()
            .map(|c| !(c.is_ascii_alphanumeric() || c == '-' || c == '_'))
            .unwrap_or(true),
        None => false,
    }
}

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

    #[test]
    fn from_str_accepts_0_0_forms() {
        for s in ["0.0", "v0.0", "V0.0"] {
            assert_eq!(
                s.parse::<RustyfiVersion>().unwrap_or_else(|e| panic!("{s:?}: {e}")),
                RustyfiVersion::V0_0,
                "input {s:?}"
            );
        }
    }

    #[test]
    fn from_str_accepts_0_1_forms() {
        for s in ["0.1", "0.1.x", "0.1.0", "v0.1"] {
            assert_eq!(
                s.parse::<RustyfiVersion>().unwrap_or_else(|e| panic!("{s:?}: {e}")),
                RustyfiVersion::V0_1,
                "input {s:?}"
            );
        }
    }

    #[test]
    fn from_str_rejects_unknown_forms() {
        // `0.0.6`/`v0.0.6` are deliberately NOT aliases: the language tag
        // names a GENERATION, never an upstream patch release.
        for s in ["", "1.0", "0.0.6", "v0.0.6", "0.0.7", "garbage", "0.2"] {
            let err = s.parse::<RustyfiVersion>().unwrap_err();
            assert_eq!(err.input, s);
            let msg = err.to_string();
            assert!(msg.contains("0.0"), "message should list supported values: {msg}");
            assert!(msg.contains("0.1"), "message should list supported values: {msg}");
        }
    }

    #[test]
    fn default_is_v0_0() {
        assert_eq!(RustyfiVersion::DEFAULT, RustyfiVersion::V0_0);
        assert_eq!(RustyfiVersion::default(), RustyfiVersion::V0_0);
    }

    #[test]
    fn capability_probes() {
        assert!(RustyfiVersion::V0_0.is_implemented());
        assert!(RustyfiVersion::V0_1.is_implemented());

        assert!(!RustyfiVersion::V0_0.has_module_system());
        assert!(RustyfiVersion::V0_1.has_module_system());

        assert!(!RustyfiVersion::V0_0.has_row_polymorphism());
        assert!(RustyfiVersion::V0_1.has_row_polymorphism());

        assert!(RustyfiVersion::V0_0.has_page_adt());
        assert!(!RustyfiVersion::V0_1.has_page_adt());

        assert!(!RustyfiVersion::V0_0.math_is_split());
        assert!(RustyfiVersion::V0_1.math_is_split());

        assert!(!RustyfiVersion::V0_0.graphics_is_collection());
        assert!(RustyfiVersion::V0_1.graphics_is_collection());

        assert!(!RustyfiVersion::V0_0.has_per_binding_stage());
        assert!(RustyfiVersion::V0_1.has_per_binding_stage());

        assert!(!RustyfiVersion::V0_0.has_code_type_syntax());
        assert!(RustyfiVersion::V0_1.has_code_type_syntax());
    }

    #[test]
    fn display_round_trips_through_from_str() {
        for v in RustyfiVersion::all() {
            let s = v.to_string();
            assert_eq!(&s.parse::<RustyfiVersion>().unwrap(), v, "round-trip of {s:?}");
        }
    }

    #[test]
    fn sniff_none_for_headerless_document() {
        assert_eq!(sniff_version("let x = 1 in x"), None);
        assert_eq!(sniff_version(""), None);
        assert_eq!(sniff_version("   \n% just a comment\n"), None);
    }

    #[test]
    fn sniff_require_import_are_transparent_stage_still_pins() {
        // `@require:`/`@import:` do not pin a version by themselves —
        // with no other signal on the first content line (a bare,
        // non-hyphenated `let`), the result is `None` (falling to
        // `RustyfiVersion::DEFAULT` downstream in `resolve_version`, not
        // sniffed here).
        assert_eq!(sniff_version("@require: stdlib\nlet x = 1 in x"), None);
        assert_eq!(sniff_version("@import: helper\nlet x = 1 in x"), None);
        // Leading blank lines / comments before a transparent header must
        // still not confuse the sniffer into inventing a signal.
        assert_eq!(
            sniff_version("% a comment\n\n@require: stdlib\nlet x = 1 in x"),
            None
        );
        // `@stage:` is the one header that IS still a real, direct signal
        // (0.1's lexer rejects it outright).
        assert_eq!(
            sniff_version("@stage: 0\nlet x = 1 in x"),
            Some(RustyfiVersion::V0_0)
        );
    }

    #[test]
    fn sniff_require_then_module_is_none() {
        // A legacy-header-then-module-body file (a V0_1-syntax library
        // reached through the unmodified `@require:` loader) must sniff
        // `None`, not `V0_0` and not `V0_1`
        // (no positive signal either way — `module` is deliberately not a
        // signal).
        assert_eq!(
            sniff_version("@require: pervasives\nmodule V01Mini = struct\nval x = 1\nend"),
            None
        );
        assert_eq!(
            sniff_version("@import: helper\n@require: pervasives\nmodule M = struct\nend"),
            None
        );
    }

    #[test]
    fn sniff_val_head_is_v0_1() {
        assert_eq!(
            sniff_version("@require: pervasives\nval x = 1"),
            Some(RustyfiVersion::V0_1)
        );
        // No headers at all — `val` at the very first content line still
        // signals V0_1.
        assert_eq!(sniff_version("val f x = x"), Some(RustyfiVersion::V0_1));
    }

    #[test]
    fn sniff_hyphenated_let_head_is_v0_0() {
        for src in [
            "let-rec f x = x",
            "let-inline ctx \\emph x = x",
            "let-block ctx +p x = x",
            "let-math \\frac x y = x",
            "let-mutable r <- 0",
        ] {
            assert_eq!(sniff_version(src), Some(RustyfiVersion::V0_0), "src: {src:?}");
        }
    }

    #[test]
    fn sniff_use_shapes_broader_than_bare_ident() {
        for src in ["use package foo", "use open Foo", "use #[attr] Foo"] {
            assert_eq!(sniff_version(src), Some(RustyfiVersion::V0_1), "src: {src:?}");
        }
    }

    #[test]
    fn sniff_lib_rustyfi_corpus_never_v0_1() {
        // Every vendored 0.0.6 package must sniff `None` or `Some(V0_0)`,
        // never `Some(V0_1)`.
        let root = concat!(env!("CARGO_MANIFEST_DIR"), "/../../lib-rustyfi/dist/packages");
        let mut checked = 0usize;
        for entry in std::fs::read_dir(root).expect("lib-rustyfi/dist/packages must exist") {
            let path = entry.expect("readable dir entry").path();
            // The vendored 29-package corpus uses both `.satyh` (27 of them,
            // plus this port's own `stdja-mini.satyh`) and `.satyg` (`list`,
            // `option` — 2 of them) extensions; a `.satyh`-only filter would
            // undercount the real corpus to 28 and never reach the `>= 29`
            // floor below.
            if !matches!(path.extension().and_then(|e| e.to_str()), Some("satyh") | Some("satyg")) {
                continue;
            }
            let src = std::fs::read_to_string(&path).unwrap_or_else(|e| panic!("{path:?}: {e}"));
            let sniffed = sniff_version(&src);
            assert_ne!(
                sniffed,
                Some(RustyfiVersion::V0_1),
                "{path:?} sniffed as V0_1 (got {sniffed:?})"
            );
            checked += 1;
        }
        assert!(checked >= 29, "expected to check the full 29-package corpus, got {checked}");
    }

    #[test]
    fn sniff_v0_0_fixtures_are_never_mistaken_for_v0_1() {
        // A representative sample of this port's own 0.0.6 fixtures/tests
        // must not sniff as V0_1.
        for src in [
            "document (|title = {Hello};|) '<+p{Hello, world!}>",
            "@import: helper\nlet x = 1 in x",
            "@require: stdlib\nlet x = 1 in x",
            "let x = 1",
        ] {
            assert_ne!(sniff_version(src), Some(RustyfiVersion::V0_1), "src: {src:?}");
        }
    }

    #[test]
    fn sniff_best_effort_v0_1_use_header() {
        assert_eq!(
            sniff_version("use Foo\nlet x = 1 in x"),
            Some(RustyfiVersion::V0_1)
        );
    }

    #[test]
    fn sniff_headers_reports_envelope_axis() {
        // A `use`-shaped header pins BOTH axes: version V0_1 and the Axis-B
        // Envelopes signal.
        for src in ["use package foo", "use open Foo", "use Foo\nlet x = 1 in x"] {
            let sniff = sniff_headers(src);
            assert_eq!(sniff.version, Some(RustyfiVersion::V0_1), "src: {src:?}");
            assert!(sniff.envelope_headers, "src: {src:?}");
        }
    }

    #[test]
    fn sniff_headers_no_envelope_axis_for_legacy_or_ambiguous() {
        // `@require:`-only / `val`-head / headerless files never set the
        // Envelopes signal.
        for src in [
            "@require: pervasives\nval x = 1",
            "@stage: 0\nlet x = 1 in x",
            "let x = 1 in x",
            "",
        ] {
            assert!(
                !sniff_headers(src).envelope_headers,
                "src {src:?} must not pin Envelopes"
            );
        }
    }

    #[test]
    fn sniff_version_is_a_sniff_headers_wrapper() {
        // The wrapper must agree with the struct's `version` field for every
        // representative input.
        for src in [
            "use package foo",
            "@require: stdlib\nlet x = 1 in x",
            "@stage: 0\nx",
            "val f x = x",
            "let-rec f x = x",
            "",
        ] {
            assert_eq!(sniff_version(src), sniff_headers(src).version, "src: {src:?}");
        }
    }
}