makeover_build/

drift.rs

//! Checks that a hand-written frontend still agrees with the crate that
//! generates its siblings.
//!
//! The generated files cannot drift: they ask makeover-geometry for the answer.
//! The hand-written ones state it, and a stylesheet or a script that disagrees
//! with the crate is not an error at any point -- it is a rule that quietly
//! stops matching where it used to. Cheaper to read a panic naming the line.
//!
//! Deliberately assertions and not substitutions. A JS or CSS file that has to
//! be generated to be correct stops being readable on its own, and it is worth
//! something that you can still open the frontend in a browser and have it
//! work.

use std::path::{Path, PathBuf};

use makeover_geometry::{Density, SizeClass};
use makeover_webview::Emit;

/// The declaration this check reads. Shared vocabulary, not a parameter: two
/// apps and a server naming the same string want the same name for it.
const CONST_NAME: &str = "TOUCH_DENSITY";

/// The capability sniffs the media query replaced, so neither can come back by
/// copy-paste.
///
/// Both ask the hardware what it has rather than what is pointing at the
/// screen, so both say yes to a touchscreen laptop driving a mouse.
const SNIFFS: &[&str] = &["ontouchstart", "maxTouchPoints"];

/// Fail the build if a JS copy of the touch-density query has drifted from
/// [`Density::Touch`].
///
/// Every `.js` file under `js_dir`, recursively, must state the crate's own
/// media condition in a `const TOUCH_DENSITY = '...'`, at least one file must
/// declare it, and no file may name a capability sniff.
///
/// The string is the crate's and no app gets a say in it, which is why this
/// check takes no policy argument. The generated `geometry.css` already keys
/// its touch gap overrides on the same condition, so the gestures and the
/// spacing agree by construction rather than by two people remembering.
///
/// Emits `cargo:rerun-if-changed` for every file it read.
///
/// # Panics
///
/// If `js_dir` cannot be read, if no declaration is found, or if any file
/// disagrees with the crate. A build script has nowhere useful to return an
/// error to, and a frontend that disagrees with its own stylesheet is worse
/// than a failed build.
pub fn check_touch_density(js_dir: impl AsRef<Path>) {
    let js_dir = js_dir.as_ref();
    let want = Density::Touch.media_condition();
    let mut wrong: Vec<String> = Vec::new();
    let mut found = 0usize;

    let files = js_files(js_dir);
    for path in &files {
        let src = std::fs::read_to_string(path).expect("read js file");
        let name = path
            .strip_prefix(js_dir)
            .unwrap_or(path)
            .display()
            .to_string();

        for (offset, literal) in touch_density_literals(&src) {
            found += 1;
            if literal != want {
                wrong.push(format!(
                    "  {name}:{}  {CONST_NAME} = '{literal}'",
                    line_of(&src, offset)
                ));
            }
        }

        for needle in SNIFFS {
            if let Some(offset) = src.find(needle) {
                wrong.push(format!(
                    "  {name}:{}  {needle} -- device sniff, not a density question",
                    line_of(&src, offset)
                ));
            }
        }
    }

    assert!(
        found > 0,
        "no {CONST_NAME} literal found under {}.\n\n\
         A frontend that asks whether it is being touched states\n\
         makeover_geometry::Density::Touch's media condition in a const of that\n\
         name, and this check exists to keep every copy equal to it. If the\n\
         const was renamed, rename it back rather than dropping the check; if\n\
         this frontend genuinely asks no density question, drop the call.",
        js_dir.display()
    );

    assert!(
        wrong.is_empty(),
        "hand-written touch detection disagrees with makeover_geometry::Density.\n\n\
         Density::Touch.media_condition() is: {want}\n\n\
         Wrong:\n{}\n\n\
         Fix the JS to state the crate's string. Never widen it to catch a\n\
         device the query misses: density is what is pointing at the screen,\n\
         and a laptop with a touchscreen and a mouse is a pointer device.",
        wrong.join("\n")
    );

    for path in &files {
        println!("cargo:rerun-if-changed={}", path.display());
    }
}

/// Every `.js` file under `dir`, recursively, sorted.
fn js_files(dir: &Path) -> Vec<PathBuf> {
    files_with_extension(dir, "js")
}

/// Every file under `dir` with extension `ext`, recursively, sorted.
///
/// Recursive because a consumer's frontend is not always one flat directory:
/// the Tauri apps keep `js/*.js`, the server keeps subdirectories under
/// `static/`, and a check that silently skipped the nested half would report
/// clean on the files most likely to have been copied.
fn files_with_extension(dir: &Path, ext: &str) -> Vec<PathBuf> {
    let mut out = Vec::new();
    let mut stack = vec![dir.to_path_buf()];
    while let Some(d) = stack.pop() {
        for entry in std::fs::read_dir(&d)
            .unwrap_or_else(|e| panic!("read {}: {e}", d.display()))
            .flatten()
        {
            let path = entry.path();
            if path.is_dir() {
                stack.push(path);
            } else if path.extension().is_some_and(|x| x == ext) {
                out.push(path);
            }
        }
    }
    out.sort();
    out
}

/// `(byte offset of the declaration, the literal's contents)` for every
/// `const TOUCH_DENSITY = '...'` in a JS source.
fn touch_density_literals(src: &str) -> Vec<(usize, &str)> {
    let mut out = Vec::new();
    let mut at = 0;
    while let Some(i) = src[at..].find(CONST_NAME) {
        let start = at + i;
        at = start + CONST_NAME.len();
        // Only the declaration states the string; a use site reads the const.
        let Some(rest) = src[at..].strip_prefix(" = ") else {
            continue;
        };
        let open = at + " = ".len();
        let Some(quote @ ('\'' | '"')) = rest.chars().next() else {
            continue;
        };
        let body = open + 1;
        if let Some(j) = src[body..].find(quote) {
            out.push((start, &src[body..body + j]));
            at = body + j + 1;
        }
    }
    out
}

fn line_of(src: &str, offset: usize) -> usize {
    src[..offset].matches('\n').count() + 1
}

/// Fail the build if a hand-written breakpoint has drifted from [`SizeClass`].
///
/// Every pixel width named by a media query under `frontend/css` or
/// `frontend/js`, recursively, must be a [`SizeClass`] boundary or one of
/// `tuning_widths`.
///
/// Without this, moving `SizeClass::Medium::min_px` regenerates the emitted
/// stylesheets and silently leaves every hand-written query behind, and what
/// you get is not an error but a stylesheet that disagrees with itself at the
/// old boundary.
///
/// `tuning_widths` is the one thing an app gets a say in, which is why this
/// takes a parameter where [`check_touch_density`] does not. A shell boundary
/// is a [`SizeClass`] edge and belongs to makeover-geometry; a tuning width is
/// a point inside a shell where something reflows without the shell changing --
/// a dashboard dropping from three columns to two, a pane's width cap ending.
/// Nothing switches shells at one, so it should not move when a size class
/// does. Pass `&[]` if the app has none, and treat every addition as owing a
/// note saying what it tunes: the list is where a genuine boundary goes to hide
/// from this check.
///
/// The generated stylesheets are scanned too, and pass by construction: they
/// ask makeover-geometry for the number rather than stating it. Scanning them
/// costs nothing and means a consumer never has to name which files are
/// hand-written.
///
/// Emits `cargo:rerun-if-changed` for every file it read.
///
/// # Panics
///
/// If `frontend/css` or `frontend/js` cannot be read, or if any width is
/// neither a size-class boundary nor a declared tuning width. A build script
/// has nowhere useful to return an error to.
pub fn check_breakpoints(frontend: impl AsRef<Path>, tuning_widths: &[u16]) {
    let frontend = frontend.as_ref();
    let mut files = files_with_extension(&frontend.join("css"), "css");
    files.extend(js_files(&frontend.join("js")));
    check_paths(&files, tuning_widths, Some(frontend));
}

/// [`check_breakpoints`] against a named list of files rather than a tree.
///
/// For a frontend whose generated and hand-written files share a directory, so
/// there is nothing to point a directory scan at: the MNW server keeps both
/// under `static/` alongside a bundler's output, and bundled third-party CSS
/// is exactly the place a width nobody chose would come from.
///
/// The cost is that the list is hand-maintained, and a stylesheet nobody adds
/// to it is unchecked rather than failing. Prefer [`check_breakpoints`] where
/// the layout allows it.
///
/// A `.js` path is parsed as script and anything else as stylesheet, which is
/// the only difference: a media condition is parenthesised in both.
///
/// # Panics
///
/// If a listed file cannot be read -- a listed path that no longer exists is a
/// check silently covering less than it says -- or if any width is neither a
/// size-class boundary nor a declared tuning width.
pub fn check_breakpoints_files<P: AsRef<Path>>(paths: &[P], tuning_widths: &[u16]) {
    let paths: Vec<PathBuf> = paths.iter().map(|p| p.as_ref().to_path_buf()).collect();
    check_paths(&paths, tuning_widths, None);
}

/// The check itself. `root`, when given, is stripped from reported paths.
fn check_paths(paths: &[PathBuf], tuning_widths: &[u16], root: Option<&Path>) {
    let allowed = allowed_widths(tuning_widths);
    let mut stale: Vec<String> = Vec::new();

    for path in paths {
        let raw = std::fs::read_to_string(path)
            .unwrap_or_else(|e| panic!("read {}: {e}", path.display()));
        let name = match root {
            Some(root) => display_name(root, path),
            None => path.display().to_string(),
        };

        if path.extension().is_some_and(|x| x == "js") {
            // No declarations in JS, so any parenthesised width is a query.
            for (offset, px) in js_widths(&raw) {
                if !allowed.contains(&px) {
                    stale.push(format!("  {name}:{}  ({px}px)", line_of(&raw, offset)));
                }
            }
            continue;
        }

        // Comments first: a note about a breakpoint that used to be here is
        // prose, not a rule, and should not fail a build.
        let src = strip_block_comments(&raw);
        for (offset, condition) in media_conditions(&src) {
            for px in media_widths(condition) {
                if !allowed.contains(&px) {
                    stale.push(format!(
                        "  {name}:{}  @media{condition}  ({px}px)",
                        line_of(&src, offset)
                    ));
                }
            }
        }
    }

    assert!(
        stale.is_empty(),
        "hand-written breakpoints disagree with makeover_geometry::SizeClass.\n\n\
         Allowed: {allowed:?}\n\
         ({:?} come from SizeClass; {tuning_widths:?} were passed as tuning widths.)\n\n\
         Stale:\n{}\n\n\
         If a size class moved, update these to match. If one of these is a new\n\
         tuning width inside the wide shell rather than a shell boundary, add it\n\
         to the caller's tuning list with a note saying what it tunes.\n\n\
         Best of all, make the rule dimensional so it needs no threshold: a grid\n\
         wants repeat(auto-fit, minmax(<content floor>, 1fr)) and a size wants\n\
         clamp(). A threshold is for what appears and disappears.",
        allowed
            .iter()
            .filter(|px| !tuning_widths.contains(px))
            .collect::<Vec<_>>(),
        stale.join("\n")
    );

    for path in paths {
        println!("cargo:rerun-if-changed={}", path.display());
    }
}

/// A path as the frontend sees it, for an error a reader can act on.
fn display_name(frontend: &Path, path: &Path) -> String {
    path.strip_prefix(frontend)
        .unwrap_or(path)
        .display()
        .to_string()
}

/// Every width a hand-written media query is allowed to name.
///
/// Read out of [`SizeClass::media_condition`] rather than typed, which is the
/// whole point: that is the one place the numbers come from, and a bump in
/// makeover-geometry has to reach the stylesheet through here.
fn allowed_widths(tuning_widths: &[u16]) -> Vec<u16> {
    let mut widths: Vec<u16> = SizeClass::all()
        .iter()
        .flat_map(|c| media_widths(&c.media_condition()))
        .collect();
    widths.extend_from_slice(tuning_widths);
    widths.sort_unstable();
    widths.dedup();
    widths
}

/// The pixel values in a media condition, in the order they appear.
fn media_widths(condition: &str) -> Vec<u16> {
    let mut out = Vec::new();
    let mut rest = condition;
    while let Some(i) = rest.find("-width:") {
        rest = &rest[i + "-width:".len()..];
        let digits: String = rest
            .trim_start()
            .chars()
            .take_while(char::is_ascii_digit)
            .collect();
        if let Ok(px) = digits.parse() {
            out.push(px);
        }
    }
    out
}

/// `(byte offset of the `@media`, the condition text before the `{`)`.
fn media_conditions(css: &str) -> Vec<(usize, &str)> {
    let mut out = Vec::new();
    let mut at = 0;
    while let Some(i) = css[at..].find("@media") {
        let start = at + i;
        let after = start + "@media".len();
        match css[after..].find('{') {
            Some(j) => {
                out.push((start, &css[after..after + j]));
                at = after + j;
            }
            None => break,
        }
    }
    out
}

/// `(byte offset, pixel value)` for every `(max-width: Npx)` in a JS source.
///
/// The parentheses are the whole test, and they have to be: a media condition
/// is always parenthesized and a CSS declaration never is, so `'max-width:
/// 320px'` in an inline-style string is not a breakpoint and must not read as
/// one. goingson's shared-updater.js builds exactly that, and the first version
/// of this check failed the build on it.
fn js_widths(src: &str) -> Vec<(usize, u16)> {
    let mut out = Vec::new();
    for pat in ["(max-width:", "(min-width:"] {
        let mut at = 0;
        while let Some(i) = src[at..].find(pat) {
            let start = at + i;
            let rest = src[start + pat.len()..].trim_start();
            let digits: String = rest.chars().take_while(char::is_ascii_digit).collect();
            if let Ok(px) = digits.parse()
                && rest[digits.len()..].starts_with("px)")
            {
                out.push((start, px));
            }
            at = start + pat.len();
        }
    }
    out
}

/// Replace every `/* ... */` with spaces, so byte offsets still line up.
fn strip_block_comments(css: &str) -> String {
    let bytes = css.as_bytes();
    let mut out = String::with_capacity(css.len());
    let mut i = 0;
    while i < bytes.len() {
        if bytes[i..].starts_with(b"/*") {
            let end = css[i..].find("*/").map_or(bytes.len(), |j| i + j + 2);
            for c in css[i..end].chars() {
                out.push(if c == '\n' { '\n' } else { ' ' });
            }
            i = end;
        } else {
            let c = css[i..].chars().next().unwrap();
            out.push(c);
            i += c.len_utf8();
        }
    }
    out
}

/// Fail the build if a hand-written stylesheet takes a property the generated
/// one already sets on the same class.
///
/// The generated sheet sits in `@layer makeover`. Unlayered app CSS beats a
/// layer by construction, whatever the specificity, so an app declaration for a
/// property makeover already sets does not merge with it: it wins, silently,
/// and the design system's version of that component stops applying. Both
/// sort-caret defects found on 2026-08-11 were this, and both were live for
/// months because nothing looked.
///
/// # Why properties and not class names
///
/// A shared class name is not by itself a divergence, and the first run of this
/// check against goingson is what settled it: nine classes are shared and every
/// one is deliberate. `.badge` sets shape in the app and colour in the
/// generated sheet, and the app's own comment beside it reads "Fill, edge and
/// text colour come from the generated .badge in layout.css. Do not add
/// background, border or box-shadow here." That arrangement is correct, so a
/// check on names would have asked for it to be deleted. On properties, the
/// comment becomes the check.
///
/// # The exception list
///
/// `allowed` is `(class, property)` pairs this app has reviewed and kept.
/// Deciding which are legitimate here would need a selector matcher, and a check
/// that guesses wrong about specificity fails correct builds -- so the app
/// declares it instead, the same shape as quasi-webview's `RENDERER_OWN`.
///
/// The example this section used to give was the sort caret: `content` on
/// `.table-heading`'s unsorted arm reserved the gap, `content` on the sorted arm
/// was the generated glyph, and the two were a pairing rather than a collision.
/// makeover-webview 0.31.0 emits both arms itself, so that pair is now an app
/// overriding the caret and the check is right to fail it. A reviewed pairing is
/// a claim about who owns a property, and it expires when the design system
/// takes the property back.
///
/// A pair that stops colliding fails too. A licence nobody is using is where
/// the next real collision lands and reads as company.
///
/// `frontend` is the directory holding `css/`. `generated` names the sheets
/// this crate writes, relative to `frontend/css`, which are skipped: the
/// generated file setting a generated property is the point.
///
/// Emits `cargo:rerun-if-changed` for every file it read.
///
/// # Panics
///
/// If `frontend/css` cannot be read, if any hand-written sheet takes a
/// generated property without declaring it, or if a declared pair no longer
/// collides. A build script has nowhere useful to return an error to, and an
/// app quietly overriding its own design system is worse than a failed build.
pub fn check_vocabulary(
    frontend: impl AsRef<Path>,
    opts: &Emit,
    generated: &[&str],
    allowed: &[(&str, &str)],
) {
    let frontend = frontend.as_ref();
    let css = frontend.join("css");
    let files: Vec<PathBuf> = files_with_extension(&css, "css")
        .into_iter()
        .filter(|p| {
            let name = p.strip_prefix(&css).unwrap_or(p).display().to_string();
            !generated.contains(&name.as_str())
        })
        .collect();
    check_vocabulary_paths(&files, opts, Some(frontend), allowed);
}

/// [`check_vocabulary`] against a named list of files rather than a tree.
///
/// For a frontend whose generated and hand-written sheets share a directory, so
/// a directory scan has nothing to point at. Same trade as
/// [`check_breakpoints_files`]: the list is hand-maintained, and a stylesheet
/// nobody adds to it is unchecked rather than failing.
///
/// # Panics
///
/// As [`check_vocabulary`].
pub fn check_vocabulary_files<P: AsRef<Path>>(paths: &[P], opts: &Emit, allowed: &[(&str, &str)]) {
    let paths: Vec<PathBuf> = paths.iter().map(|p| p.as_ref().to_path_buf()).collect();
    check_vocabulary_paths(&paths, opts, None, allowed);
}

/// The check itself. `root`, when given, is stripped from reported paths.
fn check_vocabulary_paths(
    paths: &[PathBuf],
    opts: &Emit,
    root: Option<&Path>,
    allowed: &[(&str, &str)],
) {
    let generated =
        makeover_webview::vocabulary::declarations_by_class(&makeover_webview::stylesheet(opts));
    let mut clashes: Vec<String> = Vec::new();
    let mut seen: Vec<(String, String)> = Vec::new();

    for path in paths {
        println!("cargo::rerun-if-changed={}", path.display());
        let raw = std::fs::read_to_string(path)
            .unwrap_or_else(|e| panic!("read {}: {e}", path.display()));
        let name = match root {
            Some(root) => display_name(root, path),
            None => path.display().to_string(),
        };
        // Read the app's sheet the same way the crate reads its own, or the two
        // sides are not comparable.
        let local = makeover_webview::vocabulary::declarations_by_class(&raw);
        for (class, properties) in &local {
            let Some(theirs) = generated.get(class) else {
                continue;
            };
            for property in properties.intersection(theirs) {
                seen.push((class.clone(), property.clone()));
                if allowed.contains(&(class.as_str(), property.as_str())) {
                    continue;
                }
                clashes.push(format!("  {name}  .{class} {{ {property} }}"));
            }
        }
    }

    assert!(
        clashes.is_empty(),
        "{} hand-written declaration(s) take a property the generated stylesheet \
         already sets on the same class. App CSS is unlayered and beats \
         @layer makeover, so each of these wins over the design system \
         silently:\n{}\n\nDelete the declaration, or, if it is a deliberate pairing \
         on a different selector arm, add (class, property) to this check's \
         allowed list and say why beside it. Count the consumers before deciding \
         a divergence is worth keeping.",
        clashes.len(),
        clashes.join("\n")
    );

    let stale: Vec<&(&str, &str)> = allowed
        .iter()
        .filter(|(class, property)| {
            !seen.contains(&((*class).to_string(), (*property).to_string()))
        })
        .collect();
    assert!(
        stale.is_empty(),
        "the allowed list declares {stale:?}, which no longer collides with \
         anything. Delete the entries: an exception nobody is using is where the \
         next real collision lands and reads as company."
    );
}

/// Warn when the generated vocabulary has grown dead, and fail when it grows
/// deader than the recorded high-water mark.
///
/// A generated class no markup emits is a rule shipped to every user for
/// nothing, and the proportion was large when it was first measured: 42% of the
/// vocabulary unused in goingson, 67% in the MNW server, 84% in Balanced
/// Breakfast. Those are not failures on their own or no app would build. What
/// this converts is the direction: dead vocabulary becoming a number in a build
/// script means a change that worsens it stops being something somebody
/// notices.
///
/// One-sided, the same shape as the MNW server's `frontend_globals` seal:
/// exceeding `high_water` fails, coming in under it warns and asks for the seal
/// to be lowered. A build that fails because dead CSS was deleted would teach
/// the wrong lesson.
///
/// `markup` is every file that can carry a class: templates, `.js`, `.html`,
/// and any Rust that writes markup. A class is counted as used if its name
/// appears in any of them, which is deliberately generous. A stricter reading
/// would need to know how each app builds its class strings, and a check that
/// guesses wrong fails a correct build.
///
/// # Panics
///
/// If a listed file cannot be read, or if more classes are unused than
/// `high_water`.
pub fn check_vocabulary_use<P: AsRef<Path>>(markup: &[P], opts: &Emit, high_water: usize) {
    let generated = makeover_webview::vocabulary::names(opts);
    let mut haystack = String::new();
    for path in markup {
        let path = path.as_ref();
        println!("cargo::rerun-if-changed={}", path.display());
        haystack.push_str(
            &std::fs::read_to_string(path)
                .unwrap_or_else(|e| panic!("read {}: {e}", path.display())),
        );
        haystack.push('\n');
    }

    let unused: Vec<&String> = generated
        .iter()
        .filter(|class| !haystack.contains(class.as_str()))
        .collect();

    assert!(
        unused.len() <= high_water,
        "{} of {} generated classes are emitted by no markup, above the recorded {}. \
         The vocabulary grew or the markup stopped using it:\n{}",
        unused.len(),
        generated.len(),
        high_water,
        unused
            .iter()
            .map(|c| format!("  .{c}"))
            .collect::<Vec<_>>()
            .join("\n")
    );

    if unused.len() < high_water {
        println!(
            "cargo::warning=dead makeover vocabulary is down to {} from a sealed {}; \
             lower the seal so it cannot grow back",
            unused.len(),
            high_water
        );
    }
}

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

    fn scratch(name: &str) -> PathBuf {
        let dir =
            std::env::temp_dir().join(format!("makeover-drift-{}-{name}", std::process::id()));
        let _ = std::fs::remove_dir_all(&dir);
        std::fs::create_dir_all(&dir).expect("create scratch");
        dir
    }

    fn write(dir: &Path, name: &str, src: &str) {
        if let Some(parent) = dir.join(name).parent() {
            std::fs::create_dir_all(parent).unwrap();
        }
        std::fs::write(dir.join(name), src).unwrap();
    }

    fn declaring() -> String {
        format!(
            "const {CONST_NAME} = '{}';\n",
            Density::Touch.media_condition()
        )
    }

    #[test]
    fn the_crates_own_string_passes() {
        let dir = scratch("ok");
        write(&dir, "touch.js", &declaring());
        check_touch_density(&dir);
    }

    #[test]
    #[should_panic(expected = "disagrees with makeover_geometry::Density")]
    fn a_drifted_literal_fails() {
        let dir = scratch("drift");
        write(&dir, "touch.js", &declaring());
        write(
            &dir,
            "haptics.js",
            &format!("const {CONST_NAME} = '(pointer: coarse)';\n"),
        );
        check_touch_density(&dir);
    }

    #[test]
    #[should_panic(expected = "device sniff")]
    fn the_sniff_cannot_come_back() {
        let dir = scratch("sniff");
        write(&dir, "touch.js", &declaring());
        write(&dir, "legacy.js", "if ('ontouchstart' in window) {}\n");
        check_touch_density(&dir);
    }

    #[test]
    #[should_panic(expected = "no TOUCH_DENSITY literal found")]
    fn a_frontend_that_states_nothing_fails() {
        let dir = scratch("empty");
        write(&dir, "app.js", "export const x = 1;\n");
        check_touch_density(&dir);
    }

    #[test]
    fn a_use_site_is_not_a_declaration() {
        // The const is read far more often than it is declared, and a read
        // states no string. Counting one as a declaration would make the
        // `found > 0` assertion pass on a frontend that only imports it.
        let src =
            format!("import {{ {CONST_NAME} }} from './touch.js';\nmatchMedia({CONST_NAME});\n");
        assert!(touch_density_literals(&src).is_empty());
    }

    #[test]
    fn nested_files_are_read() {
        // The server keeps its scripts in subdirectories, and the nested half
        // is the half most likely to be a copy.
        let dir = scratch("nested");
        write(&dir, "touch.js", &declaring());
        write(&dir, "screens/legacy.js", "navigator.maxTouchPoints > 0;\n");
        let files = js_files(&dir);
        assert_eq!(files.len(), 2);
    }

    #[test]
    fn a_non_js_file_is_ignored() {
        let dir = scratch("nonjs");
        write(&dir, "touch.js", &declaring());
        write(&dir, "styles.css", "body { }\n");
        assert_eq!(js_files(&dir).len(), 1);
    }

    fn frontend(name: &str) -> PathBuf {
        let dir = scratch(name);
        std::fs::create_dir_all(dir.join("css")).unwrap();
        std::fs::create_dir_all(dir.join("js")).unwrap();
        dir
    }

    /// A width every size class agrees is a boundary.
    fn boundary() -> u16 {
        SizeClass::Medium.min_px()
    }

    #[test]
    fn the_crates_own_boundaries_pass() {
        let dir = frontend("bp-ok");
        write(
            &dir,
            "css/styles.css",
            &format!("@media (min-width: {}px) {{ body {{ }} }}\n", boundary()),
        );
        check_breakpoints(&dir, &[]);
    }

    #[test]
    #[should_panic(expected = "disagree with makeover_geometry::SizeClass")]
    fn a_stale_css_width_fails() {
        let dir = frontend("bp-css");
        write(&dir, "css/styles.css", "@media (max-width: 768px) { }\n");
        check_breakpoints(&dir, &[]);
    }

    #[test]
    #[should_panic(expected = "disagree with makeover_geometry::SizeClass")]
    fn a_stale_js_width_fails() {
        let dir = frontend("bp-js");
        write(&dir, "js/shell.js", "matchMedia('(max-width: 768px)');\n");
        check_breakpoints(&dir, &[]);
    }

    #[test]
    fn a_declared_tuning_width_passes() {
        let dir = frontend("bp-tuning");
        write(&dir, "css/styles.css", "@media (min-width: 1400px) { }\n");
        check_breakpoints(&dir, &[1400]);
    }

    #[test]
    fn a_width_in_a_comment_is_prose() {
        // The note explaining which breakpoint used to be here is not a rule,
        // and failing a build on documentation would teach people to delete it.
        let dir = frontend("bp-comment");
        write(
            &dir,
            "css/styles.css",
            "/* was @media (max-width: 768px) until the size classes landed */\n",
        );
        check_breakpoints(&dir, &[]);
    }

    #[test]
    fn an_unparenthesized_width_is_not_a_breakpoint() {
        // A JS string building an inline style states `max-width: 320px` with
        // no parentheses. It is a declaration, not a query, and the first
        // version of this check failed the build on one.
        let dir = frontend("bp-inline");
        write(
            &dir,
            "js/style.js",
            "el.style.cssText = 'max-width: 320px; display: block';\n",
        );
        check_breakpoints(&dir, &[]);
    }

    #[test]
    fn nested_css_is_read() {
        // Same argument as the touch check: the nested half is the half most
        // likely to be a copy.
        let dir = frontend("bp-nested");
        write(
            &dir,
            "css/screens/detail.css",
            "@media (max-width: 768px) { }\n",
        );
        let found = std::panic::catch_unwind(|| check_breakpoints(&dir, &[]));
        assert!(found.is_err(), "a nested stylesheet must be scanned");
    }

    #[test]
    fn a_named_list_is_checked() {
        let dir = frontend("bp-list");
        write(&dir, "css/style.css", "@media (max-width: 768px) { }\n");
        let listed = dir.join("css/style.css");
        let err =
            std::panic::catch_unwind(|| check_breakpoints_files(&[&listed], &[])).unwrap_err();
        let msg = err.downcast_ref::<String>().expect("String payload");
        assert!(msg.contains("style.css:1"), "got: {msg}");
    }

    #[test]
    #[should_panic(expected = "read ")]
    fn a_listed_file_that_is_gone_fails() {
        // The list is hand-maintained, so a path that stopped existing is a
        // check quietly covering less than it claims. Louder than skipping it.
        let dir = frontend("bp-missing");
        check_breakpoints_files(&[dir.join("css/never-written.css")], &[]);
    }

    #[test]
    fn a_listed_js_file_is_parsed_as_script() {
        // The unparenthesized-declaration rule is what separates the two, and
        // picking the parser off the extension is the whole difference.
        let dir = frontend("bp-list-js");
        write(
            &dir,
            "js/style.js",
            "el.style.cssText = 'max-width: 320px';\n",
        );
        check_breakpoints_files(&[dir.join("js/style.js")], &[]);
    }

    #[test]
    fn the_error_names_the_file_and_line() {
        let dir = frontend("bp-message");
        write(
            &dir,
            "css/styles.css",
            "body { }\n@media (max-width: 768px) { }\n",
        );
        let err = std::panic::catch_unwind(|| check_breakpoints(&dir, &[])).unwrap_err();
        let msg = err
            .downcast_ref::<String>()
            .expect("panic payload is a String");
        assert!(msg.contains("css/styles.css:2"), "got: {msg}");
    }

    #[test]
    fn a_rule_restating_a_generated_class_fails_and_names_it() {
        let dir = scratch("vocab-clash");
        // `.card` is makeover's. An app rule for it beats the generated one,
        // because app CSS is unlayered and the generated sheet is not.
        write(
            &dir,
            "css/styles.css",
            "body { color: red; }\n.card { box-shadow: none; }\n",
        );
        let err = std::panic::catch_unwind(|| check_vocabulary(&dir, &Emit::default(), &[], &[]))
            .unwrap_err();
        let msg = err
            .downcast_ref::<String>()
            .expect("panic payload is a String");
        assert!(msg.contains(".card"), "got: {msg}");
        assert!(msg.contains("box-shadow"), "got: {msg}");
        assert!(msg.contains("css/styles.css"), "got: {msg}");
    }

    #[test]
    fn an_app_class_of_its_own_is_left_alone() {
        let dir = scratch("vocab-clean");
        write(
            &dir,
            "css/styles.css",
            ".task-list-container { overflow: auto; }\n.day-plan-slot { height: 1rem; }\n",
        );
        check_vocabulary(&dir, &Emit::default(), &[], &[]);
    }

    #[test]
    fn the_generated_sheet_is_skipped_rather_than_reported_against_itself() {
        let dir = scratch("vocab-generated");
        let opts = Emit::default();
        write(&dir, "css/layout.css", &makeover_webview::stylesheet(&opts));
        // Without the skip this is the loudest failure possible: every class in
        // the vocabulary, reported as a clash with the vocabulary.
        check_vocabulary(&dir, &opts, &["layout.css"], &[]);
    }

    #[test]
    fn a_prefixed_app_is_checked_against_its_own_prefix() {
        let dir = scratch("vocab-prefix");
        let opts = Emit {
            class_prefix: "mo-",
            ..Emit::default()
        };
        // Bare `.card` is the app's own class once the generated sheet writes
        // `.mo-card`, so this has to pass.
        write(&dir, "css/styles.css", ".card { box-shadow: none; }\n");
        check_vocabulary(&dir, &opts, &[], &[]);

        let dir = scratch("vocab-prefix-clash");
        write(&dir, "css/styles.css", ".mo-card { box-shadow: none; }\n");
        assert!(std::panic::catch_unwind(|| check_vocabulary(&dir, &opts, &[], &[])).is_err());
    }

    #[test]
    fn a_class_shared_without_a_shared_property_is_left_alone() {
        let dir = scratch("vocab-additive");
        // What goingson actually does: the generated `.badge` sets the text
        // colour and the app sets the shape. Same class, no argument.
        write(
            &dir,
            "css/styles.css",
            ".badge { padding: 2px; border-radius: 3px; font-weight: 600; }\n",
        );
        check_vocabulary(&dir, &Emit::default(), &[], &[]);
    }

    #[test]
    fn a_reviewed_pair_passes_and_stops_passing_when_it_stops_colliding() {
        let dir = scratch("vocab-allowed");
        write(&dir, "css/styles.css", ".card { box-shadow: none; }\n");
        check_vocabulary(&dir, &Emit::default(), &[], &[("card", "box-shadow")]);

        // The same licence against a sheet that no longer collides has to fail,
        // or the list only ever grows.
        let dir = scratch("vocab-allowed-stale");
        write(&dir, "css/styles.css", ".card { padding: 2px; }\n");
        let err = std::panic::catch_unwind(|| {
            check_vocabulary(&dir, &Emit::default(), &[], &[("card", "box-shadow")]);
        })
        .unwrap_err();
        let msg = err
            .downcast_ref::<String>()
            .expect("panic payload is a String");
        assert!(msg.contains("no longer collides"), "got: {msg}");
    }

    #[test]
    fn dead_vocabulary_above_the_seal_fails_and_below_it_passes() {
        let dir = scratch("vocab-seal");
        let opts = Emit::default();
        let all = makeover_webview::vocabulary::names(&opts).len();
        // Markup naming nothing: every class is unused.
        write(&dir, "index.html", "<div></div>\n");
        let markup = [dir.join("index.html")];

        check_vocabulary_use(&markup, &opts, all);
        assert!(
            std::panic::catch_unwind(|| check_vocabulary_use(&markup, &opts, all - 1)).is_err(),
            "a vocabulary deader than the seal has to fail"
        );
    }

    #[test]
    fn both_quote_styles_read() {
        let want = Density::Touch.media_condition();
        for q in ['\'', '"'] {
            let src = format!("const {CONST_NAME} = {q}{want}{q};\n");
            let found = touch_density_literals(&src);
            assert_eq!(found.len(), 1);
            assert_eq!(found[0].1, want);
        }
    }
}