bern-compiler 0.1.0

//! `Bern.toml`: project, language, theme, source, resource and target
//! configuration.

use bern_ir::{LayoutConfig, ResourceDef, SourceLocation, Srgb, SvgPicture, ThemeMode};
use bern_target_api::{Diagnostic, TargetConfig, WINDOWS_FRONTENDS};
use serde::Deserialize;
use std::collections::BTreeMap;
use std::path::{Path, PathBuf};

#[derive(Debug, Deserialize)]
#[serde(deny_unknown_fields)]
struct RawConfig {
    app: RawApp,
    languages: RawLanguages,
    #[serde(default)]
    theme: RawTheme,
    protocol: RawProtocol,
    engine: RawEngine,
    ui: RawUi,
    #[serde(default)]
    targets: BTreeMap<String, RawTarget>,
    #[serde(default)]
    libraries: Vec<RawLibraryRef>,
    #[serde(default)]
    modules: Vec<RawModuleRef>,
    resources: Option<RawResources>,
    layouts: Option<RawLayouts>,
    /// Slot id to the application's own components placed there, before
    /// the modules': a module may leave room in its pages for the shell.
    #[serde(default)]
    contributes: BTreeMap<String, Vec<String>>,
}

/// `[[modules]]`: a module directory holding its own `Bern.toml`.
#[derive(Debug, Deserialize)]
#[serde(deny_unknown_fields)]
struct RawModuleRef {
    path: String,
}

/// A module manifest: `[module]` with its protocol, engine and UI, and the
/// languages its translations cover.
#[derive(Debug, Deserialize)]
#[serde(deny_unknown_fields)]
struct RawModuleConfig {
    module: RawModule,
    languages: RawLanguages,
    #[serde(default)]
    pages: Vec<RawPage>,
    /// Slot id to the module's components placed there, in order.
    #[serde(default)]
    contributes: BTreeMap<String, Vec<String>>,
}

/// `[[pages]]`: a page the module adds to one of the shell's page slots.
#[derive(Debug, Deserialize)]
#[serde(deny_unknown_fields)]
struct RawPage {
    slot: String,
    id: String,
    label: BTreeMap<String, String>,
    icon: Option<String>,
    badge: Option<String>,
    /// Boolean state field of the module: the page's navigation item shows
    /// only while it is true.
    when: Option<String>,
    /// The slot's selection starts on this page.
    #[serde(default)]
    start: bool,
    /// Whether a tab bar shows the page; `false` leaves it to sidebars.
    tab: Option<bool>,
    component: String,
}

#[derive(Debug, Deserialize)]
#[serde(deny_unknown_fields)]
struct RawModule {
    id: String,
    name: BTreeMap<String, String>,
    #[serde(default)]
    depends: Vec<String>,
    #[serde(default)]
    optional: bool,
    /// Whether an optional module runs before the application saved a
    /// choice; by default it does.
    enabled: Option<bool>,
    protocol: RawProtocol,
    engine: RawEngine,
    ui: Option<RawModuleUi>,
}

#[derive(Debug, Deserialize)]
#[serde(deny_unknown_fields)]
struct RawModuleUi {
    package: String,
    sources: RawSources,
}

/// Source files: a list of `.rs` files, or one directory whose `.rs` files
/// are all collected.
#[derive(Debug, Deserialize)]
#[serde(untagged)]
enum RawSources {
    Directory(String),
    Files(Vec<String>),
}

/// One module of the application.
#[derive(Clone, Debug)]
pub struct ModuleConfig {
    pub id: String,
    pub dir: PathBuf,
    pub manifest: PathBuf,
    pub name: BTreeMap<String, String>,
    pub depends: Vec<String>,
    pub optional: bool,
    /// Whether an optional module runs before the application saved a choice.
    pub enabled: bool,
    pub protocol_package: Package,
    pub protocol_source: SourceFile,
    pub engine_package: Package,
    /// Rust path of the module engine type, which implements `Default`.
    pub engine_type: String,
    pub ui_package: Option<Package>,
    pub ui_sources: Vec<SourceFile>,
    pub languages: Vec<String>,
    /// Pages the module adds to the shell's page slots.
    pub pages: Vec<PageConfig>,
    /// Slot id to the module's components placed there, in order.
    pub contributes: BTreeMap<String, Vec<String>>,
}

/// A page a module contributes to a page slot.
#[derive(Clone, Debug)]
pub struct PageConfig {
    pub slot: String,
    pub id: String,
    pub label: BTreeMap<String, String>,
    pub icon: Option<String>,
    /// Numeric state field of this module shown as the page's live badge.
    pub badge: Option<String>,
    /// Boolean state field of this module while which the page's
    /// navigation item shows.
    pub when: Option<String>,
    /// The page's variant comes first in the slot's enum, so a selection
    /// starts on it.
    pub start: bool,
    /// A `Tabs` lists the page; `false` leaves it to sidebars, for a page a
    /// phone reaches some other way.
    pub tab: bool,
    /// The module component showing the page.
    pub component: String,
}

/// `[layouts]`: breakpoints between layout sizes.
#[derive(Debug, Deserialize)]
#[serde(deny_unknown_fields)]
struct RawLayouts {
    /// Available width, in logical units, below which `compact` applies.
    compact_below: f64,
    /// Below which `medium` applies; without it there is no `medium`.
    medium_below: Option<f64>,
    /// Below which `expanded` applies, `large` from it; without it there
    /// is no `large`.
    expanded_below: Option<f64>,
}

/// `[resources]`: files and directories, relative to `Bern.toml`, that ship
/// with the built application.
#[derive(Debug, Deserialize)]
#[serde(deny_unknown_fields)]
struct RawResources {
    paths: Vec<toml::Spanned<String>>,
}

#[derive(Debug, Deserialize)]
#[serde(deny_unknown_fields)]
struct RawLibraryRef {
    manifest: String,
}

#[derive(Debug, Deserialize)]
#[serde(deny_unknown_fields)]
struct RawLibraryConfig {
    library: RawLibrary,
    languages: RawLanguages,
}

#[derive(Debug, Deserialize)]
#[serde(deny_unknown_fields)]
struct RawLibrary {
    package: String,
    sources: Vec<String>,
}

/// A component library crate, described by its own `Bern.toml`.
#[derive(Clone, Debug)]
pub struct LibraryConfig {
    pub dir: PathBuf,
    pub manifest: PathBuf,
    pub package: Package,
    pub version: String,
    pub sources: Vec<SourceFile>,
    pub languages: Vec<String>,
    pub default_language: String,
    pub strict: bool,
}

#[derive(Debug, Deserialize)]
#[serde(deny_unknown_fields)]
struct RawApp {
    id: String,
    bundle_id: String,
    version: String,
    name: BTreeMap<String, String>,
    /// A square PNG, relative to `Bern.toml`, or a table giving platforms
    /// their own icons; the Bern logo without it.
    icon: Option<toml::Spanned<RawIcon>>,
    /// Icons the application can switch to at run time, by name, each as
    /// `icon` is written.
    alternate_icons: Option<BTreeMap<String, toml::Spanned<RawIcon>>>,
    /// Who publishes the application, for installers and packages.
    publisher: Option<String>,
    /// iOS shows the application's Documents folder in Files.
    #[serde(default)]
    files_folder: bool,
    /// The application plays audio on behind the lock screen and in the
    /// background.
    #[serde(default)]
    background_audio: bool,
    /// The application draws text over other apps (`bern::overlay`).
    #[serde(default)]
    overlays: bool,
}

/// `[app].icon`: one square PNG for every platform, or `[app.icon]` with
/// `default` for every platform and an entry per platform name.
#[derive(Debug, Deserialize)]
#[serde(untagged)]
enum RawIcon {
    One(String),
    Platforms(BTreeMap<String, String>),
}

#[derive(Debug, Deserialize)]
#[serde(deny_unknown_fields)]
struct RawLanguages {
    supported: Vec<String>,
    default: String,
    #[serde(default = "yes")]
    strict: bool,
}

fn yes() -> bool {
    true
}

#[derive(Debug, Default, Deserialize)]
#[serde(deny_unknown_fields)]
struct RawTheme {
    mode: Option<String>,
    brand_seed: Option<String>,
}

#[derive(Debug, Deserialize)]
#[serde(deny_unknown_fields)]
struct RawProtocol {
    package: String,
    source: String,
}

#[derive(Debug, Deserialize)]
#[serde(deny_unknown_fields)]
struct RawEngine {
    package: String,
    #[serde(rename = "type")]
    type_path: String,
    /// The package directory, relative to the manifest; by default the
    /// directory named like the package.
    path: Option<String>,
}

#[derive(Debug, Deserialize)]
#[serde(deny_unknown_fields)]
struct RawUi {
    package: String,
    sources: RawSources,
    root: String,
}

#[derive(Debug, Deserialize)]
#[serde(deny_unknown_fields)]
struct RawTarget {
    platform: String,
    ui: Option<String>,
    web_mode: Option<String>,
    web_extension: Option<bern_target_api::WebExtension>,
    application_transport: Option<String>,
    application_codec: Option<String>,
    #[serde(default)]
    channels: Vec<String>,
    frontends: Option<Vec<String>>,
    webview: Option<bool>,
    #[serde(default)]
    javascript: bool,
    android: Option<bern_target_api::AndroidOptions>,
}

/// A Rust source file listed in the configuration.
#[derive(Clone, Debug)]
pub struct SourceFile {
    /// Path as written in `Bern.toml`, used in diagnostics.
    pub display: String,
    pub path: PathBuf,
    /// Module path inside its crate (`[]` for `lib.rs`).
    pub module: Vec<String>,
}

#[derive(Clone, Debug)]
pub struct Package {
    pub name: String,
    pub dir: PathBuf,
}

impl Package {
    /// Rust crate name of the package.
    pub fn crate_name(&self) -> String {
        self.name.replace('-', "_")
    }
}

#[derive(Clone, Debug)]
pub struct Config {
    pub dir: PathBuf,
    pub app_id: String,
    pub bundle_id: String,
    pub version: String,
    pub name: BTreeMap<String, String>,
    /// `[app].icon`, or `default` in `[app.icon]`: a checked square PNG
    /// relative to `dir`.
    pub icon: Option<String>,
    /// The other entries of `[app.icon]`: platform name to a checked square
    /// PNG, or a file or folder in the platform's own form, relative to `dir`.
    pub platform_icons: BTreeMap<String, String>,
    /// `[app.alternate_icons.<name>]`: name to its checked entries, as
    /// `[app.icon]` has them, with `default` for every platform.
    pub alternate_icons: BTreeMap<String, BTreeMap<String, String>>,
    /// `[app].publisher`, trimmed; `None` when absent or blank.
    pub publisher: Option<String>,
    /// `[app].files_folder`.
    pub files_folder: bool,
    /// `[app].background_audio`.
    pub background_audio: bool,
    /// `[app].overlays`.
    pub overlays: bool,
    pub languages: Vec<String>,
    pub default_language: String,
    pub strict: bool,
    pub theme_mode: ThemeMode,
    pub brand_seed: Option<Srgb>,
    pub protocol_package: Package,
    pub protocol_source: SourceFile,
    pub engine_package: Package,
    pub engine_type: String,
    pub ui_package: Package,
    pub ui_sources: Vec<SourceFile>,
    pub root: String,
    pub targets: Vec<TargetConfig>,
    /// Manifests of component libraries the UI uses.
    pub libraries: Vec<PathBuf>,
    /// The application's modules, in the order `Bern.toml` lists them.
    pub modules: Vec<ModuleConfig>,
    /// Declared modules and whether this build includes them.
    pub build_modules: bern_syntax::build::Modules,
    /// Slot id to the application's own components placed there, before
    /// the modules'.
    pub contributes: BTreeMap<String, Vec<String>>,
    /// Files shipped with the application, directories expanded, sorted by
    /// name.
    pub resources: Vec<ResourceDef>,
    /// Breakpoints from `[layouts]`, if declared.
    pub layouts: Option<LayoutConfig>,
}

fn valid_language(tag: &str) -> bool {
    let mut parts = tag.split('-');
    let Some(language) = parts.next() else {
        return false;
    };
    (2..=3).contains(&language.len())
        && language.chars().all(|c| c.is_ascii_lowercase())
        && parts.all(|part| {
            (2..=8).contains(&part.len()) && part.chars().all(|c| c.is_ascii_alphanumeric())
        })
}

/// The source files `sources` names, relative to `base` inside the project
/// `dir`: listed files as written, or every `.rs` file below a directory,
/// sorted by path.
fn expand_sources(dir: &Path, base: &str, sources: &RawSources) -> Result<Vec<String>, Diagnostic> {
    let join = |written: &str| {
        if base.is_empty() {
            written.to_string()
        } else {
            format!("{base}/{written}")
        }
    };
    match sources {
        RawSources::Files(files) => Ok(files.iter().map(|file| join(file)).collect()),
        RawSources::Directory(directory) if directory.ends_with(".rs") => Ok(vec![join(directory)]),
        RawSources::Directory(directory) => {
            let relative = join(directory.trim_end_matches('/'));
            let mut found = Vec::new();
            rust_files(&dir.join(&relative), &relative, &mut found)?;
            found.sort();
            if found.is_empty() {
                return Err(Diagnostic::error(format!(
                    "source directory `{relative}` holds no .rs files"
                )));
            }
            Ok(found)
        }
    }
}

fn rust_files(path: &Path, written: &str, found: &mut Vec<String>) -> Result<(), Diagnostic> {
    let entries = std::fs::read_dir(path).map_err(|error| {
        Diagnostic::error(format!(
            "cannot read source directory {}: {error}",
            path.display()
        ))
    })?;
    for entry in entries.flatten() {
        let name = entry.file_name().to_string_lossy().into_owned();
        if name.starts_with('.') {
            continue;
        }
        let child = format!("{written}/{name}");
        match entry.file_type() {
            Ok(kind) if kind.is_dir() => rust_files(&entry.path(), &child, found)?,
            Ok(kind) if kind.is_file() && name.ends_with(".rs") => found.push(child),
            _ => {}
        }
    }
    Ok(())
}

/// Resolve `pkg/src/a/b.rs` into the package directory and module path.
fn source_file(dir: &Path, written: &str) -> Result<(PathBuf, Vec<String>), Diagnostic> {
    let relative = Path::new(written);
    let components: Vec<_> = relative
        .components()
        .map(|component| component.as_os_str().to_string_lossy().to_string())
        .collect();
    let src = components
        .iter()
        .position(|part| part == "src")
        .ok_or_else(|| {
            Diagnostic::error(format!(
                "source `{written}` must be inside a package's `src` directory"
            ))
        })?;
    let package_dir = dir.join(components[..src].iter().collect::<PathBuf>());
    let mut module: Vec<String> = components[src + 1..].to_vec();
    let file = module
        .pop()
        .ok_or_else(|| Diagnostic::error(format!("source `{written}` does not name a file")))?;
    let stem = file
        .strip_suffix(".rs")
        .ok_or_else(|| Diagnostic::error(format!("source `{written}` must be a `.rs` file")))?;
    if !matches!(stem, "lib" | "main" | "mod") {
        module.push(stem.to_string());
    }
    if matches!(stem, "lib" | "main") && !module.is_empty() {
        return Err(Diagnostic::error(format!(
            "`{written}`: only the crate root may be named lib.rs or main.rs"
        )));
    }
    Ok((package_dir, module))
}

fn read_package_field(dir: &Path, field: &str) -> Result<String, Diagnostic> {
    let manifest = dir.join("Cargo.toml");
    let text = std::fs::read_to_string(&manifest).map_err(|error| {
        Diagnostic::error(format!("cannot read {}: {error}", manifest.display()))
    })?;
    let value: toml::Value = text
        .parse()
        .map_err(|error| Diagnostic::error(format!("{}: {error}", manifest.display())))?;
    value
        .get("package")
        .and_then(|package| package.get(field))
        .and_then(|value| match value {
            toml::Value::String(text) => Some(text.clone()),
            // `field.workspace = true` inherits from the workspace manifest.
            toml::Value::Table(table) if table.get("workspace").is_some() => {
                workspace_package_field(dir, field)
            }
            _ => None,
        })
        .ok_or_else(|| Diagnostic::error(format!("{} has no package {field}", manifest.display())))
}

fn workspace_package_field(dir: &Path, field: &str) -> Option<String> {
    let mut directory = dir.parent();
    while let Some(current) = directory {
        if let Ok(text) = std::fs::read_to_string(current.join("Cargo.toml"))
            && let Ok(value) = text.parse::<toml::Value>()
            && let Some(found) = value
                .get("workspace")
                .and_then(|workspace| workspace.get("package"))
                .and_then(|package| package.get(field))
                .and_then(toml::Value::as_str)
        {
            return Some(found.to_string());
        }
        directory = current.parent();
    }
    None
}

fn read_package_name(dir: &Path) -> Result<String, Diagnostic> {
    let manifest = dir.join("Cargo.toml");
    let text = std::fs::read_to_string(&manifest).map_err(|error| {
        Diagnostic::error(format!("cannot read {}: {error}", manifest.display()))
    })?;
    let value: toml::Value = text
        .parse()
        .map_err(|error| Diagnostic::error(format!("{}: {error}", manifest.display())))?;
    value
        .get("package")
        .and_then(|package| package.get("name"))
        .and_then(toml::Value::as_str)
        .map(str::to_string)
        .ok_or_else(|| Diagnostic::error(format!("{} has no package name", manifest.display())))
}

fn package(
    dir: &Path,
    expected: &str,
    sources: &[(String, PathBuf)],
    what: &str,
) -> Result<Package, Diagnostic> {
    let package_dir = sources
        .first()
        .map(|(_, path)| path.clone())
        .unwrap_or_else(|| dir.join(expected));
    if sources.iter().any(|(_, path)| *path != package_dir) {
        return Err(Diagnostic::error(format!(
            "all {what} sources must belong to the package `{expected}`"
        )));
    }
    let name = read_package_name(&package_dir)?;
    if name != expected {
        return Err(Diagnostic::error(format!(
            "{what} sources are in package `{name}`, but Bern.toml names `{expected}`"
        )));
    }
    Ok(Package {
        name,
        dir: package_dir,
    })
}

/// Line and column (both from 1) of a byte offset in the manifest.
fn manifest_location(file: &str, text: &str, offset: usize) -> SourceLocation {
    let before = &text[..offset.min(text.len())];
    let line_start = before.rfind('\n').map_or(0, |index| index + 1);
    SourceLocation {
        file: file.to_string(),
        line: before.matches('\n').count() as u32 + 1,
        column: before[line_start..].chars().count() as u32 + 1,
    }
}

/// Check `[app].icon`: one square PNG for every platform, or `[app.icon]`
/// with `default` for every platform and an icon per platform name. Returns
/// the one for every platform and the platforms' own.
fn app_icons(
    dir: &Path,
    manifest: &str,
    text: &str,
    (parent, leaf): (&str, &str),
    entry: &toml::Spanned<RawIcon>,
    errors: &mut Vec<Diagnostic>,
) -> (Option<String>, BTreeMap<String, String>) {
    let declared = manifest_location(manifest, text, entry.span().start);
    let mut platforms = BTreeMap::new();
    match entry.get_ref() {
        RawIcon::One(written) => (
            app_icon(
                dir,
                &format!("[{parent}].{leaf}"),
                None,
                written,
                &declared,
                errors,
            ),
            platforms,
        ),
        RawIcon::Platforms(table) => {
            let mut every = None;
            for (key, written) in table {
                let name = format!("[{parent}.{leaf}].{key}");
                if key == "default" {
                    every = app_icon(dir, &name, None, written, &declared, errors);
                } else if bern_target_api::icon::PLATFORMS.contains(&key.as_str()) {
                    if let Some(icon) = app_icon(dir, &name, Some(key), written, &declared, errors)
                    {
                        platforms.insert(key.clone(), icon);
                    }
                } else {
                    errors.push(
                        Diagnostic::error(format!(
                            "{name}: `{key}` is not a platform; use `default` or one of {}",
                            bern_target_api::icon::PLATFORMS.join(", ")
                        ))
                        .at(declared.clone()),
                    );
                }
            }
            (every, platforms)
        }
    }
}

/// Check one icon: a file or folder inside the project, reached without
/// symbolic links. For every platform (`platform` is `None`) it is a square
/// PNG of a size every platform scales down from; for one platform it can
/// also be in that platform's own form.
fn app_icon(
    dir: &Path,
    name: &str,
    platform: Option<&str>,
    written: &str,
    declared: &SourceLocation,
    errors: &mut Vec<Diagnostic>,
) -> Option<String> {
    let error = |message: String| Diagnostic::error(message).at(declared.clone());
    if let Err(message) = bern_protocol::check_resource_name(written) {
        errors.push(error(format!("{name}: {message}")));
        return None;
    }
    let mut path = dir.to_path_buf();
    for segment in written.split('/') {
        path.push(segment);
        match std::fs::symlink_metadata(&path) {
            Ok(metadata) if metadata.file_type().is_symlink() => {
                errors.push(error(format!(
                    "{name} `{written}`: {} is a symbolic link; name the file it points to",
                    path.display()
                )));
                return None;
            }
            Ok(_) => {}
            Err(_) => {
                errors.push(error(format!(
                    "{name} `{written}` does not exist: {}",
                    dir.join(written).display()
                )));
                return None;
            }
        }
    }
    let checked = match platform {
        Some(platform) if !bern_target_api::icon::is_png_name(written) => {
            bern_target_api::icon::check_native(platform, &path)
        }
        _ if path.is_dir() => Err(format!(
            "is a folder; {}",
            match platform {
                Some(platform) => format!("give {}", bern_target_api::icon::accepted(platform)),
                None => "give a square PNG".to_string(),
            }
        )),
        _ => std::fs::read(&path)
            .map_err(|failure| format!("cannot be read: {failure}"))
            .and_then(|bytes| bern_target_api::icon::check(&bytes).map(drop)),
    };
    if let Err(message) = checked {
        errors.push(error(format!("{name} `{written}` {message}")));
        return None;
    }
    Some(written.to_string())
}

/// Check the `[resources]` entries and expand directories into the files
/// they ship. Every problem is an error at the entry that declared it.
fn resources(
    dir: &Path,
    manifest: &str,
    text: &str,
    raw: &RawResources,
    errors: &mut Vec<Diagnostic>,
) -> Vec<ResourceDef> {
    let mut found: Vec<ResourceDef> = Vec::new();
    for entry in &raw.paths {
        let written = entry.get_ref().as_str();
        let declared = manifest_location(manifest, text, entry.span().start);
        let error = |message: String| Diagnostic::error(message).at(declared.clone());
        if let Err(message) = bern_protocol::check_resource_name(written) {
            errors.push(error(message));
            continue;
        }
        // No part of the path may be a symbolic link: what ships is what
        // the entry names, inside the project directory.
        let mut path = dir.to_path_buf();
        let mut kind = None;
        for segment in written.split('/') {
            path.push(segment);
            match std::fs::symlink_metadata(&path) {
                Ok(metadata) if metadata.file_type().is_symlink() => {
                    kind = Some(Err(format!(
                        "resource `{written}`: {} is a symbolic link; list the file it points to",
                        path.display()
                    )));
                    break;
                }
                Ok(metadata) => kind = Some(Ok(metadata.file_type())),
                Err(_) => {
                    kind = Some(Err(format!(
                        "resource `{written}` does not exist: {}",
                        dir.join(written).display()
                    )));
                    break;
                }
            }
        }
        match kind {
            Some(Ok(file_type)) if file_type.is_file() => found.push(ResourceDef {
                name: written.to_string(),
                declared,
                picture: svg_picture(&path),
            }),
            Some(Ok(file_type)) if file_type.is_dir() => {
                let before = found.len();
                if let Err(message) = directory_files(&path, written, &declared, &mut found) {
                    errors.push(error(message));
                } else if found.len() == before {
                    errors.push(error(format!(
                        "resource directory `{written}` has no files to ship"
                    )));
                }
            }
            Some(Ok(_)) => errors.push(error(format!(
                "resource `{written}` is neither a file nor a directory"
            ))),
            Some(Err(message)) => errors.push(error(message)),
            None => {}
        }
    }
    // One name, one file: no duplicates, and no names a case-insensitive
    // file system would merge.
    let mut by_name: std::collections::BTreeMap<String, &ResourceDef> = Default::default();
    for resource in &found {
        match by_name.get(&resource.name.to_lowercase()) {
            Some(first) if first.name == resource.name => errors.push(
                Diagnostic::error(format!(
                    "resource `{}` is listed twice; it is already declared at line {}",
                    resource.name, first.declared.line
                ))
                .at(resource.declared.clone()),
            ),
            Some(first) => errors.push(
                Diagnostic::error(format!(
                    "resources `{}` and `{}` differ only in case",
                    first.name, resource.name
                ))
                .at(resource.declared.clone()),
            ),
            None => {
                by_name.insert(resource.name.to_lowercase(), resource);
            }
        }
    }
    found.sort_by(|a, b| a.name.cmp(&b.name));
    found.dedup_by(|a, b| a.name == b.name);
    found
}

/// Every non-hidden file below `path`, named `prefix/relative/path`.
fn directory_files(
    path: &Path,
    prefix: &str,
    declared: &SourceLocation,
    found: &mut Vec<ResourceDef>,
) -> Result<(), String> {
    let mut entries: Vec<_> = std::fs::read_dir(path)
        .and_then(|entries| entries.collect::<Result<Vec<_>, _>>())
        .map_err(|error| format!("cannot read resource directory {}: {error}", path.display()))?;
    entries.sort_by_key(|entry| entry.file_name());
    for entry in entries {
        let file_name = entry.file_name().to_string_lossy().into_owned();
        if file_name.starts_with('.') {
            continue;
        }
        let name = format!("{prefix}/{file_name}");
        bern_protocol::check_resource_name(&name)?;
        let file_type = entry
            .file_type()
            .map_err(|error| format!("cannot read {}: {error}", entry.path().display()))?;
        if file_type.is_symlink() {
            return Err(format!(
                "resource `{name}`: {} is a symbolic link; list the file it points to",
                entry.path().display()
            ));
        } else if file_type.is_dir() {
            directory_files(&entry.path(), &name, declared, found)?;
        } else if file_type.is_file() {
            found.push(ResourceDef {
                picture: svg_picture(&entry.path()),
                name,
                declared: declared.clone(),
            });
        } else {
            return Err(format!(
                "resource `{name}` is neither a file nor a directory"
            ));
        }
    }
    Ok(())
}

/// How the file, when it is an SVG document, shows as a picture of it.
fn svg_picture(path: &Path) -> Option<SvgPicture> {
    if !path
        .extension()
        .is_some_and(|extension| extension.eq_ignore_ascii_case("svg"))
    {
        return None;
    }
    let source = std::fs::read_to_string(path).ok()?;
    Some(match bern_svg::picture(&source)? {
        bern_svg::Picture::Still => SvgPicture::Still,
        bern_svg::Picture::Tinted => SvgPicture::Tinted,
        bern_svg::Picture::Themed => SvgPicture::Themed,
    })
}

/// Check `[app].id` and `[app].bundle_id`.
fn check_app(app: &RawApp, errors: &mut Vec<Diagnostic>) {
    if !bern_protocol::valid_name(&app.id) {
        errors.push(Diagnostic::error(format!(
            "[app].id `{}` must be lower snake case",
            app.id
        )));
    }
    let bundle_ok = app.bundle_id.split('.').count() >= 2
        && app.bundle_id.split('.').all(|part| {
            !part.is_empty() && part.chars().all(|c| c.is_ascii_alphanumeric() || c == '-')
        });
    if !bundle_ok {
        errors.push(Diagnostic::error(format!(
            "[app].bundle_id `{}` must be reverse-DNS, e.g. `com.example.app`",
            app.bundle_id
        )));
    }
}

/// Check `[languages]` and that `[app].name` translates exactly them;
/// with `strict`, a missing translation is B102.
fn check_languages(
    languages: &RawLanguages,
    name: &BTreeMap<String, String>,
    errors: &mut Vec<Diagnostic>,
) {
    let mut seen = std::collections::BTreeSet::new();
    for tag in &languages.supported {
        if !valid_language(tag) {
            errors.push(Diagnostic::error(format!(
                "language tag `{tag}` is not a standard tag such as `zh-Hans` or `en`"
            )));
        }
        if !seen.insert(tag) {
            errors.push(Diagnostic::error(format!(
                "language `{tag}` is listed twice"
            )));
        }
    }
    if languages.supported.is_empty() {
        errors.push(Diagnostic::error("[languages].supported is empty"));
    }
    if !languages.supported.contains(&languages.default) {
        errors.push(Diagnostic::error(format!(
            "default language `{}` is not in [languages].supported",
            languages.default
        )));
    }
    for language in name.keys() {
        if !languages.supported.contains(language) {
            errors.push(Diagnostic::error(format!(
                "[app].name has language `{language}`, which is not supported"
            )));
        }
    }
    if languages.strict {
        for language in &languages.supported {
            if !name.contains_key(language) {
                errors.push(
                    Diagnostic::error(format!(
                        "Missing translation\nProperty: [app].name\nMissing language: {language}"
                    ))
                    .code("B102"),
                );
            }
        }
    }
}

/// `[theme].mode`, the system's by default.
fn theme_mode(theme: &RawTheme, errors: &mut Vec<Diagnostic>) -> ThemeMode {
    match theme.mode.as_deref().unwrap_or("system") {
        "system" => ThemeMode::System,
        "light" => ThemeMode::Light,
        "dark" => ThemeMode::Dark,
        other => {
            errors.push(Diagnostic::error(format!(
                "[theme].mode `{other}` must be system, light or dark"
            )));
            ThemeMode::System
        }
    }
}

/// The breakpoints of `[layouts]`, each wider than the ones before it.
fn layout_config(
    layouts: Option<&RawLayouts>,
    errors: &mut Vec<Diagnostic>,
) -> Option<LayoutConfig> {
    match layouts {
        None => None,
        Some(layouts) if layouts.compact_below.is_finite() && layouts.compact_below > 0.0 => {
            // Each breakpoint lies beyond the ones before it.
            let mut previous = ("compact_below", layouts.compact_below);
            let mut ordered = true;
            for (name, value) in [
                ("medium_below", layouts.medium_below),
                ("expanded_below", layouts.expanded_below),
            ] {
                let Some(value) = value else { continue };
                if !value.is_finite() || value <= previous.1 {
                    errors.push(Diagnostic::error(format!(
                        "[layouts].{name} must be wider than {} ({}), not {value}",
                        previous.0, previous.1
                    )));
                    ordered = false;
                }
                previous = (name, value);
            }
            ordered.then_some(LayoutConfig {
                compact_below: layouts.compact_below,
                medium_below: layouts.medium_below,
                expanded_below: layouts.expanded_below,
            })
        }
        Some(layouts) => {
            errors.push(Diagnostic::error(format!(
                "[layouts].compact_below must be a positive width, not {}",
                layouts.compact_below
            )));
            None
        }
    }
}

/// `[theme].brand_seed`, a `#RRGGBB` color.
fn brand_seed(theme: &RawTheme, errors: &mut Vec<Diagnostic>) -> Option<Srgb> {
    let seed = theme.brand_seed.as_ref()?;
    let parsed = Srgb::parse(seed);
    if parsed.is_none() {
        errors.push(Diagnostic::error(format!(
            "[theme].brand_seed `{seed}` must be a `#RRGGBB` color"
        )));
    }
    parsed
}

/// The application's protocol and UI sources and its protocol, UI and
/// engine packages; a part is missing once its problem is reported.
struct AppSources {
    protocol_source: Option<SourceFile>,
    protocol_package: Option<Package>,
    ui_sources: Vec<SourceFile>,
    ui_package: Option<Package>,
    engine_package: Option<Package>,
}

/// Resolve the sources `[protocol]` and `[ui]` list, and check that each
/// kind belongs to the package the manifest names, like the engine.
fn app_sources(
    dir: &Path,
    protocol: &RawProtocol,
    ui: &RawUi,
    engine: &RawEngine,
    errors: &mut Vec<Diagnostic>,
) -> AppSources {
    let ui_written = expand_sources(dir, "", &ui.sources).unwrap_or_else(|error| {
        errors.push(error);
        Vec::new()
    });
    let mut resolve = |written: &str| -> Option<SourceFile> {
        match source_file(dir, written) {
            Ok((_, module)) => Some(SourceFile {
                display: written.to_string(),
                path: dir.join(written),
                module,
            }),
            Err(error) => {
                errors.push(error);
                None
            }
        }
    };
    let protocol_source = resolve(&protocol.source);
    let ui_sources: Vec<SourceFile> = ui_written.iter().filter_map(|s| resolve(s)).collect();

    let protocol_package = protocol_source.as_ref().and_then(|source| {
        let package_dir = source_file(dir, &source.display).ok()?.0;
        package(
            dir,
            &protocol.package,
            &[(source.display.clone(), package_dir)],
            "protocol",
        )
        .map_err(|error| errors.push(error))
        .ok()
    });
    let ui_dirs: Vec<(String, PathBuf)> = ui_sources
        .iter()
        .filter_map(|source| {
            source_file(dir, &source.display)
                .ok()
                .map(|(package_dir, _)| (source.display.clone(), package_dir))
        })
        .collect();
    let ui_package = package(dir, &ui.package, &ui_dirs, "UI")
        .map_err(|error| errors.push(error))
        .ok();
    let engine_dir = dir.join(engine.path.as_deref().unwrap_or(&engine.package));
    let engine_package = package(
        dir,
        &engine.package,
        &[(engine.package.clone(), engine_dir)],
        "engine",
    )
    .map_err(|error| errors.push(error))
    .ok();
    if ui_written.is_empty() {
        errors.push(Diagnostic::error("[ui].sources lists no files"));
    }
    AppSources {
        protocol_source,
        protocol_package,
        ui_sources,
        ui_package,
        engine_package,
    }
}

/// Check one `[targets.<name>]` table and turn it into its configuration.
fn target_config(name: String, target: RawTarget, errors: &mut Vec<Diagnostic>) -> TargetConfig {
    check_web_mode(&name, &target, errors);
    if target.platform == "browser" && target.webview == Some(false) {
        errors.push(Diagnostic::error(format!(
            "target `{name}`: the browser provides JavaScript; webview cannot be disabled"
        )));
    }
    if target.platform == "tvos" && target.webview == Some(true) {
        errors.push(Diagnostic::error(format!(
            "target `{name}`: tvOS has no WebView; omit webview or set it to false"
        )));
    }
    if target.javascript && target.web_mode.as_deref() == Some("ui") {
        errors.push(Diagnostic::error(format!(
            "target `{name}`: JavaScript hosting currently requires web_mode = \"app\""
        )));
    }
    if target.web_extension.is_some() && target.platform != "browser" {
        errors.push(Diagnostic::error(format!(
            "target `{name}`: web_extension requires a browser target"
        )));
    }
    if target.android.is_some() && target.platform != "android" {
        errors.push(Diagnostic::error(format!(
            "target `{name}`: android host options require an Android target"
        )));
    }

    let frontends = windows_frontends(&name, &target.platform, target.frontends, errors);
    for channel in &target.channels {
        if channel != "ipc" {
            errors.push(Diagnostic::error(format!(
                "target `{name}`: unknown channel `{channel}`; supported: ipc"
            )));
        }
    }
    TargetConfig {
        name,
        platform: target.platform,
        ui: target.ui,
        web_mode: target.web_mode,
        web_extension: target.web_extension,
        channels: target.channels,
        frontends,
        webview: target.webview,
        javascript: target.javascript,
        android: target.android,
    }
}

/// A browser target says whether the engine runs in the page, and the
/// transport and codec it declares follow from that; other targets have
/// no `web_mode`.
fn check_web_mode(name: &str, target: &RawTarget, errors: &mut Vec<Diagnostic>) {
    if target.platform == "browser" {
        match target.web_mode.as_deref() {
            None => errors.push(Diagnostic::error(format!(
                "target `{name}`: browser targets must set `web_mode = \"app\"` or `\"ui\"`"
            ))),
            Some("app") | Some("ui") => {}
            Some(other) => errors.push(Diagnostic::error(format!(
                "target `{name}`: `web_mode = \"{other}\"` is unknown; use \"app\" or \"ui\""
            ))),
        }
        // `app` runs the engine in the page; `ui` reaches a separate
        // engine over a browser transport. Mismatches fail here
        // instead of building a page that cannot reach its engine.
        let (transport, codec) = match target.web_mode.as_deref() {
            Some("ui") => ("websocket", Some("json")),
            _ => ("in-process", None),
        };
        if let Some(declared) = &target.application_transport
            && declared != transport
        {
            errors.push(Diagnostic::error(format!(
                "target `{name}`: `web_mode = \"{}\"` uses `application_transport = \"{transport}\"`, not `\"{declared}\"`",
                target.web_mode.as_deref().unwrap_or("app")
            )));
        }
        if let Some(declared) = &target.application_codec
            && Some(declared.as_str()) != codec
        {
            errors.push(Diagnostic::error(format!(
                "target `{name}`: `application_codec = \"{declared}\"` does not apply; {}",
                match codec {
                    Some(codec) => format!("the WebUI channel uses `{codec}`"),
                    None => "the in-page engine is called directly".into(),
                }
            )));
        }
    } else if target.web_mode.is_some() {
        errors.push(Diagnostic::error(format!(
            "target `{name}`: `web_mode` applies to browser targets only"
        )));
    }
}

/// The front ends a target builds. Windows builds both unless the target
/// names fewer; other platforms take none.
fn windows_frontends(
    name: &str,
    platform: &str,
    frontends: Option<Vec<String>>,
    errors: &mut Vec<Diagnostic>,
) -> Vec<String> {
    match (platform, frontends) {
        ("windows", None) => WINDOWS_FRONTENDS.map(str::to_string).to_vec(),
        ("windows", Some(frontends)) => {
            if frontends.is_empty() {
                errors.push(Diagnostic::error(format!(
                    "target `{name}`: `frontends` lists none; name \"winui3\", \"xaml-islands\" or both"
                )));
            }
            for (index, frontend) in frontends.iter().enumerate() {
                if !WINDOWS_FRONTENDS.contains(&frontend.as_str()) {
                    errors.push(Diagnostic::error(format!(
                        "target `{name}`: unknown front end `{frontend}`; use \"winui3\" or \"xaml-islands\""
                    )));
                } else if frontends[..index].contains(frontend) {
                    errors.push(Diagnostic::error(format!(
                        "target `{name}`: `frontends` lists `{frontend}` twice"
                    )));
                }
            }
            frontends
        }
        (_, Some(_)) => {
            errors.push(Diagnostic::error(format!(
                "target `{name}`: `frontends` applies to Windows targets only"
            )));
            Vec::new()
        }
        (_, None) => Vec::new(),
    }
}

/// The manifests `[[libraries]]` lists, which must exist.
fn library_manifests(
    dir: &Path,
    libraries: &[RawLibraryRef],
    errors: &mut Vec<Diagnostic>,
) -> Vec<PathBuf> {
    let libraries: Vec<PathBuf> = libraries
        .iter()
        .map(|library| dir.join(&library.manifest))
        .collect();
    for library in &libraries {
        if !library.is_file() {
            errors.push(Diagnostic::error(format!(
                "library manifest {} does not exist",
                library.display()
            )));
        }
    }
    libraries
}

/// Load the modules `[[modules]]` lists. Each is listed once and
/// translates every language the application supports.
fn load_modules(
    dir: &Path,
    entries: &[RawModuleRef],
    languages: &[String],
    selection: &bern_syntax::build::Modules,
    errors: &mut Vec<Diagnostic>,
) -> Vec<ModuleConfig> {
    let mut modules: Vec<ModuleConfig> = Vec::new();
    for entry in entries {
        let manifest = dir.join(&entry.path).join("Bern.toml");
        let id = std::fs::read_to_string(&manifest)
            .ok()
            .and_then(|text| text.parse::<toml::Value>().ok())
            .and_then(|value| value.get("module")?.get("id")?.as_str().map(str::to_string));
        if id
            .as_ref()
            .is_some_and(|id| selection.0.get(id) == Some(&false))
        {
            continue;
        }
        match load_module(dir, &entry.path) {
            Ok(module) => {
                if modules.iter().any(|other| other.id == module.id) {
                    errors.push(Diagnostic::error(format!(
                        "module `{}` is listed twice",
                        module.id
                    )));
                }
                for language in languages {
                    if !module.languages.contains(language) {
                        errors.push(Diagnostic::error(format!(
                            "module `{}` does not translate `{language}`, which the application supports; add it to {}",
                            module.id,
                            module.manifest.display()
                        )));
                    }
                }
                modules.push(module);
            }
            Err(module_errors) => errors.extend(module_errors),
        }
    }
    check_module_order(&modules, errors);
    modules
}

/// A module depends only on modules listed before it, and one that
/// always runs never on an optional one.
fn check_module_order(modules: &[ModuleConfig], errors: &mut Vec<Diagnostic>) {
    for (index, module) in modules.iter().enumerate() {
        for dependency in &module.depends {
            match modules.iter().position(|other| &other.id == dependency) {
                Some(position) if position < index && modules[position].optional && !module.optional => {
                    errors.push(Diagnostic::error(format!(
                        "module `{}` always runs but depends on the optional module `{dependency}`; make it optional too",
                        module.id
                    )))
                }
                Some(position) if position < index => {}
                Some(_) => errors.push(Diagnostic::error(format!(
                    "module `{}` depends on `{dependency}`, which Bern.toml lists after it; list modules after the ones they depend on",
                    module.id
                ))),
                None => errors.push(Diagnostic::error(format!(
                    "module `{}` depends on `{dependency}`, which is not a module of this application",
                    module.id
                ))),
            }
        }
    }
}

/// `[contributes]`: every slot named there is a lower snake case id.
fn check_contributes(
    contributes: &BTreeMap<String, Vec<String>>,
    manifest: &str,
    errors: &mut Vec<Diagnostic>,
) {
    for slot in contributes.keys() {
        if !bern_protocol::valid_name(slot) {
            errors.push(Diagnostic::error(format!(
                "{manifest}: slot `{slot}` must be lower snake case"
            )));
        }
    }
}

/// Read identity and dependency metadata before touching any module sources.
fn module_selection(
    dir: &Path,
    entries: &[RawModuleRef],
    excluded: &[String],
) -> Result<bern_syntax::build::Modules, Vec<Diagnostic>> {
    let mut catalog = BTreeMap::<String, Vec<String>>::new();
    let mut errors = Vec::new();
    for entry in entries {
        let path = dir.join(&entry.path).join("Bern.toml");
        let result = std::fs::read_to_string(&path)
            .map_err(|e| e.to_string())
            .and_then(|text| text.parse::<toml::Value>().map_err(|e| e.to_string()));
        match result {
            Ok(value) => {
                let module = value.get("module");
                if let Some(id) = module
                    .and_then(|m| m.get("id"))
                    .and_then(toml::Value::as_str)
                {
                    let depends = module
                        .and_then(|m| m.get("depends"))
                        .and_then(toml::Value::as_array)
                        .into_iter()
                        .flatten()
                        .filter_map(toml::Value::as_str)
                        .map(str::to_string)
                        .collect();
                    if !bern_protocol::valid_name(id) {
                        errors.push(Diagnostic::error(format!(
                            "invalid module id `{id}` in {}",
                            path.display()
                        )));
                    }
                    if catalog.insert(id.to_string(), depends).is_some() {
                        errors.push(Diagnostic::error(format!("module `{id}` is listed twice")));
                    }
                } else {
                    errors.push(Diagnostic::error(format!(
                        "{} needs [module].id",
                        path.display()
                    )));
                }
            }
            Err(e) => errors.push(Diagnostic::error(format!("{}: {e}", path.display()))),
        }
    }
    for id in excluded {
        if !catalog.contains_key(id) {
            errors.push(Diagnostic::error(format!(
                "unknown module `{id}` in --exclude-module; declared modules: {}",
                catalog.keys().cloned().collect::<Vec<_>>().join(", ")
            )));
        }
    }
    fn chain(
        id: &str,
        catalog: &BTreeMap<String, Vec<String>>,
        excluded: &[String],
        path: &mut Vec<String>,
    ) -> Option<Vec<String>> {
        if path.iter().any(|p| p == id) {
            return None;
        }
        path.push(id.to_string());
        if excluded.iter().any(|e| e == id) {
            return Some(path.clone());
        }
        for dep in catalog.get(id).into_iter().flatten() {
            if let Some(found) = chain(dep, catalog, excluded, path) {
                return Some(found);
            }
        }
        path.pop();
        None
    }
    for id in catalog.keys().filter(|id| !excluded.contains(id)) {
        if let Some(path) = chain(id, &catalog, excluded, &mut Vec::new()) {
            errors.push(Diagnostic::error(format!("cannot exclude module `{}`: retained dependency chain {}; also exclude the dependent module or keep its dependency", path.last().unwrap(), path.join(" -> "))));
        }
    }
    if !errors.is_empty() {
        return Err(errors);
    }
    Ok(bern_syntax::build::Modules(
        catalog
            .keys()
            .map(|id| (id.clone(), !excluded.contains(id)))
            .collect(),
    ))
}

/// Load and validate a project configuration.
pub fn load(path: &Path) -> Result<Config, Vec<Diagnostic>> {
    load_excluding(path, &[])
}

/// Load only the selected modules; excluded source files are never opened.
pub fn load_excluding(path: &Path, excluded: &[String]) -> Result<Config, Vec<Diagnostic>> {
    let text = std::fs::read_to_string(path).map_err(|error| {
        vec![Diagnostic::error(format!(
            "cannot read {}: {error}",
            path.display()
        ))]
    })?;
    let raw: RawConfig = toml::from_str(&text)
        .map_err(|error| vec![Diagnostic::error(format!("{}: {error}", path.display()))])?;
    let dir = path
        .parent()
        .map(Path::to_path_buf)
        .unwrap_or_else(|| PathBuf::from("."));
    let dir = canonical(dir);
    let mut errors = Vec::new();

    check_app(&raw.app, &mut errors);
    check_languages(&raw.languages, &raw.app.name, &mut errors);
    let theme_mode = theme_mode(&raw.theme, &mut errors);
    let layouts = layout_config(raw.layouts.as_ref(), &mut errors);
    let brand_seed = brand_seed(&raw.theme, &mut errors);
    let sources = app_sources(&dir, &raw.protocol, &raw.ui, &raw.engine, &mut errors);
    let targets: Vec<TargetConfig> = raw
        .targets
        .into_iter()
        .map(|(name, target)| target_config(name, target, &mut errors))
        .collect();
    let libraries = library_manifests(&dir, &raw.libraries, &mut errors);
    let build_modules = module_selection(&dir, &raw.modules, excluded)?;
    let modules = load_modules(
        &dir,
        &raw.modules,
        &raw.languages.supported,
        &build_modules,
        &mut errors,
    );
    let manifest = path.display().to_string();
    check_contributes(&raw.contributes, &manifest, &mut errors);
    let resources = raw
        .resources
        .as_ref()
        .map(|raw| resources(&dir, &manifest, &text, raw, &mut errors))
        .unwrap_or_default();
    let (icon, platform_icons) = raw
        .app
        .icon
        .as_ref()
        .map(|entry| app_icons(&dir, &manifest, &text, ("app", "icon"), entry, &mut errors))
        .unwrap_or_default();
    let mut alternate_icons = BTreeMap::new();
    for (name, entry) in raw.app.alternate_icons.iter().flatten() {
        // `WindowSet(icon:)` names it by an enum variant: `DarkSkin` is
        // `dark_skin`, and `Default` is `[app.icon]`.
        let named = name.starts_with(|c: char| c.is_ascii_lowercase())
            && name
                .chars()
                .all(|c| c.is_ascii_lowercase() || c.is_ascii_digit() || c == '_')
            && name != "default";
        if !named {
            errors.push(
                Diagnostic::error(format!(
                    "[app.alternate_icons].{name}: name an alternate icon with lowercase letters, digits and `_`, starting with a letter; `default` is `[app.icon]`"
                ))
                .at(manifest_location(&manifest, &text, entry.span().start)),
            );
            continue;
        }
        let (every, mut entries) = app_icons(
            &dir,
            &manifest,
            &text,
            ("app.alternate_icons", name),
            entry,
            &mut errors,
        );
        if let Some(every) = every {
            entries.insert("default".to_string(), every);
        }
        if !entries.is_empty() {
            alternate_icons.insert(name.clone(), entries);
        }
    }

    if !errors.is_empty() {
        return Err(errors);
    }
    Ok(Config {
        dir,
        app_id: raw.app.id,
        bundle_id: raw.app.bundle_id,
        version: raw.app.version,
        name: raw.app.name,
        icon,
        platform_icons,
        alternate_icons,
        publisher: raw
            .app
            .publisher
            .map(|publisher| publisher.trim().to_string())
            .filter(|publisher| !publisher.is_empty()),
        files_folder: raw.app.files_folder,
        background_audio: raw.app.background_audio,
        overlays: raw.app.overlays,
        languages: raw.languages.supported,
        default_language: raw.languages.default,
        strict: raw.languages.strict,
        theme_mode,
        brand_seed,
        protocol_package: sources.protocol_package.unwrap(),
        protocol_source: sources.protocol_source.unwrap(),
        engine_package: sources.engine_package.unwrap(),
        engine_type: raw.engine.type_path,
        ui_package: sources.ui_package.unwrap(),
        ui_sources: sources.ui_sources,
        root: raw.ui.root,
        targets,
        libraries,
        modules,
        build_modules,
        contributes: raw.contributes,
        resources,
        layouts,
    })
}

/// Load the module at `written` (relative to the project directory `dir`).
/// Its source paths are kept relative to `dir`, like the application's.
fn load_module(dir: &Path, written: &str) -> Result<ModuleConfig, Vec<Diagnostic>> {
    let base = written.trim_end_matches('/');
    let manifest = dir.join(base).join("Bern.toml");
    let text = std::fs::read_to_string(&manifest).map_err(|error| {
        vec![Diagnostic::error(format!(
            "cannot read module manifest {}: {error}",
            manifest.display()
        ))]
    })?;
    let raw: RawModuleConfig = toml::from_str(&text).map_err(|error| {
        vec![Diagnostic::error(format!(
            "{}: {error}",
            manifest.display()
        ))]
    })?;
    let mut errors = Vec::new();
    let id = raw.module.id;
    if !bern_protocol::valid_name(&id) {
        errors.push(Diagnostic::error(format!(
            "{}: module id `{id}` must be lower snake case",
            manifest.display()
        )));
    }
    let mut resolve = |written: &str| -> Option<SourceFile> {
        match source_file(dir, written) {
            Ok((_, module)) => Some(SourceFile {
                display: written.to_string(),
                path: dir.join(written),
                module,
            }),
            Err(error) => {
                errors.push(error);
                None
            }
        }
    };
    let protocol_source = resolve(&format!("{base}/{}", raw.module.protocol.source));
    let mut ui_sources = Vec::new();
    let mut ui_dirs = Vec::new();
    if let Some(ui) = &raw.module.ui {
        match expand_sources(dir, base, &ui.sources) {
            Ok(files) => {
                for file in files {
                    if let Ok((package_dir, _)) = source_file(dir, &file) {
                        ui_dirs.push((file.clone(), package_dir));
                    }
                    ui_sources.extend(resolve(&file));
                }
            }
            Err(error) => errors.push(error),
        }
    }
    let protocol_package = protocol_source.as_ref().and_then(|source| {
        let package_dir = source_file(dir, &source.display).ok()?.0;
        package(
            dir,
            &raw.module.protocol.package,
            &[(source.display.clone(), package_dir)],
            "protocol",
        )
        .map_err(|error| errors.push(error))
        .ok()
    });
    let ui_package = raw.module.ui.as_ref().and_then(|ui| {
        package(dir, &ui.package, &ui_dirs, "UI")
            .map_err(|error| errors.push(error))
            .ok()
    });
    let engine_dir = dir.join(base).join(
        raw.module
            .engine
            .path
            .as_deref()
            .unwrap_or(&raw.module.engine.package),
    );
    let engine_package = package(
        dir,
        &raw.module.engine.package,
        &[(raw.module.engine.package.clone(), engine_dir)],
        "engine",
    )
    .map_err(|error| errors.push(error))
    .ok();
    for page in &raw.pages {
        for (what, field) in [("badge", &page.badge), ("when", &page.when)] {
            if let Some(field) = field
                && !bern_protocol::valid_name(field)
            {
                errors.push(Diagnostic::error(format!(
                    "{}: page {what} `{field}` must name a lower snake case state field",
                    manifest.display()
                )));
            }
        }
        for (what, name) in [("slot", &page.slot), ("page id", &page.id)] {
            if !bern_protocol::valid_name(name) {
                errors.push(Diagnostic::error(format!(
                    "{}: {what} `{name}` must be lower snake case",
                    manifest.display()
                )));
            }
        }
        if raw.module.ui.is_none() {
            errors.push(Diagnostic::error(format!(
                "{}: page `{}` needs the module's [module.ui] to show it",
                manifest.display(),
                page.id
            )));
        }
    }
    for slot in raw.contributes.keys() {
        if !bern_protocol::valid_name(slot) {
            errors.push(Diagnostic::error(format!(
                "{}: slot `{slot}` must be lower snake case",
                manifest.display()
            )));
        }
    }
    if raw.module.enabled.is_some() && !raw.module.optional {
        errors.push(Diagnostic::error(format!(
            "{}: `enabled` applies to optional modules; add `optional = true` or remove it",
            manifest.display()
        )));
    }
    if !errors.is_empty() {
        return Err(errors);
    }
    Ok(ModuleConfig {
        id,
        dir: canonical(dir.join(base)),
        manifest,
        name: raw.module.name,
        depends: raw.module.depends,
        optional: raw.module.optional,
        enabled: raw.module.enabled.unwrap_or(true),
        protocol_package: protocol_package.unwrap(),
        protocol_source: protocol_source.unwrap(),
        engine_package: engine_package.unwrap(),
        engine_type: raw.module.engine.type_path,
        ui_package,
        ui_sources,
        languages: raw.languages.supported,
        pages: raw
            .pages
            .into_iter()
            .map(|page| PageConfig {
                slot: page.slot,
                id: page.id,
                label: page.label,
                icon: page.icon,
                badge: page.badge,
                when: page.when,
                start: page.start,
                tab: page.tab.unwrap_or(true),
                component: page.component,
            })
            .collect(),
        contributes: raw.contributes,
    })
}

/// Load a component library manifest (`[library]` + `[languages]`).
pub fn load_library(path: &Path) -> Result<LibraryConfig, Vec<Diagnostic>> {
    let text = std::fs::read_to_string(path).map_err(|error| {
        vec![Diagnostic::error(format!(
            "cannot read {}: {error}",
            path.display()
        ))]
    })?;
    let raw: RawLibraryConfig = toml::from_str(&text)
        .map_err(|error| vec![Diagnostic::error(format!("{}: {error}", path.display()))])?;
    let dir = path
        .parent()
        .map(Path::to_path_buf)
        .unwrap_or_else(|| PathBuf::from("."));
    let dir = canonical(dir);
    let mut errors = Vec::new();
    let mut sources = Vec::new();
    let mut dirs = Vec::new();
    for written in &raw.library.sources {
        match source_file(&dir, written) {
            Ok((package_dir, module)) => {
                dirs.push((written.clone(), package_dir));
                sources.push(SourceFile {
                    display: format!("{}/{written}", raw.library.package),
                    path: dir.join(written),
                    module,
                });
            }
            Err(error) => errors.push(error),
        }
    }
    for tag in &raw.languages.supported {
        if !valid_language(tag) {
            errors.push(Diagnostic::error(format!(
                "language tag `{tag}` is not a standard tag"
            )));
        }
    }
    let package = package(&dir, &raw.library.package, &dirs, "library")
        .map_err(|error| errors.push(error))
        .ok();
    let version = package.as_ref().and_then(|package| {
        read_package_field(&package.dir, "version")
            .map_err(|error| errors.push(error))
            .ok()
    });
    if !errors.is_empty() {
        return Err(errors);
    }
    Ok(LibraryConfig {
        dir,
        manifest: path.to_path_buf(),
        package: package.unwrap(),
        version: version.unwrap(),
        sources,
        languages: raw.languages.supported,
        default_language: raw.languages.default,
        strict: raw.languages.strict,
    })
}

/// The absolute form of `dir`, without the verbatim prefix Windows gives
/// canonical paths (`\\?\C:\…`), which Cargo manifests and tools reject.
fn canonical(dir: PathBuf) -> PathBuf {
    let Ok(path) = dir.canonicalize() else {
        return dir;
    };
    if cfg!(windows)
        && let Some(rest) = path.to_string_lossy().strip_prefix(r"\\?\")
        && !rest.starts_with(r"UNC\")
    {
        return PathBuf::from(rest);
    }
    path
}

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

    #[test]
    fn android_host_options_are_explicit_and_platform_scoped() {
        let parse = |text: &str| toml::from_str::<RawTarget>(text).unwrap();
        let mut errors = Vec::new();
        let target = target_config(
            "phone".into(),
            parse("platform = 'android'\nandroid = { network = true, multicast = true }"),
            &mut errors,
        );
        assert!(errors.is_empty(), "{errors:?}");
        let options = target.android.unwrap();
        assert!(options.network && options.multicast);

        let default = target_config("phone".into(), parse("platform = 'android'"), &mut errors);
        assert!(default.android.is_none());
        target_config(
            "desktop".into(),
            parse("platform = 'macos'\nandroid = { network = true }"),
            &mut errors,
        );
        assert_eq!(errors.len(), 1);
        assert!(errors[0].message.contains("require an Android target"));
        assert!(
            toml::from_str::<RawTarget>("platform = 'android'\nandroid = { netwrok = true }")
                .is_err()
        );
    }

    #[test]
    fn language_tags_are_validated() {
        for tag in ["zh-Hans", "en", "ja", "pt-BR", "zh-Hant-TW"] {
            assert!(valid_language(tag), "{tag}");
        }
        for tag in ["", "EN", "english", "zh_Hans", "zh-"] {
            assert!(!valid_language(tag), "{tag}");
        }
    }

    /// Check `[resources]` written as `entries` in a project holding
    /// `files` (paths relative to the project, created empty unless they
    /// end in `/`).
    fn check_resources(files: &[&str], entries: &str) -> (Vec<ResourceDef>, Vec<Diagnostic>) {
        static NEXT: std::sync::atomic::AtomicUsize = std::sync::atomic::AtomicUsize::new(0);
        let dir = std::env::temp_dir().join(format!(
            "bern-resources-test-{}-{}",
            std::process::id(),
            NEXT.fetch_add(1, std::sync::atomic::Ordering::Relaxed)
        ));
        let _ = std::fs::remove_dir_all(&dir);
        std::fs::create_dir_all(&dir).unwrap();
        for file in files {
            let path = dir.join(file);
            if file.ends_with('/') {
                std::fs::create_dir_all(&path).unwrap();
            } else {
                std::fs::create_dir_all(path.parent().unwrap()).unwrap();
                std::fs::write(&path, b"x").unwrap();
            }
        }
        #[derive(Deserialize)]
        struct Manifest {
            resources: RawResources,
        }
        let text = format!("# Bern.toml\n[resources]\npaths = [\n{entries}\n]\n");
        let raw: Manifest = toml::from_str(&text).unwrap();
        let mut errors = Vec::new();
        let found = resources(&dir, "Bern.toml", &text, &raw.resources, &mut errors);
        let _ = std::fs::remove_dir_all(&dir);
        (found, errors)
    }

    fn names(found: &[ResourceDef]) -> Vec<&str> {
        found
            .iter()
            .map(|resource| resource.name.as_str())
            .collect()
    }

    #[test]
    fn resources_expand_directories_and_point_at_their_entries() {
        let (found, errors) = check_resources(
            &[
                "media/b.mp4",
                "data/seed.json",
                "data/nested/more.json",
                "data/.DS_Store",
                "data/.git/config",
            ],
            "  \"media/b.mp4\",\n  \"data\",",
        );
        assert!(errors.is_empty(), "{errors:?}");
        assert_eq!(
            names(&found),
            ["data/nested/more.json", "data/seed.json", "media/b.mp4"]
        );
        // Each file points at the entry that declared it: line 4 is the
        // first entry, line 5 the directory.
        let media = &found[2].declared;
        assert_eq!(
            (media.file.as_str(), media.line, media.column),
            ("Bern.toml", 4, 3)
        );
        assert_eq!(found[0].declared.line, 5);
    }

    #[test]
    fn resource_errors_are_strict_and_located() {
        let cases: &[(&[&str], &str, &str)] = &[
            (&[], "\"media/missing.mp4\"", "does not exist"),
            (&["a.mp4"], "\"/a.mp4\"", "is absolute"),
            (&["a.mp4"], "\"../a.mp4\"", "starts with `.`"),
            (&["a b.mp4"], "\"a b.mp4\"", "contains ` `"),
            (&["empty/"], "\"empty\"", "has no files to ship"),
            (&["only/.hidden"], "\"only\"", "has no files to ship"),
            (&["d/a b.txt"], "\"d\"", "contains ` `"),
            (&["a.mp4"], "\"a.mp4\", \"a.mp4\"", "listed twice"),
            (&["d/a.mp4"], "\"d\", \"d/a.mp4\"", "listed twice"),
            (&["d/A.mp4", "e/a.mp4"], "\"d/A.mp4\", \"e/a.mp4\"", ""),
        ];
        for (files, entries, expected) in cases {
            let (_, errors) = check_resources(files, entries);
            if expected.is_empty() {
                assert!(errors.is_empty(), "{entries}: {errors:?}");
                continue;
            }
            assert_eq!(errors.len(), 1, "{entries}: {errors:?}");
            assert!(
                errors[0].message.contains(expected),
                "{entries}: {}",
                errors[0].message
            );
            let location = errors[0].location.as_ref().expect("located");
            assert_eq!((location.file.as_str(), location.line), ("Bern.toml", 4));
        }
    }

    #[cfg(unix)]
    #[test]
    fn symbolic_links_and_case_collisions_are_rejected() {
        let (_, errors) = check_resources(&["a.mp4", "A.MP4"], "\"a.mp4\", \"A.MP4\"");
        // A case-insensitive file system has one file; a case-sensitive one
        // has two that would merge on another machine. Both are errors.
        assert_eq!(errors.len(), 1, "{errors:?}");
        assert!(
            errors[0].message.contains("differ only in case")
                || errors[0].message.contains("listed twice"),
            "{}",
            errors[0].message
        );

        let dir = std::env::temp_dir().join(format!("bern-resources-link-{}", std::process::id()));
        let _ = std::fs::remove_dir_all(&dir);
        std::fs::create_dir_all(dir.join("real")).unwrap();
        std::fs::write(dir.join("real/a.mp4"), b"x").unwrap();
        std::os::unix::fs::symlink(dir.join("real"), dir.join("linked")).unwrap();
        std::os::unix::fs::symlink(dir.join("real/a.mp4"), dir.join("real/b.mp4")).unwrap();
        #[derive(Deserialize)]
        struct Manifest {
            resources: RawResources,
        }
        for entry in ["linked/a.mp4", "real"] {
            let text = format!("[resources]\npaths = [\"{entry}\"]\n");
            let raw: Manifest = toml::from_str(&text).unwrap();
            let mut errors = Vec::new();
            resources(&dir, "Bern.toml", &text, &raw.resources, &mut errors);
            assert_eq!(errors.len(), 1, "{entry}: {errors:?}");
            assert!(
                errors[0].message.contains("symbolic link"),
                "{}",
                errors[0].message
            );
        }
        let _ = std::fs::remove_dir_all(&dir);
    }

    #[test]
    fn module_paths_follow_cargo_layout() {
        let dir = Path::new("/p");
        assert_eq!(
            source_file(dir, "ui/src/lib.rs").unwrap().1,
            Vec::<String>::new()
        );
        assert_eq!(
            source_file(dir, "ui/src/pages.rs").unwrap().1,
            vec!["pages"]
        );
        assert_eq!(
            source_file(dir, "ui/src/a/b/mod.rs").unwrap().1,
            vec!["a", "b"]
        );
        assert_eq!(
            source_file(dir, "ui/src/pages.rs").unwrap().0,
            PathBuf::from("/p/ui")
        );
        assert!(source_file(dir, "ui/pages.rs").is_err());
    }

    /// Check `icon = <value>` (TOML) in a project holding `files`.
    fn check_icons(
        files: &[(&str, Vec<u8>)],
        value: &str,
    ) -> (Option<String>, BTreeMap<String, String>, Vec<Diagnostic>) {
        static NEXT: std::sync::atomic::AtomicUsize = std::sync::atomic::AtomicUsize::new(0);
        let dir = std::env::temp_dir().join(format!(
            "bern-icon-test-{}-{}",
            std::process::id(),
            NEXT.fetch_add(1, std::sync::atomic::Ordering::Relaxed)
        ));
        let _ = std::fs::remove_dir_all(&dir);
        std::fs::create_dir_all(&dir).unwrap();
        for (file, bytes) in files {
            let path = dir.join(file);
            std::fs::create_dir_all(path.parent().unwrap()).unwrap();
            std::fs::write(&path, bytes).unwrap();
        }
        #[derive(Deserialize)]
        struct Manifest {
            icon: toml::Spanned<RawIcon>,
        }
        let text = format!("# Bern.toml\nicon = {value}\n");
        let raw: Manifest = toml::from_str(&text).unwrap();
        let mut errors = Vec::new();
        let (every, platforms) = app_icons(
            &dir,
            "Bern.toml",
            &text,
            ("app", "icon"),
            &raw.icon,
            &mut errors,
        );
        let _ = std::fs::remove_dir_all(&dir);
        (every, platforms, errors)
    }

    /// Check `[app].icon = entry` in a project holding `files`.
    fn check_icon(files: &[(&str, Vec<u8>)], entry: &str) -> (Option<String>, Vec<Diagnostic>) {
        let (every, _, errors) = check_icons(files, &format!("\"{entry}\""));
        (every, errors)
    }

    /// The first bytes of a PNG of `width` × `height` pixels.
    fn png(width: u32, height: u32) -> Vec<u8> {
        let mut bytes = b"\x89PNG\r\n\x1a\n\0\0\0\x0dIHDR".to_vec();
        bytes.extend_from_slice(&width.to_be_bytes());
        bytes.extend_from_slice(&height.to_be_bytes());
        bytes
    }

    #[test]
    fn app_icons_are_square_pngs_in_the_project() {
        let (found, errors) = check_icon(&[("art/icon.png", png(1024, 1024))], "art/icon.png");
        assert!(errors.is_empty(), "{errors:?}");
        assert_eq!(found.as_deref(), Some("art/icon.png"));
        for (files, entry, expected) in [
            (vec![], "icon.png", "does not exist"),
            (vec![("icon.png", png(300, 300))], "icon.png", "1024"),
            (vec![("icon.png", png(512, 256))], "icon.png", "square"),
            (
                vec![("icon.png", b"GIF89a".to_vec())],
                "icon.png",
                "not a PNG",
            ),
            (vec![], "../icon.png", "[app].icon"),
        ] {
            let (found, errors) = check_icon(&files, entry);
            assert!(found.is_none(), "{entry}");
            assert_eq!(errors.len(), 1, "{entry}: {errors:?}");
            assert!(
                errors[0].message.contains(expected),
                "{entry}: {}",
                errors[0].message
            );
            assert_eq!(errors[0].location.as_ref().map(|at| at.line), Some(2));
        }
    }

    #[test]
    fn platforms_take_their_own_icons() {
        let icns = {
            let mut bytes = b"icns\0\0\0\x18ic10\0\0\0\x10".to_vec();
            bytes.extend_from_slice(&png(1024, 1024)[..8]);
            bytes
        };
        let ico = {
            let mut bytes = vec![0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 32, 0];
            bytes.extend_from_slice(&24u32.to_le_bytes());
            bytes.extend_from_slice(&22u32.to_le_bytes());
            bytes.extend_from_slice(&png(256, 256));
            bytes
        };
        let files = vec![
            ("icon.png", png(1024, 1024)),
            ("mac/App.icns", icns),
            ("win/app.ico", ico),
            (
                "ios/AppIcon.appiconset/Contents.json",
                br#"{"images":[{"filename":"AppIcon.png","idiom":"universal","platform":"ios","size":"1024x1024"}]}"#.to_vec(),
            ),
            ("ios/AppIcon.appiconset/AppIcon.png", png(1024, 1024)),
            (
                "apple/App.icon/icon.json",
                br#"{"fill":"automatic","groups":[{"layers":[{"image-name":"Shape.svg","name":"Shape","glass":true}]}]}"#.to_vec(),
            ),
            ("apple/App.icon/Assets/Shape.svg", b"<svg/>".to_vec()),
            ("android/res/mipmap-anydpi-v26/ic_launcher.xml", b"<adaptive-icon/>".to_vec()),
            ("android/res/mipmap-hdpi/ic_launcher_foreground.png", png(162, 162)),
            ("android/res/mipmap-hdpi/ic_launcher_round.png", png(72, 72)),
            ("android/res/values/ic_launcher_background.xml", b"<resources/>".to_vec()),
            ("linux/hicolor/48x48/apps/app.png", png(48, 48)),
            ("linux/hicolor/256x256/apps/app.png", png(256, 256)),
            ("linux/hicolor/scalable/apps/app.svg", b"<svg/>".to_vec()),
            ("linux/hicolor/symbolic/apps/app-symbolic.svg", b"<svg/>".to_vec()),
            ("web/favicon.svg", b"<svg/>".to_vec()),
            ("web/apple-touch-icon.png", png(180, 180)),
            ("web/site.webmanifest", b"{}".to_vec()),
            (
                "tv/App.brandassets/Contents.json",
                br#"{"assets":[{"filename":"App Icon.imagestack","idiom":"tv","role":"primary-app-icon","size":"400x240"}]}"#.to_vec(),
            ),
            (
                "tv/App.brandassets/App Icon.imagestack/Contents.json",
                br#"{"layers":[{"filename":"Front.imagestacklayer"},{"filename":"Back.imagestacklayer"}]}"#.to_vec(),
            ),
            (
                "tv/App.brandassets/App Icon.imagestack/Front.imagestacklayer/Content.imageset/Contents.json",
                br#"{"images":[{"filename":"front.png","idiom":"tv"}]}"#.to_vec(),
            ),
            (
                "tv/App.brandassets/App Icon.imagestack/Front.imagestacklayer/Content.imageset/front.png",
                png(400, 240),
            ),
            (
                "tv/App.brandassets/App Icon.imagestack/Back.imagestacklayer/Content.imageset/Contents.json",
                br#"{"images":[{"filename":"back.png","idiom":"tv"}]}"#.to_vec(),
            ),
            (
                "tv/App.brandassets/App Icon.imagestack/Back.imagestacklayer/Content.imageset/back.png",
                png(400, 240),
            ),
        ];
        let (every, platforms, errors) = check_icons(
            &files,
            r#"{ default = "icon.png", macos = "mac/App.icns", windows = "win/app.ico", ios = "ios/AppIcon.appiconset", tvos = "tv/App.brandassets", android = "android/res", linux = "linux/hicolor", browser = "web" }"#,
        );
        assert!(errors.is_empty(), "{errors:?}");
        assert_eq!(every.as_deref(), Some("icon.png"));
        assert_eq!(platforms.len(), 7);
        assert_eq!(platforms["linux"], "linux/hicolor");
        // A platform can also take another PNG, and needs no `default`.
        let (every, platforms, errors) = check_icons(&files, r#"{ android = "icon.png" }"#);
        assert!(errors.is_empty(), "{errors:?}");
        assert_eq!(every, None);
        assert_eq!(platforms["android"], "icon.png");
        // An Icon Composer document serves macOS and iOS alike.
        let (_, platforms, errors) = check_icons(
            &files,
            r#"{ macos = "apple/App.icon", ios = "apple/App.icon" }"#,
        );
        assert!(errors.is_empty(), "{errors:?}");
        assert_eq!(platforms["macos"], "apple/App.icon");
        assert_eq!(platforms["ios"], "apple/App.icon");

        for (extra, value, expected) in [
            (vec![], r#"{ watchos = "icon.png" }"#, "not a platform"),
            (vec![], r#"{ tvos = "win/app.ico" }"#, "`.brandassets`"),
            (
                vec![(
                    "tv/App.brandassets/App Icon.imagestack/Contents.json",
                    br#"{"layers":[{"filename":"Front.imagestacklayer"}]}"#.to_vec(),
                )],
                r#"{ tvos = "tv/App.brandassets" }"#,
                "two to five",
            ),
            (vec![], r#"{ macos = "win/app.ico" }"#, "`.icns`"),
            (vec![], r#"{ default = "mac/App.icns" }"#, "not a PNG"),
            (vec![], r#"{ windows = "web" }"#, "`.ico`"),
            (
                vec![("bad.icns", b"icns\0\0\0\x40".to_vec())],
                r#"{ macos = "bad.icns" }"#,
                "bytes long",
            ),
            (
                vec![("android/res/values/strings.xml", b"<resources/>".to_vec())],
                r#"{ android = "android/res" }"#,
                "Bern writes itself",
            ),
            (
                vec![("other/res/mipmap-hdpi/ic_foo.png", png(72, 72))],
                r#"{ android = "other/res" }"#,
                "ic_launcher",
            ),
            (
                vec![("linux/hicolor/64x64/apps/app.png", png(48, 48))],
                r#"{ linux = "linux/hicolor" }"#,
                "48 × 48 pixels, not 64 × 64",
            ),
            (
                vec![("linux/hicolor/32x32/apps/other.png", png(32, 32))],
                r#"{ linux = "linux/hicolor" }"#,
                "one icon",
            ),
            (
                vec![(
                    "ios/AppIcon.appiconset/Contents.json",
                    br#"{"images":[{"filename":"Gone.png"}]}"#.to_vec(),
                )],
                r#"{ ios = "ios/AppIcon.appiconset" }"#,
                "Gone.png",
            ),
            (
                vec![("web/notes.txt", b"x".to_vec())],
                r#"{ browser = "web" }"#,
                "notes.txt",
            ),
            (
                vec![(
                    "apple/App.icon/icon.json",
                    br#"{"groups":[{"layers":[{"image-name":"Gone.svg"}]}]}"#.to_vec(),
                )],
                r#"{ macos = "apple/App.icon" }"#,
                "Gone.svg",
            ),
            (vec![], r#"{ windows = "apple/App.icon" }"#, "`.ico`"),
        ] {
            let mut all = files.clone();
            all.retain(|(path, _)| !extra.iter().any(|(other, _)| other == path));
            all.extend(extra);
            let (_, platforms, errors) = check_icons(&all, value);
            assert_eq!(errors.len(), 1, "{value}: {errors:?}");
            assert!(platforms.is_empty(), "{value}");
            assert!(
                errors[0].message.contains(expected),
                "{value}: {}",
                errors[0].message
            );
        }
    }
}