bamts-compiler 0.1.0

//! Compiler-owned whole-program loading and canonical module identity.

use std::{
    collections::{BTreeMap, BTreeSet, HashMap, HashSet},
    fmt, fs, io,
    path::{Path, PathBuf},
    sync::Arc,
};

use bamts_bytecode::{
    Binding, BindingId, BindingKind, Constant, ConstantId, EcmaString, EcmaStringBuilder, Edge,
    EdgeId, EdgeKind, EdgeTarget, Export, ExportSource, ModuleId, Program as BytecodeProgram,
    ProgramModule, ProgramVerifyError, Verified,
};

use crate::{
    lower::{self, LowerError, LowerOptions},
    parser,
    pipeline::ProgramFrontendOutput,
    project::{
        CompilerOptions, ModuleResolutionError, PackageError, PackageJson, PackageMode,
        PackageTarget, ProjectRoot, ResolutionConditions, ResolutionFlavor, plan_relative_module,
    },
    scanner,
    source::{ScriptKind, SourceId, SourceIdentity, SourceText, TextRange, Utf16Pos},
    syntax::{
        ExportDeclaration, ExportDefaultValue, ExportNamedDeclaration, ExportSpecifierMode,
        ImportBinding, ImportSpecifierMode, ModuleExportName, SourceFile, Statement, TokenKind,
        VariableKind,
    },
};

/// The semantic role of one resolved module dependency.
#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
pub enum ModuleEdgeKind {
    StaticRuntime,
    TypeOnly,
    DynamicRuntime,
}

/// The canonical identity of a resolved module dependency.
#[derive(Clone, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
pub enum ModuleTarget {
    Local(SourceId),
    External(Arc<str>),
}

impl ModuleTarget {
    #[must_use]
    pub const fn local_source_id(&self) -> Option<SourceId> {
        match self {
            Self::Local(source_id) => Some(*source_id),
            Self::External(_) => None,
        }
    }

    #[must_use]
    pub fn external_specifier(&self) -> Option<&str> {
        match self {
            Self::Local(_) => None,
            Self::External(specifier) => Some(specifier),
        }
    }
}

/// One source-anchored, resolved dependency.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct ModuleEdge {
    kind: ModuleEdgeKind,
    specifier: Arc<str>,
    target: ModuleTarget,
    range: TextRange,
}

impl ModuleEdge {
    #[must_use]
    pub const fn kind(&self) -> ModuleEdgeKind {
        self.kind
    }

    #[must_use]
    pub fn specifier(&self) -> &str {
        &self.specifier
    }

    #[must_use]
    pub const fn target(&self) -> &ModuleTarget {
        &self.target
    }

    #[must_use]
    pub const fn range(&self) -> TextRange {
        self.range
    }
}

/// A module loaded exactly once under its canonical filesystem identity.
#[derive(Clone, Debug)]
pub struct ResolvedModule {
    identity: SourceIdentity,
    script_kind: ScriptKind,
    source: Arc<SourceText>,
    dependencies: Arc<[ModuleEdge]>,
}

impl ResolvedModule {
    #[must_use]
    pub const fn identity(&self) -> &SourceIdentity {
        &self.identity
    }

    #[must_use]
    pub const fn source_id(&self) -> SourceId {
        self.identity.source_id()
    }

    #[must_use]
    pub fn path(&self) -> &Path {
        self.identity.path()
    }

    #[must_use]
    pub const fn script_kind(&self) -> ScriptKind {
        self.script_kind
    }

    #[must_use]
    pub const fn source(&self) -> &Arc<SourceText> {
        &self.source
    }

    #[must_use]
    pub fn dependencies(&self) -> &[ModuleEdge] {
        &self.dependencies
    }
}

/// The canonical whole-program value shared by every compiler and execution phase.
///
/// Modules are stored in deterministic dependency-first DFS postorder. Cycles are
/// retained as ordinary edges; each canonical file still appears exactly once.
#[derive(Clone, Debug)]
pub struct ResolvedProgram {
    root: ProjectRoot,
    entrypoint: SourceId,
    modules: Arc<[ResolvedModule]>,
    module_indices: HashMap<SourceId, usize>,
}

impl ResolvedProgram {
    #[must_use]
    pub const fn root(&self) -> &ProjectRoot {
        &self.root
    }

    #[must_use]
    pub const fn entrypoint_id(&self) -> SourceId {
        self.entrypoint
    }

    #[must_use]
    pub fn entrypoint(&self) -> &ResolvedModule {
        self.module(self.entrypoint)
            .expect("resolved program always contains its entrypoint")
    }

    #[must_use]
    pub fn modules(&self) -> &[ResolvedModule] {
        &self.modules
    }

    #[must_use]
    pub fn module(&self, source_id: SourceId) -> Option<&ResolvedModule> {
        self.module_indices
            .get(&source_id)
            .map(|index| &self.modules[*index])
    }

    /// Returns the eager runtime closure in the program's canonical order.
    /// Type-only, dynamic, and external edges do not cause eager runtime initialization.
    #[must_use]
    pub fn runtime_modules(&self) -> Vec<&ResolvedModule> {
        let mut reachable = HashSet::new();
        let mut pending = vec![self.entrypoint];
        while let Some(source_id) = pending.pop() {
            if !reachable.insert(source_id) {
                continue;
            }
            let module = self
                .module(source_id)
                .expect("every local edge target belongs to the resolved program");
            pending.extend(module.dependencies().iter().filter_map(|edge| {
                match (edge.kind, edge.target()) {
                    (ModuleEdgeKind::StaticRuntime, ModuleTarget::Local(source_id)) => {
                        Some(*source_id)
                    }
                    _ => None,
                }
            }));
        }
        self.modules
            .iter()
            .filter(|module| reachable.contains(&module.source_id()))
            .collect()
    }
}

/// A typed module-resolution failure anchored at the importing source.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct UnresolvedModuleDiagnostic {
    importer: Arc<Path>,
    specifier: Arc<str>,
    kind: ModuleEdgeKind,
    range: TextRange,
}

impl UnresolvedModuleDiagnostic {
    #[must_use]
    pub fn importer(&self) -> &Path {
        &self.importer
    }

    #[must_use]
    pub fn specifier(&self) -> &str {
        &self.specifier
    }

    #[must_use]
    pub const fn kind(&self) -> ModuleEdgeKind {
        self.kind
    }

    #[must_use]
    pub const fn range(&self) -> TextRange {
        self.range
    }
}

/// Fail-fast program loading errors. No partially resolved graph is exposed.
#[derive(Debug)]
pub enum ProgramLoadError {
    InvalidRoot(io::Error),
    EntryOutsideRoot(PathBuf),
    TraversalRejected {
        path: PathBuf,
        root: PathBuf,
    },
    Read {
        path: PathBuf,
        source: io::Error,
    },
    UnsupportedSource(PathBuf),
    TooManySources,
    IllFormedModuleSpecifier {
        importer: PathBuf,
        range: TextRange,
    },
    InvalidSpecifier {
        diagnostic: UnresolvedModuleDiagnostic,
        source: ModuleResolutionError,
    },
    InvalidPackage {
        diagnostic: UnresolvedModuleDiagnostic,
        source: PackageError,
    },
    UnresolvedModule(UnresolvedModuleDiagnostic),
}

impl fmt::Display for ProgramLoadError {
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::InvalidRoot(error) => {
                write!(formatter, "cannot canonicalize project root: {error}")
            }
            Self::EntryOutsideRoot(path) => {
                write!(
                    formatter,
                    "entrypoint {} is outside the project root",
                    path.display()
                )
            }
            Self::TraversalRejected { path, root } => write!(
                formatter,
                "resolved path {} escapes project root {}",
                path.display(),
                root.display()
            ),
            Self::Read { path, source } => {
                write!(formatter, "cannot read {}: {source}", path.display())
            }
            Self::UnsupportedSource(path) => {
                write!(
                    formatter,
                    "unsupported source extension: {}",
                    path.display()
                )
            }
            Self::TooManySources => {
                formatter.write_str("program contains more than u32::MAX sources")
            }
            Self::IllFormedModuleSpecifier { importer, .. } => write!(
                formatter,
                "module specifier in {} is not well-formed UTF-16",
                importer.display()
            ),
            Self::InvalidSpecifier { diagnostic, source } => write!(
                formatter,
                "invalid module specifier {:?} in {}: {source}",
                diagnostic.specifier(),
                diagnostic.importer().display()
            ),
            Self::InvalidPackage { diagnostic, source } => write!(
                formatter,
                "invalid package specifier {:?} in {}: {source}",
                diagnostic.specifier(),
                diagnostic.importer().display()
            ),
            Self::UnresolvedModule(diagnostic) => write!(
                formatter,
                "cannot resolve {:?} from {}",
                diagnostic.specifier(),
                diagnostic.importer().display()
            ),
        }
    }
}

impl std::error::Error for ProgramLoadError {
    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
        match self {
            Self::InvalidRoot(error) | Self::Read { source: error, .. } => Some(error),
            Self::InvalidSpecifier { source, .. } => Some(source),
            Self::InvalidPackage { source, .. } => Some(source),
            _ => None,
        }
    }
}

/// Loads one entrypoint and its complete local module graph.
#[derive(Clone, Debug)]
pub struct ProgramLoader {
    root: ProjectRoot,
    options: CompilerOptions,
}

impl ProgramLoader {
    /// Creates a loader using the project's already-validated compiler options.
    pub fn new(root: &ProjectRoot, options: &CompilerOptions) -> Result<Self, ProgramLoadError> {
        let canonical = fs::canonicalize(root.path()).map_err(ProgramLoadError::InvalidRoot)?;
        let root = ProjectRoot::new(canonical).map_err(|error| {
            ProgramLoadError::InvalidRoot(io::Error::new(io::ErrorKind::InvalidInput, error))
        })?;
        Ok(Self {
            root,
            options: options.clone(),
        })
    }

    /// Resolves and loads an entrypoint. The entrypoint may be root-relative or absolute.
    pub fn load(&self, entrypoint: impl AsRef<Path>) -> Result<ResolvedProgram, ProgramLoadError> {
        let requested = self
            .root
            .resolve(entrypoint.as_ref())
            .map_err(|_| ProgramLoadError::EntryOutsideRoot(entrypoint.as_ref().to_path_buf()))?;
        let entrypoint = self
            .select_absolute(&requested, ResolutionFlavor::Runtime)?
            .ok_or_else(|| ProgramLoadError::Read {
                path: requested,
                source: io::Error::new(io::ErrorKind::NotFound, "entrypoint does not exist"),
            })?;

        let mut state = LoadState {
            loader: self,
            identities: HashMap::new(),
            modules: Vec::new(),
        };
        let entrypoint = state.visit(entrypoint)?;
        let module_indices = state
            .modules
            .iter()
            .enumerate()
            .map(|(index, module)| (module.source_id(), index))
            .collect();
        Ok(ResolvedProgram {
            root: self.root.clone(),
            entrypoint,
            modules: Arc::from(state.modules),
            module_indices,
        })
    }

    fn select_absolute(
        &self,
        requested: &Path,
        flavor: ResolutionFlavor,
    ) -> Result<Option<PathBuf>, ProgramLoadError> {
        let relative = requested.strip_prefix(self.root.path()).map_err(|_| {
            ProgramLoadError::TraversalRejected {
                path: requested.to_path_buf(),
                root: self.root.path().to_path_buf(),
            }
        })?;
        let specifier = format!("./{}", relative.to_string_lossy().replace('\\', "/"));
        let synthetic_importer = self.root.path().join("__bamts_program__.ts");
        let plan = plan_relative_module(
            &self.root,
            synthetic_importer,
            &specifier,
            flavor,
            self.options.resolve_json_module(),
        )
        .map_err(|source| ProgramLoadError::InvalidSpecifier {
            diagnostic: diagnostic(
                self.root.path(),
                &specifier,
                edge_kind(flavor),
                TextRange::new(Utf16Pos::ZERO, Utf16Pos::ZERO)
                    .expect("equal range endpoints are valid"),
            ),
            source,
        })?;
        self.canonical_selection(plan.candidates(), flavor)
    }

    fn canonical_selection(
        &self,
        candidates: &[PathBuf],
        flavor: ResolutionFlavor,
    ) -> Result<Option<PathBuf>, ProgramLoadError> {
        if flavor == ResolutionFlavor::Runtime {
            for candidate in candidates {
                if is_declaration_path(candidate) || !candidate.is_file() {
                    continue;
                }
                return self.canonical_candidate(candidate).map(Some);
            }
        }
        for candidate in candidates {
            if candidate.is_file() {
                return self.canonical_candidate(candidate).map(Some);
            }
        }
        Ok(None)
    }

    fn canonical_candidate(&self, candidate: &Path) -> Result<PathBuf, ProgramLoadError> {
        let canonical = fs::canonicalize(candidate).map_err(|source| ProgramLoadError::Read {
            path: candidate.to_path_buf(),
            source,
        })?;
        if !canonical.starts_with(self.root.path()) {
            return Err(ProgramLoadError::TraversalRejected {
                path: canonical,
                root: self.root.path().to_path_buf(),
            });
        }
        Ok(canonical)
    }

    fn resolve_edge(
        &self,
        importer: &Path,
        edge: &UnresolvedEdge,
    ) -> Result<ResolvedEdgeTarget, ProgramLoadError> {
        if edge.specifier.starts_with("node:") {
            return Ok(ResolvedEdgeTarget::External(Arc::clone(&edge.specifier)));
        }

        let flavor = match edge.kind {
            ModuleEdgeKind::TypeOnly => ResolutionFlavor::Types,
            ModuleEdgeKind::StaticRuntime | ModuleEdgeKind::DynamicRuntime => {
                ResolutionFlavor::Runtime
            }
        };
        let selected = if edge.specifier.starts_with("./") || edge.specifier.starts_with("../") {
            let plan = plan_relative_module(
                &self.root,
                importer,
                &edge.specifier,
                flavor,
                self.options.resolve_json_module(),
            )
            .map_err(|source| ProgramLoadError::InvalidSpecifier {
                diagnostic: diagnostic(importer, &edge.specifier, edge.kind, edge.range),
                source,
            })?;
            self.canonical_selection(plan.candidates(), flavor)?
                .map(ResolvedEdgeTarget::Local)
        } else if edge.specifier.starts_with('#') {
            self.resolve_package_import(importer, edge, flavor)?
        } else {
            match self.resolve_mapped(&edge.specifier, flavor)? {
                Some(mapped) => Some(ResolvedEdgeTarget::Local(mapped)),
                None => self
                    .resolve_package(importer, edge, flavor)?
                    .map(ResolvedEdgeTarget::Local),
            }
        };
        if let Some(target) = selected {
            return Ok(target);
        }
        if edge.kind == ModuleEdgeKind::TypeOnly
            && split_package_specifier(&edge.specifier).is_some()
        {
            return Ok(ResolvedEdgeTarget::External(Arc::clone(&edge.specifier)));
        }
        Err(ProgramLoadError::UnresolvedModule(diagnostic(
            importer,
            &edge.specifier,
            edge.kind,
            edge.range,
        )))
    }

    fn resolve_mapped(
        &self,
        specifier: &str,
        flavor: ResolutionFlavor,
    ) -> Result<Option<PathBuf>, ProgramLoadError> {
        for mapping in self.options.paths() {
            let Some(capture) = pattern_capture(mapping.pattern(), specifier) else {
                continue;
            };
            for target in mapping.targets() {
                let target = PathBuf::from(target.to_string_lossy().replace('*', capture));
                if let Some(selected) = self.select_absolute(&target, flavor)? {
                    return Ok(Some(selected));
                }
            }
        }
        Ok(None)
    }

    fn resolve_package(
        &self,
        importer: &Path,
        edge: &UnresolvedEdge,
        flavor: ResolutionFlavor,
    ) -> Result<Option<PathBuf>, ProgramLoadError> {
        let Some((package_name, subpath)) = split_package_specifier(&edge.specifier) else {
            return Ok(None);
        };
        let mut directory = importer.parent();
        while let Some(current) = directory {
            if !current.starts_with(self.root.path()) {
                break;
            }
            let package_directory = current.join("node_modules").join(package_name);
            let package_path = package_directory.join("package.json");
            if package_path.is_file() {
                let package_source =
                    fs::read_to_string(&package_path).map_err(|source| ProgramLoadError::Read {
                        path: package_path.clone(),
                        source,
                    })?;
                let package = PackageJson::parse(&self.root, &package_path, &package_source)
                    .map_err(|source| ProgramLoadError::InvalidPackage {
                        diagnostic: diagnostic(importer, &edge.specifier, edge.kind, edge.range),
                        source,
                    })?;
                let mode = if flavor == ResolutionFlavor::Types {
                    PackageMode::Types
                } else {
                    PackageMode::Import
                };
                let conditions = ResolutionConditions::for_mode(mode);
                let target = package
                    .resolve_export(&self.root, &subpath, mode, &conditions)
                    .map_err(|source| ProgramLoadError::InvalidPackage {
                        diagnostic: diagnostic(importer, &edge.specifier, edge.kind, edge.range),
                        source,
                    })?;
                return self.select_absolute(&target, flavor);
            }
            if current == self.root.path() {
                break;
            }
            directory = current.parent();
        }
        Ok(None)
    }
    fn resolve_package_import(
        &self,
        importer: &Path,
        edge: &UnresolvedEdge,
        flavor: ResolutionFlavor,
    ) -> Result<Option<ResolvedEdgeTarget>, ProgramLoadError> {
        let mut directory = importer.parent();
        while let Some(current) = directory {
            if !current.starts_with(self.root.path()) {
                break;
            }
            let package_path = current.join("package.json");
            if package_path.is_file() {
                let package_source =
                    fs::read_to_string(&package_path).map_err(|source| ProgramLoadError::Read {
                        path: package_path.clone(),
                        source,
                    })?;
                let package = PackageJson::parse(&self.root, &package_path, &package_source)
                    .map_err(|source| ProgramLoadError::InvalidPackage {
                        diagnostic: diagnostic(importer, &edge.specifier, edge.kind, edge.range),
                        source,
                    })?;
                let mode = if flavor == ResolutionFlavor::Types {
                    PackageMode::Types
                } else {
                    PackageMode::Import
                };
                let conditions = ResolutionConditions::for_mode(mode);
                let target = package
                    .resolve_import(&self.root, &edge.specifier, &conditions)
                    .map_err(|source| ProgramLoadError::InvalidPackage {
                        diagnostic: diagnostic(importer, &edge.specifier, edge.kind, edge.range),
                        source,
                    })?;
                return match target {
                    PackageTarget::Path(path) => Ok(self
                        .select_absolute(&path, flavor)?
                        .map(ResolvedEdgeTarget::Local)),
                    PackageTarget::External(specifier) => {
                        let external = UnresolvedEdge {
                            kind: edge.kind,
                            specifier,
                            range: edge.range,
                        };
                        match self.resolve_mapped(&external.specifier, flavor)? {
                            Some(mapped) => Ok(Some(ResolvedEdgeTarget::Local(mapped))),
                            None => match self.resolve_package(importer, &external, flavor)? {
                                Some(package) => Ok(Some(ResolvedEdgeTarget::Local(package))),
                                None => Ok(Some(ResolvedEdgeTarget::External(external.specifier))),
                            },
                        }
                    }
                };
            }
            if current == self.root.path() {
                break;
            }
            directory = current.parent();
        }
        Ok(None)
    }
}

#[derive(Clone, Debug)]
enum ResolvedEdgeTarget {
    Local(PathBuf),
    External(Arc<str>),
}

struct LoadState<'a> {
    loader: &'a ProgramLoader,
    identities: HashMap<PathBuf, SourceId>,
    modules: Vec<ResolvedModule>,
}

impl LoadState<'_> {
    fn visit(&mut self, path: PathBuf) -> Result<SourceId, ProgramLoadError> {
        if let Some(source_id) = self.identities.get(&path) {
            return Ok(*source_id);
        }
        let source_id = SourceId::new(
            u32::try_from(self.identities.len()).map_err(|_| ProgramLoadError::TooManySources)?,
        );
        self.identities.insert(path.clone(), source_id);

        let script_kind =
            script_kind(&path).ok_or_else(|| ProgramLoadError::UnsupportedSource(path.clone()))?;
        let text = fs::read_to_string(&path).map_err(|source| ProgramLoadError::Read {
            path: path.clone(),
            source,
        })?;
        let source = Arc::new(SourceText::new(text));
        let parsed = parser::parse(scanner::scan(source_id, script_kind, Arc::clone(&source)));
        let unresolved = collect_edges(parsed.product()).map_err(|range| {
            ProgramLoadError::IllFormedModuleSpecifier {
                importer: path.clone(),
                range,
            }
        })?;
        let mut dependencies = Vec::with_capacity(unresolved.len());
        for edge in unresolved {
            let target = match self.loader.resolve_edge(&path, &edge)? {
                ResolvedEdgeTarget::Local(target_path) => {
                    ModuleTarget::Local(self.visit(target_path)?)
                }
                ResolvedEdgeTarget::External(specifier) => ModuleTarget::External(specifier),
            };
            dependencies.push(ModuleEdge {
                kind: edge.kind,
                specifier: edge.specifier,
                target,
                range: edge.range,
            });
        }
        self.modules.push(ResolvedModule {
            identity: SourceIdentity::new(source_id, Arc::from(path)),
            script_kind,
            source,
            dependencies: Arc::from(dependencies),
        });
        Ok(source_id)
    }
}

#[derive(Clone, Debug)]
struct UnresolvedEdge {
    kind: ModuleEdgeKind,
    specifier: Arc<str>,
    range: TextRange,
}

fn collect_edges(source: &SourceFile) -> Result<Vec<UnresolvedEdge>, TextRange> {
    let mut edges = Vec::new();
    for statement in source.statements() {
        match statement.data() {
            Statement::Import(import) => {
                let kind = if import.type_only || import_clause_is_type_only(import.clause.as_ref())
                {
                    ModuleEdgeKind::TypeOnly
                } else {
                    ModuleEdgeKind::StaticRuntime
                };
                push_literal_edge(source, &mut edges, kind, &import.source)?;
            }
            Statement::ImportEquals(import) => {
                if let crate::syntax::ExternalModuleReference::Require(specifier) =
                    &import.reference
                {
                    let kind = if import.is_type_only {
                        ModuleEdgeKind::TypeOnly
                    } else {
                        ModuleEdgeKind::StaticRuntime
                    };
                    push_literal_edge(source, &mut edges, kind, specifier)?;
                }
            }
            Statement::Export(ExportDeclaration::All(export)) => {
                let kind = if export.type_only {
                    ModuleEdgeKind::TypeOnly
                } else {
                    ModuleEdgeKind::StaticRuntime
                };
                push_literal_edge(source, &mut edges, kind, &export.source)?;
            }
            Statement::Export(ExportDeclaration::Named(ExportNamedDeclaration::Specifiers {
                type_only,
                specifiers,
                source: Some(module),
                ..
            })) => {
                let only_types = *type_only
                    || (!specifiers.is_empty()
                        && specifiers.iter().all(|specifier| {
                            specifier.data().mode == ExportSpecifierMode::TypeOnly
                        }));
                push_literal_edge(
                    source,
                    &mut edges,
                    if only_types {
                        ModuleEdgeKind::TypeOnly
                    } else {
                        ModuleEdgeKind::StaticRuntime
                    },
                    module,
                )?;
            }
            _ => {}
        }
    }
    let ill_formed = {
        let mut collector = DynamicEdgeCollector {
            source,
            edges: &mut edges,
            ill_formed: None,
        };
        collector.scan_statements(source.statements());
        collector.ill_formed
    };
    if let Some(range) = ill_formed {
        return Err(range);
    }
    let tokens: Vec<_> = source
        .tokens()
        .iter()
        .filter(|token| {
            !matches!(
                token.kind(),
                TokenKind::Whitespace
                    | TokenKind::LineComment
                    | TokenKind::BlockComment
                    | TokenKind::Shebang
            )
        })
        .collect();
    for window in tokens.windows(3) {
        if window[0].kind() != TokenKind::KwImport
            || window[1].kind() != TokenKind::LParen
            || window[2].kind() != TokenKind::StringLiteral
            || edges.iter().any(|edge| edge.range == window[2].range())
        {
            continue;
        }
        let Some(value) = source.token_text(window[2]).and_then(unquote) else {
            continue;
        };
        let specifier = value.to_utf8_strict().map_err(|_| window[2].range())?;
        edges.push(UnresolvedEdge {
            kind: ModuleEdgeKind::TypeOnly,
            specifier: Arc::from(specifier),
            range: window[2].range(),
        });
    }
    Ok(edges)
}

struct DynamicEdgeCollector<'a> {
    source: &'a SourceFile,
    edges: &'a mut Vec<UnresolvedEdge>,
    ill_formed: Option<TextRange>,
}

impl DynamicEdgeCollector<'_> {
    fn push_literal_edge(
        &mut self,
        kind: ModuleEdgeKind,
        literal: &crate::syntax::StringLiteralNode,
    ) {
        if self.ill_formed.is_none() {
            self.ill_formed = push_literal_edge(self.source, self.edges, kind, literal).err();
        }
    }

    fn scan_statements(&mut self, statements: &[crate::syntax::Stmt]) {
        for statement in statements {
            self.scan_statement(statement);
        }
    }

    fn scan_statement(&mut self, statement: &crate::syntax::Stmt) {
        use crate::syntax::{ExportDefaultValue, ForInitializer, Statement};

        match statement.data() {
            Statement::Variable(declaration) => {
                for declarator in &declaration.declarations {
                    self.scan_pattern(&declarator.data().binding);
                    if let Some(initializer) = &declarator.data().initializer {
                        self.scan_expression(initializer);
                    }
                }
            }
            Statement::Function(declaration) => self.scan_function(&declaration.function),
            Statement::Class(class) => self.scan_class(class),
            Statement::Namespace(namespace) => {
                self.scan_statements(&namespace.body.data().statements)
            }
            Statement::Declare(inner)
            | Statement::Labeled(crate::syntax::LabeledStatement { body: inner, .. }) => {
                self.scan_statement(inner)
            }
            Statement::Block(block) => self.scan_statements(&block.data().statements),
            Statement::Expression(expression) => self.scan_expression(&expression.expression),
            Statement::If(value) => {
                self.scan_expression(&value.test);
                self.scan_statement(&value.consequent);
                if let Some(alternate) = &value.alternate {
                    self.scan_statement(alternate);
                }
            }
            Statement::Switch(value) => {
                self.scan_expression(&value.discriminant);
                for case in &value.cases {
                    if let Some(test) = &case.data().test {
                        self.scan_expression(test);
                    }
                    self.scan_statements(&case.data().consequent);
                }
            }
            Statement::For(value) => {
                if let Some(initializer) = &value.initializer {
                    match initializer {
                        ForInitializer::Variable(declaration) => {
                            for declarator in &declaration.declarations {
                                self.scan_pattern(&declarator.data().binding);
                                if let Some(initializer) = &declarator.data().initializer {
                                    self.scan_expression(initializer);
                                }
                            }
                        }
                        ForInitializer::Expression(expression) => self.scan_expression(expression),
                    }
                }
                if let Some(test) = &value.test {
                    self.scan_expression(test);
                }
                if let Some(update) = &value.update {
                    self.scan_expression(update);
                }
                self.scan_statement(&value.body);
            }
            Statement::ForIn(value) => {
                self.scan_for_binding(&value.binding);
                self.scan_expression(&value.object);
                self.scan_statement(&value.body);
            }
            Statement::ForOf(value) => {
                self.scan_for_binding(&value.binding);
                self.scan_expression(&value.iterable);
                self.scan_statement(&value.body);
            }
            Statement::While(value) => {
                self.scan_expression(&value.test);
                self.scan_statement(&value.body);
            }
            Statement::DoWhile(value) => {
                self.scan_statement(&value.body);
                self.scan_expression(&value.test);
            }
            Statement::Try(value) => {
                self.scan_statements(&value.block.data().statements);
                if let Some(handler) = &value.handler {
                    if let Some(binding) = &handler.data().binding {
                        self.scan_pattern(binding);
                    }
                    self.scan_statements(&handler.data().body.data().statements);
                }
                if let Some(finalizer) = &value.finalizer {
                    self.scan_statements(&finalizer.data().statements);
                }
            }
            Statement::With(value) => {
                self.scan_expression(&value.object);
                self.scan_statement(&value.body);
            }
            Statement::Return(value) => {
                if let Some(argument) = &value.argument {
                    self.scan_expression(argument);
                }
            }
            Statement::Throw(value) => self.scan_expression(&value.argument),
            Statement::Export(ExportDeclaration::Named(ExportNamedDeclaration::Declaration(
                inner,
            ))) => self.scan_statement(inner),
            Statement::Export(ExportDeclaration::Default(value)) => match &value.value {
                ExportDefaultValue::Function(function) => self.scan_function(function),
                ExportDefaultValue::Class(class) => self.scan_class(class),
                ExportDefaultValue::Expression(expression) => self.scan_expression(expression),
                ExportDefaultValue::Missing(_) => {}
            },
            Statement::Export(ExportDeclaration::Assignment(expression)) => {
                self.scan_expression(expression)
            }
            _ => {}
        }
    }

    fn scan_for_binding(&mut self, binding: &crate::syntax::ForBinding) {
        match binding {
            crate::syntax::ForBinding::Variable(declaration) => {
                for declarator in &declaration.declarations {
                    self.scan_pattern(&declarator.data().binding);
                    if let Some(initializer) = &declarator.data().initializer {
                        self.scan_expression(initializer);
                    }
                }
            }
            crate::syntax::ForBinding::Target(target) => self.scan_target(target),
        }
    }

    fn scan_parameters(&mut self, parameters: &[crate::syntax::ParameterNode]) {
        for parameter in parameters {
            for decorator in &parameter.data().decorators {
                self.scan_expression(&decorator.data().expression);
            }
            self.scan_pattern(&parameter.data().binding);
            if let Some(initializer) = &parameter.data().initializer {
                self.scan_expression(initializer);
            }
        }
    }

    fn scan_pattern(&mut self, pattern: &crate::syntax::Pattern) {
        use crate::syntax::{ArrayBindingElement, BindingPattern, PropertyName};
        match pattern.data() {
            BindingPattern::Object(object) => {
                for property in &object.properties {
                    if let PropertyName::Computed(expression) = &property.name {
                        self.scan_expression(expression);
                    }
                    if let Some(initializer) = &property.initializer {
                        self.scan_expression(initializer);
                    }
                    self.scan_pattern(&property.binding);
                }
            }
            BindingPattern::Array(array) => {
                for element in &array.elements {
                    if let ArrayBindingElement::Binding(inner) = element {
                        self.scan_pattern(inner);
                    }
                }
            }
            BindingPattern::Rest(rest) => self.scan_pattern(&rest.argument),
            BindingPattern::Assignment(value) => {
                self.scan_pattern(&value.left);
                self.scan_expression(&value.right);
            }
            BindingPattern::Identifier(_) | BindingPattern::Missing(_) => {}
        }
    }

    fn scan_function(&mut self, function: &crate::syntax::FunctionLike) {
        self.scan_parameters(&function.parameters);
        if let Some(body) = &function.body {
            match body {
                crate::syntax::FunctionBody::Block(block) => {
                    self.scan_statements(&block.data().statements)
                }
                crate::syntax::FunctionBody::Expression(expression) => {
                    self.scan_expression(expression)
                }
                crate::syntax::FunctionBody::Missing(_) => {}
            }
        }
    }

    fn scan_class(&mut self, class: &crate::syntax::ClassDeclaration) {
        use crate::syntax::{ClassMember, PropertyName};
        for decorator in &class.decorators {
            self.scan_expression(&decorator.data().expression);
        }
        if let Some(heritage) = &class.extends {
            self.scan_expression(&heritage.expression);
        }
        for member in &class.members {
            match member.data() {
                ClassMember::Constructor(value) => {
                    self.scan_parameters(&value.parameters);
                    self.scan_statements(&value.body.data().statements);
                }
                ClassMember::Method(value) => {
                    if let PropertyName::Computed(expression) = &value.name {
                        self.scan_expression(expression);
                    }
                    self.scan_function(&value.function);
                }
                ClassMember::Property(value) => {
                    if let PropertyName::Computed(expression) = &value.name {
                        self.scan_expression(expression);
                    }
                    if let Some(initializer) = &value.initializer {
                        self.scan_expression(initializer);
                    }
                }
                ClassMember::AutoAccessor(value) => {
                    if let PropertyName::Computed(expression) = &value.name {
                        self.scan_expression(expression);
                    }
                    if let Some(initializer) = &value.initializer {
                        self.scan_expression(initializer);
                    }
                }
                ClassMember::StaticBlock(block) => self.scan_statements(&block.data().statements),
                ClassMember::IndexSignature(_) | ClassMember::Missing(_) => {}
            }
        }
    }

    fn scan_expression(&mut self, expression: &crate::syntax::Expr) {
        use crate::syntax::{
            ArrayElement, Expression, Literal, MemberProperty, ObjectMember, PropertyName,
        };
        match expression.data() {
            Expression::Template(value) => {
                for expression in &value.expressions {
                    self.scan_expression(expression);
                }
            }
            Expression::TaggedTemplate(value) => {
                self.scan_expression(&value.tag);
                for expression in &value.template.expressions {
                    self.scan_expression(expression);
                }
            }
            Expression::Array(value) => {
                for element in &value.elements {
                    match element {
                        ArrayElement::Expression(value) => self.scan_expression(value),
                        ArrayElement::Spread(value) => self.scan_expression(&value.argument),
                        _ => {}
                    }
                }
            }
            Expression::Object(value) => {
                for member in &value.members {
                    match member.data() {
                        ObjectMember::Property(value) => {
                            if let PropertyName::Computed(key) = &value.name {
                                self.scan_expression(key);
                            }
                            self.scan_expression(&value.value);
                        }
                        ObjectMember::Method(value) => {
                            if let PropertyName::Computed(key) = &value.name {
                                self.scan_expression(key);
                            }
                            self.scan_function(&value.function);
                        }
                        ObjectMember::Spread(value) => self.scan_expression(&value.argument),
                        ObjectMember::Missing(_) => {}
                    }
                }
            }
            Expression::Function(value) => self.scan_function(&value.function),
            Expression::Class(value) => self.scan_class(&value.class),
            Expression::Arrow(value) => {
                self.scan_parameters(&value.parameters);
                match &value.body {
                    crate::syntax::FunctionBody::Block(block) => {
                        self.scan_statements(&block.data().statements)
                    }
                    crate::syntax::FunctionBody::Expression(value) => self.scan_expression(value),
                    crate::syntax::FunctionBody::Missing(_) => {}
                }
            }
            Expression::Call(value) => {
                self.scan_expression(&value.callee);
                self.scan_arguments(&value.arguments);
            }
            Expression::New(value) => {
                self.scan_expression(&value.callee);
                self.scan_arguments(&value.arguments);
            }
            Expression::Member(value) => {
                self.scan_expression(&value.object);
                if let MemberProperty::Computed(value) = &value.property {
                    self.scan_expression(value);
                }
            }
            Expression::Await(value) => self.scan_expression(&value.argument),
            Expression::Yield(value) => {
                if let Some(argument) = &value.argument {
                    self.scan_expression(argument);
                }
            }
            Expression::Unary(value) => self.scan_expression(&value.argument),
            Expression::Update(value) => self.scan_target(&value.argument),
            Expression::Binary(value) => {
                self.scan_expression(&value.left);
                self.scan_expression(&value.right);
            }
            Expression::Logical(value) => {
                self.scan_expression(&value.left);
                self.scan_expression(&value.right);
            }
            Expression::Conditional(value) => {
                self.scan_expression(&value.test);
                self.scan_expression(&value.consequent);
                self.scan_expression(&value.alternate);
            }
            Expression::Assignment(value) => {
                self.scan_target(&value.left);
                self.scan_expression(&value.right);
            }
            Expression::Sequence(value) => {
                for expression in &value.expressions {
                    self.scan_expression(expression);
                }
            }
            Expression::Parenthesized(value) => self.scan_expression(value),
            Expression::As(value) => self.scan_expression(&value.expression),
            Expression::Satisfies(value) => self.scan_expression(&value.expression),
            Expression::TypeAssertion(value) => self.scan_expression(&value.expression),
            Expression::NonNull(value) => self.scan_expression(&value.expression),
            Expression::Import(value) => {
                if let Expression::Literal(Literal::String(literal)) = value.source.data() {
                    self.push_literal_edge(ModuleEdgeKind::DynamicRuntime, literal);
                }
                self.scan_expression(&value.source);
                if let Some(options) = &value.options {
                    self.scan_expression(options);
                }
            }
            Expression::Identifier(_)
            | Expression::This
            | Expression::Super
            | Expression::Literal(_)
            | Expression::Meta(_)
            | Expression::Missing(_) => {}
        }
    }

    fn scan_arguments(&mut self, arguments: &[crate::syntax::CallArgument]) {
        for argument in arguments {
            match argument {
                crate::syntax::CallArgument::Expression(value) => self.scan_expression(value),
                crate::syntax::CallArgument::Spread(value) => self.scan_expression(&value.argument),
                crate::syntax::CallArgument::Missing(_) => {}
            }
        }
    }

    fn scan_target(&mut self, target: &crate::syntax::AssignmentTargetNode) {
        use crate::syntax::{
            AssignmentArrayElement, AssignmentTarget, MemberProperty, PropertyName,
        };
        match target.data() {
            AssignmentTarget::Member(value) => {
                self.scan_expression(&value.object);
                if let MemberProperty::Computed(value) = &value.property {
                    self.scan_expression(value);
                }
            }
            AssignmentTarget::Object(value) => {
                for property in &value.properties {
                    if let PropertyName::Computed(key) = &property.name {
                        self.scan_expression(key);
                    }
                    if let Some(initializer) = &property.initializer {
                        self.scan_expression(initializer);
                    }
                    self.scan_target(&property.target);
                }
            }
            AssignmentTarget::Array(value) => {
                for element in &value.elements {
                    if let AssignmentArrayElement::Target(value) = element {
                        self.scan_target(value);
                    }
                }
            }
            AssignmentTarget::Identifier(_) | AssignmentTarget::Missing(_) => {}
        }
    }
}

fn import_clause_is_type_only(clause: Option<&crate::syntax::ImportClause>) -> bool {
    let Some(clause) = clause else {
        return false;
    };
    clause.default.is_none()
        && matches!(
            &clause.binding,
            Some(ImportBinding::Named(specifiers))
                if !specifiers.is_empty()
                    && specifiers.iter().all(|specifier| {
                        specifier.data().mode == ImportSpecifierMode::TypeOnly
                    })
        )
}

fn push_literal_edge(
    source: &SourceFile,
    edges: &mut Vec<UnresolvedEdge>,
    kind: ModuleEdgeKind,
    literal: &crate::syntax::StringLiteralNode,
) -> Result<(), TextRange> {
    let Some(value) = source.token_text(literal.data().token()).and_then(unquote) else {
        return Ok(());
    };
    let specifier = value.to_utf8_strict().map_err(|_| literal.range())?;
    edges.push(UnresolvedEdge {
        kind,
        specifier: Arc::from(specifier),
        range: literal.range(),
    });
    Ok(())
}

fn unquote(text: &str) -> Option<EcmaString> {
    let quote = text.as_bytes().first().copied()?;
    if !matches!(quote, b'\'' | b'"') || text.as_bytes().last().copied() != Some(quote) {
        return None;
    }
    let body = &text[1..text.len() - 1];
    let bytes = body.as_bytes();
    let mut output = EcmaStringBuilder::with_capacity(body.encode_utf16().count());
    let mut index = 0;
    while index < bytes.len() {
        if bytes[index] != b'\\' {
            let character = body[index..].chars().next()?;
            output.push_code_point(u32::from(character)).ok()?;
            index += character.len_utf8();
            continue;
        }
        index += 1;
        let escaped = *bytes.get(index)?;
        index += 1;
        match escaped {
            b'b' => output.push_unit(0x0008),
            b'f' => output.push_unit(0x000C),
            b'n' => output.push_unit(u16::from(b'\n')),
            b'r' => output.push_unit(u16::from(b'\r')),
            b't' => output.push_unit(u16::from(b'\t')),
            b'v' => output.push_unit(0x000B),
            b'0' => output.push_unit(0),
            b'\n' => {}
            b'\r' => {
                if bytes.get(index) == Some(&b'\n') {
                    index += 1;
                }
            }
            b'x' => {
                let value = parse_hex(bytes.get(index..index + 2)?)?;
                output.push_unit(value as u16);
                index += 2;
            }
            b'u' if bytes.get(index) == Some(&b'{') => {
                let end = bytes[index + 1..].iter().position(|byte| *byte == b'}')? + index + 1;
                let value = parse_hex(bytes.get(index + 1..end)?)?;
                output.push_code_point(value).ok()?;
                index = end + 1;
            }
            b'u' => {
                let value = parse_hex(bytes.get(index..index + 4)?)?;
                output.push_unit(value as u16);
                index += 4;
            }
            _ if escaped.is_ascii() => output.push_unit(u16::from(escaped)),
            _ => {
                let character = body[index - 1..].chars().next()?;
                output.push_code_point(u32::from(character)).ok()?;
                index += character.len_utf8() - 1;
            }
        }
    }
    Some(output.finish())
}

fn parse_hex(bytes: &[u8]) -> Option<u32> {
    if bytes.is_empty() {
        return None;
    }
    bytes.iter().try_fold(0_u32, |value, byte| {
        char::from(*byte)
            .to_digit(16)
            .map(|digit| value * 16 + digit)
    })
}

fn script_kind(path: &Path) -> Option<ScriptKind> {
    match path.extension()?.to_str()? {
        "ts" | "mts" | "cts" => Some(ScriptKind::TypeScript),
        "tsx" => Some(ScriptKind::TypeScriptReact),
        "js" | "mjs" | "cjs" => Some(ScriptKind::JavaScript),
        "jsx" => Some(ScriptKind::JavaScriptReact),
        "json" => Some(ScriptKind::Json),
        _ => None,
    }
}

fn is_declaration_path(path: &Path) -> bool {
    let name = path
        .file_name()
        .and_then(|name| name.to_str())
        .unwrap_or_default();
    name.ends_with(".d.ts") || name.ends_with(".d.mts") || name.ends_with(".d.cts")
}

fn pattern_capture<'a>(pattern: &str, specifier: &'a str) -> Option<&'a str> {
    let Some(star) = pattern.find('*') else {
        return (pattern == specifier).then_some("");
    };
    let (prefix, suffix_with_star) = pattern.split_at(star);
    let suffix = &suffix_with_star[1..];
    specifier.strip_prefix(prefix)?.strip_suffix(suffix)
}

fn split_package_specifier(specifier: &str) -> Option<(&str, String)> {
    if specifier.is_empty() || specifier.starts_with('/') || specifier.starts_with('#') {
        return None;
    }
    let component_count = if specifier.starts_with('@') { 2 } else { 1 };
    let mut boundaries = specifier.match_indices('/').map(|(index, _)| index);
    let boundary = if component_count == 1 {
        boundaries.next()
    } else {
        boundaries.nth(1)
    };
    match boundary {
        Some(index) => Some((
            &specifier[..index],
            format!("./{}", &specifier[index + 1..]),
        )),
        None if component_count == 1 || specifier.matches('/').count() == 1 => {
            Some((specifier, ".".to_owned()))
        }
        None => None,
    }
}

fn diagnostic(
    importer: &Path,
    specifier: &str,
    kind: ModuleEdgeKind,
    range: TextRange,
) -> UnresolvedModuleDiagnostic {
    UnresolvedModuleDiagnostic {
        importer: Arc::from(importer),
        specifier: Arc::from(specifier),
        kind,
        range,
    }
}

const fn edge_kind(flavor: ResolutionFlavor) -> ModuleEdgeKind {
    match flavor {
        ResolutionFlavor::Runtime => ModuleEdgeKind::StaticRuntime,
        ResolutionFlavor::Types => ModuleEdgeKind::TypeOnly,
    }
}

/// Compiler-only identity and resolved-edge provenance for one executable module.
#[derive(Clone, Debug)]
pub struct ExecutableModuleProvenance {
    module: ModuleId,
    source: SourceIdentity,
    edges: Arc<[ModuleEdge]>,
}

impl ExecutableModuleProvenance {
    #[must_use]
    pub const fn module(&self) -> ModuleId {
        self.module
    }

    #[must_use]
    pub const fn source(&self) -> &SourceIdentity {
        &self.source
    }

    /// Canonical compiler edges, including identities intentionally absent from the wire format.
    #[must_use]
    pub fn edges(&self) -> &[ModuleEdge] {
        &self.edges
    }

    pub fn type_only_edges(&self) -> impl Iterator<Item = &ModuleEdge> {
        self.edges
            .iter()
            .filter(|edge| edge.kind() == ModuleEdgeKind::TypeOnly)
    }
}

/// The compiler's sole executable product: one verified wire program plus non-wire provenance.
#[derive(Clone, Debug)]
pub struct ExecutableProgram {
    wire: BytecodeProgram<Verified>,
    provenance: Vec<ExecutableModuleProvenance>,
}

impl ExecutableProgram {
    #[must_use]
    pub const fn wire(&self) -> &BytecodeProgram<Verified> {
        &self.wire
    }

    #[must_use]
    pub fn provenance(&self) -> &[ExecutableModuleProvenance] {
        &self.provenance
    }
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum ProgramLowerPhase {
    Frontend,
    Metadata,
    Module,
    Link,
}

#[derive(Clone, Debug, Eq, PartialEq)]
pub enum ProgramLowerErrorKind {
    FrontendEntrypointMismatch {
        resolved: SourceId,
        frontend: SourceId,
    },
    MissingFrontend {
        source: SourceId,
    },
    UnexpectedFrontend {
        source: SourceId,
    },
    InvalidModuleName,
    IllFormedMetadataString,
    MissingRuntimeEdge {
        specifier: String,
    },
    ConflictingRuntimeEdge {
        specifier: String,
    },
    Lower(LowerError),
    Link(ProgramVerifyError),
}

/// A whole-program lowering failure anchored to a canonical module path and phase.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct ProgramLowerError {
    pub module: PathBuf,
    pub phase: ProgramLowerPhase,
    pub kind: ProgramLowerErrorKind,
}

impl fmt::Display for ProgramLowerError {
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(
            formatter,
            "program lowering failed in {} during {:?}: {:?}",
            self.module.display(),
            self.phase,
            self.kind
        )
    }
}

impl std::error::Error for ProgramLowerError {
    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
        match &self.kind {
            ProgramLowerErrorKind::Lower(error) => Some(error),
            ProgramLowerErrorKind::Link(error) => Some(error),
            _ => None,
        }
    }
}

#[derive(Clone)]
struct RawEdge {
    specifier: String,
    target: EdgeTarget,
    external_identity: Option<String>,
    kind: EdgeKind,
}

#[derive(Clone)]
enum RawBindingKind {
    Hoisted,
    Lexical,
    Imported { edge: EdgeId, name: String },
    Namespace { edge: EdgeId },
}

#[derive(Clone)]
struct RawBinding {
    name: String,
    kind: RawBindingKind,
}

#[derive(Clone)]
enum RawExportSource {
    Local(String),
    Indirect { edge: EdgeId, name: String },
}

#[derive(Clone)]
struct RawExport {
    name: String,
    source: RawExportSource,
}

struct RawModule {
    name: String,
    edges: Vec<RawEdge>,
    bindings: Vec<RawBinding>,
    exports: Vec<RawExport>,
    stars: Vec<EdgeId>,
}

#[derive(Clone, Debug, Eq, Ord, PartialEq, PartialOrd)]
enum ExportOrigin {
    Local(ModuleId, String),
    Indirect(ModuleId, String),
    External(String, String),
}

/// Lowers one canonical resolved program and its matching frontend products.
///
/// Static linkage becomes live metadata only. Dynamic imports remain instructions
/// backed by dynamic-capable edges.
///
/// # Errors
/// Returns a path- and phase-typed failure for frontend mismatch, metadata construction,
/// module lowering/verification, or final program linking.
pub fn lower_program(
    resolved: &ResolvedProgram,
    frontend: &ProgramFrontendOutput,
    options: LowerOptions,
) -> Result<ExecutableProgram, ProgramLowerError> {
    if frontend.entrypoint_id() != resolved.entrypoint_id() {
        return Err(program_lower_error(
            resolved.entrypoint().path(),
            ProgramLowerPhase::Frontend,
            ProgramLowerErrorKind::FrontendEntrypointMismatch {
                resolved: resolved.entrypoint_id(),
                frontend: frontend.entrypoint_id(),
            },
        ));
    }
    for output in frontend.modules() {
        let source = output.source_file().source_id();
        if resolved.module(source).is_none() {
            return Err(program_lower_error(
                resolved.entrypoint().path(),
                ProgramLowerPhase::Frontend,
                ProgramLowerErrorKind::UnexpectedFrontend { source },
            ));
        }
    }

    let module_ids: HashMap<_, _> = resolved
        .modules()
        .iter()
        .enumerate()
        .map(|(index, module)| (module.source_id(), ModuleId::new(index as u32)))
        .collect();
    let mut raw_modules = Vec::with_capacity(resolved.modules().len());
    for module in resolved.modules() {
        let output = frontend.module(module.source_id()).ok_or_else(|| {
            program_lower_error(
                module.path(),
                ProgramLowerPhase::Frontend,
                ProgramLowerErrorKind::MissingFrontend {
                    source: module.source_id(),
                },
            )
        })?;
        let name = normalized_module_name(resolved.root(), module.path()).ok_or_else(|| {
            program_lower_error(
                module.path(),
                ProgramLowerPhase::Metadata,
                ProgramLowerErrorKind::InvalidModuleName,
            )
        })?;
        raw_modules.push(collect_raw_module(
            module,
            output.source_file(),
            name,
            &module_ids,
        )?);
    }
    expand_star_exports(&mut raw_modules);

    let mut linked_modules = Vec::with_capacity(raw_modules.len());
    let mut provenance = Vec::with_capacity(raw_modules.len());
    for (index, (resolved_module, raw)) in resolved
        .modules()
        .iter()
        .zip(raw_modules.iter())
        .enumerate()
    {
        let file = frontend
            .module(resolved_module.source_id())
            .expect("frontend presence checked above")
            .source_file();
        let strings = linkage_strings(raw);
        let code = lower::assemble_program_module(file, options, &strings)
            .and_then(|module| {
                module.verify().map_err(|error| LowerError {
                    source: file.source_id(),
                    range: file.range(),
                    kind: lower::LowerErrorKind::Verify(error),
                })
            })
            .map_err(|error| {
                program_lower_error(
                    resolved_module.path(),
                    ProgramLowerPhase::Module,
                    ProgramLowerErrorKind::Lower(error),
                )
            })?;
        linked_modules.push(materialize_program_module(code, raw));
        provenance.push(ExecutableModuleProvenance {
            module: ModuleId::new(index as u32),
            source: resolved_module.identity().clone(),
            edges: Arc::from(resolved_module.dependencies()),
        });
    }
    let entry = module_ids[&resolved.entrypoint_id()];
    let wire = BytecodeProgram::link(linked_modules, entry).map_err(|error| {
        let path = error
            .module
            .and_then(|module| resolved.modules().get(module.get() as usize))
            .map_or_else(|| resolved.entrypoint().path(), ResolvedModule::path);
        program_lower_error(
            path,
            ProgramLowerPhase::Link,
            ProgramLowerErrorKind::Link(error),
        )
    })?;
    Ok(ExecutableProgram { wire, provenance })
}

fn collect_raw_module(
    module: &ResolvedModule,
    file: &SourceFile,
    name: String,
    module_ids: &HashMap<SourceId, ModuleId>,
) -> Result<RawModule, ProgramLowerError> {
    let mut edges: Vec<RawEdge> = Vec::new();
    let mut edge_ids: HashMap<String, EdgeId> = HashMap::new();
    for dependency in module
        .dependencies()
        .iter()
        .filter(|edge| edge.kind() != ModuleEdgeKind::TypeOnly)
    {
        let kind = match dependency.kind() {
            ModuleEdgeKind::StaticRuntime => EdgeKind::Static,
            ModuleEdgeKind::DynamicRuntime => EdgeKind::Dynamic,
            ModuleEdgeKind::TypeOnly => unreachable!("type-only edges were filtered"),
        };
        let (target, external_identity) = match dependency.target() {
            ModuleTarget::Local(source) => (EdgeTarget::Local(module_ids[source]), None),
            ModuleTarget::External(identity) => (EdgeTarget::External, Some(identity.to_string())),
        };
        if let Some(existing) = edge_ids.get(dependency.specifier()).copied() {
            let edge: &mut RawEdge = &mut edges[existing.get() as usize];
            if edge.target != target || edge.external_identity != external_identity {
                return Err(program_lower_error(
                    module.path(),
                    ProgramLowerPhase::Metadata,
                    ProgramLowerErrorKind::ConflictingRuntimeEdge {
                        specifier: dependency.specifier().to_owned(),
                    },
                ));
            }
            edge.kind = edge.kind.union(kind);
            continue;
        }
        let id = EdgeId::new(edges.len() as u32);
        edge_ids.insert(dependency.specifier().to_owned(), id);
        edges.push(RawEdge {
            specifier: dependency.specifier().to_owned(),
            target,
            external_identity,
            kind,
        });
    }

    let edge = |specifier: String| {
        edge_ids.get(&specifier).copied().ok_or_else(|| {
            program_lower_error(
                module.path(),
                ProgramLowerPhase::Metadata,
                ProgramLowerErrorKind::MissingRuntimeEdge { specifier },
            )
        })
    };
    let mut bindings = Vec::new();
    let mut hoisted = Vec::new();
    lower::collect_var_names(file, file.statements(), &mut hoisted);
    bindings.extend(hoisted.into_iter().map(|name| RawBinding {
        name,
        kind: RawBindingKind::Hoisted,
    }));
    let mut exports = Vec::new();
    let mut stars = Vec::new();
    for statement in file.statements() {
        collect_top_level_statement(
            module,
            file,
            statement.data(),
            &edge,
            &mut bindings,
            &mut exports,
            &mut stars,
        )?;
    }
    let mut hoisted_names = HashSet::new();
    bindings.retain(|binding| {
        !matches!(binding.kind, RawBindingKind::Hoisted)
            || hoisted_names.insert(binding.name.clone())
    });
    let binding_names: HashSet<_> = bindings
        .iter()
        .map(|binding| binding.name.as_str())
        .collect();
    exports.retain(|export| match &export.source {
        RawExportSource::Local(name) => binding_names.contains(name.as_str()),
        RawExportSource::Indirect { .. } => true,
    });
    Ok(RawModule {
        name,
        edges,
        bindings,
        exports,
        stars,
    })
}

fn collect_top_level_statement(
    module: &ResolvedModule,
    file: &SourceFile,
    statement: &Statement,
    edge: &impl Fn(String) -> Result<EdgeId, ProgramLowerError>,
    bindings: &mut Vec<RawBinding>,
    exports: &mut Vec<RawExport>,
    stars: &mut Vec<EdgeId>,
) -> Result<(), ProgramLowerError> {
    match statement {
        Statement::Import(import) if !import.type_only => {
            let runtime = import.clause.as_ref().is_none_or(|clause| {
                clause.default.is_some()
                    || !matches!(
                        &clause.binding,
                        Some(ImportBinding::Named(specifiers))
                            if specifiers.iter().all(|specifier| {
                                specifier.data().mode == ImportSpecifierMode::TypeOnly
                            })
                    )
            });
            if !runtime {
                return Ok(());
            }
            let edge_id = edge(metadata_string_literal(module, file, &import.source)?)?;
            if let Some(clause) = &import.clause {
                if let Some(default) = &clause.default {
                    bindings.push(RawBinding {
                        name: identifier(file, default),
                        kind: RawBindingKind::Imported {
                            edge: edge_id,
                            name: "default".to_owned(),
                        },
                    });
                }
                match &clause.binding {
                    Some(ImportBinding::Namespace(local)) => bindings.push(RawBinding {
                        name: identifier(file, local),
                        kind: RawBindingKind::Namespace { edge: edge_id },
                    }),
                    Some(ImportBinding::Named(specifiers)) => {
                        for specifier in specifiers {
                            let specifier = specifier.data();
                            if specifier.mode == ImportSpecifierMode::TypeOnly {
                                continue;
                            }
                            bindings.push(RawBinding {
                                name: identifier(file, &specifier.local),
                                kind: RawBindingKind::Imported {
                                    edge: edge_id,
                                    name: metadata_export_name(module, file, &specifier.imported)?,
                                },
                            });
                        }
                    }
                    None => {}
                }
            }
        }
        Statement::Variable(declaration)
            if matches!(declaration.kind, VariableKind::Let | VariableKind::Const) =>
        {
            for declarator in &declaration.declarations {
                let mut names = Vec::new();
                lower::collect_pattern_names(file, &declarator.data().binding, &mut names);
                bindings.extend(names.into_iter().map(|name| RawBinding {
                    name,
                    kind: RawBindingKind::Lexical,
                }));
            }
        }
        Statement::Function(declaration) => {
            if declaration.function.body.is_some()
                && let Some(name) = &declaration.function.name
            {
                bindings.push(RawBinding {
                    name: identifier(file, name),
                    kind: RawBindingKind::Hoisted,
                });
            }
        }
        Statement::Class(class) => {
            if let Some(name) = &class.name {
                bindings.push(RawBinding {
                    name: identifier(file, name),
                    kind: RawBindingKind::Lexical,
                });
            }
        }
        Statement::Export(export) => {
            collect_export(module, file, export, edge, bindings, exports, stars)?
        }
        _ => {}
    }
    Ok(())
}

fn collect_export(
    module: &ResolvedModule,
    file: &SourceFile,
    declaration: &ExportDeclaration,
    edge: &impl Fn(String) -> Result<EdgeId, ProgramLowerError>,
    bindings: &mut Vec<RawBinding>,
    exports: &mut Vec<RawExport>,
    stars: &mut Vec<EdgeId>,
) -> Result<(), ProgramLowerError> {
    match declaration {
        ExportDeclaration::Named(ExportNamedDeclaration::Declaration(statement)) => {
            collect_top_level_statement(
                module,
                file,
                statement.data(),
                edge,
                bindings,
                exports,
                stars,
            )?;
            let has_runtime_value = !matches!(
                statement.data(),
                Statement::Function(declaration) if declaration.function.body.is_none()
            );
            if has_runtime_value {
                for name in lower::declared_names(file, statement) {
                    exports.push(RawExport {
                        name: name.clone(),
                        source: RawExportSource::Local(name),
                    });
                }
            }
        }
        ExportDeclaration::Named(ExportNamedDeclaration::Specifiers {
            type_only,
            specifiers,
            source,
            ..
        }) if !type_only => {
            if let Some(source) = source {
                let edge_id = edge(metadata_string_literal(module, file, source)?)?;
                for specifier in specifiers {
                    let specifier = specifier.data();
                    if specifier.mode == ExportSpecifierMode::TypeOnly {
                        continue;
                    }
                    exports.push(RawExport {
                        name: metadata_export_name(module, file, &specifier.exported)?,
                        source: RawExportSource::Indirect {
                            edge: edge_id,
                            name: metadata_export_name(module, file, &specifier.local)?,
                        },
                    });
                }
            } else {
                for specifier in specifiers {
                    let specifier = specifier.data();
                    if specifier.mode == ExportSpecifierMode::TypeOnly {
                        continue;
                    }
                    exports.push(RawExport {
                        name: metadata_export_name(module, file, &specifier.exported)?,
                        source: RawExportSource::Local(metadata_export_name(
                            module,
                            file,
                            &specifier.local,
                        )?),
                    });
                }
            }
        }
        ExportDeclaration::All(all) if !all.type_only => {
            let edge_id = edge(metadata_string_literal(module, file, &all.source)?)?;
            if let Some(exported) = &all.exported {
                let exported = metadata_export_name(module, file, exported)?;
                let binding = format!("*namespace:{exported}*");
                bindings.push(RawBinding {
                    name: binding.clone(),
                    kind: RawBindingKind::Namespace { edge: edge_id },
                });
                exports.push(RawExport {
                    name: exported,
                    source: RawExportSource::Local(binding),
                });
            } else {
                stars.push(edge_id);
            }
        }
        ExportDeclaration::Default(default) => {
            let kind = match &default.value {
                ExportDefaultValue::Function(function) if function.body.is_some() => {
                    if let Some(name) = &function.name {
                        bindings.push(RawBinding {
                            name: identifier(file, name),
                            kind: RawBindingKind::Hoisted,
                        });
                    }
                    RawBindingKind::Hoisted
                }
                ExportDefaultValue::Class(class) => {
                    if let Some(name) = &class.name {
                        bindings.push(RawBinding {
                            name: identifier(file, name),
                            kind: RawBindingKind::Lexical,
                        });
                    }
                    RawBindingKind::Lexical
                }
                ExportDefaultValue::Expression(_) => RawBindingKind::Lexical,
                _ => return Ok(()),
            };
            bindings.push(RawBinding {
                name: "*default*".to_owned(),
                kind,
            });
            exports.push(RawExport {
                name: "default".to_owned(),
                source: RawExportSource::Local("*default*".to_owned()),
            });
        }
        _ => {}
    }
    Ok(())
}

fn expand_star_exports(modules: &mut [RawModule]) {
    let explicit: Vec<BTreeSet<String>> = modules
        .iter()
        .map(|module| {
            module
                .exports
                .iter()
                .map(|export| export.name.clone())
                .collect()
        })
        .collect();
    let mut origins: Vec<BTreeMap<String, BTreeSet<ExportOrigin>>> = modules
        .iter()
        .enumerate()
        .map(|(index, module)| {
            module
                .exports
                .iter()
                .map(|export| {
                    (
                        export.name.clone(),
                        BTreeSet::from([canonical_export_origin(
                            modules,
                            export_origin(ModuleId::new(index as u32), module, export),
                            &mut BTreeSet::new(),
                        )]),
                    )
                })
                .collect()
        })
        .collect();
    loop {
        let previous = origins.clone();
        let mut changed = false;
        for (index, module) in modules.iter().enumerate() {
            for star in &module.stars {
                let EdgeTarget::Local(target) = module.edges[star.get() as usize].target else {
                    continue;
                };
                for (name, candidates) in &previous[target.get() as usize] {
                    if name == "default" || explicit[index].contains(name) {
                        continue;
                    }
                    let entry = origins[index].entry(name.clone()).or_default();
                    let before = entry.len();
                    entry.extend(candidates.iter().cloned());
                    changed |= entry.len() != before;
                }
            }
        }
        if !changed {
            break;
        }
    }
    for (index, module) in modules.iter_mut().enumerate() {
        for (name, candidates) in &origins[index] {
            if explicit[index].contains(name) || candidates.len() != 1 {
                continue;
            }
            let origin = candidates.first().expect("singleton candidate");
            if let Some(edge) = module.stars.iter().copied().find(|edge| {
                let EdgeTarget::Local(target) = module.edges[edge.get() as usize].target else {
                    return false;
                };
                origins[target.get() as usize]
                    .get(name)
                    .is_some_and(|origins| origins.contains(origin))
            }) {
                module.exports.push(RawExport {
                    name: name.clone(),
                    source: RawExportSource::Indirect {
                        edge,
                        name: name.clone(),
                    },
                });
            }
        }
    }
}

fn export_origin(module_id: ModuleId, module: &RawModule, export: &RawExport) -> ExportOrigin {
    match &export.source {
        RawExportSource::Local(name) => {
            if let Some(binding) = module.bindings.iter().find(|binding| binding.name == *name) {
                match &binding.kind {
                    RawBindingKind::Imported { edge, name } => match module.edges
                        [edge.get() as usize]
                        .target
                    {
                        EdgeTarget::Local(target) => ExportOrigin::Indirect(target, name.clone()),
                        EdgeTarget::External => ExportOrigin::External(
                            module.edges[edge.get() as usize]
                                .external_identity
                                .clone()
                                .unwrap_or_else(|| {
                                    module.edges[edge.get() as usize].specifier.clone()
                                }),
                            name.clone(),
                        ),
                    },
                    _ => ExportOrigin::Local(module_id, name.clone()),
                }
            } else {
                ExportOrigin::Local(module_id, name.clone())
            }
        }
        RawExportSource::Indirect { edge, name } => {
            match module.edges[edge.get() as usize].target {
                EdgeTarget::Local(target) => ExportOrigin::Indirect(target, name.clone()),
                EdgeTarget::External => ExportOrigin::External(
                    module.edges[edge.get() as usize]
                        .external_identity
                        .clone()
                        .unwrap_or_else(|| module.edges[edge.get() as usize].specifier.clone()),
                    name.clone(),
                ),
            }
        }
    }
}

fn canonical_export_origin(
    modules: &[RawModule],
    origin: ExportOrigin,
    visited: &mut BTreeSet<(ModuleId, String)>,
) -> ExportOrigin {
    let ExportOrigin::Indirect(module_id, name) = &origin else {
        return origin;
    };
    if !visited.insert((*module_id, name.clone())) {
        return origin;
    }
    let module = &modules[module_id.get() as usize];
    let Some(export) = module.exports.iter().find(|export| export.name == *name) else {
        return origin;
    };
    let next = export_origin(*module_id, module, export);
    if next == origin {
        origin
    } else {
        canonical_export_origin(modules, next, visited)
    }
}

fn linkage_strings(module: &RawModule) -> Vec<String> {
    let mut strings = Vec::new();
    strings.push(module.name.clone());
    strings.extend(module.edges.iter().map(|edge| edge.specifier.clone()));
    for binding in &module.bindings {
        strings.push(binding.name.clone());
        if let RawBindingKind::Imported { name, .. } = &binding.kind {
            strings.push(name.clone());
        }
    }
    for export in &module.exports {
        strings.push(export.name.clone());
        if let RawExportSource::Indirect { name, .. } = &export.source {
            strings.push(name.clone());
        }
    }
    strings
}

fn materialize_program_module(
    code: bamts_bytecode::Module<Verified>,
    raw: &RawModule,
) -> ProgramModule<Verified> {
    let constant = |value: &str| {
        ConstantId::new(
            code.constants()
                .iter()
                .position(|constant| matches!(constant, Constant::String(text) if text.as_units().iter().copied().eq(value.encode_utf16())))
                .expect("all linkage strings were interned before verification") as u32,
        )
    };
    let binding_ids: HashMap<_, _> = raw
        .bindings
        .iter()
        .enumerate()
        .map(|(index, binding)| (binding.name.as_str(), BindingId::new(index as u32)))
        .collect();
    let name = constant(&raw.name);
    let edges = raw
        .edges
        .iter()
        .map(|edge| Edge {
            specifier: constant(&edge.specifier),
            target: edge.target,
            kind: edge.kind,
        })
        .collect();
    let bindings = raw
        .bindings
        .iter()
        .map(|binding| Binding {
            name: constant(&binding.name),
            kind: match &binding.kind {
                RawBindingKind::Hoisted => BindingKind::Hoisted,
                RawBindingKind::Lexical => BindingKind::Lexical,
                RawBindingKind::Imported { edge, name } => BindingKind::Imported {
                    edge: *edge,
                    name: constant(name),
                },
                RawBindingKind::Namespace { edge } => BindingKind::Namespace { edge: *edge },
            },
        })
        .collect();
    let exports = raw
        .exports
        .iter()
        .map(|export| Export {
            name: constant(&export.name),
            source: match &export.source {
                RawExportSource::Local(name) => ExportSource::Local(binding_ids[name.as_str()]),
                RawExportSource::Indirect { edge, name } => ExportSource::Indirect {
                    edge: *edge,
                    name: constant(name),
                },
            },
        })
        .collect();
    ProgramModule {
        name,
        code,
        edges,
        bindings,
        exports,
    }
}

fn normalized_module_name(root: &ProjectRoot, path: &Path) -> Option<String> {
    let relative = path.strip_prefix(root.path()).ok()?;
    let mut name = String::new();
    for component in relative.components() {
        if !name.is_empty() {
            name.push('/');
        }
        name.push_str(component.as_os_str().to_str()?);
    }
    (!name.is_empty()).then_some(name)
}

fn identifier(file: &SourceFile, node: &crate::syntax::IdentifierNode) -> String {
    file.token_text(node.data().token())
        .expect("parser identifier range belongs to its source")
        .to_owned()
}

fn metadata_string_literal(
    module: &ResolvedModule,
    file: &SourceFile,
    node: &crate::syntax::StringLiteralNode,
) -> Result<String, ProgramLowerError> {
    let value = file
        .token_text(node.data().token())
        .and_then(unquote)
        .ok_or_else(|| malformed_metadata_error(module))?;
    value
        .to_utf8_strict()
        .map_err(|_| malformed_metadata_error(module))
}

fn metadata_export_name(
    module: &ResolvedModule,
    file: &SourceFile,
    name: &ModuleExportName,
) -> Result<String, ProgramLowerError> {
    match name {
        ModuleExportName::Identifier(identifier_node) => Ok(identifier(file, identifier_node)),
        ModuleExportName::String(string) => metadata_string_literal(module, file, string),
        ModuleExportName::Missing(_) => Ok(String::new()),
    }
}

fn malformed_metadata_error(module: &ResolvedModule) -> ProgramLowerError {
    program_lower_error(
        module.path(),
        ProgramLowerPhase::Metadata,
        ProgramLowerErrorKind::IllFormedMetadataString,
    )
}

fn program_lower_error(
    module: &Path,
    phase: ProgramLowerPhase,
    kind: ProgramLowerErrorKind,
) -> ProgramLowerError {
    ProgramLowerError {
        module: module.to_path_buf(),
        phase,
        kind,
    }
}

#[cfg(test)]
mod tests {
    use std::{
        fs,
        path::{Path, PathBuf},
        sync::{
            Arc,
            atomic::{AtomicU64, Ordering},
        },
    };

    use super::{
        ExecutableProgram, ModuleEdgeKind, ModuleTarget, ProgramLoadError, ProgramLoader,
        ProgramLowerErrorKind, ProgramLowerPhase, lower_program,
    };
    use crate::{
        lower::LowerOptions,
        pipeline::{FrontendMode, compile_program_frontend},
        project::{ProjectConfig, ProjectRoot},
    };
    use bamts_bytecode::{
        BindingKind, EcmaString, EdgeKind, EdgeTarget, ExportSource, Instruction, ProgramModule,
        ProgramVerifyErrorKind, ResolvedExport, Verified,
    };

    static NEXT_FIXTURE: AtomicU64 = AtomicU64::new(0);

    struct Fixture(PathBuf);

    impl Fixture {
        fn new() -> Self {
            let path = std::env::temp_dir().join(format!(
                "bamts-program-{}-{}",
                std::process::id(),
                NEXT_FIXTURE.fetch_add(1, Ordering::Relaxed)
            ));
            fs::create_dir_all(&path).unwrap();
            Self(path)
        }

        fn write(&self, path: &str, source: &str) {
            let path = self.0.join(path);
            fs::create_dir_all(path.parent().unwrap()).unwrap();
            fs::write(path, source).unwrap();
        }

        fn loader(&self) -> ProgramLoader {
            let root = ProjectRoot::new(fs::canonicalize(&self.0).unwrap()).unwrap();
            let config = ProjectConfig::parse(&root, self.0.join("tsconfig.json"), "{}").unwrap();
            ProgramLoader::new(&root, config.options()).unwrap()
        }
    }

    impl Drop for Fixture {
        fn drop(&mut self) {
            fs::remove_dir_all(&self.0).unwrap();
        }
    }

    fn lower_fixture(fixture: &Fixture, entrypoint: &str) -> ExecutableProgram {
        let resolved = fixture.loader().load(entrypoint).unwrap();
        let frontend = compile_program_frontend(&resolved, FrontendMode::Check);
        lower_program(
            &resolved,
            &frontend,
            LowerOptions {
                javascript_compatibility: true,
            },
        )
        .unwrap()
    }

    #[test]
    fn malformed_surrogate_metadata_is_a_typed_error() {
        let fixture = Fixture::new();
        fixture.write("main.ts", "const x = 1; export { x as \"\\uD800\" };");
        let resolved = fixture.loader().load("main.ts").unwrap();
        let frontend = compile_program_frontend(&resolved, FrontendMode::Check);
        let error = lower_program(
            &resolved,
            &frontend,
            LowerOptions {
                javascript_compatibility: true,
            },
        )
        .expect_err("ill-formed metadata must not reach host String conversion");
        assert_eq!(error.phase, ProgramLowerPhase::Metadata);
        assert_eq!(error.kind, ProgramLowerErrorKind::IllFormedMetadataString);
    }

    fn module_name(module: &ProgramModule<Verified>) -> String {
        match &module.code().constants()[module.name().get() as usize] {
            bamts_bytecode::Constant::String(name) => name
                .to_utf8_strict()
                .expect("compiler-produced module metadata is well-formed"),
            _ => panic!("verified module name is a string"),
        }
    }

    fn module<'a>(program: &'a ExecutableProgram, name: &str) -> &'a ProgramModule<Verified> {
        program
            .wire()
            .modules()
            .iter()
            .find(|module| module_name(module) == name)
            .unwrap_or_else(|| panic!("missing module {name}"))
    }

    fn constant_string(module: &ProgramModule<Verified>, id: bamts_bytecode::ConstantId) -> String {
        match &module.code().constants()[id.get() as usize] {
            bamts_bytecode::Constant::String(value) => value
                .to_utf8_strict()
                .expect("compiler-produced linkage metadata is well-formed"),
            _ => panic!("verified linkage constant is a string"),
        }
    }

    fn instructions(module: &ProgramModule<Verified>) -> impl Iterator<Item = Instruction> + '_ {
        module
            .code()
            .functions()
            .iter()
            .flat_map(|function| function.code().iter().copied())
    }

    fn names(program: &super::ResolvedProgram) -> Vec<&str> {
        program
            .modules()
            .iter()
            .map(|module| module.path().file_name().unwrap().to_str().unwrap())
            .collect()
    }

    #[test]
    fn program_lowering_keeps_static_imports_live_without_snapshot_opcodes() {
        let fixture = Fixture::new();
        fixture.write("dep.ts", "export let value = 1; value = 2;");
        fixture.write(
            "main.ts",
            "import { value as observed } from './dep.js'; export { observed };",
        );

        let executable = lower_fixture(&fixture, "main.ts");
        let main = module(&executable, "main.ts");
        assert_eq!(main.edges().len(), 1);
        assert_eq!(main.edges()[0].kind, EdgeKind::Static);
        let binding = main
            .bindings()
            .iter()
            .find(|binding| constant_string(main, binding.name) == "observed")
            .unwrap();
        assert!(matches!(binding.kind, BindingKind::Imported { .. }));
        assert!(!instructions(main).any(|instruction| matches!(
            instruction,
            Instruction::Import { .. }
                | Instruction::GetProperty { .. }
                | Instruction::Export { .. }
        )));

        let main_id = executable.wire().entry();
        let export = main
            .exports()
            .iter()
            .find(|export| constant_string(main, export.name) == "observed")
            .unwrap();
        assert!(matches!(export.source, ExportSource::Local(_)));
        assert!(matches!(
            executable.wire().resolve_export(main_id, &EcmaString::from_utf8("observed")),
            Some(ResolvedExport::Local { module, .. })
                if module != main_id
        ));
    }

    #[test]
    fn program_lowering_records_namespace_imports() {
        let fixture = Fixture::new();
        fixture.write("dep.ts", "export const value = 1; export default 2;");
        fixture.write(
            "main.ts",
            "import fallback, * as namespace from './dep.js'; fallback; namespace.value;",
        );

        let executable = lower_fixture(&fixture, "main.ts");
        let main = module(&executable, "main.ts");
        assert!(main.bindings().iter().any(|binding| {
            constant_string(main, binding.name) == "namespace"
                && matches!(binding.kind, BindingKind::Namespace { .. })
        }));
        assert!(main.bindings().iter().any(|binding| {
            constant_string(main, binding.name) == "fallback"
                && matches!(
                    binding.kind,
                    BindingKind::Imported { name, .. }
                        if constant_string(main, name) == "default"
                )
        }));
    }

    #[test]
    fn program_lowering_resolves_alias_reexports() {
        let fixture = Fixture::new();
        fixture.write("dep.ts", "export const original = 1;");
        fixture.write("main.ts", "export { original as renamed } from './dep.js';");

        let executable = lower_fixture(&fixture, "main.ts");
        let main = module(&executable, "main.ts");
        let export = main
            .exports()
            .iter()
            .find(|export| constant_string(main, export.name) == "renamed")
            .unwrap();
        assert!(matches!(export.source, ExportSource::Indirect { .. }));
        assert!(matches!(
            executable
                .wire()
                .resolve_export(executable.wire().entry(), &EcmaString::from_utf8("renamed")),
            Some(ResolvedExport::Local { module, .. })
                if module != executable.wire().entry()
        ));
    }

    #[test]
    fn program_lowering_omits_ambiguous_star_exports() {
        let fixture = Fixture::new();
        fixture.write(
            "a.ts",
            "export const collision = 1; export const onlyA = 1;",
        );
        fixture.write(
            "b.ts",
            "export const collision = 2; export const onlyB = 2;",
        );
        fixture.write("main.ts", "export * from './a.js'; export * from './b.js';");

        let executable = lower_fixture(&fixture, "main.ts");
        let main = module(&executable, "main.ts");
        let names: Vec<_> = main
            .exports()
            .iter()
            .map(|export| constant_string(main, export.name))
            .collect();
        assert!(names.iter().any(|name| name == "onlyA"));
        assert!(names.iter().any(|name| name == "onlyB"));
        assert!(!names.iter().any(|name| name == "collision"));
    }

    #[test]
    fn program_lowering_keeps_diamond_star_reexports_unambiguous() {
        let fixture = Fixture::new();
        fixture.write("a.ts", "export const value = 1;");
        fixture.write("b.ts", "export { value } from './a.js';");
        fixture.write("main.ts", "export * from './a.js'; export * from './b.js';");

        let executable = lower_fixture(&fixture, "main.ts");
        let main = module(&executable, "main.ts");
        assert_eq!(
            main.exports()
                .iter()
                .filter(|export| constant_string(main, export.name) == "value")
                .count(),
            1
        );
        assert!(
            executable
                .wire()
                .resolve_export(executable.wire().entry(), &EcmaString::from_utf8("value"))
                .is_some()
        );
    }

    #[test]
    fn program_lowering_canonicalizes_external_reexport_identity() {
        let fixture = Fixture::new();
        fixture.write("a.ts", "export { readFile } from 'node:fs';");
        fixture.write("b.ts", "export { readFile } from 'node:fs';");
        fixture.write("main.ts", "export * from './a.js'; export * from './b.js';");

        let executable = lower_fixture(&fixture, "main.ts");
        let main = module(&executable, "main.ts");
        assert_eq!(
            main.exports()
                .iter()
                .filter(|export| constant_string(main, export.name) == "readFile")
                .count(),
            1
        );
        assert!(matches!(
            executable.wire().resolve_export(
                executable.wire().entry(),
                &EcmaString::from_utf8("readFile")
            ),
            Some(ResolvedExport::External { .. })
        ));
    }

    #[test]
    fn program_lowering_materializes_default_expression_binding() {
        let fixture = Fixture::new();
        fixture.write("main.ts", "export default 1 + 2;");

        let executable = lower_fixture(&fixture, "main.ts");
        let main = module(&executable, "main.ts");
        let binding_index = main
            .bindings()
            .iter()
            .position(|binding| constant_string(main, binding.name) == "*default*")
            .unwrap();
        assert_eq!(main.bindings()[binding_index].kind, BindingKind::Lexical);
        assert!(main.exports().iter().any(|export| {
            constant_string(main, export.name) == "default"
                && export.source
                    == ExportSource::Local(bamts_bytecode::BindingId::new(binding_index as u32))
        }));
        assert!(
            !instructions(main)
                .any(|instruction| matches!(instruction, Instruction::Export { .. }))
        );
    }

    #[test]
    fn program_lowering_initializes_default_named_class_binding() {
        let fixture = Fixture::new();
        fixture.write("main.ts", "export default class Foo {}; Foo;");

        let executable = lower_fixture(&fixture, "main.ts");
        let main = module(&executable, "main.ts");
        assert!(main.bindings().iter().any(|binding| {
            constant_string(main, binding.name) == "Foo" && binding.kind == BindingKind::Lexical
        }));
        let stored: Vec<_> = instructions(main)
            .filter_map(|instruction| match instruction {
                Instruction::StoreGlobal { name, .. } => Some(constant_string(main, name)),
                _ => None,
            })
            .collect();
        assert!(stored.iter().any(|name| name == "Foo"));
        assert!(stored.iter().any(|name| name == "*default*"));
    }

    #[test]
    fn program_lowering_erases_type_only_edges_from_wire_but_retains_provenance() {
        let fixture = Fixture::new();
        fixture.write("types.ts", "export interface Shape { value: number }");
        fixture.write(
            "main.ts",
            "import type { Shape } from './types.js'; let x: Shape;",
        );

        let executable = lower_fixture(&fixture, "main.ts");
        let main = module(&executable, "main.ts");
        assert!(main.edges().is_empty());
        assert!(
            main.bindings()
                .iter()
                .all(|binding| { constant_string(main, binding.name) != "Shape" })
        );
        let provenance = executable
            .provenance()
            .iter()
            .find(|item| item.source().path().ends_with("main.ts"))
            .unwrap();
        assert_eq!(provenance.type_only_edges().count(), 1);
    }

    #[test]
    fn program_lowering_links_cycles_with_hoisted_and_tdz_bindings() {
        let fixture = Fixture::new();
        fixture.write(
            "a.ts",
            "import { fromB } from './b.js'; export let fromA = fromB; export var hoistedVar; export class LexicalClass {}",
        );
        fixture.write(
            "b.ts",
            "import { fromA } from './a.js'; export function fromB() { return fromA; }",
        );

        let executable = lower_fixture(&fixture, "a.ts");
        let a = module(&executable, "a.ts");
        let b = module(&executable, "b.ts");
        assert!(a.bindings().iter().any(|binding| {
            constant_string(a, binding.name) == "fromA" && binding.kind == BindingKind::Lexical
        }));
        assert!(a.bindings().iter().any(|binding| {
            constant_string(a, binding.name) == "hoistedVar" && binding.kind == BindingKind::Hoisted
        }));
        assert!(a.bindings().iter().any(|binding| {
            constant_string(a, binding.name) == "LexicalClass"
                && binding.kind == BindingKind::Lexical
        }));
        assert!(b.bindings().iter().any(|binding| {
            constant_string(b, binding.name) == "fromB" && binding.kind == BindingKind::Hoisted
        }));
        assert!(a.edges().iter().all(|edge| edge.kind == EdgeKind::Static));
        assert!(b.edges().iter().all(|edge| edge.kind == EdgeKind::Static));
    }

    #[test]
    fn program_lowering_keeps_dynamic_import_as_dynamic_instruction_edge() {
        let fixture = Fixture::new();
        fixture.write("dep.ts", "export const value = 1;");
        fixture.write("main.ts", "const pending = import('./dep.js');");

        let executable = lower_fixture(&fixture, "main.ts");
        let main = module(&executable, "main.ts");
        assert_eq!(main.edges().len(), 1);
        assert_eq!(main.edges()[0].kind, EdgeKind::Dynamic);
        assert!(
            instructions(main).any(|instruction| matches!(instruction, Instruction::Import { .. }))
        );
    }

    #[test]
    fn program_lowering_coalesces_static_and_dynamic_imports_of_one_target() {
        let fixture = Fixture::new();
        fixture.write("dep.ts", "export const value = 1;");
        fixture.write(
            "main.ts",
            "import { value } from './dep.js'; const pending = import('./dep.js'); value;",
        );

        let executable = lower_fixture(&fixture, "main.ts");
        let main = module(&executable, "main.ts");
        assert_eq!(main.edges().len(), 1);
        assert_eq!(main.edges()[0].kind, EdgeKind::StaticAndDynamic);
        assert!(main.bindings().iter().any(|binding| {
            constant_string(main, binding.name) == "value"
                && matches!(binding.kind, BindingKind::Imported { .. })
        }));
        assert!(
            instructions(main).any(|instruction| matches!(instruction, Instruction::Import { .. }))
        );
    }

    #[test]
    fn program_lowering_rejects_same_specifier_with_different_targets() {
        let fixture = Fixture::new();
        fixture.write("dep.ts", "export const value = 1;");
        fixture.write("other.ts", "export const other = 2;");
        fixture.write(
            "main.ts",
            "import { value } from './dep.js'; const pending = import('./dep.js'); import './other.js'; value;",
        );
        let mut resolved = fixture.loader().load("main.ts").unwrap();
        let other = resolved
            .modules()
            .iter()
            .find(|module| module.path().ends_with("other.ts"))
            .unwrap()
            .source_id();
        let modules = Arc::get_mut(&mut resolved.modules).unwrap();
        let main = modules
            .iter_mut()
            .find(|module| module.path().ends_with("main.ts"))
            .unwrap();
        let dependencies = Arc::make_mut(&mut main.dependencies);
        dependencies
            .iter_mut()
            .find(|edge| edge.kind == ModuleEdgeKind::DynamicRuntime)
            .unwrap()
            .target = ModuleTarget::Local(other);

        let frontend = compile_program_frontend(&resolved, FrontendMode::Check);
        let error = lower_program(&resolved, &frontend, LowerOptions::default()).unwrap_err();
        assert_eq!(error.phase, ProgramLowerPhase::Metadata);
        assert_eq!(
            error.kind,
            ProgramLowerErrorKind::ConflictingRuntimeEdge {
                specifier: "./dep.js".to_owned(),
            }
        );
    }

    #[test]
    fn program_lowering_rejects_duplicate_exports_during_link() {
        let fixture = Fixture::new();
        fixture.write(
            "main.ts",
            "const value = 1; export { value }; export { value };",
        );
        let resolved = fixture.loader().load("main.ts").unwrap();
        let frontend = compile_program_frontend(&resolved, FrontendMode::Check);
        let error = lower_program(&resolved, &frontend, LowerOptions::default()).unwrap_err();
        assert_eq!(error.phase, ProgramLowerPhase::Link);
        assert!(matches!(
            error.kind,
            ProgramLowerErrorKind::Link(bamts_bytecode::ProgramVerifyError {
                kind: ProgramVerifyErrorKind::DuplicateExport { .. },
                ..
            })
        ));
    }

    #[test]
    fn program_lowering_preserves_external_identity_only_in_provenance() {
        let fixture = Fixture::new();
        fixture.write("main.ts", "import * as fs from 'node:fs'; fs.readFile;");

        let executable = lower_fixture(&fixture, "main.ts");
        let main = module(&executable, "main.ts");
        assert_eq!(main.edges().len(), 1);
        assert_eq!(main.edges()[0].target, EdgeTarget::External);
        let provenance = executable
            .provenance()
            .iter()
            .find(|item| item.source().path().ends_with("main.ts"))
            .unwrap();
        assert!(matches!(
            provenance.edges()[0].target(),
            ModuleTarget::External(specifier) if specifier.as_ref() == "node:fs"
        ));
    }

    #[test]
    fn program_lowering_is_deterministic_and_names_modules_root_relatively() {
        let fixture = Fixture::new();
        fixture.write("lib/dep.ts", "export const value = 1;");
        fixture.write("src/main.ts", "export { value } from '../lib/dep.js';");

        let first = lower_fixture(&fixture, "src/main.ts");
        let second = lower_fixture(&fixture, "src/main.ts");
        assert_eq!(first.wire().encode(), second.wire().encode());
        assert_eq!(
            first
                .wire()
                .modules()
                .iter()
                .map(module_name)
                .collect::<Vec<_>>(),
            ["lib/dep.ts", "src/main.ts"]
        );
        for (left, right) in first.wire().modules().iter().zip(second.wire().modules()) {
            assert_eq!(left.code().encode(), right.code().encode());
        }
    }

    #[test]
    fn resolves_extensions_and_directory_indexes_dependency_first() {
        let fixture = Fixture::new();
        fixture.write("main.ts", "import './leaf.js'; import './branch';");
        fixture.write("leaf.ts", "export const leaf = 1;");
        fixture.write("branch/index.ts", "export const branch = 1;");

        let program = fixture.loader().load("main.ts").unwrap();

        assert_eq!(names(&program), ["leaf.ts", "index.ts", "main.ts"]);
    }

    #[test]
    fn excludes_type_only_dependencies_from_runtime_closure() {
        let fixture = Fixture::new();
        fixture.write(
            "main.ts",
            "import type { Shape } from './shape'; import { value } from './value'; void value;",
        );
        fixture.write("shape.ts", "export interface Shape { x: number }");
        fixture.write("value.ts", "export const value = 1;");

        let program = fixture.loader().load("main.ts").unwrap();
        let runtime: Vec<_> = program
            .runtime_modules()
            .iter()
            .map(|module| module.path().file_name().unwrap().to_str().unwrap())
            .collect();

        assert_eq!(runtime, ["value.ts", "main.ts"]);
        assert!(program.entrypoint().dependencies().iter().any(|edge| {
            edge.kind() == ModuleEdgeKind::TypeOnly && edge.specifier() == "./shape"
        }));
    }

    #[test]
    fn deduplicates_diamond_dependencies_by_canonical_path() {
        let fixture = Fixture::new();
        fixture.write("main.ts", "import './left'; import './right';");
        fixture.write("left.ts", "import './shared';");
        fixture.write("right.ts", "import './shared';");
        fixture.write("shared.ts", "export const shared = 1;");

        let program = fixture.loader().load("main.ts").unwrap();

        assert_eq!(
            names(&program),
            ["shared.ts", "left.ts", "right.ts", "main.ts"]
        );
        assert_eq!(program.modules().len(), 4);
    }

    #[test]
    fn preserves_cycles_without_duplicate_modules() {
        let fixture = Fixture::new();
        fixture.write("a.ts", "import './b';");
        fixture.write("b.ts", "import './a';");

        let program = fixture.loader().load("a.ts").unwrap();
        let b = &program.modules()[0];

        assert_eq!(names(&program), ["b.ts", "a.ts"]);
        assert_eq!(
            b.dependencies()[0].target(),
            &ModuleTarget::Local(program.entrypoint_id())
        );
    }

    #[test]
    fn resolves_package_exports_entry() {
        let fixture = Fixture::new();
        fixture.write("main.ts", "import { answer } from 'waybread'; void answer;");
        fixture.write(
            "node_modules/waybread/package.json",
            r#"{"name":"waybread","exports":{".":{"import":"./src/entry.js"}}}"#,
        );
        fixture.write(
            "node_modules/waybread/src/entry.ts",
            "export const answer = 42;",
        );

        let program = fixture.loader().load("main.ts").unwrap();

        assert_eq!(names(&program), ["entry.ts", "main.ts"]);
    }
    #[test]
    fn resolves_package_import_maps() {
        let fixture = Fixture::new();
        fixture.write(
            "package.json",
            r##"{"name":"root","imports":{"#waybread":"./src/alias.js"}}"##,
        );
        fixture.write(
            "main.ts",
            "import { answer } from '#waybread'; void answer;",
        );
        fixture.write("src/alias.ts", "export const answer = 42;");

        let program = fixture.loader().load("main.ts").unwrap();

        assert_eq!(names(&program), ["alias.ts", "main.ts"]);
    }

    #[test]
    fn decodes_escaped_module_specifiers() {
        let fixture = Fixture::new();
        fixture.write("main.ts", r#"import './\u0066oo';"#);
        fixture.write("foo.ts", "export const answer = 42;");

        let program = fixture.loader().load("main.ts").unwrap();

        assert_eq!(names(&program), ["foo.ts", "main.ts"]);
    }

    #[test]
    fn rejects_ill_formed_utf16_module_specifiers() {
        for source in [
            r#"import type { T } from "\uD800";"#,
            r#"type T = import("\uD800").T;"#,
        ] {
            let fixture = Fixture::new();
            fixture.write("main.ts", source);

            assert!(matches!(
                fixture.loader().load("main.ts"),
                Err(ProgramLoadError::IllFormedModuleSpecifier { .. })
            ));
        }
    }

    #[test]
    fn rejects_relative_traversal_before_loading() {
        let fixture = Fixture::new();
        fixture.write("main.ts", "import '../outside.ts';");

        let error = fixture.loader().load("main.ts").unwrap_err();

        assert!(matches!(
            error,
            ProgramLoadError::InvalidSpecifier { .. } | ProgramLoadError::UnresolvedModule(_)
        ));
    }

    #[test]
    fn retains_literal_dynamic_import_edges() {
        let fixture = Fixture::new();
        fixture.write(
            "main.ts",
            "async function load() { return import('./later'); }",
        );
        fixture.write("later.ts", "export const later = 1;");

        let program = fixture.loader().load("main.ts").unwrap();

        assert_eq!(names(&program), ["later.ts", "main.ts"]);
        assert_eq!(
            program.entrypoint().dependencies()[0].kind(),
            ModuleEdgeKind::DynamicRuntime
        );
        assert_eq!(program.runtime_modules().len(), 1);
    }
    #[test]
    fn classifies_import_types_without_creating_dynamic_runtime_edges() {
        let fixture = Fixture::new();
        fixture.write("main.ts", "type Shape = import('./shape').Shape; void 0;");
        fixture.write("shape.ts", "export interface Shape { x: number }");

        let program = fixture.loader().load("main.ts").unwrap();

        assert_eq!(names(&program), ["shape.ts", "main.ts"]);
        assert_eq!(
            program.entrypoint().dependencies()[0].kind(),
            ModuleEdgeKind::TypeOnly
        );
        assert_eq!(program.runtime_modules().len(), 1);
    }

    #[test]
    fn unresolved_runtime_edge_reports_typed_diagnostic() {
        let fixture = Fixture::new();
        fixture.write("main.ts", "import './missing';");

        let ProgramLoadError::UnresolvedModule(diagnostic) =
            fixture.loader().load("main.ts").unwrap_err()
        else {
            panic!("expected unresolved-module diagnostic");
        };

        assert_eq!(diagnostic.kind(), ModuleEdgeKind::StaticRuntime);
        assert_eq!(diagnostic.specifier(), "./missing");
        assert_eq!(
            diagnostic.importer().file_name(),
            Some(Path::new("main.ts").as_os_str())
        );
    }

    #[test]
    fn retains_node_builtin_as_external_static_runtime_edge() {
        let fixture = Fixture::new();
        fixture.write(
            "main.ts",
            "import { parseArgs } from 'node:util'; void parseArgs;",
        );

        let program = fixture.loader().load("main.ts").unwrap();
        let edge = &program.entrypoint().dependencies()[0];

        assert_eq!(names(&program), ["main.ts"]);
        assert_eq!(edge.kind(), ModuleEdgeKind::StaticRuntime);
        assert_eq!(edge.target().external_specifier(), Some("node:util"));
        assert_eq!(program.runtime_modules().len(), 1);
    }

    #[test]
    fn preserves_unresolved_type_package_as_external_identity() {
        let fixture = Fixture::new();
        fixture.write("main.ts", "import type { JsonValue } from 'type-fest';");

        let program = fixture.loader().load("main.ts").unwrap();
        let edge = &program.entrypoint().dependencies()[0];

        assert_eq!(edge.kind(), ModuleEdgeKind::TypeOnly);
        assert_eq!(edge.target().external_specifier(), Some("type-fest"));
        assert_eq!(program.runtime_modules().len(), 1);
    }

    #[test]
    fn unresolved_ordinary_runtime_package_is_rejected() {
        let fixture = Fixture::new();
        fixture.write("main.ts", "import 'waybread';");

        let ProgramLoadError::UnresolvedModule(diagnostic) =
            fixture.loader().load("main.ts").unwrap_err()
        else {
            panic!("expected unresolved-module diagnostic");
        };

        assert_eq!(diagnostic.kind(), ModuleEdgeKind::StaticRuntime);
        assert_eq!(diagnostic.specifier(), "waybread");
    }

    #[test]
    fn retains_dynamic_engine_module_as_external_edge() {
        let fixture = Fixture::new();
        fixture.write(
            "package.json",
            r##"{"name":"root","imports":{"#engine":"engine:clock"}}"##,
        );
        fixture.write(
            "main.ts",
            "async function load() { return import('#engine'); }",
        );

        let program = fixture.loader().load("main.ts").unwrap();
        let edge = &program.entrypoint().dependencies()[0];

        assert_eq!(edge.kind(), ModuleEdgeKind::DynamicRuntime);
        assert_eq!(edge.specifier(), "#engine");
        assert_eq!(edge.target().external_specifier(), Some("engine:clock"));
        assert_eq!(program.runtime_modules().len(), 1);
    }

    #[test]
    fn local_type_package_takes_precedence_over_external_fallback() {
        let fixture = Fixture::new();
        fixture.write("main.ts", "import type { Shape } from 'waybread';");
        fixture.write(
            "node_modules/waybread/package.json",
            r#"{"name":"waybread","types":"./index.d.ts"}"#,
        );
        fixture.write(
            "node_modules/waybread/index.d.ts",
            "export interface Shape { x: number }",
        );

        let program = fixture.loader().load("main.ts").unwrap();
        let edge = &program.entrypoint().dependencies()[0];

        assert_eq!(names(&program), ["index.d.ts", "main.ts"]);
        assert!(matches!(edge.target(), ModuleTarget::Local(_)));
    }

    #[test]
    fn lowers_and_verifies_exactly_the_twenty_pinned_corpus_programs() {
        let repository = Path::new(env!("CARGO_MANIFEST_DIR"))
            .join("../..")
            .canonicalize()
            .unwrap();
        let manifest = fs::read_to_string(repository.join("corpus/manifest.toml")).unwrap();
        let entrypoints: Vec<_> = manifest
            .lines()
            .filter_map(|line| {
                line.strip_prefix("entrypoint = \"")
                    .and_then(|value| value.strip_suffix('"'))
            })
            .collect();
        assert_eq!(entrypoints.len(), 20);

        let root = ProjectRoot::new(repository).unwrap();
        let config = ProjectConfig::parse(&root, root.path().join("tsconfig.json"), "{}").unwrap();
        let loader = ProgramLoader::new(&root, config.options()).unwrap();
        for entrypoint in entrypoints {
            let resolved = loader
                .load(entrypoint)
                .unwrap_or_else(|error| panic!("{entrypoint}: {error}"));
            let frontend = compile_program_frontend(&resolved, FrontendMode::Check);
            let executable = lower_program(
                &resolved,
                &frontend,
                LowerOptions {
                    javascript_compatibility: true,
                },
            )
            .unwrap_or_else(|error| panic!("{entrypoint}: {error}"));
            assert_eq!(executable.wire().modules().len(), resolved.modules().len());
        }
    }
}