fix(js,ts): a named class expression is a class with its own members (#2825)

A named class expression, like register(class Widget extends Base {})
or module.exports = class Router {}, was not indexed as a class, as
issue #2499 found. Its methods became free functions, its fields and
supertypes were dropped, and calls in it had no class to start from,
so its this-calls, super calls and own static calls went unresolved or
to a by-name guess, and calls elsewhere guessed into its methods.

Both engines now index a named class expression as a class, with its
methods, properties, extends and implements. An anonymous one is still
passed over. Its head (class Widget extends Base) is its signature,
which marks it as an expression, and it is never exported by itself.

JavaScript binds the name only inside the expression, and the resolver
now scopes it the same way. A reference written outside every class
expression resolves in a view of the graph that hides class
expressions and their members, so new Widget() elsewhere links
nothing, and a same-named class, function or binding keeps its links.
A name only class expressions carry is unknown there. A reference
inside one sees the whole graph, unless it names another class
expression. A class a CommonJS module exports, module.exports = class
Router {} or exports.Store = class Store {}, is the module's value,
which require hands to every importer, so it is not scoped: it reads
as a declaration does, and a require of it reaches its static methods
and its instances' methods. The reader of CommonJS named exports takes
exports.X = class Y {} too. Super calls in a class expression now
resolve through the super-call matcher.

Validation: the new test fails 11 of 13 on main d5fc1fbb and passes 13
of 13 on the fix, and a mutation of each of 7 parts (the view, the
inside check, the name rule, the expression marker, the class node,
the CommonJS export rule, the named-export reader) fails a test.
A/B against main d5fc1fbb on 22 repos (20 TS/JS, flask and gin): 193
classes are added in 10 repos with their members, and 801 edge sites
change in 7 repos, each bucketed and sampled by hand. 563 are jest's
calls to its global test(), 0.4 guesses that move from one wrong
namesake to another: the old one, a class expression's test() in an
e2e fixture, is now a method. Of the rest, 85 are new extends,
implements and type references of class expressions; 74 calls, news
and references move to the member they are written in; 65 calls and
news gain or change a target, inside class expressions (this-calls,
own static calls) and through require (static calls, typed instance
calls, new); and 14 guesses are removed, among them 3 super calls
whose parent the index can't name. 12 repos' dumps, the controls among
them, are byte-identical. Kernel parity holds on 22 repos. Three sync
scenarios match a fresh index. Index time, median of 5 interleaved
runs: lit +0.8%, webpack +2.7%, jest +0.6%; insomnia +12.8%, though it
indexes byte-identically, holds no class expression, and its resolver
time is the same on both arms, so that gap is other jobs' load.

Fixes #2499

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/extraction/languages/javascript.ts

@@ -4,7 +4,8 @@ import { classifyTsClassMember, hasStaticModifier } from './typescript';
 
 export const javascriptExtractor: LanguageExtractor = {
   functionTypes: ['function_declaration', 'generator_function_declaration', 'arrow_function', 'function_expression', 'generator_function'],
-  classTypes: ['class_declaration'],
+  // A named class expression too, as in TypeScript (#2499).
+  classTypes: ['class_declaration', 'class'],
   methodTypes: ['method_definition', 'field_definition'],
   // JS `field_definition` ≙ TS `public_field_definition`: plain fields are
   // properties, function-valued fields are methods (#808).

src/extraction/languages/typescript.ts

@@ -150,7 +150,10 @@ export const typescriptExtractor: LanguageExtractor = {
   preParse: blankFlowSyntax,
   functionTypes: ['function_declaration', 'generator_function_declaration', 'arrow_function', 'function_expression', 'generator_function'],
   isAmbientFunction: isAmbientFunctionSignature,
-  classTypes: ['class_declaration', 'abstract_class_declaration'],
+  // `class` is a class expression, `register(class Widget extends Base {…})`:
+  // a named one is a class with its members and supertypes (#2499), and an
+  // anonymous one is passed over (TreeSitterExtractor.isClassTypeNode).
+  classTypes: ['class_declaration', 'abstract_class_declaration', 'class'],
   // `method_signature` is the interface/type-literal form of a method; without it
   // an interface's members never enter the graph, so a `.d.ts` platform API has
   // no declaration node for call sites to attach to (#1638). Java/C# don't need

src/extraction/tree-sitter.ts

@@ -430,6 +430,14 @@ const LITERAL_RECEIVER_TYPES = new Set([
  */
 const TS_JS_CHAIN_LANGUAGES = new Set(['typescript', 'tsx', 'javascript', 'jsx']);
 
+/** Languages whose `class` node is a class expression (#2499). */
+const CLASS_EXPRESSION_LANGUAGES = new Set(['typescript', 'tsx', 'javascript', 'jsx', 'arkts']);
+
+/** A class expression's head, `class Widget extends Base`: its text up to the body. Mirrored in the kernel (tsjs extract_class). */
+function classExpressionHead(source: string, node: SyntaxNode, body: SyntaxNode): string {
+  return source.substring(node.startIndex, body.startIndex).replace(/[ \t\r\n]+$/, '');
+}
+
 /** Receiver node types (TS/JS grammars) that continue a member chain downward. */
 const TS_JS_CHAIN_RECEIVER_TYPES = new Set(['member_expression', 'subscript_expression']);
 
@@ -1543,7 +1551,7 @@ export class TreeSitterExtractor {
       skipChildren = true;
     }
     // Check for class declarations
-    else if (this.extractor.classTypes.includes(nodeType)) {
+    else if (this.isClassTypeNode(node, nodeType)) {
       // Some languages reuse class_declaration for structs/enums (e.g. Swift)
       const classification = this.extractor.classifyClassNode?.(node) ?? 'class';
       if (classification === 'struct') {
@@ -2540,6 +2548,16 @@ export class TreeSitterExtractor {
   /**
    * Extract a class
    */
+  /**
+   * Whether `node` is a class to extract: one of the language's class types,
+   * except a TS/JS class expression without a name (`register(class extends
+   * Base {…})`), which is passed over as before (#2499).
+   */
+  private isClassTypeNode(node: SyntaxNode, nodeType: string): boolean {
+    if (!this.extractor!.classTypes.includes(nodeType)) return false;
+    return nodeType !== 'class' || !CLASS_EXPRESSION_LANGUAGES.has(this.language) || !!getChildByField(node, 'name');
+  }
+
   private extractClass(node: SyntaxNode, kind: NodeKind = 'class'): void {
     if (!this.extractor) return;
 
@@ -2555,13 +2573,19 @@ export class TreeSitterExtractor {
     const name = extractName(node, this.source, this.extractor);
     const docstring = this.docstringFor(node);
     const visibility = this.extractor.getVisibility?.(node);
-    const isExported = this.extractor.isExported?.(node, this.source);
+    // A class expression's name is bound inside the expression alone, so the
+    // class is never what a module exports by it, and it carries its head
+    // (`class Widget extends Base`) as its signature: a class declaration
+    // has none, which is how resolution tells the two apart (#2499).
+    const expression = node.type === 'class' && CLASS_EXPRESSION_LANGUAGES.has(this.language);
+    const isExported = expression ? false : this.extractor.isExported?.(node, this.source);
     const scoped = this.writtenScopeQualifiedName(node, name);
 
     const classNode = this.createNode(kind, name, node, {
       docstring,
       visibility,
       isExported,
+      ...(expression && resolvedBody ? { signature: classExpressionHead(this.source, node, resolvedBody) } : {}),
       ...this.cppBodyEnd(resolvedBody),
       ...(scoped !== undefined ? { qualifiedName: scoped } : {}),
     });
@@ -7420,7 +7444,7 @@ export class TreeSitterExtractor {
 
       // Extract structural nodes found inside function bodies.
       // Each extract method visits its own children, so we return after extracting.
-      if (this.extractor!.classTypes.includes(nodeType)) {
+      if (this.isClassTypeNode(node, nodeType)) {
         const classification = this.extractor!.classifyClassNode?.(node) ?? 'class';
         if (classification === 'struct') this.extractStruct(node);
         else if (classification === 'enum') this.extractEnum(node);

src/resolution/alias-binding.ts

@@ -131,11 +131,12 @@ export function extractLocalExportAliases(content: string): Array<{ exportedName
       }
     }
   }
-  // CommonJS: `exports.setCharset = function setCharset(…)`, `module.exports.x = impl`.
-  const memberRe = /^[ \t]*(?:module\.)?exports\.([A-Za-z_$][\w$]*)\s*=\s*(?:(?:async\s+)?function\s*\*?\s*([A-Za-z_$][\w$]*)\s*\(|([A-Za-z_$][\w$]*)\s*;?[ \t]*$)/gm;
+  // CommonJS: `exports.setCharset = function setCharset(…)`, `module.exports.x = impl`,
+  // and a named class expression, `exports.Router = class Router {…}` (#2499).
+  const memberRe = /^[ \t]*(?:module\.)?exports\.([A-Za-z_$][\w$]*)\s*=\s*(?:(?:async\s+)?function\s*\*?\s*([A-Za-z_$][\w$]*)\s*\(|class\s+(?!extends\b)([A-Za-z_$][\w$]*)|([A-Za-z_$][\w$]*)\s*;?[ \t]*$)/gm;
   let member: RegExpExecArray | null;
   while ((member = memberRe.exec(content)) !== null) {
-    out.push({ exportedName: member[1]!, localName: member[2] ?? member[3]! });
+    out.push({ exportedName: member[1]!, localName: member[2] ?? member[3] ?? member[4]! });
   }
   // `module.exports = { parse, format: formatDate }`.
   const objectRe = /^[ \t]*module\.exports\s*=\s*\{([^{}]*)\}/gm;

src/resolution/index.ts

@@ -40,6 +40,7 @@ import { clearCFeatureVariantMemos } from './c-feature-variants';
 import { clearAmbientModuleMemos, ambientModuleDeclarations } from './ambient-modules';
 import { matchShopifyThemeFile } from './shopify-themes';
 import { isJsSuperCallLanguage, isJsSuperCallSite, matchJsSuperCall } from './js-super-calls';
+import { CLASS_EXPRESSION_REF_LANGUAGES, isCommonJsExportedClass, isJsClassExpression, writtenIn, type ClassExpressionIndex } from './js-class-expressions';
 import { resolveViaImport, resolvePhpImportedStaticCall, resolvePhpQualifiedClassRef, resolveTsQualifiedTypeRef, resolveJvmImport, extractImportMappings, extractReExports, loadCppIncludeDirs, isPhpIncludePathRef, isCobolCopybookRef, isNixPathImportRef, isDartImportRef, isLuaRequireRef, isJsPathImportRef, isBoundToOutOfRepoImport, reachesAmbientModule, importBindingTail, clearImportResolverMemos, resolveImportPath, isExternalImport, ESM_IMPORT_LANGUAGES, jsModuleFile, pythonRootFingerprint, pythonReopenScope, pythonPackageImporters, moduleDefaultExport, isJsFamilyFile, isModuleBindingName } from './import-resolver';
 import { ResolverPool, minRefsForPool, shouldEngageAdaptively } from './resolver-pool';
 import { resolveAliasBinding } from './alias-binding';
@@ -575,6 +576,10 @@ export class ReferenceResolver {
     this.mocklessContext = null;
     this.mocklessBase = null;
     this.manualMocks = undefined;
+    this.classExpressionFreeViews = new WeakMap();
+    this.classExpressionFreeBases = new WeakMap();
+    this.classExpressionIndex = undefined;
+    this.classExpressionOnlyNameSet = null;
     this.nodeCache.clear();
     this.fileCache.clear();
     this.importMappingCache.clear();
@@ -1193,33 +1198,37 @@ export class ReferenceResolver {
    */
   private hasAnyPossibleMatch(name: string): boolean {
     if (!this.knownNames) return true; // no pre-filter available
+    // In the view outside the class expressions, names only their classes
+    // and members carry name nothing (classExpressionFreeContextFor).
+    const only = this.classExpressionFreeBases.has(this.context) ? this.classExpressionOnlyNames() : null;
+    const known = (n: string): boolean => this.knownNames!.has(n) && !(only?.has(n) ?? false);
 
     // Direct name match
-    if (this.knownNames.has(name)) return true;
+    if (known(name)) return true;
 
     // For qualified names like "obj.method" or "Class::method", check the parts
     const dotIdx = name.indexOf('.');
     if (dotIdx > 0) {
       const receiver = name.substring(0, dotIdx);
       const member = name.substring(dotIdx + 1);
-      if (this.knownNames.has(receiver) || this.knownNames.has(member)) return true;
+      if (known(receiver) || known(member)) return true;
       // Also check capitalized receiver (instance-method resolution)
       const capitalized = receiver.charAt(0).toUpperCase() + receiver.slice(1);
-      if (this.knownNames.has(capitalized)) return true;
+      if (known(capitalized)) return true;
       // JVM FQN: `com.example.foo.Bar` — the only useful segment is the
       // last one (`Bar`); the earlier check finds `example.foo.Bar` which
       // never matches a node name.
       const lastDot = name.lastIndexOf('.');
       if (lastDot > dotIdx) {
         const tail = name.substring(lastDot + 1);
-        if (tail && this.knownNames.has(tail)) return true;
+        if (tail && known(tail)) return true;
       }
     }
     const colonIdx = name.indexOf('::');
     if (colonIdx > 0) {
       const receiver = name.substring(0, colonIdx);
       const member = name.substring(colonIdx + 2);
-      if (this.knownNames.has(receiver) || this.knownNames.has(member)) return true;
+      if (known(receiver) || known(member)) return true;
       // Multi-segment path `a::b::c` (a Rust/C++ module call like
       // `database::profiles::find`) — the only segment that names a symbol is
       // the last (`c`); `member` above is `b::c`, which never matches a node
@@ -1228,7 +1237,7 @@ export class ReferenceResolver {
       const lastColon = name.lastIndexOf('::');
       if (lastColon > colonIdx) {
         const tail = name.substring(lastColon + 2);
-        if (tail && this.knownNames.has(tail)) return true;
+        if (tail && known(tail)) return true;
       }
     }
 
@@ -1242,9 +1251,9 @@ export class ReferenceResolver {
       if (sepIdx > 0) {
         const receiver = name.substring(0, sepIdx);
         const member = name.substring(sepIdx + 1);
-        if (this.knownNames.has(member) || this.knownNames.has(receiver)) return true;
+        if (known(member) || known(receiver)) return true;
         const capitalized = receiver.charAt(0).toUpperCase() + receiver.slice(1);
-        if (this.knownNames.has(capitalized)) return true;
+        if (known(capitalized)) return true;
       }
     }
 
@@ -1252,7 +1261,7 @@ export class ReferenceResolver {
     const slashIdx = name.lastIndexOf('/');
     if (slashIdx > 0) {
       const fileName = name.substring(slashIdx + 1);
-      if (this.knownNames.has(fileName)) return true;
+      if (known(fileName)) return true;
     }
 
     return false;
@@ -1380,11 +1389,20 @@ export class ReferenceResolver {
 
   resolveOne(ref: UnresolvedRef): ResolvedRef | null {
     // Production code is resolved as if the project's manual mocks were not
-    // indexed (see mocklessContextFor); every strategy below reads the graph
-    // through this.context, so it answers for that view.
+    // indexed (see mocklessContextFor), and code outside the named class
+    // expressions as if their classes were not (classExpressionFreeContextFor);
+    // every strategy below reads the graph through this.context, so it
+    // answers for that view.
+    const outer = this.context;
+    const unviewed = this.classExpressionFreeBases.get(outer) ?? outer;
+    const base = unviewed === this.mocklessContext && this.mocklessBase ? this.mocklessBase : unviewed;
+    const mockless = this.mocklessContextFor(ref, base) ?? base;
+    return this.resolveOneWith(this.classExpressionFreeContextFor(ref, mockless) ?? mockless, ref);
+  }
+
+  /** resolveOneIn with every strategy reading the graph through `context`. */
+  private resolveOneWith(context: ResolutionContext, ref: UnresolvedRef): ResolvedRef | null {
     const outer = this.context;
-    const base = outer === this.mocklessContext && this.mocklessBase ? this.mocklessBase : outer;
-    const context = this.mocklessContextFor(ref, base) ?? base;
     if (context === outer) return this.resolveOneIn(ref);
     this.context = context;
     try {
@@ -3959,6 +3977,149 @@ export class ReferenceResolver {
     return this.manualMocks;
   }
 
+  /**
+   * The context a TS/JS reference is resolved in outside the named class
+   * expressions (#2499): one without the classes they declare or their
+   * members. An expression's name is bound inside it alone, and its class's
+   * value travels in ways resolution doesn't follow. So outside, a reference
+   * means what it would were those classes not indexed, with the confidence
+   * it had: `const Panel = class Panel {…}` keeps `new Panel()` on the
+   * constant, an interface beside a same-named class expression keeps its
+   * typed calls, and an `HTMLElement` type stays clear of lit's
+   * `HTMLElementShim = class HTMLElement {…}`. A class a CommonJS module
+   * exports isn't among them (classExpressions). Null inside a class
+   * expression, where the whole graph applies.
+   */
+  private classExpressionFreeContextFor(ref: UnresolvedRef, base: ResolutionContext): ResolutionContext | null {
+    if (!CLASS_EXPRESSION_REF_LANGUAGES.has(ref.language)) return null;
+    const expressions = this.classExpressions();
+    if (!expressions) return null;
+    const dot = ref.referenceName.indexOf('.');
+    const named = expressions.byName.get(dot > 0 ? ref.referenceName.slice(0, dot) : ref.referenceName);
+    // Written in a class expression, a reference sees its class and the
+    // classes around it, as JavaScript scopes them, unless it names another
+    // one, which is bound only inside that one.
+    const inside = expressions.byFile.get(ref.filePath)?.some((n) => writtenIn(n, ref)) ?? false;
+    if (inside && !(named && !named.some((n) => writtenIn(n, ref)))) return null;
+    let view = this.classExpressionFreeViews.get(base);
+    if (!view) {
+      view = this.classExpressionFreeView(base);
+      this.classExpressionFreeViews.set(base, view);
+      this.classExpressionFreeBases.set(view, base);
+    }
+    return view;
+  }
+
+  /**
+   * `base` without the classes class expressions declare and their members.
+   * The lookups an import reads a module's exports by (getNodesInFileNamed,
+   * getExportedNodesInFile) are left whole.
+   */
+  private classExpressionFreeView(base: ResolutionContext): ResolutionContext {
+    const { hiddenIds } = this.classExpressions()!;
+    const hidden = (n: Node): boolean => hiddenIds.has(n.id);
+    const keep = (nodes: Node[]): Node[] => (nodes.some(hidden) ? nodes.filter((n) => !hidden(n)) : nodes);
+    const byKind = new Map<Node['kind'], Node[]>();
+    const getMethodMatches = base.getMethodMatches;
+    const iterateNodesByKind = base.iterateNodesByKind;
+    const { files } = this.classExpressions()!;
+    return {
+      ...base,
+      getNodesByName: (name) => keep(base.getNodesByName(name)),
+      getNodesByLowerName: (lowerName) => keep(base.getNodesByLowerName(lowerName)),
+      getNodesByQualifiedName: (qualifiedName) => keep(base.getNodesByQualifiedName(qualifiedName)),
+      getNodesInFile: (filePath) => (files.has(filePath) ? keep(base.getNodesInFile(filePath)) : base.getNodesInFile(filePath)),
+      getNodesByKind: (kind) => {
+        let nodes = byKind.get(kind);
+        if (!nodes) byKind.set(kind, (nodes = keep(base.getNodesByKind(kind))));
+        return nodes;
+      },
+      getMethodMatches: getMethodMatches
+        ? (typeName, methodName, language) => keep(getMethodMatches(typeName, methodName, language))
+        : undefined,
+      iterateNodesByKind: iterateNodesByKind
+        ? function* (kind) {
+          for (const n of iterateNodesByKind(kind)) if (!hidden(n)) yield n;
+        }
+        : undefined,
+    };
+  }
+
+  /** classExpressionFreeContextFor's views, by the context each hides from and what it hides, and each view's context; clearCaches drops both. */
+  private classExpressionFreeViews = new WeakMap<ResolutionContext, ResolutionContext>();
+  private classExpressionFreeBases = new WeakMap<ResolutionContext, ResolutionContext>();
+  /**
+   * The names that only class expressions' classes and members carry, which
+   * name nothing where classExpressionFreeView hides those: lit's DOM shims
+   * (`class HTMLElement`, `class Event`) would otherwise send every
+   * `HTMLElement` and `new Event()` across the project through the whole
+   * resolution only to find nothing, where before the name pre-filter
+   * dropped them. Read once per cache window.
+   */
+  private classExpressionOnlyNames(): Set<string> {
+    if (this.classExpressionOnlyNameSet) return this.classExpressionOnlyNameSet;
+    const only = new Set<string>();
+    const expressions = this.classExpressions();
+    if (expressions) {
+      const names = new Set<string>();
+      for (const id of expressions.hiddenIds) {
+        const n = this.nodeById(id);
+        if (n) names.add(n.name);
+      }
+      for (const name of names) {
+        if (!this.queries.getNodesByName(name).some((n) => !expressions.hiddenIds.has(n.id))) only.add(name);
+      }
+    }
+    this.classExpressionOnlyNameSet = only;
+    return only;
+  }
+
+  /** classExpressionOnlyNames' answer; clearCaches drops it. */
+  private classExpressionOnlyNameSet: Set<string> | null = null;
+
+  /**
+   * The classes named class expressions declare: by name, the files holding
+   * them, the ids of them and their members, and the one a member belongs
+   * to. Null when there are none. Read once per cache window. A class a
+   * CommonJS module exports is left out: the module binds it, so it is read
+   * as a declaration is.
+   */
+  private classExpressionIndex: ClassExpressionIndex | null | undefined;
+
+  private classExpressions(): ClassExpressionIndex | null {
+    if (this.classExpressionIndex !== undefined) return this.classExpressionIndex;
+    const byName = new Map<string, Node[]>();
+    const byFile = new Map<string, Node[]>();
+    const byKey = new Map<string, Node>();
+    const files = new Set<string>();
+    const hiddenIds = new Set<string>();
+    const linesOf = (file: string): readonly string[] =>
+      this.context.getFileLines?.(file) ?? this.context.readFile(file)?.split(/\r?\n/) ?? [];
+    for (const n of this.queries.getNodesByKind('class')) {
+      if (!isJsClassExpression(n) || isCommonJsExportedClass(n, linesOf(n.filePath))) continue;
+      const named = byName.get(n.name);
+      if (named) named.push(n); else byName.set(n.name, [n]);
+      const inFile = byFile.get(n.filePath);
+      if (inFile) inFile.push(n); else byFile.set(n.filePath, [n]);
+      byKey.set(`${n.filePath}\0${n.qualifiedName}`, n);
+      files.add(n.filePath);
+      hiddenIds.add(n.id);
+    }
+    // A member is its class's when it is declared in its file under its
+    // qualified name (`Widget::run` of `Widget`).
+    const ownerOf = (member: Node): Node | undefined => {
+      const cut = member.qualifiedName.lastIndexOf('::');
+      return cut > 0 ? byKey.get(`${member.filePath}\0${member.qualifiedName.slice(0, cut)}`) : undefined;
+    };
+    if (files.size > 0) {
+      for (const n of this.queries.getNodesByFiles([...files])) {
+        if ((n.kind === 'method' || n.kind === 'property' || n.kind === 'field') && ownerOf(n)) hiddenIds.add(n.id);
+      }
+    }
+    this.classExpressionIndex = byName.size > 0 ? { byName, byFile, files, hiddenIds, ownerOf } : null;
+    return this.classExpressionIndex;
+  }
+
   /** Is `filePath` (project-relative) one of the files the index holds? */
   private isIndexedFile(filePath: string): boolean {
     const normalized = filePath.replace(/\\/g, '/');

src/resolution/js-class-expressions.ts

@@ -0,0 +1,66 @@
+/**
+ * A named class expression's name is bound inside the expression alone
+ * (#2499): `register(class Gadget {…})` declares no `Gadget` for the code
+ * around it, where `new Gadget()` throws a ReferenceError. The extractor gives
+ * such a class a node, so its members are its own and its `extends` is
+ * known, and marks it with its head as its signature (`class Gadget`), which
+ * a class declaration doesn't carry.
+ *
+ * The class's name is bound nowhere outside the expression, and its value
+ * travels in ways resolution doesn't follow, except an import of what a
+ * module exports. So the resolver reads a reference outside the class
+ * expressions without their classes and members (ReferenceResolver's
+ * classExpressionFreeContextFor): there the reference means what it meant
+ * before those classes were indexed. A binding of the same name around an
+ * expression, like the `Panel` of `const Panel = class Panel {…}`, keeps the
+ * name, at the confidence it had. A class a CommonJS module exports,
+ * `module.exports = class Router {…}`, is the module's value, which every
+ * importer binds, so it isn't scoped: it is read as a declaration is.
+ */
+import type { Node } from '../types';
+import type { UnresolvedRef } from './types';
+
+/** Languages a class expression's class and the references to its name can be written in: TS/JS, and the scripts of Vue, Svelte and Astro files. */
+export const CLASS_EXPRESSION_REF_LANGUAGES: ReadonlySet<string> = new Set(['typescript', 'tsx', 'javascript', 'jsx', 'arkts', 'vue', 'svelte', 'astro']);
+
+/** What the resolver knows of the classes named class expressions declare (ReferenceResolver.classExpressions). */
+export interface ClassExpressionIndex {
+  /** The classes, by name. */
+  byName: Map<string, Node[]>;
+  /** The classes, by the file that holds them. */
+  byFile: Map<string, Node[]>;
+  /** The files that hold them. */
+  files: Set<string>;
+  /** The ids of the classes and of their members. */
+  hiddenIds: Set<string>;
+  /** The class a member belongs to, when it is one of them. */
+  ownerOf: (member: Node) => Node | undefined;
+}
+
+/** Whether `node` is a class a named class expression declares. */
+export function isJsClassExpression(node: Node): boolean {
+  return node.kind === 'class' && !!node.signature && CLASS_EXPRESSION_REF_LANGUAGES.has(node.language);
+}
+
+/** The end of the text before a class a CommonJS module exports: `module.exports = `, `exports.Router = `, `module.exports.Router = `. */
+const COMMONJS_EXPORT_BEFORE = /(?:^|[^\w$.])(?:module\.)?exports(?:\.[A-Za-z_$][\w$]*)?\s*=\s*$/;
+
+/**
+ * Whether a class expression is what its CommonJS module exports, as in
+ * `module.exports = class Router {…}` or `exports.Router = class Router {…}`
+ * (`lines`: its file's lines). An importer reaches that class, its statics
+ * and, through an instance, its methods, as it reaches a declaration's.
+ */
+export function isCommonJsExportedClass(node: Node, lines: readonly string[]): boolean {
+  const line = lines[node.startLine - 1];
+  if (line === undefined) return false;
+  return COMMONJS_EXPORT_BEFORE.test(`${lines[node.startLine - 2] ?? ''}\n${line.slice(0, node.startColumn)}`);
+}
+
+/** Whether the reference is written inside `node`'s source range. */
+export function writtenIn(node: Node, ref: UnresolvedRef): boolean {
+  if (node.filePath !== ref.filePath) return false;
+  const afterStart = ref.line > node.startLine || (ref.line === node.startLine && ref.column >= node.startColumn);
+  const beforeEnd = ref.line < node.endLine || (ref.line === node.endLine && ref.column <= node.endColumn);
+  return afterStart && beforeEnd;
+}