Exports aliases for CJS exports.Foo = ... assignments when appropriate

[ahejlsberg]

With this PR, we export alias symbols for CJS exports.Foo = ... assignments where the expression is an entity name or a class expression. This is similar to our behavior in Strada and ensures type and/or namespace meanings are preserved for such exports. For example

class C {
    x = 1;
}
exports.Foo = C;  // CJS export of both value and type

is now similar in behavior to

class C {
    x = 1;
}
exports { C as Foo };  // ESM export of both value and type

The PR makes a best effort to emit correct declaration files, but there are still issues when the exported entity is a qualified name or a class expression.

[Copilot]

Pull request overview

Adds CommonJS-export alias support so exports.Foo = <aliasable expression> can preserve type/namespace meanings (similar to export { C as Foo }), improving typechecking and declaration emit for many JS/CJS patterns in the TypeScript-Go compiler/LS.

Changes:

• Emit export { source as name }-style declarations for eligible CommonJS export property assignments in the declaration transformer.
• Treat exports.<prop> = <alias> assignments as CommonJS module exports for alias marking/visibility and alias-declaration detection.
• Update a large set of submodule reference baselines to reflect the new symbol/type/error behavior and .d.ts emit changes.

Reviewed changes

Copilot reviewed 90 out of 90 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
testdata/baselines/reference/submodule/fourslash/goToDefinition/goToDefinitionImportedNames10.baseline.jsonc.diff	Baseline diff removed due to updated go-to-definition expectation.
testdata/baselines/reference/submodule/fourslash/goToDefinition/goToDefinitionImportedNames10.baseline.jsonc	Updates fourslash baseline markers/targets for definition resolution.
testdata/baselines/reference/submodule/conformance/typeFromParamTagForFunction.types.diff	Updates expected type baseline diff for improved CJS export typing.
testdata/baselines/reference/submodule/conformance/typeFromParamTagForFunction.types	Updates inferred types (e.g. property types) after alias export changes.
testdata/baselines/reference/submodule/conformance/typeFromParamTagForFunction.symbols.diff	Updates expected symbol baseline diff for improved symbol binding.
testdata/baselines/reference/submodule/conformance/typeFromParamTagForFunction.symbols	Updates symbol resolution for JSDoc/CJS exported class cases.
testdata/baselines/reference/submodule/conformance/typeFromParamTagForFunction.errors.txt.diff	Updates expected diagnostic baseline diff after behavior changes.
testdata/baselines/reference/submodule/conformance/typeFromParamTagForFunction.errors.txt	Updates diagnostics (notably removing value-as-type error for B).
testdata/baselines/reference/submodule/conformance/nestedDestructuringOfRequire.js.diff	Updates .d.ts emit baseline diff for CJS export shape.
testdata/baselines/reference/submodule/conformance/nestedDestructuringOfRequire.js	Updates emitted declaration form (declare const + export {} pattern).
testdata/baselines/reference/submodule/conformance/moduleExportsAliasLoop2.symbols.diff	Updates symbol-baseline diff for alias-loop scenarios.
testdata/baselines/reference/submodule/conformance/moduleExportsAliasLoop2.symbols	Updates symbol resolutions in alias-loop cases.
testdata/baselines/reference/submodule/conformance/moduleExportsAliasLoop1.symbols.diff	Updates symbol-baseline diff for alias-loop scenarios.
testdata/baselines/reference/submodule/conformance/moduleExportsAliasLoop1.symbols	Updates symbol resolutions in alias-loop cases.
testdata/baselines/reference/submodule/conformance/moduleExportNestedNamespaces.types.diff	Updates type-baseline diff for nested namespace export scenarios.
testdata/baselines/reference/submodule/conformance/moduleExportNestedNamespaces.types	Updates type results for nested namespace exports.
testdata/baselines/reference/submodule/conformance/moduleExportNestedNamespaces.symbols.diff	Updates symbol-baseline diff for nested namespace exports.
testdata/baselines/reference/submodule/conformance/moduleExportNestedNamespaces.symbols	Updates symbol bindings for nested namespace exports.
testdata/baselines/reference/submodule/conformance/moduleExportNestedNamespaces.errors.txt.diff	Updates diagnostics baseline diff for nested namespace exports.
testdata/baselines/reference/submodule/conformance/moduleExportNestedNamespaces.errors.txt	Updates diagnostics after alias export behavior change.
testdata/baselines/reference/submodule/conformance/moduleExportAliasElementAccessExpression.js.diff	Updates .d.ts emit baseline diff for element-access export names.
testdata/baselines/reference/submodule/conformance/moduleExportAliasElementAccessExpression.js	Updates .d.ts output and associated TS18057 error locations.
testdata/baselines/reference/submodule/conformance/lateBoundAssignmentDeclarationSupport7.symbols.diff	Updates symbol-baseline diff for late-bound assignment cases.
testdata/baselines/reference/submodule/conformance/lateBoundAssignmentDeclarationSupport7.symbols	Updates symbol identity/qualification in late-bound assignment.
testdata/baselines/reference/submodule/conformance/jsdocTypeFromChainedAssignment3.types.diff	Baseline diff removed due to updated type output alignment.
testdata/baselines/reference/submodule/conformance/jsdocTypeFromChainedAssignment3.types	Updates type results around chained assignments on exports.
testdata/baselines/reference/submodule/conformance/jsdocTypeFromChainedAssignment3.symbols.diff	Updates symbol-baseline diff for chained assignment scenario.
testdata/baselines/reference/submodule/conformance/jsdocTypeFromChainedAssignment3.symbols	Updates symbol resolution for undefined in chained exports assignment.
testdata/baselines/reference/submodule/conformance/jsdocTypeFromChainedAssignment3.errors.txt.diff	Updates diagnostic baseline diff around many-member export assignment.
testdata/baselines/reference/submodule/conformance/jsdocTypeFromChainedAssignment3.errors.txt	Updates diagnostics/counts for member-based export typing.
testdata/baselines/reference/submodule/conformance/jsdocImportTypeReferenceToClassAlias.types.diff	Baseline diff removed due to improved typing for import('./mod1').C.
testdata/baselines/reference/submodule/conformance/jsdocImportTypeReferenceToClassAlias.types	Updates types to correctly resolve imported class alias as a type.
testdata/baselines/reference/submodule/conformance/jsdocImportTypeReferenceToClassAlias.symbols.diff	Updates symbol-baseline diff for imported type reference scenario.
testdata/baselines/reference/submodule/conformance/jsdocImportTypeReferenceToClassAlias.symbols	Updates symbol resolution for c.s against exported class alias.
testdata/baselines/reference/submodule/conformance/jsdocImportTypeReferenceToClassAlias.errors.txt.diff	Baseline diff removed after eliminating TS2694 error.
testdata/baselines/reference/submodule/conformance/jsdocImportTypeReferenceToClassAlias.errors.txt	Removes now-unexpected TS2694 diagnostic baseline content.
testdata/baselines/reference/submodule/conformance/jsDeclarationsImportAliasExposedWithinNamespaceCjs.js.diff	Updates .d.ts baseline diff for namespace/type export shape.
testdata/baselines/reference/submodule/conformance/jsDeclarationsImportAliasExposedWithinNamespaceCjs.js	Updates .d.ts output to include declare const myTypes plus type exports.
testdata/baselines/reference/submodule/conformance/jsDeclarationsFunctionsCjs.js.diff	Updates .d.ts baseline diff for function exports (export {} forms).
testdata/baselines/reference/submodule/conformance/jsDeclarationsFunctionsCjs.js	Updates emitted d.ts exports from export declare var to export { ... }.
testdata/baselines/reference/submodule/conformance/jsDeclarationsExportSubAssignments(target=es2015).js.diff	Updates .d.ts baseline diff for secondary exports alongside export =.
testdata/baselines/reference/submodule/conformance/jsDeclarationsExportSubAssignments(target=es2015).js	Updates .d.ts output to declare const + export { Strings }.
testdata/baselines/reference/submodule/conformance/jsDeclarationsExportForms(target=es2015).js.diff	Updates .d.ts baseline diff for CJS export forms and error set.
testdata/baselines/reference/submodule/conformance/jsDeclarationsExportForms(target=es2015).js	Updates .d.ts output and expected TS2502 errors after export-shape change.
testdata/baselines/reference/submodule/conformance/jsDeclarationsExportAssignmentExpressionPlusSecondary(target=es2015).js.diff	Updates .d.ts baseline diff for export = + secondary export.
testdata/baselines/reference/submodule/conformance/jsDeclarationsExportAssignmentExpressionPlusSecondary(target=es2015).js	Updates .d.ts output to declare const Strings then export { Strings }.
testdata/baselines/reference/submodule/conformance/jsDeclarationsExportAssignedClassExpressionShadowing(target=es2015).js.diff	Updates .d.ts baseline diff for class-expression export aliasing.
testdata/baselines/reference/submodule/conformance/jsDeclarationsExportAssignedClassExpressionShadowing(target=es2015).js	Updates .d.ts to export { Q as Another }.
testdata/baselines/reference/submodule/conformance/jsDeclarationsClassStatic(target=es2015).js.diff	Updates .d.ts baseline diff for static + secondary export handling.
testdata/baselines/reference/submodule/conformance/jsDeclarationsClassStatic(target=es2015).js	Updates .d.ts output to declare const Strings + export { Strings }.
testdata/baselines/reference/submodule/conformance/jsDeclarationsClassExtendsVisibility(target=es2015).js.diff	Updates .d.ts baseline diff for extends + secondary export handling.
testdata/baselines/reference/submodule/conformance/jsDeclarationsClassExtendsVisibility(target=es2015).js	Updates .d.ts output to declare const Strings + export { Strings }.
testdata/baselines/reference/submodule/conformance/exportPropertyAssignmentNameResolution.types.diff	Baseline diff removed due to updated type/error expectations.
testdata/baselines/reference/submodule/conformance/exportPropertyAssignmentNameResolution.types	Updates type outputs for property-assignment name resolution case.
testdata/baselines/reference/submodule/conformance/exportPropertyAssignmentNameResolution.symbols.diff	Updates symbol-baseline diff for property-assignment name resolution.
testdata/baselines/reference/submodule/conformance/exportPropertyAssignmentNameResolution.symbols	Updates symbol output (notably for new D() case).
testdata/baselines/reference/submodule/conformance/exportPropertyAssignmentNameResolution.errors.txt.diff	Baseline diff removed due to diagnostic expectation change.
testdata/baselines/reference/submodule/conformance/exportPropertyAssignmentNameResolution.errors.txt	Updates diagnostic output for new D() name resolution.
testdata/baselines/reference/submodule/conformance/exportNestedNamespaces.types.diff	Updates type-baseline diff for nested namespace exports.
testdata/baselines/reference/submodule/conformance/exportNestedNamespaces.types	Updates type results for nested namespace exports.
testdata/baselines/reference/submodule/conformance/exportNestedNamespaces.symbols.diff	Updates symbol-baseline diff for nested namespace exports.
testdata/baselines/reference/submodule/conformance/exportNestedNamespaces.symbols	Updates symbol bindings for nested namespace exports.
testdata/baselines/reference/submodule/conformance/exportNestedNamespaces.errors.txt.diff	Updates diagnostic baseline diff for nested namespace exports.
testdata/baselines/reference/submodule/conformance/exportNestedNamespaces.errors.txt	Updates diagnostics after alias export behavior change.
testdata/baselines/reference/submodule/conformance/commonJSImportExportedClassExpression.types.diff	Baseline diff removed due to updated type output alignment.
testdata/baselines/reference/submodule/conformance/commonJSImportExportedClassExpression.types	Updates types for exported class-expression import usage.
testdata/baselines/reference/submodule/conformance/commonJSImportExportedClassExpression.symbols.diff	Updates symbol-baseline diff for exported class-expression import usage.
testdata/baselines/reference/submodule/conformance/commonJSImportExportedClassExpression.symbols	Updates symbol resolution for k.values against exported class expression.
testdata/baselines/reference/submodule/conformance/commonJSImportExportedClassExpression.js.diff	Updates .d.ts baseline diff; now includes DtsFileErrors output section.
testdata/baselines/reference/submodule/conformance/commonJSImportExportedClassExpression.js	Updates .d.ts output for exported class expression (constructor return type now references K).
testdata/baselines/reference/submodule/conformance/commonJSImportExportedClassExpression.errors.txt.diff	Baseline diff removed after diagnostic expectation change.
testdata/baselines/reference/submodule/conformance/commonJSImportExportedClassExpression.errors.txt	Removes now-unexpected diagnostic baseline content.
testdata/baselines/reference/submodule/conformance/commonJSImportClassTypeReference.types.diff	Baseline diff removed due to updated type output alignment.
testdata/baselines/reference/submodule/conformance/commonJSImportClassTypeReference.types	Updates types for class type reference import scenario.
testdata/baselines/reference/submodule/conformance/commonJSImportClassTypeReference.symbols.diff	Updates symbol-baseline diff for class type reference import scenario.
testdata/baselines/reference/submodule/conformance/commonJSImportClassTypeReference.symbols	Updates symbol resolution for k.values against imported class symbol.
testdata/baselines/reference/submodule/conformance/commonJSImportClassTypeReference.js.diff	Updates .d.ts baseline diff to prefer export { K }.
testdata/baselines/reference/submodule/conformance/commonJSImportClassTypeReference.js	Updates .d.ts output to declare class K + export { K }.
testdata/baselines/reference/submodule/conformance/commonJSImportClassTypeReference.errors.txt.diff	Baseline diff removed after diagnostic expectation change.
testdata/baselines/reference/submodule/conformance/commonJSImportClassTypeReference.errors.txt	Removes now-unexpected diagnostic baseline content.
testdata/baselines/reference/submodule/conformance/commonJSAliasedExport.js.diff	Updates .d.ts baseline diff for CJS aliased export secondary member.
testdata/baselines/reference/submodule/conformance/commonJSAliasedExport.js	Updates .d.ts output to export { funky }.
testdata/baselines/reference/submodule/compiler/resolveNameWithNamspace.types.diff	Baseline diff removed due to updated type output alignment.
testdata/baselines/reference/submodule/compiler/resolveNameWithNamspace.types	Updates type results for exports.equal resolution in compiler baseline.
internal/transformers/declarations/transform.go	Adds export { source as name } emission for eligible CJS exports and helper isCommonJSAliasExport.
internal/checker/emitresolver.go	Treats exports.<prop> assignments as CommonJS exports for alias marking.
internal/checker/checker.go	Adjusts logic that ignores undefined assignments to repeated CJS export properties.
internal/binder/nameresolver.go	Adds CommonJS-specific filtering when resolving module exports (now flags-dependent).
internal/binder/binder.go	Marks eligible CJS export-property assignments as alias symbols at bind time.
internal/ast/utilities.go	Extends alias-symbol-declaration detection to cover exports.<symbol> = <alias>.

[Copilot]

The CommonJS-specific filter here clears result whenever the found export has no SymbolFlagsType, even if the lookup meaning is for values. That will make value-only CommonJS exports (e.g. functions/vars) fail to resolve from moduleExports, which can break typing for patterns like exports.foo = ...; exports.foo().

Consider restricting this logic to type/namespace lookups only (e.g. only apply the filter when meaning includes type/namespace and the symbol lacks those meanings), rather than filtering all module-member lookups in CommonJS files.

Suggested change

	if ast.IsSourceFile(location) && location.AsSourceFile().CommonJSModuleIndicator != nil && result.Flags&ast.SymbolFlagsType == 0 {
	result = nil
	if ast.IsSourceFile(location) && location.AsSourceFile().CommonJSModuleIndicator != nil {
	requestedNonValueMeaning := meaning & ast.SymbolFlagsModuleMember &^ ast.SymbolFlagsValue
	if requestedNonValueMeaning != 0 && result.Flags&requestedNonValueMeaning == 0 {
	result = nil
	} else {
	break loop
	}

[ahejlsberg]

This is the intended behavior. A CJS module can't see it's own value exports (because they appear to be properties on the exports object). However, @typedef types are visible within the module.

[jakebailey]

This does sort of tie in with the other comment, in that I think what this means is that exports.Foo = class {} will cause a type Foo to appear in scope?

[ahejlsberg]

No, exports.Foo = class {} creates an alias named Foo, not a type. So it is not in scope inside the module.

[Copilot]

isCommonJSAliasExport only treats exports.X = <identifier> as an alias export. But elsewhere (e.g. ast.ExpressionIsAlias) class expressions are also treated as aliases, and the PR description says class-expression exports should be supported. With the current restriction, exports.X = class ... will fall back to the export var X: ... path, which can yield self-referential/invalid .d.ts types (e.g. a constructor signature returning X when X is only a value).

Either extend alias-export handling to cover class expressions (by emitting a corresponding declare class + export) or explicitly fall back to a structural type to avoid emitting .d.ts that produces TS2749/TS2502 errors.

Suggested change

	if ast.IsBinaryExpression(node) && ast.IsIdentifier(node.AsBinaryExpression().Right) {
	if symbol := node.Symbol(); symbol != nil && len(symbol.Declarations) == 1 {
	return true
	if ast.IsBinaryExpression(node) {
	right := node.AsBinaryExpression().Right
	if ast.ExpressionIsAlias(right) {
	if symbol := node.Symbol(); symbol != nil && len(symbol.Declarations) == 1 {
	return true
	}

[ahejlsberg]

Agreed, there's more work to be done for class expressions. But doesn't need to be in this PR.

[jakebailey]

Seems okay for now given the edge cases already noted here