fix(checker): reject exports originating from global augmentations

[erantianantha]

Fixes #64152.

Problem

When exporting bindings from a module without a local declaration (e.g. export { Math };), TypeScript correctly issues error TS2661 (Cannot export '{0}'. Only local declarations can be exported from a module.).

However, exports originating from a global scope augmentation (declare global { ... }) were previously permitted without error:

declare global {
    var XYZ: number;
}

export { XYZ }; // ❌ Permitted without error

Root Cause

In checkExportSpecifier (tsc/internal/checker/checker.go), the global declaration check only tested whether the declaration container was a global source file (ast.IsGlobalSourceFile(declarationContainer)). Declarations inside a global augmentation have an ast.ModuleBlock declaration container whose parent is a global scope augmentation (ast.IsGlobalScopeAugmentation(declarationContainer.Parent)), bypassing the error check.

Fix

Update checkExportSpecifier to treat declarations inside module blocks of global scope augmentations as non-local export sources:

isGlobalDeclaration := false
if symbol != nil && symbol.Declarations != nil {
	declarationContainer := ast.GetDeclarationContainer(symbol.Declarations[0])
	isGlobalDeclaration = ast.IsGlobalSourceFile(declarationContainer) || ast.IsModuleBlock(declarationContainer) && ast.IsGlobalScopeAugmentation(declarationContainer.Parent)
}

Add compiler test case exportSpecifierForAGlobalAugmentation.ts and reference baselines.

[Copilot]

🟢 Approval recommended

The focused checker change correctly addresses the reported hole and includes matching regression coverage.

Pull request overview

Fixes rejection of exports sourced from global augmentations.

Changes:

• Detects declarations within global augmentation module blocks.
• Adds a compiler regression test and reference baselines.
• Includes an unrelated whitespace-only change.

File summaries

File	Description
tsc/internal/checker/checker.go	Rejects exports originating from global augmentations.
tsc/internal/checker/relater.go	Adds a non-functional blank line.
tsc/testdata/tests/cases/compiler/exportSpecifierForAGlobalAugmentation.ts	Adds the regression case.
tsc/testdata/baselines/reference/compiler/exportSpecifierForAGlobalAugmentation.errors.txt	Captures expected TS2661.
tsc/testdata/baselines/reference/compiler/exportSpecifierForAGlobalAugmentation.js	Captures emitted output.
tsc/testdata/baselines/reference/compiler/exportSpecifierForAGlobalAugmentation.symbols	Captures symbol information.
tsc/testdata/baselines/reference/compiler/exportSpecifierForAGlobalAugmentation.types	Captures inferred types.

Review details

• Files reviewed: 7/7 changed files
• Comments generated: 0
• Review effort level: Balanced

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[Daniel Rosenwasser (DanielRosenwasser)]

Sorry, there's already a PR out at #64162.