Handle numeric literal export names in declaration emit by Copilot · Pull Request #3919 · microsoft/typescript-go

Copilot · 2026-05-16T19:41:45Z

The printer panics when emitting declarations for CommonJS files with numeric export names (e.g. exports[1] = 2). emitModuleExportName only handled KindIdentifier and KindStringLiteral, missing KindNumericLiteral. Additionally, the declaration transformer passed numeric literals through unchanged, producing invalid syntax like export { _exported as 1 }.

Added numeric-to-string conversion in getNameExpressionPreferringIdentifier in the declaration transformer, since numeric property names in JS are string properties — now emits valid export { _exported as "1" } syntax
No printer changes needed since the transformer converts numeric literals to string literals before they reach emitModuleExportName
Added test case covering exports[1], module.exports[1], and Object.defineProperty(exports, 1, {})

Add KindNumericLiteral case to emitModuleExportName in the printer, which was causing a panic when emitting declarations for CommonJS files with numeric export names like `exports[1] = 2`. Agent-Logs-Url: https://github.com/microsoft/typescript-go/sessions/9f3fe2c6-afe3-4d4b-9709-13e88c7271b6 Co-authored-by: jakebailey <5341706+jakebailey@users.noreply.github.com>

jakebailey · 2026-05-16T20:04:33Z

+//// [DtsFileErrors]
+
+
+bug.d.ts(2,22): error TS2300: Duplicate identifier '(Missing)'.
+bug.d.ts(2,23): error TS1003: Identifier expected.
+bug.d.ts(2,25): error TS1128: Declaration or statement expected.
+bug.d.ts(4,24): error TS2300: Duplicate identifier '(Missing)'.
+bug.d.ts(4,25): error TS1003: Identifier expected.
+bug.d.ts(4,27): error TS1128: Declaration or statement expected.
+bug.d.ts(6,24): error TS2300: Duplicate identifier '(Missing)'.
+bug.d.ts(6,25): error TS1003: Identifier expected.
+bug.d.ts(6,27): error TS1128: Declaration or statement expected.


@copilot Probably this indicates further brokenness, but compare to Strada.

I'd think we'd want to export as "1" etc since numeric props are just number props in disguise? Not sure. Look into it.

You're right — numeric props are just string props in disguise. Fixed in 0019d09 by converting NumericLiteral to StringLiteral in getNameExpressionPreferringIdentifier in the declaration transformer. Now emits export { _exported as "1" } instead of the invalid export { _exported as 1 }, eliminating the parse errors from the baseline (down from 9 to just 3 duplicate identifier errors, which are expected since all 3 exports share the same name "1").

…ration emit Numeric property names in JS are string properties; convert NumericLiteral to StringLiteral in getNameExpressionPreferringIdentifier so declarations emit valid syntax like `export { _exported as "1" }` instead of the invalid `export { _exported as 1 }`. Agent-Logs-Url: https://github.com/microsoft/typescript-go/sessions/0d9fa6e3-1d16-42fa-824c-c7baf31e67ee Co-authored-by: jakebailey <5341706+jakebailey@users.noreply.github.com>

jakebailey

Seems plausible

ahejlsberg · 2026-05-17T12:08:21Z

+		// Numeric property names are string properties in JS; convert to string literal
+		nameExpr = tx.Factory().NewStringLiteral(nameExpr.Text(), ast.TokenFlagsNone)
+	}
 	if ast.IsStringLiteralLike(nameExpr) && scanner.IsIdentifierText(nameExpr.Text(), core.LanguageVariantStandard) {


Suggested change

if ast.IsStringLiteralLike(nameExpr) && scanner.IsIdentifierText(nameExpr.Text(), core.LanguageVariantStandard) {

if ast.IsStringOrNumericLiteralLike(nameExpr) && scanner.IsIdentifierText(nameExpr.Text(), core.LanguageVariantStandard) {

ahejlsberg · 2026-05-17T12:09:21Z

 }

 func (tx *DeclarationTransformer) getNameExpressionPreferringIdentifier(nameExpr *ast.Node) *ast.Node {
+	if ast.IsNumericLiteral(nameExpr) {


This change isn't correct or necessary. Just use isStringOrNumericLiteralLike in the check below.

ahejlsberg

@copilot Please make the requested changes.

ahejlsberg · 2026-05-17T12:12:10Z

@copilot Please make the requested changes.

ahejlsberg · 2026-05-17T12:44:41Z

Nevermind on the above comments. I agree that converting numeric literals to string literals is the best option here, though it is different from what Strada does. Strada converts the numeric literal 1 to the identifier _1. Similarly, it converts non-identifier strings by injecting underscores, e.g. "a b" becomes _a_b. I think it is better to just export using string literals.

Copilot

Pull request overview

This PR fixes declaration emit for CommonJS numeric export names by converting numeric property names into string-literal export names and adding regression coverage.

Changes:

Converts numeric CommonJS export names to string literals during declaration transformation.
Updates module export-name printing behavior.
Adds a compiler test and baselines for numeric export declarations.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
`internal/transformers/declarations/transform.go`	Converts numeric export property names to string literals before declaration emit.
`internal/printer/printer.go`	Adds numeric literal handling in module export-name emission.
`testdata/tests/cases/compiler/numericExportNameDeclaration.ts`	Adds regression input covering numeric CommonJS export patterns.
`testdata/baselines/reference/compiler/numericExportNameDeclaration.js`	Adds emitted declaration baseline and dts diagnostics.
`testdata/baselines/reference/compiler/numericExportNameDeclaration.symbols`	Adds symbol baseline for the new test.
`testdata/baselines/reference/compiler/numericExportNameDeclaration.types`	Adds type baseline for the new test.

jakebailey · 2026-05-17T14:38:30Z

+	case ast.KindNumericLiteral:
+		p.emitNumericLiteral(node.AsNumericLiteral())


@copilot double check and then make this change

Fixed in 4304c9f. The KindNumericLiteral case in emitModuleExportName now emits the numeric literal as a quoted string literal ("1" instead of bare 1), since ModuleExportName syntax only accepts identifiers or string literals.

@copilot what? That's not what I asked, the comment was saying the code was dead and I asked you to confirm

Confirmed — the KindNumericLiteral case was dead code. The declaration transformer's getNameExpressionPreferringIdentifier (line 2176) converts all numeric literals to string literals before they reach the printer. The parser's parseModuleExportName/canParseModuleExportName only produces identifiers or string literals, never numeric literals. Removed the dead case in 95b66cc.

… printer Agent-Logs-Url: https://github.com/microsoft/typescript-go/sessions/1ec9206d-7bdc-4410-a06d-8ea7247652c9 Co-authored-by: jakebailey <5341706+jakebailey@users.noreply.github.com>

Agent-Logs-Url: https://github.com/microsoft/typescript-go/sessions/4efd5625-7022-4615-84fe-f09fae670b06 Co-authored-by: jakebailey <5341706+jakebailey@users.noreply.github.com>

Initial plan

682fd6d

Copilot AI assigned Copilot and jakebailey May 16, 2026

Copilot started work on behalf of jakebailey May 16, 2026 19:41 View session

Copilot AI linked an issue May 16, 2026 that may be closed by this pull request

tsgo printer panics when emitting declarations for CommonJS files with numeric export names #3886

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Copilot AI changed the title ~~[WIP] Fix tsgo printer panics when emitting declarations for CommonJS files~~ Handle numeric literal in emitModuleExportName May 16, 2026

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Copilot AI changed the title ~~Handle numeric literal in emitModuleExportName~~ Handle numeric literal export names in declaration emit May 16, 2026

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Copilot AI requested a review from jakebailey May 16, 2026 20:45

Merge branch 'main' into copilot/fix-tsgo-printer-panics

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ahejlsberg marked this pull request as ready for review May 17, 2026 12:48

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fix: emit numeric literals as string literals in emitModuleExportName…

4304c9f

… printer Agent-Logs-Url: https://github.com/microsoft/typescript-go/sessions/1ec9206d-7bdc-4410-a06d-8ea7247652c9 Co-authored-by: jakebailey <5341706+jakebailey@users.noreply.github.com>

Copilot finished work on behalf of jakebailey May 17, 2026 14:52

Copilot started work on behalf of jakebailey May 17, 2026 15:05 View session

Remove dead KindNumericLiteral case from emitModuleExportName

95b66cc

Agent-Logs-Url: https://github.com/microsoft/typescript-go/sessions/4efd5625-7022-4615-84fe-f09fae670b06 Co-authored-by: jakebailey <5341706+jakebailey@users.noreply.github.com>

Copilot finished work on behalf of jakebailey May 17, 2026 15:21

RyanCavanaugh approved these changes May 18, 2026

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ahejlsberg added this pull request to the merge queue May 18, 2026

Merged via the queue into main with commit 7119345 May 18, 2026
21 checks passed

ahejlsberg deleted the copilot/fix-tsgo-printer-panics branch May 18, 2026 17:59

	if ast.IsStringLiteralLike(nameExpr) && scanner.IsIdentifierText(nameExpr.Text(), core.LanguageVariantStandard) {
	if ast.IsStringOrNumericLiteralLike(nameExpr) && scanner.IsIdentifierText(nameExpr.Text(), core.LanguageVariantStandard) {

		case ast.KindNumericLiteral:
		p.emitNumericLiteral(node.AsNumericLiteral())

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Pull request overview

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