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fix: Warning when export before enum #18157

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fix: Warning when export before enum #18157

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7b400dc
fix
liuxingbaoyu Jul 30, 2026
1301497
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liuxingbaoyu Jul 30, 2026
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@liuxingbaoyu
liuxingbaoyu committed Jul 30, 2026
commit 7b400dc3d67d8be1c49f415025781c4d561f9be3
3 changes: 2 additions & 1 deletion packages/babel-plugin-transform-typescript/src/const-enum.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -43,7 +43,7 @@ export default function transpileConstEnum(
),
);

if (path.scope.hasOwnBinding(name)) {
if (!(path.scope.getOwnBinding(name)?.kind === "unknown")) {

@chatgpt-codex-connector chatgpt-codex-connector Bot Jul 30, 2026

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P1 Badge Preserve compatibility with cores that do not bind enums

When this plugin version is loaded by an older but supported @babel/core/@babel/traverse (the plugin's peer range is ^8.0.0), enums have no scope binding, so with optimizeConstEnums an input such as export const enum E { A } takes this branch and becomes Object.assign(E, ...) without ever declaring E, throwing during module evaluation. A missing binding must follow the declaration-creation path, and the paired traverse change must likewise remain compatible with older plugin versions.

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@liuxingbaoyu liuxingbaoyu Jul 30, 2026

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I am surprised that AI has also discovered this.

(parentIsExport ? path.parentPath : path).replaceWith(
t.expressionStatement(
t.callExpression(
Expand All @@ -53,6 +53,7 @@ export default function transpileConstEnum(
),
);
} else {
path.scope.removeOwnBinding(name);
path.replaceWith(
t.variableDeclaration("const", [
t.variableDeclarator(path.node.id, obj),
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4 changes: 4 additions & 0 deletions ...lugin-transform-typescript/test/fixtures/optimize-const-enums/export-before-enum/input.ts
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@@ -0,0 +1,4 @@

export { Enum };

const enum Enum {}
5 changes: 5 additions & 0 deletions ...n-transform-typescript/test/fixtures/optimize-const-enums/export-before-enum/options.json
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@@ -0,0 +1,5 @@
{
"plugins": [["transform-typescript"]],
"sourceType": "module",
"validateLogs": true
}
4 changes: 4 additions & 0 deletions ...gin-transform-typescript/test/fixtures/optimize-const-enums/export-before-enum/output.mjs
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@@ -0,0 +1,4 @@
export { Enum };
var Enum = /*#__PURE__*/function (Enum) {
return Enum;
}(Enum || {});
15 changes: 0 additions & 15 deletions ...-typescript/test/fixtures/optimize-const-enums/export-const-enum-type-no-deopt/stderr.txt
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@@ -1,16 +1 @@
The exported identifier "WhitespaceFlag" is not declared in Babel's scope tracker
as a JavaScript value binding, and "@babel/plugin-transform-typescript"
never encountered it as a TypeScript type declaration.
It will be treated as a JavaScript value.

This problem is likely caused by another plugin injecting
"WhitespaceFlag" without registering it in the scope tracker. If you are the author
of that plugin, please use "scope.registerDeclaration(declarationPath)".
The exported identifier "WhitespaceFlag" is not declared in Babel's scope tracker
as a JavaScript value binding, and "@babel/plugin-transform-typescript"
never encountered it as a TypeScript type declaration.
It will be treated as a JavaScript value.

This problem is likely caused by another plugin injecting
"WhitespaceFlag" without registering it in the scope tracker. If you are the author
of that plugin, please use "scope.registerDeclaration(declarationPath)".
6 changes: 6 additions & 0 deletions packages/babel-traverse/src/scope/index.ts
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Expand Up @@ -755,6 +755,12 @@ class Scope {
return;
}

if (path.isTSEnumDeclaration() && !path.node.declare) {
const id = path.get("id");
this.registerBinding(kind, id, path);
Comment on lines +758 to +760

@chatgpt-codex-connector chatgpt-codex-connector Bot Jul 30, 2026

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P1 Badge Clear bindings when inlining local const enums

With optimizeConstEnums, a non-exported const enum merged with a following namespace now leaves this newly registered binding behind when const-enum.ts removes the enum; the generic removal hook cannot clean it because getBindingIdentifiers has no TSEnumDeclaration entry. For a module containing const enum E { A } followed by namespace E { export const B = 1 }, transpileNamespace consequently sees hasOwnBinding("E") and omits its let E declaration, producing an IIFE that reads and assigns undeclared E and throws at runtime. Remove the enum binding before the inlining branch removes the declaration.

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@liuxingbaoyu liuxingbaoyu Jul 30, 2026

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While adding tests, I discovered that const enum cannot be merged with a namespace, but removing it is fine.

Comment on lines +758 to +760

@chatgpt-codex-connector chatgpt-codex-connector Bot Jul 30, 2026

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P1 Badge Register nested enums in their block scope

When an enum appears in a nested block and an enclosing function/program has a same-named binding, this new special case registers the enum in that enclosing scope because the collector routes non-BlockScoped declarations to the function/program scope. Consequently, valid shadowing such as let E; { enum E {} } throws Duplicate declaration "E" during scope crawling, even though the enum transform emits a block-local let; register enum declarations in their block parent (or classify them as block-scoped) instead.

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return;
}

const parent = this.getProgramParent();
const ids = path.getOuterBindingIdentifiers(true);

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