fix #3205: panic with const enum inside parens

CHANGELOG.md

@@ -2,6 +2,17 @@
 
 ## Unreleased
 
+* Fix a panic with `const enum` inside parentheses ([#3205](https://github.com/evanw/esbuild/issues/3205))
+
+    This release fixes an edge case where esbuild could potentially panic if a TypeScript `const enum` statement was used inside of a parenthesized expression and was followed by certain other scope-related statements. Here's a minimal example that triggers this edge case:
+
+    ```ts
+    (() => {
+      const enum E { a };
+      () => E.a
+    })
+    ```
+
 * Allow a newline in the middle of TypeScript `export type` statement ([#3225](https://github.com/evanw/esbuild/issues/3225))
 
     Previously esbuild incorrectly rejected the following valid TypeScript code:

internal/js_parser/ts_parser.go

@@ -1427,7 +1427,10 @@ func (p *parser) parseTypeScriptEnumStmt(loc logger.Loc, opts parseStmtOpts) js_
 	if p.scopesInOrderForEnum == nil {
 		p.scopesInOrderForEnum = make(map[logger.Loc][]scopeOrder)
 	}
-	p.scopesInOrderForEnum[loc] = p.scopesInOrder[scopeIndex:]
+
+	// Make a copy of "scopesInOrder" instead of a slice since the original
+	// array may be flattened in the future by "popAndFlattenScope"
+	p.scopesInOrderForEnum[loc] = append([]scopeOrder{}, p.scopesInOrder[scopeIndex:]...)
 
 	return js_ast.Stmt{Loc: loc, Data: &js_ast.SEnum{
 		Name:     name,

internal/js_parser/ts_parser_test.go

@@ -1600,6 +1600,16 @@ var Foo = /* @__PURE__ */ ((Foo) => {
   return Foo;
 })(Foo || {});
 bar = 0 /* FOO */;
+`)
+
+	// https://github.com/evanw/esbuild/issues/3205
+	expectPrintedTS(t, "(() => { const enum Foo { A } () => Foo.A })", `() => {
+  let Foo;
+  ((Foo) => {
+    Foo[Foo["A"] = 0] = "A";
+  })(Foo || (Foo = {}));
+  () => 0 /* A */;
+};
 `)
 }
 

scripts/end-to-end-tests.js

@@ -144,6 +144,18 @@ tests.push(
       if (foo !== 1 || bar !== 3) throw 'fail'
     `,
   }),
+
+  // https://github.com/evanw/esbuild/issues/3205
+  test(['entry.ts', '--outfile=node.js'], {
+    'entry.ts': `
+      // Note: The parentheses are important here
+      let x = (() => {
+        const enum E { a = 123 }
+        return () => E.a
+      })
+      if (x()() !== 123) throw 'fail'
+    `,
+  }),
 )
 
 // Check "tsconfig.json" behavior