Merge pull request #308797 from microsoft/joh/private-fields-async-fix

build: fix async private method token fusion; inlineChat: adopt native private fields

Author: jrieken

build/next/private-to-property.ts

@@ -115,7 +115,7 @@ export function convertPrivateFields(code: string, filename: string): ConvertPri
 		lastEnd = edit.end;
 	}
 	parts.push(code.substring(lastEnd));
-return { code: parts.join(''), classCount, fieldCount: fieldCount, editCount: edits.length, elapsed: Date.now() - t1, edits };
+	return { code: parts.join(''), classCount, fieldCount: fieldCount, editCount: edits.length, elapsed: Date.now() - t1, edits };
 
 	// --- AST walking ---
 
@@ -209,10 +209,15 @@ return { code: parts.join(''), classCount, fieldCount: fieldCount, editCount: ed
 			if (ts.isPrivateIdentifier(child)) {
 				const resolved = resolvePrivateName(child.text);
 				if (resolved !== undefined) {
+					const start = child.getStart(sourceFile);
 					edits.push({
-						start: child.getStart(sourceFile),
+						start,
 						end: child.getEnd(),
-						newText: resolved
+						// In minified code, `async#run()` has no space before `#`.
+						// The `#` naturally starts a new token, but `$` does not —
+						// `async$a` would fuse into one identifier. Insert a space
+						// when the preceding character is an identifier character.
+						newText: (start > 0 && isIdentifierChar(code.charCodeAt(start - 1))) ? ' ' + resolved : resolved
 					});
 				}
 				return;
@@ -234,6 +239,11 @@ return { code: parts.join(''), classCount, fieldCount: fieldCount, editCount: ed
 	}
 }
 
+function isIdentifierChar(ch: number): boolean {
+	// a-z, A-Z, 0-9, _, $
+	return (ch >= 97 && ch <= 122) || (ch >= 65 && ch <= 90) || (ch >= 48 && ch <= 57) || ch === 95 || ch === 36;
+}
+
 /**
  * Adjusts a source map to account for text edits applied to the generated JS.
  *

build/next/test/private-to-property.test.ts

@@ -292,6 +292,54 @@ suite('convertPrivateFields', () => {
 		assert.deepStrictEqual(result.edits, []);
 	});
 
+	test('async private method — replacement must not merge with async keyword', async () => {
+		// In minified output, there is no space between `async` and `#method`:
+		//   class Foo{async#run(){await Promise.resolve(1)}}
+		// Replacing `#run` with `$a` naively produces `async$a()` which is a
+		// single identifier, not `async $a()`. The `await` inside then becomes
+		// invalid because the method is no longer async.
+		const code = 'class Foo{async#run(){return await Promise.resolve(1)}call(){return this.#run()}}';
+		const result = convertPrivateFields(code, 'test.js');
+		assert.ok(!result.code.includes('#run'), 'should replace #run');
+		// The replacement must NOT fuse with `async` into a single token
+		assert.doesNotThrow(() => new Function(result.code), 'transformed code must be valid JS');
+		// Verify it actually executes (the async method should still work)
+		const exec = new Function(`
+			${result.code}
+			return new Foo().call();
+		`);
+		const val = await exec();
+		assert.strictEqual(val, 1);
+	});
+
+	test('async private method — space inserted in declaration and not in usage', () => {
+		// More readable version: ensure that `async #method()` becomes
+		// `async $a()` (with space), while `this.#method()` becomes
+		// `this.$a()` (no extra space needed since `.` separates tokens).
+		const code = [
+			'class Foo {',
+			'  async #doWork() { return await 42; }',
+			'  run() { return this.#doWork(); }',
+			'}',
+		].join('\n');
+		const result = convertPrivateFields(code, 'test.js');
+		assert.ok(!result.code.includes('#doWork'), 'should replace #doWork');
+		assert.doesNotThrow(() => new Function(result.code), 'transformed code must be valid JS');
+	});
+
+	test('static async private method — no token fusion', async () => {
+		const code = 'class Foo{static async#init(){return await Promise.resolve(1)}static go(){return Foo.#init()}}';
+		const result = convertPrivateFields(code, 'test.js');
+		assert.doesNotThrow(() => new Function(result.code),
+			'static async private method must produce valid JS, got:\n' + result.code);
+		const exec = new Function(`
+			${result.code}
+			return Foo.go();
+		`);
+		const value = await exec();
+		assert.strictEqual(value, 1);
+	});
+
 	test('heritage clause — extends expression resolves outer private field, not inner', () => {
 		const code = [
 			'class Outer {',