From ed4a7a1afae031f8cb3eb245a9539f33f9008390 Mon Sep 17 00:00:00 2001
From: adams85 <31276480+adams85@users.noreply.github.com>
Date: Wed, 3 Apr 2024 16:14:51 +0200
Subject: [PATCH] Fix parsing of an "async of" edge case in for loop  (#1286)

FIX: Properly raise a parse error for invalid `for`/`of` statements using `async` as binding name.
---
 acorn/src/statement.js        | 16 +++++++++++-----
 test/tests-async-iteration.js |  3 +++
 2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/acorn/src/statement.js b/acorn/src/statement.js
index d5e5c6fc8..c5fea3956 100644
--- a/acorn/src/statement.js
+++ b/acorn/src/statement.js
@@ -235,13 +235,19 @@ pp.parseForStatement = function(node) {
     return this.parseFor(node, init)
   }
   let startsWithLet = this.isContextual("let"), isForOf = false
+  let containsEsc = this.containsEsc
   let refDestructuringErrors = new DestructuringErrors
-  let init = this.parseExpression(awaitAt > -1 ? "await" : true, refDestructuringErrors)
+  let initPos = this.start
+  let init = awaitAt > -1
+    ? this.parseExprSubscripts(refDestructuringErrors, "await")
+    : this.parseExpression(true, refDestructuringErrors)
   if (this.type === tt._in || (isForOf = this.options.ecmaVersion >= 6 && this.isContextual("of"))) {
-    if (this.options.ecmaVersion >= 9) {
-      if (this.type === tt._in) {
-        if (awaitAt > -1) this.unexpected(awaitAt)
-      } else node.await = awaitAt > -1
+    if (awaitAt > -1) { // implies `ecmaVersion >= 9` (see declaration of awaitAt)
+      if (this.type === tt._in) this.unexpected(awaitAt)
+      node.await = true
+    } else if (isForOf && this.options.ecmaVersion >= 8) {
+      if (init.start === initPos && !containsEsc && init.type === "Identifier" && init.name === "async") this.unexpected()
+      else if (this.options.ecmaVersion >= 9) node.await = false
     }
     if (startsWithLet && isForOf) this.raise(init.start, "The left-hand side of a for-of loop may not start with 'let'.")
     this.toAssignable(init, false, refDestructuringErrors)
diff --git a/test/tests-async-iteration.js b/test/tests-async-iteration.js
index 4f885c380..2d553bc86 100644
--- a/test/tests-async-iteration.js
+++ b/test/tests-async-iteration.js
@@ -1998,3 +1998,6 @@ test("async () => { for await (async of []); }", {}, {ecmaVersion: 9})
 test("for (async of => {}; i < 10; ++i) {}", {}, {ecmaVersion: 9})
 testFail("for (async of [1]) {}", "Unexpected token (1:14)", {ecmaVersion: 9})
 
+testFail("async () => { for (async\nof []); }", "Unexpected token (2:0)", {ecmaVersion: 9})
+testFail("async () => { for (async of\n[]); }", "Unexpected token (2:0)", {ecmaVersion: 9})
+test("for ((async) of [7]);", {}, {ecmaVersion: 9})