Properly handle 'async of' in await loops

FIX: Fix spec conformity in corner case 'for await (async of ...)'. Closes #1031
acornjs · May 4, 2021 · 134ede4 · 134ede4
1 parent b0b1030
commit 134ede4
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Showing 3 changed files with 12 additions and 2 deletions.
diff --git a/acorn/src/expression.js b/acorn/src/expression.js
@@ -124,8 +124,10 @@ pp.parseMaybeAssign = function(forInit, refDestructuringErrors, afterLeftParse)
   }
 
   let startPos = this.start, startLoc = this.startLoc
-  if (this.type === tt.parenL || this.type === tt.name)
+  if (this.type === tt.parenL || this.type === tt.name) {
     this.potentialArrowAt = this.start
+    this.potentialArrowInForAwait = forInit === "await"
+  }
   let left = this.parseMaybeConditional(forInit, refDestructuringErrors)
   if (afterLeftParse) left = afterLeftParse.call(this, left, startPos, startLoc)
   if (this.type.isAssign) {
@@ -414,7 +416,8 @@ pp.parseExprAtom = function(refDestructuringErrors) {
     if (canBeArrow && !this.canInsertSemicolon()) {
       if (this.eat(tt.arrow))
         return this.parseArrowExpression(this.startNodeAt(startPos, startLoc), [id], false)
-      if (this.options.ecmaVersion >= 8 && id.name === "async" && this.type === tt.name && !containsEsc) {
+      if (this.options.ecmaVersion >= 8 && id.name === "async" && this.type === tt.name && !containsEsc &&
+          (!this.potentialArrowInForAwait || this.value !== "of" || this.containsEsc)) {
         id = this.parseIdent(false)
         if (this.canInsertSemicolon() || !this.eat(tt.arrow))
           this.unexpected()

diff --git a/acorn/src/state.js b/acorn/src/state.js
@@ -65,6 +65,7 @@ export class Parser {
 
     // Used to signify the start of a potential arrow function
     this.potentialArrowAt = -1
+    this.potentialArrowInForAwait = false
 
     // Positions to delayed-check that yield/await does not exist in default parameters.
     this.yieldPos = this.awaitPos = this.awaitIdentPos = 0

diff --git a/test/tests-async-iteration.js b/test/tests-async-iteration.js
@@ -1992,3 +1992,9 @@ test("({async})", {}, { "ecmaVersion": 9 })
 test("({async: true})", {}, { "ecmaVersion": 9 })
 
 testFail("({async\n    foo() { }})", "Unexpected token (2:4)", { "ecmaVersion": 9 })
+
+// #1031
+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})
+