Allow await when it is not in AsyncArrowHead (#11148)

packages/babel-parser/src/parser/expression.js

@@ -560,10 +560,15 @@ export default class ExpressionParser extends LValParser {
       stop: false,
     };
     do {
+      const oldMaybeInAsyncArrowHead = this.state.maybeInAsyncArrowHead;
+      if (state.maybeAsyncArrow) {
+        this.state.maybeInAsyncArrowHead = true;
+      }
       base = this.parseSubscript(base, startPos, startLoc, noCalls, state);
 
       // After parsing a subscript, this isn't "async" for sure.
       state.maybeAsyncArrow = false;
+      this.state.maybeInAsyncArrowHead = oldMaybeInAsyncArrowHead;
     } while (!state.stop);
     return base;
   }
@@ -953,15 +958,18 @@ export default class ExpressionParser extends LValParser {
           !this.canInsertSemicolon()
         ) {
           const oldMaybeInArrowParameters = this.state.maybeInArrowParameters;
+          const oldMaybeInAsyncArrowHead = this.state.maybeInAsyncArrowHead;
           const oldYieldPos = this.state.yieldPos;
           const oldAwaitPos = this.state.awaitPos;
           this.state.maybeInArrowParameters = true;
+          this.state.maybeInAsyncArrowHead = true;
           this.state.yieldPos = -1;
           this.state.awaitPos = -1;
           const params = [this.parseIdentifier()];
           this.expect(tt.arrow);
           this.checkYieldAwaitInDefaultParams();
           this.state.maybeInArrowParameters = oldMaybeInArrowParameters;
+          this.state.maybeInAsyncArrowHead = oldMaybeInAsyncArrowHead;
           this.state.yieldPos = oldYieldPos;
           this.state.awaitPos = oldAwaitPos;
           // let foo = async bar => {};
@@ -1296,6 +1304,9 @@ export default class ExpressionParser extends LValParser {
       this.shouldParseArrow() &&
       (arrowNode = this.parseArrow(arrowNode))
     ) {
+      if (!this.isAwaitAllowed() && !this.state.maybeInAsyncArrowHead) {
+        this.state.awaitPos = oldAwaitPos;
+      }
       this.checkYieldAwaitInDefaultParams();
       this.state.yieldPos = oldYieldPos;
       this.state.awaitPos = oldAwaitPos;
@@ -2128,7 +2139,7 @@ export default class ExpressionParser extends LValParser {
       }
       if (
         this.state.awaitPos === -1 &&
-        (this.state.maybeInArrowParameters || this.isAwaitAllowed())
+        (this.state.maybeInAsyncArrowHead || this.isAwaitAllowed())
       ) {
         this.state.awaitPos = this.state.start;
       }

packages/babel-parser/src/tokenizer/state.js

@@ -59,6 +59,11 @@ export default class State {
   // Flags to track
   inParameters: boolean = false;
   maybeInArrowParameters: boolean = false;
+  // This flag is used to track async arrow head across function declarations.
+  // e.g. async (foo = function (await) {}) => {}
+  // When parsing `await` in this expression, `maybeInAsyncArrowHead` is true
+  // but `maybeInArrowParameters` is false
+  maybeInAsyncArrowHead: boolean = false;
   inPipeline: boolean = false;
   inType: boolean = false;
   noAnonFunctionType: boolean = false;

packages/babel-parser/test/fixtures/es2017/async-functions/await-as-argument-identifier-in-non-async-functions/input.js

@@ -0,0 +1 @@
+(await) => {}

packages/babel-parser/test/fixtures/es2017/async-functions/await-as-argument-identifier-in-non-async-functions/output.json

@@ -0,0 +1,104 @@
+{
+  "type": "File",
+  "start": 0,
+  "end": 13,
+  "loc": {
+    "start": {
+      "line": 1,
+      "column": 0
+    },
+    "end": {
+      "line": 1,
+      "column": 13
+    }
+  },
+  "program": {
+    "type": "Program",
+    "start": 0,
+    "end": 13,
+    "loc": {
+      "start": {
+        "line": 1,
+        "column": 0
+      },
+      "end": {
+        "line": 1,
+        "column": 13
+      }
+    },
+    "sourceType": "script",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ExpressionStatement",
+        "start": 0,
+        "end": 13,
+        "loc": {
+          "start": {
+            "line": 1,
+            "column": 0
+          },
+          "end": {
+            "line": 1,
+            "column": 13
+          }
+        },
+        "expression": {
+          "type": "ArrowFunctionExpression",
+          "start": 0,
+          "end": 13,
+          "loc": {
+            "start": {
+              "line": 1,
+              "column": 0
+            },
+            "end": {
+              "line": 1,
+              "column": 13
+            }
+          },
+          "id": null,
+          "generator": false,
+          "async": false,
+          "params": [
+            {
+              "type": "Identifier",
+              "start": 1,
+              "end": 6,
+              "loc": {
+                "start": {
+                  "line": 1,
+                  "column": 1
+                },
+                "end": {
+                  "line": 1,
+                  "column": 6
+                },
+                "identifierName": "await"
+              },
+              "name": "await"
+            }
+          ],
+          "body": {
+            "type": "BlockStatement",
+            "start": 11,
+            "end": 13,
+            "loc": {
+              "start": {
+                "line": 1,
+                "column": 11
+              },
+              "end": {
+                "line": 1,
+                "column": 13
+              }
+            },
+            "body": [],
+            "directives": []
+          }
+        }
+      }
+    ],
+    "directives": []
+  }
+}