Raise recoverable error for await expressions in sync functions (#12520)

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

@@ -492,9 +492,15 @@ export default class ExpressionParser extends LValParser {
   // Parse unary operators, both prefix and postfix.
   // https://tc39.es/ecma262/#prod-UnaryExpression
   parseMaybeUnary(refExpressionErrors: ?ExpressionErrors): N.Expression {
-    if (this.isContextual("await") && this.isAwaitAllowed()) {
-      return this.parseAwait();
+    const startPos = this.state.start;
+    const startLoc = this.state.startLoc;
+    const isAwait = this.isContextual("await");
+
+    if (isAwait && this.isAwaitAllowed()) {
+      this.next();
+      return this.parseAwait(startPos, startLoc);
     }
+
     const update = this.match(tt.incDec);
     const node = this.startNode();
     if (this.state.type.prefix) {
@@ -526,7 +532,24 @@ export default class ExpressionParser extends LValParser {
       }
     }
 
-    return this.parseUpdate(node, update, refExpressionErrors);
+    const expr = this.parseUpdate(node, update, refExpressionErrors);
+
+    const startsExpr = this.hasPlugin("v8intrinsic")
+      ? this.state.type.startsExpr
+      : this.state.type.startsExpr && !this.match(tt.modulo);
+    if (isAwait && startsExpr && !this.isAmbiguousAwait()) {
+      if (!this.state.invalidAwaitErrors.has(startPos)) {
+        this.raise(
+          startPos,
+          this.hasPlugin("topLevelAwait")
+            ? Errors.AwaitNotInAsyncContext
+            : Errors.AwaitNotInAsyncFunction,
+        );
+      }
+      return this.parseAwait(startPos, startLoc);
+    }
+
+    return expr;
   }
 
   // https://tc39.es/ecma262/#prod-UpdateExpression
@@ -2332,6 +2355,7 @@ export default class ExpressionParser extends LValParser {
             ? Errors.AwaitNotInAsyncContext
             : Errors.AwaitNotInAsyncFunction,
         );
+        this.state.invalidAwaitErrors.add(startLoc);
       } else {
         this.raise(startLoc, Errors.UnexpectedReservedWord, word);
       }
@@ -2348,10 +2372,8 @@ export default class ExpressionParser extends LValParser {
 
   // Parses await expression inside async function.
 
-  parseAwait(): N.AwaitExpression {
-    const node = this.startNode();
-
-    this.next();
+  parseAwait(startPos: number, startLoc: Position): N.AwaitExpression {
+    const node = this.startNodeAt(startPos, startLoc);
 
     this.expressionScope.recordParameterInitializerError(
       node.start,
@@ -2363,22 +2385,7 @@ export default class ExpressionParser extends LValParser {
     }
 
     if (!this.scope.inFunction && !this.options.allowAwaitOutsideFunction) {
-      if (
-        this.hasPrecedingLineBreak() ||
-        // All the following expressions are ambiguous:
-        //   await + 0, await - 0, await ( 0 ), await [ 0 ], await / 0 /u, await ``
-        this.match(tt.plusMin) ||
-        this.match(tt.parenL) ||
-        this.match(tt.bracketL) ||
-        this.match(tt.backQuote) ||
-        // Sometimes the tokenizer generates tt.slash for regexps, and this is
-        // handler by parseExprAtom
-        this.match(tt.regexp) ||
-        this.match(tt.slash) ||
-        // This code could be parsed both as a modulo operator or as an intrinsic:
-        //   await %x(0)
-        (this.hasPlugin("v8intrinsic") && this.match(tt.modulo))
-      ) {
+      if (this.isAmbiguousAwait()) {
         this.ambiguousScriptDifferentAst = true;
       } else {
         this.sawUnambiguousESM = true;
@@ -2392,6 +2399,25 @@ export default class ExpressionParser extends LValParser {
     return this.finishNode(node, "AwaitExpression");
   }
 
+  isAmbiguousAwait(): boolean {
+    return (
+      this.hasPrecedingLineBreak() ||
+      // All the following expressions are ambiguous:
+      //   await + 0, await - 0, await ( 0 ), await [ 0 ], await / 0 /u, await ``
+      this.match(tt.plusMin) ||
+      this.match(tt.parenL) ||
+      this.match(tt.bracketL) ||
+      this.match(tt.backQuote) ||
+      // Sometimes the tokenizer generates tt.slash for regexps, and this is
+      // handler by parseExprAtom
+      this.match(tt.regexp) ||
+      this.match(tt.slash) ||
+      // This code could be parsed both as a modulo operator or as an intrinsic:
+      //   await %x(0)
+      (this.hasPlugin("v8intrinsic") && this.match(tt.modulo))
+    );
+  }
+
   // Parses yield expression inside generator.
 
   parseYield(): N.YieldExpression {

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

@@ -154,6 +154,9 @@ export default class State {
   // Tokens length in token store
   tokensLength: number = 0;
 
+  // Positions of invalid await errors
+  invalidAwaitErrors: Set<number> = new Set();
+
   curPosition(): Position {
     return new Position(this.curLine, this.pos - this.lineStart);
   }

packages/babel-parser/test/fixtures/es2017/async-functions/9/output.json

@@ -0,0 +1,54 @@
+{
+  "type": "File",
+  "start":0,"end":40,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":40}},
+  "errors": [
+    "SyntaxError: 'await' is only allowed within async functions (1:24)"
+  ],
+  "program": {
+    "type": "Program",
+    "start":0,"end":40,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":40}},
+    "sourceType": "script",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "FunctionDeclaration",
+        "start":0,"end":40,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":40}},
+        "id": {
+          "type": "Identifier",
+          "start":9,"end":12,"loc":{"start":{"line":1,"column":9},"end":{"line":1,"column":12},"identifierName":"foo"},
+          "name": "foo"
+        },
+        "generator": false,
+        "async": false,
+        "params": [
+          {
+            "type": "Identifier",
+            "start":13,"end":20,"loc":{"start":{"line":1,"column":13},"end":{"line":1,"column":20},"identifierName":"promise"},
+            "name": "promise"
+          }
+        ],
+        "body": {
+          "type": "BlockStatement",
+          "start":22,"end":40,"loc":{"start":{"line":1,"column":22},"end":{"line":1,"column":40}},
+          "body": [
+            {
+              "type": "ExpressionStatement",
+              "start":24,"end":38,"loc":{"start":{"line":1,"column":24},"end":{"line":1,"column":38}},
+              "expression": {
+                "type": "AwaitExpression",
+                "start":24,"end":37,"loc":{"start":{"line":1,"column":24},"end":{"line":1,"column":37}},
+                "argument": {
+                  "type": "Identifier",
+                  "start":30,"end":37,"loc":{"start":{"line":1,"column":30},"end":{"line":1,"column":37},"identifierName":"promise"},
+                  "name": "promise"
+                }
+              }
+            }
+          ],
+          "directives": []
+        }
+      }
+    ],
+    "directives": []
+  }
+}

packages/babel-parser/test/fixtures/es2017/async-functions/allow-await-outside-function-throw/output.json

@@ -0,0 +1,52 @@
+{
+  "type": "File",
+  "start":0,"end":33,"loc":{"start":{"line":1,"column":0},"end":{"line":3,"column":1}},
+  "errors": [
+    "SyntaxError: 'await' is only allowed within async functions (2:9)"
+  ],
+  "program": {
+    "type": "Program",
+    "start":0,"end":33,"loc":{"start":{"line":1,"column":0},"end":{"line":3,"column":1}},
+    "sourceType": "script",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "FunctionDeclaration",
+        "start":0,"end":33,"loc":{"start":{"line":1,"column":0},"end":{"line":3,"column":1}},
+        "id": {
+          "type": "Identifier",
+          "start":9,"end":10,"loc":{"start":{"line":1,"column":9},"end":{"line":1,"column":10},"identifierName":"a"},
+          "name": "a"
+        },
+        "generator": false,
+        "async": false,
+        "params": [],
+        "body": {
+          "type": "BlockStatement",
+          "start":13,"end":33,"loc":{"start":{"line":1,"column":13},"end":{"line":3,"column":1}},
+          "body": [
+            {
+              "type": "ReturnStatement",
+              "start":17,"end":31,"loc":{"start":{"line":2,"column":2},"end":{"line":2,"column":16}},
+              "argument": {
+                "type": "AwaitExpression",
+                "start":24,"end":31,"loc":{"start":{"line":2,"column":9},"end":{"line":2,"column":16}},
+                "argument": {
+                  "type": "NumericLiteral",
+                  "start":30,"end":31,"loc":{"start":{"line":2,"column":15},"end":{"line":2,"column":16}},
+                  "extra": {
+                    "rawValue": 1,
+                    "raw": "1"
+                  },
+                  "value": 1
+                }
+              }
+            }
+          ],
+          "directives": []
+        }
+      }
+    ],
+    "directives": []
+  }
+}

packages/babel-parser/test/fixtures/es2017/async-functions/await-identifier-with-line-break-in-function/input.js

@@ -0,0 +1,4 @@
+function foo() {
+  await
+  foo;
+}

packages/babel-parser/test/fixtures/es2017/async-functions/await-identifier-with-line-break-in-function/output.json

@@ -0,0 +1,50 @@
+{
+  "type": "File",
+  "start":0,"end":33,"loc":{"start":{"line":1,"column":0},"end":{"line":4,"column":1}},
+  "program": {
+    "type": "Program",
+    "start":0,"end":33,"loc":{"start":{"line":1,"column":0},"end":{"line":4,"column":1}},
+    "sourceType": "script",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "FunctionDeclaration",
+        "start":0,"end":33,"loc":{"start":{"line":1,"column":0},"end":{"line":4,"column":1}},
+        "id": {
+          "type": "Identifier",
+          "start":9,"end":12,"loc":{"start":{"line":1,"column":9},"end":{"line":1,"column":12},"identifierName":"foo"},
+          "name": "foo"
+        },
+        "generator": false,
+        "async": false,
+        "params": [],
+        "body": {
+          "type": "BlockStatement",
+          "start":15,"end":33,"loc":{"start":{"line":1,"column":15},"end":{"line":4,"column":1}},
+          "body": [
+            {
+              "type": "ExpressionStatement",
+              "start":19,"end":24,"loc":{"start":{"line":2,"column":2},"end":{"line":2,"column":7}},
+              "expression": {
+                "type": "Identifier",
+                "start":19,"end":24,"loc":{"start":{"line":2,"column":2},"end":{"line":2,"column":7},"identifierName":"await"},
+                "name": "await"
+              }
+            },
+            {
+              "type": "ExpressionStatement",
+              "start":27,"end":31,"loc":{"start":{"line":3,"column":2},"end":{"line":3,"column":6}},
+              "expression": {
+                "type": "Identifier",
+                "start":27,"end":30,"loc":{"start":{"line":3,"column":2},"end":{"line":3,"column":5},"identifierName":"foo"},
+                "name": "foo"
+              }
+            }
+          ],
+          "directives": []
+        }
+      }
+    ],
+    "directives": []
+  }
+}

packages/babel-parser/test/fixtures/es2017/async-functions/await-inside-arrow-expression-disallowed/output.json

@@ -0,0 +1,48 @@
+{
+  "type": "File",
+  "start":0,"end":17,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":17}},
+  "errors": [
+    "SyntaxError: 'await' is only allowed within async functions (1:8)"
+  ],
+  "program": {
+    "type": "Program",
+    "start":0,"end":17,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":17}},
+    "sourceType": "script",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ExpressionStatement",
+        "start":0,"end":17,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":17}},
+        "expression": {
+          "type": "ArrowFunctionExpression",
+          "start":0,"end":17,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":17}},
+          "id": null,
+          "generator": false,
+          "async": false,
+          "params": [],
+          "body": {
+            "type": "BlockStatement",
+            "start":6,"end":17,"loc":{"start":{"line":1,"column":6},"end":{"line":1,"column":17}},
+            "body": [
+              {
+                "type": "ExpressionStatement",
+                "start":8,"end":15,"loc":{"start":{"line":1,"column":8},"end":{"line":1,"column":15}},
+                "expression": {
+                  "type": "AwaitExpression",
+                  "start":8,"end":15,"loc":{"start":{"line":1,"column":8},"end":{"line":1,"column":15}},
+                  "argument": {
+                    "type": "Identifier",
+                    "start":14,"end":15,"loc":{"start":{"line":1,"column":14},"end":{"line":1,"column":15},"identifierName":"x"},
+                    "name": "x"
+                  }
+                }
+              }
+            ],
+            "directives": []
+          }
+        }
+      }
+    ],
+    "directives": []
+  }
+}