Add options.allowAwaitOutsideFunction. (#7637)

packages/babylon/README.md

@@ -32,6 +32,10 @@ mind. When in doubt, use `.parse()`.
   declarations can only appear at a program's top level. Setting this
   option to `true` allows them anywhere where a statement is allowed.
 
+- **allowAwaitOutsideFunction**: By default, `await` use is not allowed
+  outside of an async function. Set this to `true` to accept such
+  code.
+
 - **allowReturnOutsideFunction**: By default, a return statement at
   the top level raises an error. Set this to `true` to accept such
   code.

packages/babylon/src/options.js

@@ -7,6 +7,7 @@ export type Options = {
   sourceType: "script" | "module",
   sourceFilename?: string,
   startLine: number,
+  allowAwaitOutsideFunction: boolean,
   allowReturnOutsideFunction: boolean,
   allowImportExportEverywhere: boolean,
   allowSuperOutsideMethod: boolean,
@@ -24,6 +25,9 @@ export const defaultOptions: Options = {
   // Line from which to start counting source. Useful for
   // integration with other tools.
   startLine: 1,
+  // When enabled, await at the top level is not considered an
+  // error.
+  allowAwaitOutsideFunction: false,
   // When enabled, a return at the top level is not considered an
   // error.
   allowReturnOutsideFunction: false,

packages/babylon/src/parser/expression.js

@@ -753,13 +753,21 @@ export default class ExpressionParser extends LValParser {
 
       case tt.name: {
         node = this.startNode();
-        const allowAwait = this.state.value === "await" && this.state.inAsync;
+        const allowAwait =
+          this.state.value === "await" &&
+          (this.state.inAsync ||
+            (!this.state.inFunction && this.options.allowAwaitOutsideFunction));
+
         const containsEsc = this.state.containsEsc;
         const allowYield = this.shouldAllowYieldIdentifier();
         const id = this.parseIdentifier(allowAwait || allowYield);
 
         if (id.name === "await") {
-          if (this.state.inAsync || this.inModule) {
+          if (
+            this.state.inAsync ||
+            this.inModule ||
+            (!this.state.inFunction && this.options.allowAwaitOutsideFunction)
+          ) {
             return this.parseAwait(node);
           }
         } else if (
@@ -1862,7 +1870,10 @@ export default class ExpressionParser extends LValParser {
 
   parseAwait(node: N.AwaitExpression): N.AwaitExpression {
     // istanbul ignore next: this condition is checked at the call site so won't be hit here
-    if (!this.state.inAsync) {
+    if (
+      !this.state.inAsync &&
+      (this.state.inFunction || !this.options.allowAwaitOutsideFunction)
+    ) {
       this.unexpected();
     }
     if (this.match(tt.star)) {

packages/babylon/test/fixtures/es2017/async-functions/allow-await-outside-function-throw/input.js

@@ -0,0 +1,3 @@
+function a() {
+  return await 1
+}

packages/babylon/test/fixtures/es2017/async-functions/allow-await-outside-function-throw/options.json

@@ -0,0 +1,4 @@
+{
+  "allowAwaitOutsideFunction": true,
+  "throws": "Unexpected token, expected \";\" (2:15)"
+}

packages/babylon/test/fixtures/es2017/async-functions/allow-await-outside-function/input.js

@@ -0,0 +1 @@
+await 1

packages/babylon/test/fixtures/es2017/async-functions/allow-await-outside-function/options.json

@@ -0,0 +1,3 @@
+{
+  "allowAwaitOutsideFunction": true
+}

packages/babylon/test/fixtures/es2017/async-functions/allow-await-outside-function/output.json

@@ -0,0 +1,84 @@
+{
+  "type": "File",
+  "start": 0,
+  "end": 7,
+  "loc": {
+    "start": {
+      "line": 1,
+      "column": 0
+    },
+    "end": {
+      "line": 1,
+      "column": 7
+    }
+  },
+  "program": {
+    "type": "Program",
+    "start": 0,
+    "end": 7,
+    "loc": {
+      "start": {
+        "line": 1,
+        "column": 0
+      },
+      "end": {
+        "line": 1,
+        "column": 7
+      }
+    },
+    "sourceType": "script",
+    "body": [
+      {
+        "type": "ExpressionStatement",
+        "start": 0,
+        "end": 7,
+        "loc": {
+          "start": {
+            "line": 1,
+            "column": 0
+          },
+          "end": {
+            "line": 1,
+            "column": 7
+          }
+        },
+        "expression": {
+          "type": "AwaitExpression",
+          "start": 0,
+          "end": 7,
+          "loc": {
+            "start": {
+              "line": 1,
+              "column": 0
+            },
+            "end": {
+              "line": 1,
+              "column": 7
+            }
+          },
+          "argument": {
+            "type": "NumericLiteral",
+            "start": 6,
+            "end": 7,
+            "loc": {
+              "start": {
+                "line": 1,
+                "column": 6
+              },
+              "end": {
+                "line": 1,
+                "column": 7
+              }
+            },
+            "extra": {
+              "rawValue": 1,
+              "raw": "1"
+            },
+            "value": 1
+          }
+        }
+      }
+    ],
+    "directives": []
+  }
+}