disallow line terminator after async contextual keyword - fixes #1711

src/acorn/src/expression.js

@@ -292,7 +292,7 @@ pp.parseExprAtom = function(refShorthandDefaultPos) {
     //
     if (this.options.features["es7.asyncFunctions"]) {
       // async functions!
-      if (id.name === "async") {
+      if (id.name === "async" && !this.canInsertSemicolon()) {
         // arrow functions
         if (this.type === tt.parenL) {
           let expr = this.parseParenAndDistinguishExpression(start, true, true)

src/acorn/src/lookahead.js

@@ -9,6 +9,7 @@ var STATE_KEYS = [
   "lastTokEnd",
   "lineStart",
   "startLoc",
+  "curLine",
   "endLoc",
   "start",
   "pos",

src/acorn/src/statement.js

@@ -83,10 +83,13 @@ pp.parseStatement = function(declaration, topLevel) {
     return starttype === tt._import ? this.parseImport(node) : this.parseExport(node)
 
   case tt.name:
-    if (this.options.features["es7.asyncFunctions"] && this.value === "async" && this.lookahead().type === tt._function) {
-      this.next();
-      this.expect(tt._function);
-      return this.parseFunction(node, true, false, true);
+    if (this.options.features["es7.asyncFunctions"] && this.value === "async") {
+      var lookahead = this.lookahead();
+      if (lookahead.type === tt._function && !this.canInsertSemicolon.call(lookahead)) {
+        this.next();
+        this.expect(tt._function);
+        return this.parseFunction(node, true, false, true);
+      }
     }
 
     // If the statement does not start with a statement keyword or a

test/acorn/tests-babel.js

@@ -620,6 +620,63 @@ testFail("function foo(promise) { await promise; }", "Unexpected token (1:30)",
   features: { "es7.asyncFunctions": true }
 });
 
+testFail("var x = async\n(x) => x + 1;", "Unexpected token (2:4)", {
+  ecmaVersion: 7,
+  features: { "es7.asyncFunctions": true }
+});
+
+test("async\nfunction foo() {}", {
+  type: "Program",
+  body: [
+    {
+      type: "ExpressionStatement",
+      expression: {
+        type: "Identifier",
+        name: "async",
+        loc: {
+          start: {line: 1, column: 0},
+          end: {line: 1, column: 5}
+        }
+      },
+      loc: {
+        start: {line: 1, column: 0},
+        end: {line: 1, column: 5}
+      }
+    },
+    {
+      type: "FunctionDeclaration",
+      id: {
+        type: "Identifier",
+        name: "foo",
+        loc: {
+          start: {line: 2, column: 9},
+          end: {line: 2, column: 12}
+        }
+      },
+      params: [],
+      body: {
+        type: "BlockStatement",
+        body: [],
+        loc: {
+          start: {line: 2, column: 15},
+          end: {line: 2, column: 17}
+        }
+      },
+      generator: false,
+      expression: false,
+      async: false,
+      loc: {
+        start: {line: 2, column: 0},
+        end: {line: 2, column: 17}
+      }
+    }
+  ]
+}, {
+  ecmaVersion: 7,
+  features: { "es7.asyncFunctions": true },
+  locations: true
+});
+
 test('async function foo(promise) { await promise; }', {
   type: "Program",
   body: [{