Fix mishandling of astral characters after "async function"

Closes #1037

FIX: Fix a bug where astral characters after `async function` were ignored.

Author: marijnh

acorn/src/statement.js

@@ -65,10 +65,11 @@ pp.isAsyncFunction = function() {
 
   skipWhiteSpace.lastIndex = this.pos
   let skip = skipWhiteSpace.exec(this.input)
-  let next = this.pos + skip[0].length
+  let next = this.pos + skip[0].length, after
   return !lineBreak.test(this.input.slice(this.pos, next)) &&
     this.input.slice(next, next + 8) === "function" &&
-    (next + 8 === this.input.length || !isIdentifierChar(this.input.charAt(next + 8)))
+    (next + 8 === this.input.length ||
+     !(isIdentifierChar(after = this.input.charCodeAt(next + 8)) || after > 0xd7ff && after < 0xdc00))
 }
 
 // Parse a single statement.

test/tests-asyncawait.js

@@ -3539,3 +3539,5 @@ test("async() => await (5 ** 6)", {}, {ecmaVersion: 8})
 testFail("async() => await (5) ** 6", "Unexpected token (1:21)", {ecmaVersion: 8})
 
 testFail("4 + async() => 2", "Unexpected token (1:12)", {ecmaVersion: 8, loose: false})
+
+testFail("async function𝐬 f() {}", "Unexpected token (1:17)", {ecmaVersion: 8})