Bug 880447 - Permit 'yield yield expr;'. r=till.

js/src/frontend/Parser.cpp

@@ -4416,8 +4416,7 @@ Parser<ParseHandler>::returnStatementOrYieldExpression()
     if (next == TOK_ERROR)
         return null();
     if (next == TOK_EOF || next == TOK_EOL || next == TOK_SEMI || next == TOK_RC ||
-        (isYield && (next == TOK_YIELD || next == TOK_RB || next == TOK_RP ||
-                     next == TOK_COLON || next == TOK_COMMA)))
+        (isYield && (next == TOK_RB || next == TOK_RP || next == TOK_COLON || next == TOK_COMMA)))
     {
         if (isYield) {
             if (!reportWithOffset(ParseWarning, false, pos().begin, JSMSG_YIELD_WITHOUT_OPERAND))

js/src/jit-test/tests/generators/yield-yield.js

@@ -0,0 +1,12 @@
+// Bug 880447
+
+load(libdir + "asserts.js");
+
+function f() {
+    yield yield 1;
+}
+
+var g = f();
+assertEq(g.next(), 1);
+assertEq(g.send("hello"), "hello");
+assertThrowsValue(() => g.next(), StopIteration);