Allow yield expressions without a RHS.

test/mjsunit/harmony/generators-parsing.js

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 17 matching lines @@
 // Flags: --harmony-generators
 
 // Test basic generator syntax.
 
 // Yield statements.
 function* g() { yield 3; yield 4; }
 
 // Yield expressions.
 function* g() { (yield 3) + (yield 4); }
 
+// Yield without a RHS.
+function* g() { yield; }
+function* g() { yield }
+function* g() {
+  yield
+}
+function* g() { (yield) }
+function* g() { [yield] }
+function* g() { {yield} }
+function* g() { yield, yield }
+function* g() { yield; yield }
+function* g() { (yield) ? yield : yield }
+function* g() {
+  (yield)
+  ? yield
+  : yield
+}
+
+// If yield has a RHS, it needs to start on the same line.  The * in a
+// yield* counts as starting the RHS.
+function* g() {
+  yield *
+  foo
+}
+assertThrows("function* g() { yield\n* foo }", SyntaxError);
+assertEquals(undefined,
+             (function*(){
+               yield
+               3
+             })().next().value);
+
+// A YieldExpression is not a LogicalORExpression.
+assertThrows("function* g() { yield ? yield : yield }", SyntaxError);
+
 // You can have a generator in strict mode.
 function* g() { "use strict"; yield 3; yield 4; }
 
 // Generators can have return statements also, which internally parse to a kind
 // of yield expression.
 function* g() { yield 1; return; }
 function* g() { yield 1; return 2; }
 function* g() { yield 1; return 2; yield "dead"; }
 
 // Generator expression.
 (function* () { yield 3; });
 
 // Named generator expression.
 (function* g() { yield 3; });
 
-// A generator without a yield is specified as causing an early error.  This
-// behavior is currently unimplemented.  See
-// https://bugs.ecmascript.org/show_bug.cgi?id=1283.
+// You can have a generator without a yield.
 function* g() { }
 
-// A YieldExpression in the RHS of a YieldExpression is currently specified as
-// causing an early error.  This behavior is currently unimplemented.  See
-// https://bugs.ecmascript.org/show_bug.cgi?id=1283.
+// A YieldExpression is valid as the RHS of a YieldExpression.
 function* g() { yield yield 1; }
 function* g() { yield 3 + (yield 4); }
 
 // Generator definitions with a name of "yield" are not specifically ruled out
 // by the spec, as the `yield' name is outside the generator itself.  However,
 // in strict-mode, "yield" is an invalid identifier.
 function* yield() { (yield 3) + (yield 4); }
 assertThrows("function* yield() { \"use strict\"; (yield 3) + (yield 4); }",
              SyntaxError);
 
 // In sloppy mode, yield is a normal identifier, outside of generators.
 function yield(yield) { yield: yield (yield + yield (0)); }
 
 // Yield is always valid as a key in an object literal.
 ({ yield: 1 });
 function* g() { yield ({ yield: 1 }) }
 function* g() { yield ({ get yield() { return 1; }}) }
 
 // Checks that yield is a valid label in sloppy mode, but not valid in a strict
 // mode or in generators.
 function f() { yield: 1 }
 assertThrows("function f() { \"use strict\"; yield: 1 }", SyntaxError)
 assertThrows("function* g() { yield: 1 }", SyntaxError)
 
 // Yield is only a keyword in the body of the generator, not in nested
 // functions.
 function* g() { function f() { yield (yield + yield (0)); } }
 
-// Yield needs a RHS.
-assertThrows("function* g() { yield; }", SyntaxError);
-
 // Yield in a generator is not an identifier.
 assertThrows("function* g() { yield = 10; }", SyntaxError);
 
 // Yield binds very loosely, so this parses as "yield (3 + yield 4)", which is
 // invalid.
 assertThrows("function* g() { yield 3 + yield 4; }", SyntaxError);
 
 // Yield is still a future-reserved-word in strict mode
 assertThrows("function f() { \"use strict\"; var yield = 13; }", SyntaxError);
 
 // The name of the NFE is let-bound in G, so is invalid.
 assertThrows("function* g() { yield (function yield() {}); }", SyntaxError);
 
 // In generators, yield is invalid as a formal argument name.
 assertThrows("function* g(yield) { yield (10); }", SyntaxError);