[generators] Implement Generator.prototype.return.

src/runtime/runtime-generator.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/runtime/runtime-utils.h"
 
 #include "src/arguments.h"
 #include "src/factory.h"
 #include "src/frames-inl.h"
 #include "src/objects-inl.h"
@@ skipping 69 matching lines @@
   }
 
   return isolate->heap()->undefined_value();
 }
 
 
 // Note that this function is the slow path for resuming generators.  It is only
 // called if the suspended activation had operands on the stack, stack handlers
 // needing rewinding, or if the resume should throw an exception.  The fast path
 // is handled directly in FullCodeGenerator::EmitGeneratorResume(), which is
-// inlined into GeneratorNext and GeneratorThrow.  EmitGeneratorResumeResume is
-// called in any case, as it needs to reconstruct the stack frame and make space
-// for arguments and operands.
+// inlined into GeneratorNext, GeneratorReturn, and GeneratorThrow.
+// EmitGeneratorResume is called in any case, as it needs to reconstruct the
+// stack frame and make space for arguments and operands.
 RUNTIME_FUNCTION(Runtime_ResumeJSGeneratorObject) {
   SealHandleScope shs(isolate);
   DCHECK(args.length() == 3);
   CONVERT_ARG_CHECKED(JSGeneratorObject, generator_object, 0);
   CONVERT_ARG_CHECKED(Object, value, 1);
   CONVERT_SMI_ARG_CHECKED(resume_mode_int, 2);
   JavaScriptFrameIterator stack_iterator(isolate);
   JavaScriptFrame* frame = stack_iterator.frame();
 
   DCHECK_EQ(frame->function(), generator_object->function());
@@ skipping 15 matching lines @@
   FixedArray* operand_stack = generator_object->operand_stack();
   int operands_count = operand_stack->length();
   if (operands_count != 0) {
     frame->RestoreOperandStack(operand_stack);
     generator_object->set_operand_stack(isolate->heap()->empty_fixed_array());
   }
 
   JSGeneratorObject::ResumeMode resume_mode =
       static_cast<JSGeneratorObject::ResumeMode>(resume_mode_int);
   switch (resume_mode) {
+    // Note: this looks like NEXT and RETURN are the same but RETURN receives
+    // special treatment in the generator code (to which we return here).
     case JSGeneratorObject::NEXT:
+    case JSGeneratorObject::RETURN:
       return value;
     case JSGeneratorObject::THROW:
       return isolate->Throw(value);
   }
 
   UNREACHABLE();
   return isolate->ThrowIllegalOperation();
 }
 
 
@@ skipping 67 matching lines @@
     Handle<Code> code(generator->function()->code(), isolate);
     int offset = generator->continuation();
     RUNTIME_ASSERT(0 <= offset && offset < code->instruction_size());
     return Smi::FromInt(code->SourcePosition(offset));
   }
 
   return isolate->heap()->undefined_value();
 }
 
 
+// Optimization for the following three functions is disabled in
+// js/generator.js and compiler/ast-graph-builder.cc.
+
+
 RUNTIME_FUNCTION(Runtime_GeneratorNext) {
-  UNREACHABLE();  // Optimization disabled in SetUpGenerators().
-  return NULL;
+  UNREACHABLE();
+  return nullptr;
+}
+
+
+RUNTIME_FUNCTION(Runtime_GeneratorReturn) {
+  UNREACHABLE();
+  return nullptr;
 }
 
 
 RUNTIME_FUNCTION(Runtime_GeneratorThrow) {
-  UNREACHABLE();  // Optimization disabled in SetUpGenerators().
-  return NULL;
+  UNREACHABLE();
+  return nullptr;
 }
 }  // namespace internal
 }  // namespace v8