From 623f2371eba0096cfbac4283af6b7c6e32c13d30 Mon Sep 17 00:00:00 2001
From: "vogelheim@chromium.org"
 <vogelheim@chromium.org@ce2b1a6d-e550-0410-aec6-3dcde31c8c00>
Date: Fri, 9 May 2014 15:36:51 +0000
Subject: [PATCH] Prevent calls to ReturnValue::Set with pointer-valued types. 
  [2nd try, after the previous version broke the build]

Currently, this code will compile:
SomePointer* p = ...;
ReturnValue r = ...;
r.Set(p);

What happens is that ReturnValue::Set has no pointer-ish overloads, but
a bool one, and hence C++ will convert the pointer to a bool and use
the Set(bool) overload. In other words, the example above is equivalent
to: r.Set(p ? true : false); Which probably isn't what the author had
in mind. This change adds a Set(void*) overload whose body forces a
compile error, to prevent this from happening inadvertently. The only
use of this indeed turned out to be an error.

(Said error was fixed/removed in crrev.com/267393002.)

Why was crrev.com/240013004 reverted?
The orginal version compiled fine on gcc (+ MSVC), but not on clang.
There's no clang try-bots, but the ASAN-based buildbots used clang
and hence the build broke. I'm slightly unsure on why, but clang -
unlike those other compilers - eagerly compiled the non-compilable
setter, which predictably broke. Now, the non-compilable setter uses
the same template logic that all other, comparable cases use. I've
tried 'make qc' with both gcc and clang versions.

BUG=
R=dcarney@chromium.org

Review URL: https://codereview.chromium.org/279883002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21228 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
---
 include/v8.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/include/v8.h b/include/v8.h
index 72dc75d42a..f4ae71d43c 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -2429,6 +2429,10 @@ class ReturnValue {
   // Convenience getter for Isolate
   V8_INLINE Isolate* GetIsolate();
 
+  // Pointer setter: Uncompilable to prevent inadvertent misuse.
+  template <typename S>
+  V8_INLINE void Set(S* whatever);
+
  private:
   template<class F> friend class ReturnValue;
   template<class F> friend class FunctionCallbackInfo;
@@ -5973,6 +5977,13 @@ Isolate* ReturnValue<T>::GetIsolate() {
   return *reinterpret_cast<Isolate**>(&value_[-2]);
 }
 
+template<typename T>
+template<typename S>
+void ReturnValue<T>::Set(S* whatever) {
+  // Uncompilable to prevent inadvertent misuse.
+  TYPE_CHECK(S*, Primitive);
+}
+
 template<typename T>
 internal::Object* ReturnValue<T>::GetDefaultValue() {
   // Default value is always the pointer below value_ on the stack.