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[libc++] Fix PR20084 - std::is_function<void() const> failed. 

Summary:
This patch introduces some black magic to detect const and volatile qualified function types such as `void () const`.

The patch works in the following way:

We first rule out any type that satisfies on of the following. These restrictions are important so that the test below works properly.
* `is_class<_Tp>::value`
* `is_union<_Tp>::value`
* `is_void<_Tp>::value`
* `is_reference<_Tp>::value`
* `__is_nullptr_t<_Tp>::value`


If none of the above is true we perform overload resolution on `__source<_Tp>(0)` to determine the return type.
*  If `_Tp&` is well-formed we select `_Tp& __source(int)`. `_Tp&` is only ill formed for cv void types and cv/ref qualified function types.
* Otherwise we select `__dummy_type __source(...)`. Since we know `_Tp` cannot be void then it must be a function type.


let `R` be the returned from `__source<_Tp>(0)`. 
We perform overload resolution on `__test<_Tp>(R)`.
* If `R` is `__dummy_type` we call `true_type __test(__dummy_type)`.
* if `R` is `_Tp&` and `_Tp&` decays to `_Tp*` we call `true_type __test(_Tp*)`.  Only references to function types decay to a pointer of the same type.
* In all other cases we call `false_type __test(...)`. 

`__source<_Tp>(0)` will try and form `_Tp&`  in the return type. if `_Tp&` is not well formed the return type of `__source<_Tp>(0)` will be dummy type. `_Tp&` is only ill-formed for cv/ref qualified function types (and void which is dealt with elsewhere).


This fixes PR20084 - http://llvm.org/bugs/show_bug.cgi?id=20084

Reviewers: rsmith, K-ballo, mclow.lists

Reviewed By: mclow.lists

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D7573

llvm-svn: 229696
This commit is contained in:
Eric Fiselier 2015-02-18 16:31:46 +00:00
parent 1779314e3c
commit 9317721beb
2 changed files with 54 additions and 15 deletions
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7
libcxx/include/type_traits
View File

@ -430,9 +430,12 @@ template <class _Tp> struct _LIBCPP_TYPE_VIS_ONLY is_same<_Tp, _Tp> :
namespace __libcpp_is_function_imp
{
struct __dummy_type {};
template <class _Tp> char __test(_Tp*);
template <class _Tp> char __test(__dummy_type);
template <class _Tp> __two __test(...);
template <class _Tp> _Tp& __source();
template <class _Tp> _Tp& __source(int);
template <class _Tp> __dummy_type __source(...);
}
template <class _Tp, bool = is_class<_Tp>::value ||
@ -441,7 +444,7 @@ template <class _Tp, bool = is_class<_Tp>::value ||
is_reference<_Tp>::value ||
__is_nullptr_t<_Tp>::value >
struct __libcpp_is_function
: public integral_constant<bool, sizeof(__libcpp_is_function_imp::__test<_Tp>(__libcpp_is_function_imp::__source<_Tp>())) == 1>
: public integral_constant<bool, sizeof(__libcpp_is_function_imp::__test<_Tp>(__libcpp_is_function_imp::__source<_Tp>(0))) == 1>
{};
template <class _Tp> struct __libcpp_is_function<_Tp, true> : public false_type {};

62
libcxx/test/std/utilities/meta/meta.unary/meta.unary.cat/function.pass.cpp
View File

@ -13,8 +13,19 @@
#include <type_traits>
using namespace std;
class Class {};
enum Enum1 {};
#if __cplusplus >= 201103L
enum class Enum2 : int {};
#else
enum Enum2 {};
#endif
template <class T>
void test_function_imp()
void test()
{
static_assert(!std::is_void<T>::value, "");
#if _LIBCPP_STD_VER > 11
@ -34,19 +45,44 @@ void test_function_imp()
static_assert( std::is_function<T>::value, "");
}
template <class T>
void test_function()
{
test_function_imp<T>();
test_function_imp<const T>();
test_function_imp<volatile T>();
test_function_imp<const volatile T>();
}
// Since we can't actually add the const volatile and ref qualifiers once
// later let's use a macro to do it.
#define TEST_REGULAR(...) \
test<__VA_ARGS__>(); \
test<__VA_ARGS__ const>(); \
test<__VA_ARGS__ volatile>(); \
test<__VA_ARGS__ const volatile>()
#define TEST_REF_QUALIFIED(...) \
test<__VA_ARGS__ &>(); \
test<__VA_ARGS__ const &>(); \
test<__VA_ARGS__ volatile &>(); \
test<__VA_ARGS__ const volatile &>(); \
test<__VA_ARGS__ &&>(); \
test<__VA_ARGS__ const &&>(); \
test<__VA_ARGS__ volatile &&>(); \
test<__VA_ARGS__ const volatile &&>()
int main()
{
test_function<void ()>();
test_function<void (int)>();
test_function<int (double)>();
test_function<int (double, char)>();
TEST_REGULAR( void () );
TEST_REGULAR( void (int) );
TEST_REGULAR( int (double) );
TEST_REGULAR( int (double, char) );
TEST_REGULAR( void (...) );
TEST_REGULAR( void (int, ...) );
TEST_REGULAR( int (double, ...) );
TEST_REGULAR( int (double, char, ...) );
#if __cplusplus >= 201103L
TEST_REF_QUALIFIED( void () );
TEST_REF_QUALIFIED( void (int) );
TEST_REF_QUALIFIED( int (double) );
TEST_REF_QUALIFIED( int (double, char) );
TEST_REF_QUALIFIED( void (...) );
TEST_REF_QUALIFIED( void (int, ...) );
TEST_REF_QUALIFIED( int (double, ...) );
TEST_REF_QUALIFIED( int (double, char, ...) );
#endif
}