libc++ fails to build with gcc 4.6

[llvmbot]

Bugzilla Link	11539
Resolution	WONTFIX
Resolved on	Feb 26, 2014 09:33
Version	unspecified
OS	Linux
Attachments	The output from gcc 4.6.1
Reporter	LLVM Bugzilla Contributor
CC	@chandlerc,@mclow

Extended Description

gcc doesn't seem to be able to compile any file including any of the libc++ headers.
I've attached the output of trying to compile a simple testcase with:

g++ test.cpp -nostdinc++ -lc++ -I/usr/include/c++/v1

The file is as follows:

#include
int main()
{}

[llvmbot]

One gets the same errors with gcc 4.7.0.

[llvmbot]

Patch to remove warnings and fix detection of is_base_of on gcc on linux
This removed the warnings cause by the lone "'" in __undef_min_max (this could be replaced with a "`" or left out.
It also correctly detects that gcc has support for is_base_of on linux (It would previously only work on windows.

This fixes some headers, for example it's now possible to use vector, however at least iostream and memory are still broken.

[llvmbot]

iostream is working if one passes -std=c++0x to gcc.

[llvmbot]

One is able to break memory when trying to construct a vector of unique_ptrs

#include
#include

int main()
{
std::vector<std::unique_ptr> b;
b.push_back( nullptr );
return 0;
}

With this testcase, one gets the following output:

In file included from test.cpp:1:0:
/usr/include/c++/v1/memory: In member function ‘void std::__1::allocator<_Tp>::construct(_Up*, _Args&& ...) [with _Up = std::__1::unique_ptr, _Args = {const std::__1::unique_ptr&}, _Tp = std::__1::unique_ptr]’:
/usr/include/c++/v1/memory:1536:14: instantiated from ‘static void std::__1::allocator_traits<_Alloc>::__construct(std::__1::true_type, std::__1::allocator_traits<_Alloc>::allocator_type&, _Tp*, _Args&& ...) [with _Tp = std::__1::unique_ptr, _Args = {const std::__1::unique_ptr&}, _Alloc = std::__1::allocator<std::__1::unique_ptr >, std::__1::true_type = std::__1::integral_constant<bool, true>, std::__1::allocator_traits<_Alloc>::allocator_type = std::__1::allocator<std::__1::unique_ptr >]’
/usr/include/c++/v1/memory:1474:14: instantiated from ‘static void std::__1::allocator_traits<_Alloc>::construct(std::__1::allocator_traits<_Alloc>::allocator_type&, _Tp*, _Args&& ...) [with _Tp = std::__1::unique_ptr, _Args = {const std::__1::unique_ptr&}, _Alloc = std::__1::allocator<std::__1::unique_ptr >, std::__1::allocator_traits<_Alloc>::allocator_type = std::__1::allocator<std::__1::unique_ptr >]’
/usr/include/c++/v1/__split_buffer:503:5: instantiated from ‘void std::__1::__split_buffer<_Tp, _Allocator>::push_front(std::__1::__split_buffer<_Tp, _Allocator>::const_reference) [with _Tp = std::__1::unique_ptr, _Allocator = std::__1::allocator<std::__1::unique_ptr >&, std::__1::__split_buffer<_Tp, _Allocator>::const_reference = const std::__1::unique_ptr&, std::__1::__split_buffer<_Tp, _Allocator>::value_type = std::__1::unique_ptr]’
/usr/include/c++/v1/vector:799:9: instantiated from ‘void std::__1::vector<_Tp, _Allocator>::__swap_out_circular_buffer(std::__1::__split_buffer<_Tp, _Allocator&>&) [with _Tp = std::__1::unique_ptr, _Allocator = std::__1::allocator<std::__1::unique_ptr >]’
/usr/include/c++/v1/vector:1477:9: instantiated from ‘void std::__1::vector<_Tp, _Allocator>::push_back(std::__1::vector<_Tp, _Allocator>::value_type&&) [with _Tp = std::__1::unique_ptr, _Allocator = std::__1::allocator<std::__1::unique_ptr >, std::__1::vector<_Tp, _Allocator>::value_type = std::__1::unique_ptr]’
test.cpp:7:26: instantiated from here
/usr/include/c++/v1/memory:2315:5: error: ‘std::__1::unique_ptr<_Tp, _Dp>::unique_ptr(const std::__1::unique_ptr<_Tp, _Dp>&) [with _Tp = int, _Dp = std::__1::default_delete, std::__1::unique_ptr<_Tp, _Dp> = std::__1::unique_ptr]’ is private
/usr/include/c++/v1/memory:1661:13: error: within this context

[llvmbot]

FYI, I see the following build errors when trying to build libcxx with GCC 4.6.3:

projects/libcxx/include/type_traits:3272:31: error: expected primary-expression before ‘decltype’
projects/libcxx/include/system_error:374:35: error: function ‘std::__1::error_category::error_category()’ defaulted on its first declaration must not have an exception-specification
projects/libcxx/include/memory:2434:49: error: function ‘std::__1::default_delete<_Tp>::default_delete()’ defaulted on its first declaration must not have an exception-specification

Looks like these are bugs in GCC diagnostics (e.g. see http://llvm.org/bugs/show_bug.cgi?id=15182), but this still causes a problem, especially after r191624: now libcxx is built automatically if it's checked out, failing the build on systems where GCC 4.6.3 is the default host compiler (e.g. Ubuntu Precise).

Shouldn't we hack the code or build rules to make libcxx fail gracefully in this case?

[mclow]

Since LLVM is moving to require gcc 4.7.x or later (as part of the switch to C++11), I believe that this bug is moot.

If anyone feels otherwise, please re-open the bug.