Fix building on linux (arm)

[karwa]

Without this, we're unable to build on Debian (armv7) because of a conflicting va_list definition.

The include doesn't seem to be required, and removing needless includes is usually a good idea anyway.

See: https://bugs.swift.org/browse/SR-1412

[hpux735]

Thanks for working on this, @karwa. It's weird that this appeared. I'm curious what caused it to happen.

[phausler]

I don't think we can merge this change as is; the include is needed by Foundation and other projects that include that on Darwin. It would be better that if this is somehow a failure on linux to include this header that perhaps we gate that include somehow? That way the change is actually mergeable into the Darwin builds of Foundation/CoreFoundation.

[karwa]

@phausler Actually, turns out we only need to remove it from the SwiftRuntime/CoreFoundation.h umbrella header. Basically - we shouldn't export stdio from CoreFoundation swift module. For some reason when it's in the module it causes conflicts between clang builtin headers and system headers.

Is that better?

[gribozavr]

because of a conflicting va_list definition

What is defining the second va_list? The only header that can define va_list is stdarg.h that is shipped with the compiler. Different compilers, and different architectures, can define va_list differently depending on the ABI. Trying to match that definition by providing a second definition else is asking for trouble.

[karwa]

@gribozavr It's in the bug report. stdarg.h has a comment about some kind of Ubuntu 'hack', and I've been finding occurrences of what looks like the same problem going back to 2012/13.

This isn't really a fix, more of a workaround.

/home/ryan/Source/build/Ninja-ReleaseAssert/swift-linux-armv7/lib/swift/clang/include/stdarg.h:30:27: note: candidate found by name lookup is 'va_list'
typedef __builtin_va_list va_list;
                          ^
/usr/include/stdio.h:79:20: note: candidate found by name lookup is 'va_list'
typedef _G_va_list va_list;

[parkera]

Hm, I'm still not sure about this one.

[rfdickerson]

Yeah- I can confirm the duplicate definition of va_args is causing Foundation and libDispatch to fail when building on ARM (like Ubuntu Mate for Raspberry Pi). Commenting out stdio.h fixes it. As an alternative, adding the following to /usr/lib/swift/clang/include/stdarg.h seems to fix it also:

#ifndef _VA_LIST
#include <_G_config.h>  //Adding this line 
typedef __builtin_va_list va_list;
#define _VA_LIST
#endif

[hpux735]

I think I have some more context to add to this.

<module-includes>:1:10: note: in file included from <module-includes>:1:
#include "dispatch.h"
         ^
/mnt/build/swift-sources/swift-corelibs-libdispatch/dispatch/dispatch.h:68:10: note: in file included from /mnt/build/swift-sources/swift-corelibs-libdispatch/dispatch/dispatch.h:68:
#include <dispatch/object.h>
         ^
/mnt/build/swift-sources/swift-corelibs-libdispatch/dispatch/object.h:554:64: error: reference to 'va_list' is ambiguous
dispatch_debugv(dispatch_object_t object, const char *message, va_list ap);
                                                               ^
/mnt/build/swift-sources/build/Ninja-ReleaseAssert/swift-linux-armv7/lib/swift/clang/include/stdarg.h:30:27: note: candidate found by name lookup is 'va_list'
typedef __builtin_va_list va_list;
                          ^
/usr/include/stdio.h:79:20: note: candidate found by name lookup is 'va_list'
typedef _G_va_list va_list;
                   ^
/mnt/build/swift-sources/swift-corelibs-libdispatch/src/swift/Block.swift:13:8: error: could not build Objective-C module 'CDispatch'
import CDispatch
       ^

Is the complete text of the same error in libdispatch (see swiftlang/swift-corelibs-libdispatch#155 ). If you look at the system /usr/include/stdio.h it defines va_list, but it makes a feeble attempt to make sure it's only defined if using GNU C:

#if defined __USE_XOPEN || defined __USE_XOPEN2K8
# ifdef __GNUC__
#  ifndef _VA_LIST_DEFINED
typedef _G_va_list va_list;
#   define _VA_LIST_DEFINED
#  endif
# else
#  include <stdarg.h>
# endif
#endif

Before #include <stdio.h> I tried #undef __GNUC__ but it didn't work for some reason. I'm a little surprised it's being redefined in such a way.

[parkera]

This has been superseded by #603.