[CMake] [2.8.12.1] Bug in Xcode generation of STATIC from OBJECT libraries

[Paul Smith]

Hi all.  I'm using CMake 2.8.12.1 on Linux, MacOS, and Windows.  I've
discovered a bug in the Xcode generator when dealing with OBJECT and
STATIC libraries.  This example works fine on Linux, and on MacOS with
the Makefile generator.  I also haven't noticed a problem on Windows
(MSVC).

What I'm doing is creating an OBJECT library then creating a STATIC
library from that (and I'm also creating a SHARED library from the same
OBJECT library, but that's not relevant to this bug).

Here's the test file:

  cmake_minimum_required(VERSION 2.8.12)
  project(TestLib C)

  add_library(mylib_OBJECTS OBJECT mylib.c)
  add_library(mylib STATIC $<TARGET_OBJECTS:mylib_OBJECTS>)

  add_executable(libtest libtest.c)
  target_link_libraries(libtest mylib)

I have trivial mylib.c and libtest.c files.

The Makefile generators work fine; the libmylib.a library is created and
linked to libtest just as you'd expect.

For Xcode, though, the link fails:

  Ld Debug/libtest normal x86_64
      cd /Users/build/xcode-bug
      /Developer/usr/bin/llvm-gcc-4.2 -arch x86_64 -isysroot /Developer/SDKs/MacOSX10.7.sdk -L/Users/build/xcode-bug/Debug -F/Users/build/xcode-bug/Debug -filelist /Users/build/xcode-bug/TestLib.build/Debug/libtest.build/Objects-normal/x86_64/libtest.LinkFileList -mmacosx-version-min=10.7 -Wl,-search_paths_first -Wl,-headerpad_max_install_names /Users/build/xcode-bug/Debug/libmylib.a -o /Users/build/xcode-bug/Debug/libtest
  Command /Developer/usr/bin/llvm-gcc-4.2 failed with exit code 1

The reason this fails is that while the link line is correctly trying to
link the Debug/libmylib.a library, the library that Xcode actually built
is quite different:

  $ find . -name libmylib\*
  ./TestLib.build/Debug/mylib_OBJECTS.build/Objects-normal/libmylib_OBJECTS.a

This is not right.

Cheers!