[llvm] r291719 - Add -Wl, -color-diagnostics if a linker supports the option.

[Davide Italiano via llvm-commits]

On Wed, Jan 11, 2017 at 2:55 PM, Rui Ueyama via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> Author: ruiu
> Date: Wed Jan 11 16:55:35 2017
> New Revision: 291719
>
> URL: http://llvm.org/viewvc/llvm-project?rev=291719&view=rev
> Log:
> Add -Wl,-color-diagnostics if a linker supports the option.
>
> Differential Revision: https://reviews.llvm.org/D28046
>
> Added:
>     llvm/trunk/cmake/modules/CheckLinkerFlag.cmake
> Modified:
>     llvm/trunk/cmake/modules/HandleLLVMOptions.cmake
>
> Added: llvm/trunk/cmake/modules/CheckLinkerFlag.cmake
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/cmake/modules/CheckLinkerFlag.cmake?rev=291719&view=auto
> ==============================================================================
> --- llvm/trunk/cmake/modules/CheckLinkerFlag.cmake (added)
> +++ llvm/trunk/cmake/modules/CheckLinkerFlag.cmake Wed Jan 11 16:55:35 2017
> @@ -0,0 +1,8 @@
> +include(CheckCXXCompilerFlag)
> +
> +function(check_linker_flag flag out_var)
> +  set(OLD_CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS}")
> +  set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} ${flag}")
> +  check_cxx_compiler_flag("" ${out_var})
> +  set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
> +endfunction()
>
> Modified: llvm/trunk/cmake/modules/HandleLLVMOptions.cmake
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/cmake/modules/HandleLLVMOptions.cmake?rev=291719&r1=291718&r2=291719&view=diff
> ==============================================================================
> --- llvm/trunk/cmake/modules/HandleLLVMOptions.cmake (original)
> +++ llvm/trunk/cmake/modules/HandleLLVMOptions.cmake Wed Jan 11 16:55:35 2017
> @@ -597,6 +597,14 @@ if (UNIX AND
>    append("-fcolor-diagnostics" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
>  endif()
>
> +# lld doesn't print colored diagnostics when invoked from Ninja
> +if (UNIX AND CMAKE_GENERATOR STREQUAL "Ninja")
> +  include(CheckLinkerFlag)
> +  check_linker_flag("-Wl,-color-diagnostics" LINKER_SUPPORTS_COLOR_DIAGNOSTICS)
> +  append_if(LINKER_SUPPORTS_COLOR_DIAGNOSTICS "-Wl,-color-diagnostics"
> +    CMAKE_EXE_LINKER_FLAGS CMAKE_MODULE_LINKER_FLAGS CMAKE_SHARED_LINKER_FLAGS)
> +endif()
> +
>  # Add flags for add_dead_strip().
>  # FIXME: With MSVS, consider compiling with /Gy and linking with /OPT:REF?
>  # But MinSizeRel seems to add that automatically, so maybe disable these
>

This has the unfortunate side effect of breaking the swift build on FreeBSD.
The link of `swift-demangle` fails with `unknown option -color-diagnostic`.
It's the result of a series of events:

1) lld is used as system linker:
$ ld --version
LLD (not GNU) 5.0.0
$ ld --help |grep colo
  --color-diagnostics=<value>
                          Use colors in diagnostics
  --color-diagnostics     Use colors in diagnostics
  --no-color-diagnostics  Do not use colors in diagnostics

The particular build uses gold (so it passes around -fuse-ld=gold).
Once that CMake check is hit, we think it passes (as it's tested with
lld) but then we switch to gold and it fails.
I'm not sure whether it's an issue in the `swift` build system or in
your patch, but I wanted to make you aware of this.

Thanks,

-- 
Davide

"There are no solved problems; there are only problems that are more
or less solved" -- Henri Poincare