Add -Wl,-color-diagnostics if a linker supports the option.

[ruiu]

Summary

Add -Wl,-color-diagnostics if a linker supports the option.

[inglorion]

llvm/cmake/modules/HandleLLVMOptions.cmake

592

Why not check_cxx_compiler_flag("-Wl,-color-diagnostics" LINKER_SUPPORTS_COLOR_DIAGNOSTICS), analogous with check_c_compiler_flag below for -fno-function-sections? Would that allow us to avoid the dance with saving CMAKE_REQUIRED_FLAGS and restoring it to its old value?

[ruiu]

llvm/cmake/modules/HandleLLVMOptions.cmake

592

check_c_compiler_flags doesn't seem to link the result. It just compiles. So it cannot be used for testing -Wl,-something flags.

[inglorion]

llvm/cmake/modules/HandleLLVMOptions.cmake

592

To clarify, I meant using check_cxx_compiler_flag (as you're doing), but passing the flag as the first argument, rather than by setting it in CMAKE_REQUIRED_FLAGS. Are you saying that passing the flag into check_cxx_compiler_flag() does not result in linking, but setting it in CMAKE_REQUIRED_FLAGS and passing an empty string to check_cxx_compiler_flag() does?

[ruiu]

• Updated as per Bob's comment.

[inglorion]

Thanks! lgtm.

[ruiu]

I had to revert to the previous version because check_cxx_compiler_flag
didn't actually work. check_cxx_compiler_flag doesn't seem to link, but
just compiles, so the previous check of -Wl,-color-diagnostics always
succeeded.

[inglorion]

Alright, well, if the more elegant way doesn't work, let's ship the way that does work.

[ruiu]

• factor out the new code as a new function.

[inglorion]

Looks good, thanks! This is ready to go.

llvm/cmake/modules/HandleLLVMOptions.cmake

 
 # clang doesn't print colored diagnostics when invoked from Ninja
 if (UNIX AND
     CMAKE_CXX_COMPILER_ID MATCHES "Clang" AND
     CMAKE_GENERATOR STREQUAL "Ninja")
   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")
+  set(OLD_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS})
+  set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -Wl,-color-diagnostics")
+  check_cxx_compiler_flag("" LINKER_SUPPORTS_COLOR_DIAGNOSTICS)
+  set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
+
+  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
 # flags instead if LLVM_NO_DEAD_STRIP is set.
 if(NOT CYGWIN AND NOT WIN32)
   if(NOT ${CMAKE_SYSTEM_NAME} MATCHES "Darwin" AND
      NOT uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG")
     check_c_compiler_flag("-Werror -fno-function-sections" C_SUPPORTS_FNO_FUNCTION_SECTIONS)