Enable colored diagnostics when building with gcc 4.9+.

[thakis]

Summary

GCC has supported -fdiagnostics-color since 4.9.

[smeenai]

Why do we hardcode compiler IDs/versions here instead of just checking whether the current compiler supports the flag?

[thakis]

It has the same effect and doesn't require yet another compiler call at cmake time, and once we uprev gcc requirements to 4.9 (soooon) we can just delete the whole condition in the parens.

[rnk]

lgtm

cmake/modules/HandleLLVMOptions.cmake

726–729

Should we simplify these compiler version checks to add_flag_if_supported("-fdiagnostics-color")? We'd still need the UNIX && ninja check.

[rnk]

cmake/modules/HandleLLVMOptions.cmake

726–729

Ignore this, I wrote it before you answered @smeenai and only hit submit just now.

[thakis]

r332793, thanks!

cmake/modules/HandleLLVMOptions.cmake

 if(LLVM_USE_SPLIT_DWARF)
   add_definitions("-gsplit-dwarf")
 endif()
 
 add_definitions( -D__STDC_CONSTANT_MACROS )
 add_definitions( -D__STDC_FORMAT_MACROS )
 add_definitions( -D__STDC_LIMIT_MACROS )
 
-# clang doesn't print colored diagnostics when invoked from Ninja
+# clang and gcc don't default-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)
+    CMAKE_GENERATOR STREQUAL "Ninja" AND
+    (CMAKE_CXX_COMPILER_ID MATCHES "Clang" OR
+     (CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND
+      NOT (CMAKE_CXX_COMPILER_VERSION VERSION_LESS 4.9))))
+  append("-fdiagnostics-color" 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)