Merge pull request #9487 from ceph/wip_control_compiler_diagnostic_colors

Allows developers to turn on diagnostic colors for compiler output when stderr is not a terminal

Reviewed-by: Casey Bodley <cbodley@redhat.com>

README.cmake.md

@@ -49,10 +49,25 @@ external dependencies:
       -DCMAKE_INSTALL_PREFIX=/opt/accelio -DCMAKE_C_FLAGS="-O0 -g3 -gdwarf-4" \
       ..
 
-More options will be implemented in the future.
+If you often pipe `make`to `less` and would like to maintain the
+diagnostic colors for errors and warnings (and if your compiler
+supports it), you can invoke `cmake` with:
+
+    $ cmake -DDIAGNOSTICS_COLOR=always [...]
+
+Then you'll get the diagnostic colors when you execute:
+
+    $ make | less -R
+
+Other available values for DIAGNOSTICS_COLOR are 'auto' (default) and
+'never'.
+
+
+**More options will be implemented in the future.**
+
 
 Targets Built
-==============
+=============
 
 * ceph-mon 
 * ceph-osd 

src/CMakeLists.txt

@@ -90,6 +90,21 @@ else()
   message(FATAL_ERROR "The compiler ${CMAKE_CXX_COMPILER} has no C++11 support.")
 endif()
 
+
+## Handle diagnostics color if compiler supports them.
+
+CHECK_C_COMPILER_FLAG("-fdiagnostics-color=always"
+  COMPILER_SUPPORTS_DIAGNOSTICS_COLOR)
+
+set(DIAGNOSTICS_COLOR "auto"
+  CACHE STRING "Used if the C/C++ compiler supports the -fdiagnostics-color option. May have one of three values -- 'auto' (default), 'always', or 'never'. If set to 'always' and the compiler supports the option, 'make [...] | less -R' will make visible diagnostics colorization of compiler output.")
+
+if(COMPILER_SUPPORTS_DIAGNOSTICS_COLOR)
+  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fdiagnostics-color=${DIAGNOSTICS_COLOR}")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fdiagnostics-color=${DIAGNOSTICS_COLOR}")
+endif()
+
+
 ## detect sse support
 
 # create a tmp file with an empty main()