How to prevent a change of a specific flag from triggering a rebuild?

Question

I've added the option -fdiagnostics-color for GCC in my build. It only changes colors in error commands so I don't want the targets to rebuild when this option is the only thing that has changed.

For example with this SConstruct:

env = Environment()
if 'color' in ARGUMENTS:
    env.Append(CPPFLAGS=f'-fdiagnostics-color={ARGUMENTS["color"]}')
env.Program('main.cc')

Calling scons color=never and then scons color=always will cause the target file to be built 2 times.

Can I somehow tell SCons to not rebuild the target if only this option has changed?

Answer 1

SCons indeed has a pair of markers $( and $).

Everything that you'll put between them will be ignored while evaluating if a target needs to be rebuilt. (It works only if the string with the markers is passed to the function subst but this happens to almost every string, including ones passed to Actions, Commands and construction variables.)

env = Environment()
if 'color' in ARGUMENTS:
    env.Append(CPPFLAGS=f'$( -fdiagnostics-color={ARGUMENTS["color"]} $)')
env.Program('main.cc')