persistent but local tweaks to a node's environment

Hi! The project I work on builds several different versions of its outputs,
like a debug version, an optimized version, etc. Also, some files in the
project, for instance automatically generated files, need to have slightly
customized build flags, like disabling certain warnings that are false
positives and/or are in source we can't change.

Right now we handle that by creating an environment for each build, which I
think is the standard approach. Unfortunately, we then have to have a
separate step which goes through and generates new environments based on
those for each file that needs its slightly customized build flags.

What I would *like* to do, is to be able to specify for any given node that
it should build using the flags that would be implied by the environment
that's pulling it in, except that they should be tweaked just a little bit.
Something like:

Object('foo.cc', '-Wno-deprecated-copy')

and then:

opt.Program('foo.opt', 'foo.cc', CCFLAGS='${CCFLAGS} -O3')
debug.Program('foo.debug', 'foo.cc', CCFLAGS='${CCFLAGS} -g',
OBJSUFFIX='.do')
etc

and then have foo.do build with "-Wno-deprecated-copy -g", and foo.o build
with "-Wno-deprecated-copy -O3"

The problem is, that as soon as I tell SCons to use custom variables, it
Clone-s the underlying environment and disassociates from the underlying
environment.

One hacky solution I found was something like this:

File('foo.cc').Tag('CCFLAGS', '-Wno-deprecated-copy')

opt.Program('foo.opt', 'foo.cc', CCFLAGS='-O3
${SOURCE[0].GetTag("CCFLAGS")')

The problems with this are that, first, the CCFLAGS tag is not considered
when checking if a target needs to be rebuilt, second that this requires
accommodating each variable that can be extended explicitly, and third this
is really not what that mechanism is for.

Is there a solution to this, other than tracking things separately in the
SConscript, and then at the end feeding things to SCons in the order we
want? And generating custom environments as the cross product of build
types and files that need tweaked build flags?

Gabe

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