[Scons-users] persistent but local tweaks to a node's environment

[Gary Oberbrunner]

I usually do something like

  Import('env') # might be opt or debug env
  objs = []
  objs.append(env.Object('foo.cc', CCFLAGS='${CCFLAGS} -specialflag1'))
  objs.append(env.Object('bar.cc'))
... then later...
  env.Program('prog.$PROGTYPE', objs)

(Of course you can build objs any way you like; you could have a list of
sources and their extra flags and loop, or whatever you like -- it's just
python.)


On Sat, Jul 24, 2021 at 6:18 AM Gabe Black <gabe.black at gmail.com> wrote:

> 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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>


-- 
Gary
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