[Scons-users] Attaching an emitter to an existing builder

[Jeremy Elson]

Thanks, everyone for the help -- PROGEMITTER worked perfectly:

        # Add map creation as a linker flag, and modify the standard Program
        # emitter to know that map generation is a side-effect
        map_filename = os.path.join(build_obj_dir, f"{target.name}.map")
        env.Append(LINKFLAGS = f"-Wl,-Map={map_filename},--cref")
        def map_emitter(target, source, env):
            assert(str(target[0]) == os.path.abspath(program_name))
            target.append(map_filename)
            return target, source
        env.Append(PROGEMITTER = [map_emitter])

My only concern with PROGEMITTER was that it was not a general solution to
this problem -- i.e., what if I want to override something other than
Program()? But from looking at MSlink.py as Mats suggested, it seems that
nearly all the standard builders have similar overrides (SHLIBEMITTER,
LDMODULEEMITTER, etc). I guess it's similar to the *COMSTR series of
constants for modifying the message printed at each build step.

Thanks again for a great build system. SCons is a pleasure to use.

-Jeremy



On Thu, Jan 28, 2021 at 7:19 AM Mats Wichmann <mats at wichmann.us> wrote:

> On 1/27/21 3:11 PM, Bill Deegan wrote:
> > Jeremy,
> >
> > Greetings!
> > You're not the first to mention adding the map file as a side effect.
> > (or target)
> > Please go ahead and file and Issue on github for this.
> > Ideally with a simple example, what the gcc flag is, and what the file
> > naming/location would be?
> >
> > So likely the easiest way to add an emitter to Program() would be the
> > following (not tested)
> >
> > env.Append(PROGEMITTER = [my_map_emitter])
> >
> > Give that a try and let us know if it works for you?
> >
> > Also there's a discord server for scons help if you'd like to ask
> > questions/get help there.
> > https://discord.gg/bXVpWAy <https://discord.gg/bXVpWAy>
> >
> > Hope that helps!
> > -Bill
>
> For inspiration, the mslink tool does this (as does the qt tool) - see
> the somewhat messy SCons/Tool/mslink.py.
>
> Meanwhile, while many tools use add_emitter, the code for add_emitter
> itself includes this comment:
>
>          This assumes that emitter has been initialized with an
>          appropriate dictionary type, and will throw a TypeError if
>          not, so the caller is responsible for knowing that this is an
>          appropriate method to call for the Builder in question.
>
> >              env["BUILDERS"]["Program"].add_emitter(
> >                  suffix = ".map",
> >                  emitter = map_emitter)
> >
> >     But it throws an exception:
> >
> >     TypeError: 'EmitterProxy' object does not support item assignment
>
> So I guess "expected"? although pretty awkward....
>
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