Re: Integrating flexc++(1) and bisonc++(1) into Makefile.am

[Nick Bowler]

Hello,

On 7/12/17, Kip Warner <address@hidden> wrote:
> My challenge is replicating their functionality for flexc++(1) and
> bisonc++(1) in the absense of macros to make their usage easier in
> Automake
[...]
> In trying to integrate the two tools into my build environment, I've
> attempted the following in Makefile.am:
[...]
>     BUILT_SOURCES = \
[...]
>       Source/ParserBase.h \
>       Source/Parser.h \
>       Source/Parser.ih \
>       Source/Parser.cpp
>
>     myprogram_SOURCES = \
[...]
>       Source/Parser.cpp
[...]
>     # Generate parser source from Backus-Naur grammar rules via bisonc++...
>     Source/ParserBase.h:
>     Source/Parser.h:
>     Source/Parser.ih:
>     Source/Parser.cpp: Source/Parser.ypp
>           $(BISONCPP) --target-directory=$(top_builddir)/Source $<
>
> FLEXCPP and BISONCPP are obtained via AC_PATH_PROG in configure.ac.
>
> This all works ok, but I suspect this is not an elegant solution and
> there are some very good suggestions from this mailing list.

There aren't really any "elegant" solutions.  Make handles this kind of
tool quite badly.  It is possible to get things to work but it is always
a tradeoff between flexibility of your build system and simplicity of
your rules.

If you are happy with this method then it is totally fine.  Do make
sure parallel builds work by testing them routinely (both clean and
incrementally) -- I think listing everything in BUILT_SOURCES like you
do probably "resolves" any parallelism problems here, (by reducing
opportunities for parallelism).

The Automake manual has section on writing portable make rules for tools
that produce multiple outputs[1], with a discussion of various approaches
and their limitations.  I generally prefer approaches using a dedicated
witness file.

Finally, consider whether you want to distribute the generated parser
sources.  That way your users don't need these tools installed just to
build your package.

[1] https://www.gnu.org/software/automake/manual/automake.html#Multiple-Outputs

Cheers,
  Nick