How to build dependencies with GCC

[boris-kolpackov]

Output of brew config

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Output of brew doctor

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Description of issue

I want to try to write a formula for ODB (an ORM for C++, Homebrew support requested by users). One of its components is the ODB compiler which is implemented as a GCC plugin. This means that the ODB compiler must be built with Homebrew GCC rather than Apple Clang (the plugin is loaded into the cc1plus process and should thus use libstdc++, etc). Homebrew GCC has plugin support enabled and we've been using it with ODB for many years without any major issues (thanks for that!)

I found a couple of formulae that seem to be doing something similar (they use GCC for OpenMP support): gromacs.rb and pythran.rb. So it seems I should be able to add a dependency on gcc and force the use of GCC as the compiler. So far so good.

What I am having trouble with is dependencies. The ODB compiler depends on two libraries, libcutl (already in Homebrew) and libstudxml (not in Homebrew but should be easy to add; it in turn will depend on the Expat library). My understanding is if I make them normal dependencies, they will be built with Apple Clang (and thus use libc++) and when I try to link them to the ODB compiler that was built with GCC (and thus uses libstdc++), things will not go well.

So my question is whether there is support for this scenario? I looked around but I don't see any mechanisms that would allow me to specify in my formula that I depend on a library but it must be built with GCC.

If there is no such mechanism (as I am suspecting), what is the recommended way to handle this? The only alternative that I can think of is to bundle these two (small) libraries with the ODB compiler and link them statically. I don't think this approach will have any major drawbacks. Specifically, the use of these libraries is not security-sensitive since they operate on local/trusted input.

I would appreciate some guidance on this from the Homebrew maintainers. Thanks in advance!