Use DUNE_BUILD_DIR to search for files

[maxim092001]

Hi.

In input.ml we use _build as a hardcoded value for search. However, some users may override DUNE_BUILD_DIR or pass it as a flag to dune as per dune docs.

This issue is a request to use DUNE_BUILD_DIR instead of _build. Note, that DUNE_BUILD_DIR=_build by default.

Let me know if this change would make sense and you'd be happy for us to contribute it!

Best,
Max.

[aantron]

Hi! I think that makes sense. I would merge such a change. It looks like DUNE_BUILD_DIR has been around since Dune 1.0.0. However, we should probably fall back to searching in a potential _build directory, as now, if the environment variable is undefined for some reason.

If a user passes in --build-dir foo, is DUNE_BUILD_DIR set to foo?