oasis: provide optional build-dependencies

[gildor478]

This feature request has been migrated from artifact #892 on forge.ocamlcore.org. It was assigned to user102.

user824 posted on 2011-01-21 19:55:24:

There should be a way to specify optional build dependencies: if dependency is not available (or too old) then _oasis could specify a way to build a local copy of the library.

What is needed is a flag() that can be used in _oasis if optional build-dep is not available. Some sort of support for "sub-project configure" would come in handy too.

For example:

Library: mylib OptionalBuildDepends: oUnit (>=1.1.0)

Library oUnit Build$: flag(missingdep_ounit) Configure-Commands: $ocaml oUnit-1.1.0/setup.ml -configure Build-Commands: $ocaml oUnit-1.1.0/setup.ml -build Build-Objects: oUnit-1.1.0/_build