If mozbuild parsing fails due to a missing file (eg: a file not existing
in UNIFIED_SOURCES), then no Makefiles are written out, but
config.status exists. This would cause mozbuild to think that configure
doesn't need to run, and rely on make to perform the backend-out-of-date
check in rebuild-backend.mk. Unfortunately since no Makefiles were
written, the make command fails immediately and no attempt is made to
re-create the backend. Note that this is only a problem if the first
mozbuild parsing from a clobber build fails, otherwise there is
typically a top-level Makefile from a previous build to call into (at
which point make can determine it is out-of-date, and re-invoke itself).
The fix is to have the RecursiveMake backend re-use the same logic that
was introduced into mozbuild for alternate backends, and remove
rebuild-backend.mk. This way, mozbuild can always determine if the
backend needs to be regenerated, even if the initial parsing failed.
Test code was also relying on rebuild-backend.mk to generate the
TestBackend, but moving backend_out_of_date() into MozbuildObject allows
this code to be shared.
Differential Revision: https://phabricator.services.mozilla.com/D26262
c04e18fa25