Looking into the config.status path some more, the reason we always rebuild when it is not present is because of the way I implemented missing files in bug 1242663. However, I think an alternate solution there would be to use $(wildcard) instead of creating dummy rules on every file. so if our dependency file contains:
config.status
foo
bar
The current rules do:
backend.TestManifestBackend: config.status foo bar
re-create backend
config.status foo bar:
Since config.status is missing, make runs the empty rule to try to create it (which does nothing), but that triggers the backend.TestManifestBackend rule. With wildcard this would look like:
backend.TestManifestBackend: $(wildcard config.status foo bar)
re-create backend
Which means make only checks dependencies on the files that actually exist (presumably foo and bar in this case, but not config.status). But when config.status is later created, we'll know to recreate the TestManifestBackend then.
MozReview-Commit-ID: 6NTTmsnxTeT
--HG--
extra : rebase_source : 737c3021cbc26074ec54eafeca203ae95c37d8b8
In bug 1320194 we want to generate a TestManifest backend without first
invoking configure. However, we still need a way to update the backend,
which is normally handled by the top-level Makefile. We can split this
logic out into a separate file, rebuild-backend.mk, which can be invoked
directly as long as the appropriate environment variables are set
(BUILD_BACKEND_FILES, BACKEND_GENERATION_SCRIPT, and PYTHON).
--HG--
extra : rebase_source : b6a486db3e3c97b406b11074fda052bd63fe1b8f
Mike Shal