A limitation of traditional docker build context generation is it
only includes files from the same directory as the Dockerfile. When
repositories have multiple, related Dockerfiles, this limitation
results file duplication or putting all Dockerfiles in the same
directory (which isn't feasible for mozilla-central since they would
need to be in the root directory).
This commit enhances Dockerfiles to allow *any* file from the
repository checkout to be ADDed to the docker build context.
Using the syntax "# %include <path>" you are able to include paths
or directories (relative from the top source directory root) in the
generated context archive. Files add this way are available under the
"topsrcdir/" path and can be ADDed to Docker images.
Since context archive generation is deterministic and the hash of
the resulting archive is used to determine when images need to be
rebuilt, any extra included file that changes will change the hash
of the context archive and force image regeneration.
Basic tests for the new feature have been added.
MozReview-Commit-ID: 4hPZesJuGQV
