Refactor build process

Reorganise the build_artifact() and build_artifacts() functions to
allow more complex work when setting up chunk builds in
build_artifact().

The staging area now holds the BuildEnvironment object (the
environment variables that should be set during build). This makes sense
because all build commands should be run inside the staging area and
therefore through the StagingArea object.

The BuildEnvironment object is now considered immutable after it is
created.  The environment is used in cache key computation when
computing what artifacts are required; if it changes after that point
we risk either computing different artifact keys for the same artifact
or missing data in the cache key that should be included in the hash.
Better to force changes into a separate 'extra_env' variable.

0 files changed, 0 insertions, 0 deletions