Other than cleaning up the code, the only change in behavior is to run
the docs build in parallel with the primary builder, saving about a
second on a Soong bootstrap (10s -> 9s).
Change-Id: Iaff51d6d1a37af842f294f12db11d5774d48d440
tl;dr: Read if you don't use the wrapper or use SKIP_NINJA
Previously, we were relying on the ninja behavior of restarting the
build when the build.ninja file was updated to switch between different
bootstrap stages. But that means that every step that could produce a
build.ninja must pass in order to switch to a different stage. That
wasn't a big problem when we had a two stage build -- there was very
little that could fail in the second stage before we chose to go back to
the first stage. But when we had a three stage build, it was possible to
get into a state (usually during development) where you were in the
second stage, but the build was failing because the first stage needed
to be run. This was fixed in d79f1af742
by adding a wrapper that always started building at the first stage.
But this kept all of the complexity of using ninja restarts without any
of the benefits, so this change removes that complexity and just runs
each stage sequentially in the wrapper. So the wrapper is now required.
Since we're no longer going through choosestage, we can also skip the
template parsing for the later stages that don't need to be templated --
this can save a couple of seconds for large files.
In addition to all of the above, this also lets Soong reduce the number
of times the main ninja file is loaded. We had been running the wrapper
once (3 stages), then running ninja again after combining the
Soong-generated build.ninja with the Kati-generated build.ninja. This
change lets us removing the intermediate parsing of Soong's build.ninja,
so that we only execute ninja 3 times per build. It also lets us have
dependencies on pools or rules from Kati in the primary builder, since
we're never executing the main build.ninja without the Kati build.ninja.
The wrapper has a new option, NINJA to provide the path to ninja. This
used to be hardcoded to `ninja`, and will still default to that. But
we'll be running the first two bootstrap stages with $NINJA even if
SKIP_NINJA is set.
The wrapper passes "-w dupbuild=err" to ninja now -- this really should
always be turned on if you care about reliable builds.
Change-Id: I6f656b74eb3d064b8b9e69d1d6dac1129d72b747
This wrapper script can be used instead of ninja to ensure the build
won't get stuck building the primary builder.
An example of when this would happen:
1. Do a successful build
2. Sync/make a change in the primary builder (soong, etc) that depends
on a blueprint change.
3. The next build would notice that change, and rewind to the primary
stage to rebuild the builder. That build would fail.
4. Sync/fix the blueprint code.
5. The next build would still fail. The bootstrap stage would need to
be run in order to fix the primary stage, but we're still stuck in the
primary stage. The only way to switch stages is to successfully
complete everything required to choose the next stage.
This generally isn't a problem in the main stage, since there is no code
being built in the dependency chain leading up to stage selection.
Any existing wrappers (like soong) can execute this wrapper (optionally
skipping ninja execution) if they're worried about the above situation.
This isn't strictly required -- running ninja directly will still work
in most cases, you'll just need to re-run bootstrap.bash if you get into
a bad state.
Change-Id: I5901d7240a1daa388a786ceb1c8259502fc14058
