The longest part of running `mach build-backend -b alternative_backend` is reading moz.build and emitting the corresponding data. Which is suboptimal, since it's already been done when running configure or `mach build-backend`. This bug is about allowing mach build-backend to build multiple backends in one pass.

- Make all backends report the time spent in their own execution - Change how the data is collected for the reader and emitter such that each of them is aware of its own data, instead of everything being tracked by the backend. This is meant to open the door to multiple backends running from the same execution of config.status.

Currently, we set a flag on each object to know whether it has been consumed by the backend. This doesn't work nicely when multiple backends try to consume the same objects.

When running mach `build-backend` or `config.status`, it is now possible to pass multiple backends to the --backend/-b option, so that they can share moz.build reading and object emitting. The command line syntax is however maybe a little awkward: mach build-backend -b Backend1 Backend2 but supporting with `-b Backend1 -b Backend2` requires more argument parser twiddling (action='append' doesn't work out of the box with choices, we'd need a custom action class) Sample output: $ ./mach build-backend -b RecursiveMake FasterMake CppEclipse Reticulating splines... Finished reading 2540 moz.build files in 2.05s Processed into 9347 build config descriptors in 2.13s RecursiveMake backend executed in 2.41s 2526 total backend files; 0 created; 1 updated; 2525 unchanged; 0 deleted; 125 -> 949 Makefile FasterMake backend executed in 0.17s 4 total backend files; 0 created; 0 updated; 4 unchanged; 0 deleted CppEclipse backend executed in 0.05s Generated Cpp Eclipse workspace in "/home/glandium/eclipse_obj-x86_64-unknown-linux-gnu". If missing, import the project using File > Import > General > Existing Project into workspace Run with: eclipse -data /home/glandium/eclipse_obj-x86_64-unknown-linux-gnu Total wall time: 7.04s; CPU time: 6.63s; Efficiency: 94%; Untracked: 0.23s

With a small change in config_status.py to still display VS and Android backend advertisement.

Comment on attachment 8665651 [details] [diff] [review] Refactor how build backend execution is summarized Review of attachment 8665651 [details] [diff] [review]: ----------------------------------------------------------------- ::: python/mozbuild/mozbuild/backend/base.py @@ -28,4 @@ > from .configenvironment import ConfigEnvironment > - > - > -class BackendConsumeSummary(object): IIRC one of the reasons I originally made this as a separate class was to prevent variable proliferation on a shared base class. But I suppose the new names are specific enough that it won't be a problem.

Comment on attachment 8665699 [details] [diff] [review] Allow to create multiple build backends at once Review of attachment 8665699 [details] [diff] [review]: ----------------------------------------------------------------- ::: python/mozbuild/mozbuild/config_status.py @@ +12,5 @@ > import os > import sys > import time > > +from argparse import ArgumentParser Thank you for killing optparse.

https://hg.mozilla.org/integration/mozilla-inbound/rev/af6ea1464daa https://hg.mozilla.org/integration/mozilla-inbound/rev/75c3e053bcfa https://hg.mozilla.org/integration/mozilla-inbound/rev/55af918cafff

https://hg.mozilla.org/mozilla-central/rev/af6ea1464daa https://hg.mozilla.org/mozilla-central/rev/75c3e053bcfa https://hg.mozilla.org/mozilla-central/rev/55af918cafff