tree 647946d28774fd85692927435dc6e6ebc128ae6d
parent 8e32da710ccc876c3ce852925f333da923333d3b
author Michael Spang <spang@google.com> 1622404436 -0400
committer CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com> 1623266151 +0000

Remove absolute paths from build command lines

The GN convention is to specify paths in command lines relative to the
build directory. Unfortunately and contrary to pigweed's expectations
this is not what rebase_path(path) does; that outputs an absolute path.

Absolute paths are not desirable in most circumstances as they contain
sources of nondeterminism such as the developer's home directory. Using
them can for example reduce hit rate in build caches.

Replace rebase_path(path) with rebase_path(path, root_build_dir) which
is the correct idiom and matches GN's builtin behavior (e.g. for
sources, include_dirs, etc).

This also removes the --directory argument to python_action(). Changing
the directory during the build while using relative paths is likely to
result in confusion and should be discouraged.

There's a couple more things to do on top of this for identical
binaries between build directories / machines / developers:

- pass options to avoid embedding the working directory
- pass options to use relative paths for the vendored clang & libc++

See [1]-[2] for how to do that.

[1] https://source.chromium.org/chromium/chromium/src/+/main:build/config/compiler/BUILD.gn;l=1170-1239;drc=ab531c265c533cba1c2f6d8240cc0bf7679f605a
[2] https://cs.opensource.google/fuchsia/fuchsia/+/main:build/config/BUILD.gn;l=145-216;drc=f6d705f0937c778d5d5f807a4580113612b02f5a

Change-Id: I17708102c03d6488d68c8571b6e9343191fd47de
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/47461
Reviewed-by: Wyatt Hepler <hepler@google.com>
Commit-Queue: Michael Spang <spang@google.com>