tree c5db948005edfb90355608e46fbc471d30d30cd1
parent 5eb3845ec2d8296b4f41da4eca85302eb111fe69
author David 'Digit' Turner <digit@google.com> 1647532121 +0100
committer Commit Bot <commit-bot@chromium.org> 1649250016 +0000

Fix output directories for generated source files.

This CL fixes an annoying issue where the local build directory path
leaks into the generated Ninja files when {{source_out_dir}} or
even {{source_gen_dir}} are expanded.

In the case of a generated source file, its path will be source-absolute
but located in the build directory, for example:

  //out/Debug/gen/header.h
  //out/Debug/toolchain/gen/src/source.cc

Before this CL, the computed output directory would leak the 'out/Debug'
prefix, i.e. compute an output path, relative to `out/Debug` as:

  obj/out/Debug/gen/
  obj/out/Debug/toolchain/gen/src/

After this CL, the build directory prefix is replaced with the
"BUILD_DIR" string literal, and the result becomes:

  obj/BUILD_DIR/gen/
  obj/BUILD_DIR/toolchain/gen/src

This makes the commands more hermetic, especially with regards to remote
builds which implement content-based caching, using the command hash as
a key.

I tested that I could still build Fuchsia, Chromium and Pigweed with
this patch (as long as Pigwedd's build system is fixed with [1] to
support upstream GN).

Note that this CL is required to unblock the GN auto-roller for the
Fuchsia project: without it, the output directory leak checks will fail
the builds since the latest Rust-related changes adds a ton of
`-Lnative=<path-with-build-directory>` to a very large number of
Rust link commands.

[1] https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/90080

Change-Id: I2dc811c295aa47dc412175bd74acc1333f8145e8
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/13240
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Commit-Queue: David Turner <digit@google.com>