Add hook to generate dawn version file using lastchange.py.

- Generating the version file is important since it ensures that even when a checkout/tarball of the chromium files do not have the git related directories, Dawn is able to build with a unique version.
- Updated lastchange.py script to add a simple hash file output option since Dawn expects a one-liner hash.
- Pass the generated file path to Dawn via BUILD overrides so that it can be used.

Bug: dawn:549
Change-Id: Ib7aa6a7dd533d0b3652e619a2992db517850e08e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3711140
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>
Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1017038}
NOKEYCHECK=True
GitOrigin-RevId: a6cc0fdd1707eb86e8a98c6e5f28e20e851ef922
1 file changed
tree: d434dbbd3d71d824ac91158aed146ffaabef8e9e
  1. angle.gni
  2. build.gni
  3. dawn.gni
  4. glslang.gni
  5. gtest.gni
  6. ipcz.gni
  7. OWNERS
  8. pdfium.gni
  9. README.md
  10. spirv_tools.gni
  11. swiftshader.gni
  12. tint.gni
  13. vulkan_common.gni
  14. vulkan_headers.gni
  15. vulkan_loader.gni
  16. vulkan_tools.gni
  17. vulkan_validation_layers.gni
  18. wayland.gni
README.md

Build overrides in GN

This directory is used to allow different products to customize settings for repos that are DEPS'ed in or shared.

For example: V8 could be built on its own (in a “standalone” configuration), and it could be built as part of Chromium. V8 might define a top-level target, //v8:d8 (a simple executable), that should only be built in the standalone configuration. To figure out whether or not it should be in a standalone configuration, v8 can create a file, build_overrides/v8.gni, that contains a variable, build_standalone_d8 = true. and import it (as import(“//build_overrides/v8.gni”) from its top-level BUILD.gn file.

Chromium, on the other hand, might not need to build d8, and so it would create its own build_overrides/v8.gni file, and in it set build_standalone_d8 = false.

The two files should define the same set of variables, but the values can vary as appropriate to the needs of the two different builds.

The build.gni file provides a way for projects to override defaults for variables used in //build itself (which we want to be shareable between projects).

TODO(crbug.com/588513): Ideally //build_overrides and, in particular, //build_overrides/build.gni should go away completely in favor of some mechanism that can re-use other required files like //.gn, so that we don't have to keep requiring projects to create a bunch of different files to use GN.