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}

DEPS

@@ -3893,6 +3893,14 @@ hooks = [
                '-s', 'src/third_party/skia',
                '--header', 'src/skia/ext/skia_commit_hash.h'],
   },
+  {
+    # Update dawn_version.h.
+    'name': 'lastchange_dawn',
+    'pattern': '.',
+    'action': ['python3', 'src/build/util/lastchange.py',
+               '-s', 'src/third_party/dawn',
+               '--revision', 'src/gpu/webgpu/DAWN_VERSION'],
+  },
   # Pull dsymutil binaries using checked-in hashes.
   {
     'name': 'dsymutil_mac_arm64',

build/util/lastchange.py

@@ -221,12 +221,22 @@ def main(argv=None):
   parser.add_argument("-m", "--version-macro",
                     help=("Name of C #define when using --header. Defaults to "
                           "LAST_CHANGE."))
-  parser.add_argument("-o", "--output", metavar="FILE",
-                    help=("Write last change to FILE. "
-                          "Can be combined with --header to write both files."))
-  parser.add_argument("--header", metavar="FILE",
-                    help=("Write last change to FILE as a C/C++ header. "
-                          "Can be combined with --output to write both files."))
+  parser.add_argument("-o",
+                      "--output",
+                      metavar="FILE",
+                      help=("Write last change to FILE. "
+                            "Can be combined with other file-output-related "
+                            "options to write multiple files."))
+  parser.add_argument("--header",
+                      metavar="FILE",
+                      help=("Write last change to FILE as a C/C++ header. "
+                            "Can be combined with other file-output-related "
+                            "options to write multiple files."))
+  parser.add_argument("--revision",
+                      metavar="FILE",
+                      help=("Write last change to FILE as a one-line revision. "
+                            "Can be combined with other file-output-related "
+                            "options to write multiple files."))
   parser.add_argument("--merge-base-ref",
                     default=None,
                     help=("Only consider changes since the merge "
@@ -255,6 +265,7 @@ def main(argv=None):
 
   out_file = args.output
   header = args.header
+  revision = args.revision
   commit_filter=args.filter
 
   while len(extras) and out_file is None:
@@ -311,7 +322,7 @@ def main(argv=None):
         "LASTCHANGE_YEAR=%s" % lastchange_year,
     ]
     contents = '\n'.join(contents_lines) + '\n'
-    if not out_file and not args.header:
+    if not out_file and not header and not revision:
       sys.stdout.write(contents)
     else:
       if out_file:
@@ -324,6 +335,8 @@ def main(argv=None):
         WriteIfChanged(header,
                        GetHeaderContents(header, args.version_macro,
                                          revision_string))
+      if revision:
+        WriteIfChanged(revision, revision_string)
 
   return 0
 

build_overrides/dawn.gni

@@ -13,3 +13,5 @@ dawn_swiftshader_dir = "//third_party/swiftshader"
 dawn_vulkan_loader_dir = "//third_party/vulkan-deps/vulkan-loader/src"
 dawn_vulkan_validation_layers_dir =
     "//third_party/vulkan-deps/vulkan-validation-layers/src"
+
+dawn_version_file = "//gpu/webgpu/DAWN_VERSION"

gpu/webgpu/.gitignore

@@ -0,0 +1,2 @@
+### Dawn version file (generated as part of DEPS hook)
+DAWN_VERSION