Add a target in GN that generates a last_change.h file for the SVN revision.

build/util/lastchange.py

Index: build/util/lastchange.py
diff --git a/build/util/lastchange.py b/build/util/lastchange.py
index 3c1ce28e28ae33965546328a4c338af64a4792c4..8d758d2a24fdfa6daefada92491d739e055e5b7e 100755
--- a/build/util/lastchange.py
+++ b/build/util/lastchange.py
@@ -168,6 +168,42 @@ def FetchVersionInfo(default_lastchange, directory=None,
       version_info = VersionInfo(None, None)
   return version_info
 
+def GetHeaderGuard(path):
+  """
+  Returns the header #define guard for the given file path.
+  This treats everything after the last instance of "src/" as being a
+  relevant part of the guard. If there is no "src/", then the entire path
+  is used.
+  """
+  src_index = path.rfind('src/')
+  if src_index != -1:
+    guard = path[src_index + 4:]
+  else:
+    guard = path
+  guard = guard.upper()
+  return guard.replace('/', '_').replace('.', '_').replace('\\', '_') + '_'
+
+def GetHeaderContents(path, define, version):
+  """
+  Returns what the contents of the header file should be that indicate the given
+  revision. Note that the #define is specified as a string, even though it's
+  currently always a SVN revision number, in case we need to move to git hashes.
+  """
+  header_guard = GetHeaderGuard(path)
+
+  header_contents = """/* Generated by lastchange.py, do not edit.*/
+
+#ifndef %(header_guard)s
+#define %(header_guard)s
+
+#define %(define)s "%(version)s"
+
+#endif  // %(header_guard)s
+"""
+  header_contents = header_contents % { 'header_guard': header_guard,
+                                        'define': define,
+                                        'version': version }
+  return header_contents
 
 def WriteIfChanged(file_name, contents):
   """
@@ -191,16 +227,26 @@ def main(argv=None):
 
   parser = optparse.OptionParser(usage="lastchange.py [options]")
   parser.add_option("-d", "--default-lastchange", metavar="FILE",
-                    help="default last change input FILE")
+                    help="Default last change input FILE.")
+  parser.add_option("-m", "--version-macro",
+                    help="Name of C #define when using --header. Defaults to " +
+                    "LAST_CHANGE.",
+                    default="LAST_CHANGE")
   parser.add_option("-o", "--output", metavar="FILE",
-                    help="write last change to FILE")
+                    help="Write last change to FILE. " +
+                    "Can be combined with --header to write both files.")
+  parser.add_option("", "--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_option("--revision-only", action='store_true',
-                    help="just print the SVN revision number")
+                    help="Just print the SVN revision number. Overrides any " +
+                    "file-output-related options.")
   parser.add_option("-s", "--source-dir", metavar="DIR",
-                    help="use repository in the given directory")
+                    help="Use repository in the given directory.")
   opts, args = parser.parse_args(argv[1:])
 
   out_file = opts.output
+  header = opts.header
 
   while len(args) and out_file is None:
     if out_file is None:
@@ -224,10 +270,15 @@ def main(argv=None):
     print version_info.revision
   else:
     contents = "LASTCHANGE=%s\n" % version_info.revision
-    if out_file:
-      WriteIfChanged(out_file, contents)
-    else:
+    if not out_file and not opts.header:
       sys.stdout.write(contents)
+    else:
+      if out_file:
+        WriteIfChanged(out_file, contents)
+      if header:
+        WriteIfChanged(header,
+                       GetHeaderContents(header, opts.version_macro,
+                                         version_info.revision))
 
   return 0