Allow depfile to depend on a Stamp file instead of the default first input.

grit/tool/build.py

Index: grit/tool/build.py
diff --git a/grit/tool/build.py b/grit/tool/build.py
index 68245a343476faa07441fca7fa163a15d33a48e5..f5254bf14ad68964460c89d7b730635cc9d7af00 100644
--- a/grit/tool/build.py
+++ b/grit/tool/build.py
@@ -116,7 +116,11 @@ Options:
                     systems to realize that dependent build steps might be
                     unnecessary, at the cost of comparing the output data at
                     grit time.
-                    
+
+  --depend-on-stamp
+                    If specified along with --depfile and --depdir, the depfile
+                    generated will depend on a stampfile instead of the first
+                    output in the input .grd file.
 
 Conditional inclusion of resources only affects the output of files which
 control which resources get linked into a binary, e.g. it affects .rc files
@@ -139,10 +143,12 @@ are exported to translation interchange files (e.g. XMB files), etc.
     rc_header_format = None
     output_all_resource_defines = None
     write_only_new = False
+    depend_on_stamp = False
     (own_opts, args) = getopt.getopt(args, 'a:o:D:E:f:w:t:h:',
         ('depdir=','depfile=','assert-file-list=',
          'output-all-resource-defines',
          'no-output-all-resource-defines',
+         'depend-on-stamp',
          'write-only-new='))
     for (key, val) in own_opts:
       if key == '-a':
@@ -179,6 +185,8 @@ are exported to translation interchange files (e.g. XMB files), etc.
         depfile = val
       elif key == '--write-only-new':
         write_only_new = val != '0'
+      elif key == '--depend-on-stamp':
+        depend_on_stamp = True
 
     if len(args):
       print 'This tool takes no tool-specific arguments.'
@@ -225,7 +233,7 @@ are exported to translation interchange files (e.g. XMB files), etc.
         return 2
 
     if depfile and depdir:
-      self.GenerateDepfile(depfile, depdir, first_ids_file)
+      self.GenerateDepfile(depfile, depdir, first_ids_file, depend_on_stamp)
 
     return 0
 
@@ -424,7 +432,7 @@ Extra output files:
     return True
 
 
-  def GenerateDepfile(self, depfile, depdir, first_ids_file):
+  def GenerateDepfile(self, depfile, depdir, first_ids_file, depend_on_stamp):
     '''Generate a depfile that contains the imlicit dependencies of the input
     grd. The depfile will be in the same format as a makefile, and will contain
     references to files relative to |depdir|. It will be put in |depfile|.
@@ -446,7 +454,9 @@ Extra output files:
       gen/blah.h: ../src/input1.xtb ../src/input2.xtb
 
     Where "gen/blah.h" is the first output (Ninja expects the .d file to list
-    the first output in cases where there is more than one).
+    the first output in cases where there is more than one). If the flag
+    --depend-on-stamp is specified, "gen/blah.rd.d.stamp" will be used that is
+    'touched' whenever a new depfile is generated.
 
     Note that all paths in the depfile are relative to ../out, the depdir.
     '''
@@ -458,11 +468,18 @@ Extra output files:
     if first_ids_file is not None:
       infiles.append(first_ids_file)
 
-    # Get the first output file relative to the depdir.
-    outputs = self.res.GetOutputFiles()
-    output_file = os.path.relpath(os.path.join(
-          self.output_directory, outputs[0].GetFilename()), depdir)
+    if (depend_on_stamp):
+      output_file = depfile + ".stamp"
+      # Touch the stamp file before generating the depfile.
+      with open(output_file, 'a'):
+        os.utime(output_file, None)
+    else:
+      # Get the first output file relative to the depdir.
+      outputs = self.res.GetOutputFiles()
+      output_file = os.path.join(self.output_directory,
+                                 outputs[0].GetFilename())
 
+    output_file = os.path.relpath(output_file, depdir)
     # The path prefix to prepend to dependencies in the depfile.
     prefix = os.path.relpath(os.getcwd(), depdir)
     deps_text = ' '.join([os.path.join(prefix, i) for i in infiles])