Make MB clobber build directories when switching between GYP and GN.

tools/mb/mb.py

 #!/usr/bin/env python
 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """MB - the Meta-Build wrapper around GYP and GN
 
 MB is a wrapper script for GYP and GN that can be used to generate build files
 for sets of canned configurations and analyze them.
 """
@@ skipping 117 matching lines @@
     vals = self.GetConfig()
     if vals['type'] == 'gn':
       return self.RunGNAnalyze(vals)
     elif vals['type'] == 'gyp':
       return self.RunGYPAnalyze(vals)
     else:
       raise MBErr('Unknown meta-build type "%s"' % vals['type'])
 
   def CmdGen(self):
     vals = self.GetConfig()
+
+    self.ClobberIfNeeded(vals)
+
     if vals['type'] == 'gn':
       return self.RunGNGen(vals)
     if vals['type'] == 'gyp':
       return self.RunGYPGen(vals)
 
     raise MBErr('Unknown meta-build type "%s"' % vals['type'])
 
   def CmdLookup(self):
     vals = self.GetConfig()
     if vals['type'] == 'gn':
@@ skipping 135 matching lines @@
                   (self.args.builder, self.args.master, self.args.config_file))
 
     return self.masters[self.args.master][self.args.builder]
 
   def FlattenConfig(self, config):
     mixins = self.configs[config]
     vals = {
       'type': None,
       'gn_args': [],
       'gyp_config': [],
-      'gyp_defines': [],
+      'gyp_defines': '',

[Dirk Pranke, 2015/09/12 00:49:41]

this was a bug caught by the new unit tests.

       'gyp_crosscompile': False,
     }
 
     visited = []
     self.FlattenMixins(mixins, vals, visited)
     return vals
 
   def FlattenMixins(self, mixins, vals, visited):
     for m in mixins:
       if m not in self.mixins:
@@ skipping 17 matching lines @@
         vals['gyp_crosscompile'] = mixin_vals['gyp_crosscompile']
       if 'gyp_defines' in mixin_vals:
         if vals['gyp_defines']:
           vals['gyp_defines'] += ' ' + mixin_vals['gyp_defines']
         else:
           vals['gyp_defines'] = mixin_vals['gyp_defines']
       if 'mixins' in mixin_vals:
         self.FlattenMixins(mixin_vals['mixins'], vals, visited)
     return vals
 
+  def ClobberIfNeeded(self, vals):
+    path = self.args.path[0]
+    build_dir = self.ToAbsPath(path)
+    mb_type_path = os.path.join(build_dir, 'mb_type')
+    needs_clobber = False
+    new_mb_type = vals['type']
+    if self.Exists(build_dir):
+      if self.Exists(mb_type_path):
+        old_mb_type = self.ReadFile(mb_type_path)
+        if old_mb_type != new_mb_type:
+          self.Print("Build type mismatch: was %s, will be %s, clobbering %s" %
+                     (old_mb_type, new_mb_type, path))
+          needs_clobber = True
+      else:
+        # There is no 'mb_type' file in the build directory, so this probably
+        # means that the prior build(s) were not done through mb, and we
+        # have no idea if this was a GYP build or a GN build. Clobber it
+        # to be safe.
+        self.Print("%s/mb_type missing, clobbering to be safe" % path)
+        needs_clobber = True
+
+    if needs_clobber:
+      self.RemoveDirectory(build_dir)
+
+    self.MaybeMakeDirectory(build_dir)
+    self.WriteFile(mb_type_path, new_mb_type)
+
   def RunGNGen(self, vals):
     path = self.args.path[0]
 
     cmd = self.GNCmd('gen', path, vals['gn_args'])
 
     swarming_targets = []
     if self.args.swarming_targets_file:
       # We need GN to generate the list of runtime dependencies for
       # the compile targets listed (one per line) in the file so
       # we can run them via swarming. We use ninja_to_gn.pyl to convert
@@ skipping 473 matching lines @@
 
   def ReadFile(self, path):
     # This function largely exists so it can be overriden for testing.
     with open(path) as fp:
       return fp.read()
 
   def RemoveFile(self, path):
     # This function largely exists so it can be overriden for testing.
     os.remove(path)
 
+  def RemoveDirectory(self, abs_path):
+    if sys.platform == 'win32':
+      # In other places in chromium, we often have to retry this command

[brettw, 2015/09/12 02:08:25]

But doesn't shutil still work? I don't see the need for special-casing this.

+      # because we're worried about other processes still holding on to
+      # file handles, but when MB is invoked, it will be early enough in the
+      # build that their should be no other processes to interfere. We
+      # can change this if need be.
+      self.Run(['cmd.exe', '/c', 'rmdir', '/q', '/s', abs_path])
+    else:
+      shutil.rmtree(abs_path, ignore_errors=True)
+
   def TempFile(self, mode='w'):
     # This function largely exists so it can be overriden for testing.
     return tempfile.NamedTemporaryFile(mode=mode, delete=False)
 
   def WriteFile(self, path, contents):
     # This function largely exists so it can be overriden for testing.
     if self.args.dryrun or self.args.verbose:
       self.Print('\nWriting """\\\n%s""" to %s.\n' % (contents, path))
     with open(path, 'w') as fp:
       return fp.write(contents)
 
 
 class MBErr(Exception):
   pass
 
 
 if __name__ == '__main__':
   try:
     sys.exit(main(sys.argv[1:]))
   except MBErr as e:
     print(e)
     sys.exit(1)
   except KeyboardInterrupt:
     print("interrupted, exiting", stream=sys.stderr)
     sys.exit(130)