[Mac/GN] Fix rebuilds when changing framework_version of a mac_framework_bundle.

Write the current framework_version to a file at gen-time, and clobber the
entire framework bundle if it differs from the current value in the file.

This has to be done at gen-time because it is not possible to run a script at
the create_bundle stage before any other dependencies in its tree run. Take
this sample graph:

                       bundle_data --> shared_library
                      /
  mac_framework_bundle
                      \
                       action("clean_framework_version")

It is not possible, from a mac_framework_bundle, to force the
clean_framework_version action to run before the shared_library. When the
action does run, its stamp will have a newer mtime than the shared_library.
Because bundle_data are hard linked into place, the link source file will
have an older mtime than the action, and the build will never stabilize.

BUG=648757
R=dpranke@chromium.org

Originally Committed: https://crrev.com/fed4fc1df8bab7159f19e04ed658c1f417e4e499
Reverted: https://crrev.com/d76ba00e6cc2625000d495e79bdc8d747645405e

Review-Url: https://codereview.chromium.org/2453043002
Cr-Commit-Position: refs/heads/master@{#428366}

.gn

@@ -227,6 +227,7 @@ exec_script_whitelist = [
   "//build/config/linux/pkg_config.gni",
   "//build/config/linux/atk/BUILD.gn",
   "//build/config/mac/mac_sdk.gni",
+  "//build/config/mac/rules.gni",
   "//build/config/posix/BUILD.gn",
   "//build/config/sysroot.gni",
   "//build/config/win/BUILD.gn",

build/config/mac/prepare_framework_version.py

@@ -0,0 +1,42 @@
+# Copyright 2016 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.
+
+import os
+import shutil
+import sys
+
+# Ensures that the current version matches the last-produced version, which is
+# stored in the version_file. If it does not, then the framework_root_dir is
+# obliterated.
+# Usage: python prepare_framework_version.py out/obj/version_file \
+#                                            out/Framework.framework \
+#                                            'A'
+
+def PrepareFrameworkVersion(version_file, framework_root_dir, version):
+  # Test what the current framework version is. Stop if it is up-to-date.
+  try:
+    with open(version_file, 'r') as f:
+      current_version = f.read()
+      if current_version == version:
+        return
+  except IOError:
+    pass
+
+  # The framework version has changed, so clobber the framework.
+  if os.path.exists(framework_root_dir):
+    shutil.rmtree(framework_root_dir)
+
+  # Write out the new framework version file, making sure its containing
+  # directory exists.
+  dirname = os.path.dirname(version_file)
+  if not os.path.isdir(dirname):
+    os.makedirs(dirname, 0700)
+
+  with open(version_file, 'w+') as f:
+    f.write(version)
+
+
+if __name__ == '__main__':
+  PrepareFrameworkVersion(sys.argv[1], sys.argv[2], sys.argv[3])
+  sys.exit(0)

build/config/mac/rules.gni

@@ -258,11 +258,13 @@ template("mac_framework_bundle") {
   # the versioned directory structure.
   _framework_target = _target_name
   _framework_name = _output_name + ".framework"
-  _framework_root_dir = "$root_out_dir/$_framework_name"
+  _framework_base_dir = "$root_out_dir/$_framework_name"
   if (defined(invoker.framework_version) && invoker.framework_version != "") {
     _framework_version = invoker.framework_version
-    _framework_root_dir += "/Versions/$_framework_version"
+    _framework_root_dir = _framework_base_dir + "/Versions/$_framework_version"
     _framework_target = _target_name + "_create_bundle"
+  } else {
+    _framework_root_dir = _framework_base_dir
   }
 
   _link_shared_library_target = target_name + "_shared_library"
@@ -302,6 +304,19 @@ template("mac_framework_bundle") {
     ]
   }
 
+  # Clean the entire framework if the framework_version changes.
+  _version_arg = ""
+  if (defined(_framework_version)) {
+    _version_arg = _framework_version
+  }
+  _version_file = "$target_out_dir/${target_name}_version"
+  exec_script("//build/config/mac/prepare_framework_version.py",
+              [
+                rebase_path(_version_file),
+                rebase_path(_framework_base_dir),
+                "'$_version_arg'",
+              ])
+
   _framework_public_config = _target_name + "_public_config"
   config(_framework_public_config) {
     # TODO(sdefresne): should we have a framework_dirs similar to lib_dirs