gclient_scm: Don't try to update file_list if it's None.

file_list can be none if gclient runs with --nohooks.
Fix apply_patch_ref so that it doesn't try to update file_list when it is
None.

TBR=agable@chromium.org

Bug: 643346
Change-Id: If00547da004415edfe68196a44cbda753b4db017
Reviewed-on: https://chromium-review.googlesource.com/989279
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>

gclient_scm.py

@@ -347,7 +347,8 @@ class GitWrapper(SCMWrapper):
         patch_repo, patch_ref, base_rev, self.checkout_path))
     self._Capture(['reset', '--hard'])
     self._Capture(['fetch', patch_repo, patch_ref])
-    file_list.extend(self._GetDiffFilenames('FETCH_HEAD'))
+    if file_list is not None:
+      file_list.extend(self._GetDiffFilenames('FETCH_HEAD'))
     self._Capture(['checkout', 'FETCH_HEAD'])
 
     if options.rebase_patch_ref:

recipes/trigger_recipe_roller.txt

-No-op file. Edit this to kick recipes. Yep. Ack.
+No-op file. Edit this to kick recipes.
 
 This is a beginning of a story in this silly file.
+Once upon a time,

tests/gclient_smoketest.py

@@ -536,7 +536,7 @@ class GClientSmokeGIT(GClientSmokeBase):
     tree['src/git_hooked2'] = 'git_hooked2'
     self.assertTree(tree)
 
-  def testSyncGerritRef(self):
+  def testSyncPatchRef(self):
     if not self.enabled:
       return
     self.gclient(['config', self.git_base + 'repo_1', '--name', 'src'])
@@ -559,6 +559,28 @@ class GClientSmokeGIT(GClientSmokeBase):
         self.githash('repo_2', 1),
         self.gitrevparse(os.path.join(self.root_dir, 'src/repo2')))
 
+  def testSyncPatchRefNoHooks(self):
+    if not self.enabled:
+      return
+    self.gclient(['config', self.git_base + 'repo_1', '--name', 'src'])
+    self.gclient([
+        'sync', '-v', '-v', '-v',
+        '--revision', 'src/repo2@%s' % self.githash('repo_2', 1),
+        '--patch-ref',
+        '%srepo_2@%s' % (self.git_base, self.githash('repo_2', 2)),
+        '--nohooks',
+    ])
+    # Assert that repo_2 files coincide with revision @2 (the patch ref)
+    tree = self.mangle_git_tree(('repo_1@2', 'src'),
+                                ('repo_2@2', 'src/repo2'),
+                                ('repo_3@2', 'src/repo2/repo_renamed'))
+    self.assertTree(tree)
+    # Assert that HEAD revision of repo_2 is @1 (the base we synced to) since we
+    # should have done a soft reset.
+    self.assertEqual(
+        self.githash('repo_2', 1),
+        self.gitrevparse(os.path.join(self.root_dir, 'src/repo2')))
+
   def testRunHooks(self):
     if not self.enabled:
       return