gclient: Support syncing deps to refs/{branch-heads,tags}:revision.

Arbitrary refs (i.e. syncing to refs/arbitrary/stuff:revision) is not
guaranteed to work.

Bug: 874501, 942229
Change-Id: If08f0d9ae257e3d9f486d3ea6b310c8d94d3b918
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1542588Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Reviewed-by: Karen Qian <karenqian@google.com>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>

gclient_scm.py

@@ -512,10 +512,13 @@ class GitWrapper(SCMWrapper):
       verbose = ['--verbose']
       printed_path = True
 
-    if revision.startswith('refs/branch-heads'):
-      options.with_branch_heads = True
-    if revision.startswith('refs/tags'):
-      options.with_tags = True
+    revision_ref = revision
+    if ':' in revision:
+      revision_ref, _, revision = revision.partition(':')
+
+    mirror = self._GetMirror(url, options, revision_ref)
+    if mirror:
+      url = mirror.mirror_path
 
     remote_ref = scm.GIT.RefToRemoteRef(revision, self.remote)
     if remote_ref:
@@ -530,10 +533,6 @@ class GitWrapper(SCMWrapper):
       # hash is also a tag, only make a distinction at checkout
       rev_type = "hash"
 
-    mirror = self._GetMirror(url, options)
-    if mirror:
-      url = mirror.mirror_path
-
     # If we are going to introduce a new project, there is a possibility that
     # we are syncing back to a state where the project was originally a
     # sub-project rolled by DEPS (realistic case: crossing the Blink merge point
@@ -955,7 +954,7 @@ class GitWrapper(SCMWrapper):
     return os.path.join(self._root_dir,
                         'old_' + self.relpath.replace(os.sep, '_')) + '.git'
 
-  def _GetMirror(self, url, options):
+  def _GetMirror(self, url, options, revision_ref=None):
     """Get a git_cache.Mirror object for the argument url."""
     if not self.cache_dir:
       return None
@@ -965,8 +964,12 @@ class GitWrapper(SCMWrapper):
     }
     if hasattr(options, 'with_branch_heads') and options.with_branch_heads:
       mirror_kwargs['refs'].append('refs/branch-heads/*')
+    elif revision_ref and revision_ref.startswith('refs/branch-heads/'):
+      mirror_kwargs['refs'].append(revision_ref)
     if hasattr(options, 'with_tags') and options.with_tags:
       mirror_kwargs['refs'].append('refs/tags/*')
+    elif revision_ref and revision_ref.startswith('refs/tags/'):
+      mirror_kwargs['refs'].append(revision_ref)
     return git_cache.Mirror(url, **mirror_kwargs)
 
   def _UpdateMirrorIfNotContains(self, mirror, options, rev_type, revision):
@@ -1307,6 +1310,10 @@ class GitWrapper(SCMWrapper):
       # refs/changes/xx ref.
       if ':' not in refspec:
         refspec += ':' + refspec
+    if (refspec and refspec.startswith('refs/remotes/branch-heads')
+        and not getattr(options, 'with_branch_heads', False)):
+      refspec = '%s:%s' % (refspec.replace('/remotes', '', 1), refspec)
+
     fetch_cmd =  cfg + [
         'fetch',
         remote or self.remote,