Add --upstream option to gclient to scrape git checkouts back to upstream state.

gclient_scm.py

Index: gclient_scm.py
diff --git a/gclient_scm.py b/gclient_scm.py
index 2cdee7df8a1d7823678c9b19048890fe5c04f2c6..62a9aa059b92d32fc1583014ea0540dc4e1402a2 100644
--- a/gclient_scm.py
+++ b/gclient_scm.py
@@ -262,7 +262,10 @@ class GitWrapper(SCMWrapper):
 
     self._CheckMinVersion("1.6.6")
 
-    default_rev = "refs/heads/master"
+    if not options.nuclear:
+      default_rev = "refs/heads/master"
+    else:
+      default_rev = "refs/remotes/origin/master"

[Dirk Pranke, 2013/06/27 19:57:52]

It seems like refs/heads/master can't be the right default rev in any case. I
also don't like using hard-coded branch names, period. Perhaps this should be
'{u}' (in both cases) ? 

Lastly, I would flip the order of the two branches so that you don't also need a
'not', if you end up w/ two branches.

     url, deps_revision = gclient_utils.SplitUrlRevision(self.url)
     rev_str = ""
     revision = deps_revision
@@ -276,6 +279,9 @@ class GitWrapper(SCMWrapper):
     if not revision:
       revision = default_rev
 
+    if revision == 'HEAD' and options.nuclear:
+      revision = 'refs/remotes/origin/master'

[Dirk Pranke, 2013/06/27 19:57:52]

This doesn't seem right. In what situation do we say -r HEAD explicitly ? 

I would be more inclined to either leave -r HEAD alone or err out saying that -r
and --nuclear are incompatible, but maybe neither of those are acceptable?

[iannucci, 2013/06/27 22:56:51]

If we have deps e.g. third_party/WebKit@HEAD

+
     if gclient_utils.IsDateRevision(revision):
       # Date-revisions only work on git-repositories if the reflog hasn't
       # expired yet. Use rev-list to get the corresponding revision.
@@ -430,7 +436,8 @@ class GitWrapper(SCMWrapper):
 
     # This is a big hammer, debatable if it should even be here...
     if options.force or options.reset:
-      self._Run(['reset', '--hard', 'HEAD'], options)
+      target = 'refs/remotes/origin/master' if options.nuclear else 'HEAD'

[Dirk Pranke, 2013/06/27 19:57:52]

Same sorts of comments as above, plus it's not clear to me that this shouldn't
just be a part of the UpstreamBranch() logic above on 401-409.

+      self._Run(['reset', '--hard', target], options)
 
     if current_type == 'detached':
       # case 0
@@ -577,7 +584,10 @@ class GitWrapper(SCMWrapper):
       # Don't reuse the args.
       return self.update(options, [], file_list)
 
-    default_rev = "refs/heads/master"
+    if options.nuclear:
+      default_rev = "refs/remotes/origin/master"
+    else:
+      default_rev = "refs/heads/master"
     _, deps_revision = gclient_utils.SplitUrlRevision(self.url)
     if not deps_revision:
       deps_revision = default_rev