git-codereview: new sync-branch and related fixes

This CL adds a new command, "git codereview sync-branch",
which does the appropriate git merge for the current branch.

This CL also fixes a bug in "git codereview branchpoint",
and therefore also commands like "git codereview pending",
which was getting the branchpoint wrong for merges,
with the effect that a merge showed too many pending CLs.

This CL also fixes a bug in "git codereview change", which was
formerly willing to run "git checkout" with a pending merge,
which had the effect of flattening the merge mysteriously.
Now it detects the merge and refuses to run.

All of this should make merges easier and less error-prone
as we use dev branches more often.

With the earlier CL in this stack that allows working directly
on local branches, this is now a great way to run a merge
updating dev.regabi:

	git change dev.regabi
	git sync-branch

(with appropriate aliases to avoid typing "codereview").

Fixes golang/go#26201.

Change-Id: Ic24603123ca5135a72004309f5bb208ff149c9eb
Reviewed-on: https://go-review.googlesource.com/c/review/+/279772
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

1 files changed, 22 insertions, 0 deletions

diff --git a/git-codereview/doc.go b/git-codereview/doc.go
index a72b6db..b9eb230 100644
--- a/git-codereview/doc.go
+++ b/git-codereview/doc.go
@@ -344,5 +344,27 @@ if different from the source repository. If set to “golang/go”, for example,
 lines such as “Fixes #123” in a commit message will be rewritten to
 “Fixes golang/go#123”.
 
+The “branch” key specifies the name of the branch on the origin server
+corresponding to the current checkout. If this setting is missing, git-codereview
+uses the name of the remote branch that the current checkout is tracking.
+If that setting is missing, git-codereview uses “main”.
+
+The “parent-branch” key specifies the name of the parent branch on
+the origin server. The parent branch is the branch from which the current
+pulls regular updates. For example the parent branch of “dev.feature”
+would typically be “main”, in which case it would have this codereview.cfg:
+
+	branch: dev.feature
+	parent-branch: main
+
+In a more complex configuration, one feature branch might depend upon
+another, like “dev.feature2” containing follow-on work for “dev.feature”,
+neither of which has merged yet. In this case, the dev.feature2 branch
+would have this codereview.cfg:
+
+	branch: dev.feature2
+	parent-branch: dev.feature
+
+The parent branch setting is used by the sync-branch command.
 */
 package main