git-codereview: begin to handle multiple-change branches

Gerrit supports multiple-change branches, and we'd like to make
git-codereview useful for people using this mode of work.
This CL is the first step.

- remove error message on detecting a multiple-change branch
- require 'git submit hash' in multiple-change branch
- make git submit, git sync cleanup safe for multiple-change branch
- adjust git pending output to show full information about multiple-change branch
- add pending -c to show only current branch, since output is getting long

We're not advertising or supporting this mode yet. For now the only
way to enter it is to run 'git commit' to create the second commit.
Perhaps eventually we will support something like 'git change -new'.

Change-Id: I8284a7c230503061d3e6d7cce0be7d8d05c9b2a3
Reviewed-on: https://go-review.googlesource.com/2110
Reviewed-by: Andrew Gerrand <adg@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

1 files changed, 18 insertions, 9 deletions

diff --git a/git-codereview/mail.go b/git-codereview/mail.go
index c6eee7e..c5ec7ce 100644
--- a/git-codereview/mail.go
+++ b/git-codereview/mail.go
@@ -23,21 +23,25 @@ func mail(args []string) {
 	flags.Var(ccList, "cc", "comma-separated list of people to CC:")
 
 	flags.Usage = func() {
-		fmt.Fprintf(stderr(), "Usage: %s mail %s [-r reviewer,...] [-cc mail,...]\n", os.Args[0], globalFlags)
+		fmt.Fprintf(stderr(), "Usage: %s mail %s [-r reviewer,...] [-cc mail,...] [commit-hash]\n", os.Args[0], globalFlags)
 	}
 	flags.Parse(args)
-	if len(flags.Args()) != 0 {
+	if len(flags.Args()) > 1 {
 		flags.Usage()
 		os.Exit(2)
 	}
 
 	b := CurrentBranch()
-	if b.ChangeID() == "" {
-		dief("no pending change; can't mail.")
+
+	var c *Commit
+	if len(flags.Args()) == 1 {
+		c = b.CommitByHash("mail", flags.Arg(0))
+	} else {
+		c = b.DefaultCommit("mail")
 	}
 
 	if *diff {
-		run("git", "diff", b.Branchpoint()+"..HEAD", "--")
+		run("git", "diff", b.Branchpoint()[:7]+".."+c.ShortHash, "--")
 		return
 	}
 
@@ -49,7 +53,7 @@ func mail(args []string) {
 	// for side effect of dying with a good message if origin is GitHub
 	loadGerritOrigin()
 
-	refSpec := b.PushSpec()
+	refSpec := b.PushSpec(c)
 	start := "%"
 	if *rList != "" {
 		refSpec += mailList(start, "r", string(*rList))
@@ -74,9 +78,14 @@ func mail(args []string) {
 	run("git", "tag", "-f", b.Name+".mailed")
 }
 
-// PushSpec returns the spec for a Gerrit push command to publish the change in b.
-func (b *Branch) PushSpec() string {
-	return "HEAD:refs/for/" + strings.TrimPrefix(b.OriginBranch(), "origin/")
+// PushSpec returns the spec for a Gerrit push command to publish the change c in b.
+// If c is nil, PushSpec returns a spec for pushing all changes in b.
+func (b *Branch) PushSpec(c *Commit) string {
+	local := "HEAD"
+	if c != nil && (len(b.Pending()) == 0 || b.Pending()[0].Hash != c.Hash) {
+		local = c.ShortHash
+	}
+	return local + ":refs/for/" + strings.TrimPrefix(b.OriginBranch(), "origin/")
 }
 
 // mailAddressRE matches the mail addresses we admit. It's restrictive but admits