1 files changed, 240 insertions, 1 deletions
diff --git a/git-codereview/sync.go b/git-codereview/sync.go
index 9ea3e67..0334341 100644
--- a/git-codereview/sync.go
+++ b/git-codereview/sync.go
@@ -4,7 +4,15 @@
 
 package main
 
-import "strings"
+import (
+	"encoding/json"
+	"flag"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strings"
+)
 
 func cmdSync(args []string) {
 	expectZeroArgs(args, "sync")
@@ -78,3 +86,234 @@ func checkUnstaged(cmd string) {
 			"\trun 'git add' and 'git-codereview change' to commit staged changes", cmd)
 	}
 }
+
+type syncBranchStatus struct {
+	Local      string
+	Parent     string
+	Branch     string
+	ParentHash string
+	BranchHash string
+	Conflicts  []string
+}
+
+func syncBranchStatusFile() string {
+	return filepath.Join(repoRoot(), ".git/codereview-sync-branch-status")
+}
+
+func readSyncBranchStatus() *syncBranchStatus {
+	data, err := ioutil.ReadFile(syncBranchStatusFile())
+	if err != nil {
+		dief("cannot sync-branch: reading status: %v", err)
+	}
+	status := new(syncBranchStatus)
+	err = json.Unmarshal(data, status)
+	if err != nil {
+		dief("cannot sync-branch: reading status: %v", err)
+	}
+	return status
+}
+
+func writeSyncBranchStatus(status *syncBranchStatus) {
+	js, err := json.MarshalIndent(status, "", "\t")
+	if err != nil {
+		dief("cannot sync-branch: writing status: %v", err)
+	}
+	if err := ioutil.WriteFile(syncBranchStatusFile(), js, 0666); err != nil {
+		dief("cannot sync-branch: writing status: %v", err)
+	}
+}
+
+func cmdSyncBranch(args []string) {
+	os.Setenv("GIT_EDITOR", ":") // do not bring up editor during merge, commit
+
+	var cont bool
+	flags.BoolVar(&cont, "continue", false, "continue after merge conflicts")
+	flags.Parse(args)
+	if len(flag.Args()) > 0 {
+		fmt.Fprintf(stderr(), "Usage: %s sync-branch %s [-continue]\n", progName, globalFlags)
+		exit(2)
+	}
+
+	parent := config()["parent-branch"]
+	if parent == "" {
+		dief("cannot sync-branch: codereview.cfg does not list parent-branch")
+	}
+
+	branch := config()["branch"]
+	if parent == "" {
+		dief("cannot sync-branch: codereview.cfg does not list branch")
+	}
+
+	b := CurrentBranch()
+	if b.DetachedHead() {
+		dief("cannot sync-branch: on detached head")
+	}
+	if len(b.Pending()) > 0 {
+		dief("cannot sync-branch: pending changes exist\n" +
+			"\trun 'git codereview pending' to see them")
+	}
+
+	if cont {
+		if _, err := os.Stat(syncBranchStatusFile()); err != nil {
+			dief("cannot sync-branch -continue: no pending sync-branch status file found")
+		}
+		syncBranchContinue(" -continue", b, readSyncBranchStatus())
+		return
+	}
+
+	if _, err := cmdOutputErr("git", "rev-parse", "--abbrev-ref", "MERGE_HEAD"); err == nil {
+		diePendingMerge("sync-branch")
+	}
+
+	// Don't sync with staged or unstaged changes.
+	// rebase is going to complain if we don't, and we can give a nicer error.
+	checkStaged("sync")
+	checkUnstaged("sync")
+
+	// Make sure client is up-to-date on current branch.
+	// Note that this does a remote fetch of b.OriginBranch() (aka branch).
+	cmdSync(nil)
+
+	// Pull down parent commits too.
+	quiet := "-q"
+	if *verbose > 0 {
+		quiet = "-v"
+	}
+	run("git", "fetch", quiet, "origin", "refs/heads/"+parent+":refs/remotes/origin/"+parent)
+
+	// Write the status file to make sure we can, before starting a merge.
+	status := &syncBranchStatus{
+		Local:      b.Name,
+		Parent:     parent,
+		ParentHash: gitHash("origin/" + parent),
+		Branch:     branch,
+		BranchHash: gitHash("origin/" + branch),
+	}
+	writeSyncBranchStatus(status)
+
+	// Start the merge.
+	_, err := cmdOutputErr("git", "merge", "origin/"+parent)
+
+	// Resolve codereview.cfg the right way (never take it from the merge).
+	cmdOutputDir(repoRoot(), "git", "checkout", "HEAD", "--", "codereview.cfg")
+
+	if err != nil {
+		// Check whether the only listed file is codereview.cfg and try again if so.
+		// Build list of unmerged files.
+		for _, s := range nonBlankLines(cmdOutputDir(repoRoot(), "git", "status", "-b", "--porcelain")) {
+			// Unmerged status is anything with a U and also AA and DD.
+			if len(s) >= 4 && s[2] == ' ' && (s[0] == 'U' || s[1] == 'U' || s[0:2] == "AA" || s[0:2] == "DD") {
+				status.Conflicts = append(status.Conflicts, s[3:])
+			}
+		}
+		if len(status.Conflicts) == 0 {
+			// Must have been codereview.cfg that was the problem.
+			// Try continuing the merge.
+			// Note that as of Git 2.12, git merge --continue is a synonym for git commit,
+			// but older Gits do not have merge --continue.
+			var out string
+			out, err = cmdOutputErr("git", "commit", "-m", "TEMPORARY MERGE MESSAGE")
+			if err != nil {
+				printf("git commit failed with no apparent unmerged files:\n%s\n", out)
+			}
+		} else {
+			writeSyncBranchStatus(status)
+		}
+	}
+
+	if err != nil {
+		if len(status.Conflicts) == 0 {
+			dief("cannot sync-branch: git merge failed but no conflicts found\n" +
+				"(unexpected error, please ask for help!)")
+		}
+		dief("sync-branch: merge conflicts in:\n\t- %s\n\n"+
+			"Please fix them (use 'git status' to see the list again),\n"+
+			"then 'git add' or 'git rm' to resolve them,\n"+
+			"and then 'git sync-branch -continue' to continue.\n"+
+			"Or run 'git merge --abort' to give up on this sync-branch.\n",
+			strings.Join(status.Conflicts, "\n\t- "))
+	}
+
+	syncBranchContinue("", b, status)
+}
+
+func diePendingMerge(cmd string) {
+	dief("cannot %s: found pending merge\n"+
+		"Run 'git codereview sync-branch -continue' if you fixed\n"+
+		"merge conflicts after a previous sync-branch operation.\n"+
+		"Or run 'git merge --abort' to give up on the sync-branch.\n",
+		cmd)
+}
+
+func syncBranchContinue(flag string, b *Branch, status *syncBranchStatus) {
+	if h := gitHash("origin/" + status.Parent); h != status.ParentHash {
+		dief("cannot sync-branch%s: parent hash changed: %.7s -> %.7s", flag, status.ParentHash, h)
+	}
+	if h := gitHash("origin/" + status.Branch); h != status.BranchHash {
+		dief("cannot sync-branch%s: branch hash changed: %.7s -> %.7s", flag, status.BranchHash, h)
+	}
+	if b.Name != status.Local {
+		dief("cannot sync-branch%s: branch changed underfoot: %s -> %s", flag, status.Local, b.Name)
+	}
+
+	branch := status.Branch
+	parent := status.Parent
+	branchHash := status.BranchHash
+	parentHash := status.ParentHash
+
+	prefix := ""
+	if strings.HasPrefix(branch, "dev.") || strings.HasPrefix(branch, "release-branch.") {
+		prefix = "[" + branch + "] "
+	}
+	msg := fmt.Sprintf("%sall: merge %s (%.7s) into %s", prefix, parent, parentHash, branch)
+
+	if flag != "" {
+		// Need to commit the merge.
+
+		// Check that the state of the client is the way we left it before any merge conflicts.
+		mergeHead, err := cmdOutputErr("git", "rev-parse", "MERGE_HEAD")
+		if err != nil {
+			dief("cannot sync-branch%s: no pending merge\n"+
+				"If you accidentally ran 'git merge --continue',\n"+
+				"then use 'git reset --hard HEAD^' to undo.\n", flag)
+		}
+		mergeHead = trim(mergeHead)
+		if mergeHead != parentHash {
+			dief("cannot sync-branch%s: MERGE_HEAD is %.7s, but origin/%s is %.7s", flag, mergeHead, parent, parentHash)
+		}
+		head := gitHash("HEAD")
+		if head != branchHash {
+			dief("cannot sync-branch%s: HEAD is %.7s, but origin/%s is %.7s", flag, head, branch, branchHash)
+		}
+
+		if HasUnstagedChanges() {
+			dief("cannot sync-branch%s: unstaged changes (unresolved conflicts)\n"+
+				"\tUse 'git status' to see them, 'git add' or 'git rm' to resolve them,\n"+
+				"\tand then run 'git sync-branch -continue' again.\n", flag)
+		}
+
+		run("git", "commit", "-m", msg)
+	}
+
+	// Amend the merge message, which may be auto-generated by git
+	// or may have been written by us during the post-conflict commit above,
+	// to use our standard format and list the incorporated CLs.
+
+	// Merge must never sync codereview.cfg,
+	// because it contains the parent and branch config.
+	// Force the on-branch copy back while amending the commit.
+	cmdOutputDir(repoRoot(), "git", "checkout", "origin/"+branch, "--", "codereview.cfg")
+
+	conflictMsg := ""
+	if len(status.Conflicts) > 0 {
+		conflictMsg = "Conflicts:\n\n- " + strings.Join(status.Conflicts, "\n- ") + "\n\n"
+	}
+	msg = fmt.Sprintf("%s\n\n%sMerge List:\n\n%s", msg, conflictMsg,
+		cmdOutput("git", "log", "--format=format:+ %cd %h %s", "--date=short", "HEAD^1..HEAD^2"))
+	run("git", "commit", "--amend", "-m", msg)
+
+	fmt.Fprintf(stderr(), "\n")
+
+	cmdPending([]string{"-c", "-l"})
+	fmt.Fprintf(stderr(), "\n* Merge commit created.\nRun 'git codereview mail' to send for review.\n")
+}