Overhaul git logic to sync only when needed
I wanted to understand it all so I ran a bunch of tests and found that it was resyncing when not required any time the rev was not == HEAD. Some stackoverflow and git manpage spelunking produced this. Nice side-effect is tha the workdir is named after the githash instead of random.
This commit is contained in:
Tim Hockin
parent
7fcc902aa7
commit
ff73d8e4f0
106
main.go
106
main.go
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@ -25,9 +25,9 @@ import (
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"io"
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"io/ioutil"
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"log"
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"math/rand"
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"os"
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"os/exec"
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"os/signal"
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"path"
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"path/filepath"
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"strconv"
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@ -132,19 +132,35 @@ func main() {
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time.Sleep(time.Duration(*flWait) * time.Second)
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continue
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}
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initialSync = false
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failCount = 0
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if *flOneTime {
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os.Exit(0)
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if initialSync {
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if isHash, err := revIsHash(*flRev, *flRoot); err != nil {
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log.Printf("can't tell if rev %s is a git hash, exiting", *flRev)
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os.Exit(1)
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} else if isHash {
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log.Printf("rev %s appears to be a git hash, no further sync needed", *flRev)
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sleepForever()
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}
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if *flOneTime {
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os.Exit(0)
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}
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initialSync = false
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}
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log.Printf("waiting %d seconds", *flWait)
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failCount = 0
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log.Printf("next sync in %d seconds", *flWait)
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time.Sleep(time.Duration(*flWait) * time.Second)
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}
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}
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// Do no work, but don't do something that triggers go's runtime into thinking
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// it is deadlocked.
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func sleepForever() {
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c := make(chan os.Signal, 1)
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signal.Notify(c, os.Interrupt, os.Kill)
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<-c
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os.Exit(0)
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}
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// updateSymlink atomically swaps the symlink to point at the specified directory and cleans up the previous worktree.
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func updateSymlink(gitRoot, link, newDir string) error {
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// Get currently-linked repo directory (to be removed), unless it doesn't exist
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@ -163,14 +179,12 @@ func updateSymlink(gitRoot, link, newDir string) error {
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if _, err := runCommand(gitRoot, "ln", "-snf", newDirRelative, "tmp-link"); err != nil {
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return fmt.Errorf("error creating symlink: %v", err)
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}
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log.Printf("create symlink %v->%v", "tmp-link", newDirRelative)
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log.Printf("created symlink %s -> %s", "tmp-link", newDirRelative)
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if _, err := runCommand(gitRoot, "mv", "-T", "tmp-link", link); err != nil {
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return fmt.Errorf("error replacing symlink: %v", err)
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}
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log.Printf("rename symlink %v to %v", "tmp-link", link)
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log.Printf("renamed symlink %s to %s", "tmp-link", link)
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// Clean up previous worktree
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if len(currentDir) > 0 {
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@ -178,14 +192,14 @@ func updateSymlink(gitRoot, link, newDir string) error {
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return fmt.Errorf("error removing directory: %v", err)
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}
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log.Printf("remove %v", currentDir)
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log.Printf("removed %s", currentDir)
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output, err := runCommand(gitRoot, "git", "worktree", "prune")
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_, err := runCommand(gitRoot, "git", "worktree", "prune")
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if err != nil {
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return err
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}
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log.Printf("worktree prune %v", output)
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log.Printf("pruned old worktrees")
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}
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return nil
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@ -193,14 +207,15 @@ func updateSymlink(gitRoot, link, newDir string) error {
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// addWorktreeAndSwap creates a new worktree and calls updateSymlink to swap the symlink to point to the new worktree
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func addWorktreeAndSwap(gitRoot, dest, branch, rev string) error {
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// fetch branch
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_, err := runCommand(gitRoot, "git", "fetch", "origin", branch)
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// Fetch the branch. This is required for the worktree to be based on the
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// current rev.
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_, err := runCommand(gitRoot, "git", "fetch", "--tags", "origin", branch)
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if err != nil {
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return err
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}
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log.Printf("fetched origin/%s", branch)
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// find the real commit for the rev
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// Find the real commit for the rev.
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output, err := runCommand(gitRoot, "git", "rev-list", "-n1", rev)
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if err != nil {
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return err
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@ -210,17 +225,18 @@ func addWorktreeAndSwap(gitRoot, dest, branch, rev string) error {
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log.Printf("rev %s resolves to %s", rev, revhash)
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}
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// add worktree in subdir
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rand.Seed(time.Now().UnixNano())
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worktreePath := path.Join(gitRoot, "rev-"+strconv.Itoa(rand.Int()))
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// Make a worktree for this exact git hash.
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worktreePath := path.Join(gitRoot, "rev-"+revhash)
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_, err = runCommand(gitRoot, "git", "worktree", "add", worktreePath, "origin/"+branch)
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if err != nil {
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return err
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}
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log.Printf("added worktree %s for origin/%s", worktreePath, branch)
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// .git file in worktree directory holds a reference to /git/.git/worktrees/<worktree-dir-name>
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// Replace it with a reference using relative paths, so that other containers can use a different volume mount name
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// The .git file in the worktree directory holds a reference to
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// /git/.git/worktrees/<worktree-dir-name>. Replace it with a reference
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// using relative paths, so that other containers can use a different volume
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// mount name.
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worktreePathRelative, err := filepath.Rel(gitRoot, worktreePath)
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if err != nil {
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return err
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@ -230,7 +246,7 @@ func addWorktreeAndSwap(gitRoot, dest, branch, rev string) error {
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return err
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}
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// reset working copy
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// Reset the worktree's working copy to the specific rev.
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_, err = runCommand(worktreePath, "git", "reset", "--hard", rev)
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if err != nil {
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return err
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@ -263,6 +279,18 @@ func cloneRepo(repo, branch, rev string, depth int, gitRoot string) error {
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return nil
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}
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func revIsHash(rev, gitRoot string) (bool, error) {
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// If a rev is a tag name or HEAD, rev-list will produce the git hash. If
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// it is already a git hash, the output will be the same hash. Of course, a
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// user could specify "abc" and match "abcdef12345678", so we just do a
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// prefix match.
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output, err := runCommand(gitRoot, "git", "rev-list", "-n1", rev)
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if err != nil {
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return false, err
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}
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return strings.HasPrefix(output, rev), nil
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}
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// syncRepo syncs the branch of a given repository to the destination at the given rev.
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func syncRepo(repo, branch, rev string, depth int, gitRoot, dest string) error {
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target := path.Join(gitRoot, dest)
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@ -277,12 +305,14 @@ func syncRepo(repo, branch, rev string, depth int, gitRoot, dest string) error {
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case err != nil:
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return fmt.Errorf("error checking if repo exist %q: %v", gitRepoPath, err)
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default:
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needUpdate, err := gitRemoteChanged(target, branch)
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needed, err := needResync(target, rev)
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if err != nil {
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return err
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}
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if !needUpdate {
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log.Printf("no change")
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if needed {
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log.Printf("update required")
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} else {
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log.Printf("no update required")
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return nil
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}
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}
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@ -290,21 +320,31 @@ func syncRepo(repo, branch, rev string, depth int, gitRoot, dest string) error {
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return addWorktreeAndSwap(gitRoot, dest, branch, rev)
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}
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// gitRemoteChanged returns true if the remote HEAD is different from the local HEAD, false otherwise
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func gitRemoteChanged(localDir, branch string) (bool, error) {
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_, err := runCommand(localDir, "git", "remote", "update")
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// needResync returns true if the upstream hash for rev is different from the local one.
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func needResync(localDir, rev string) (bool, error) {
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// Ask git what the exact hash is for rev.
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local, err := runCommand(localDir, "git", "rev-list", "-n1", rev)
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if err != nil {
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return false, err
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}
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localHead, err := runCommand(localDir, "git", "rev-parse", "HEAD")
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local = strings.Trim(local, "\n")
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// Fetch rev from upstream.
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_, err := runCommand(localDir, "git", "fetch", "origin", rev)
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if err != nil {
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return false, err
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}
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remoteHead, err := runCommand(localDir, "git", "rev-parse", fmt.Sprintf("origin/%v", branch))
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// Ask git what the exact hash is for upstream rev.
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remote, err := runCommand(localDir, "git", "rev-list", "-n1", "FETCH_HEAD")
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if err != nil {
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return false, err
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}
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return (localHead != remoteHead), nil
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remote = strings.Trim(remote, "\n")
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log.Printf("local hash: %s", local)
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log.Printf("remote hash: %s", remote)
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return (local != remote), nil
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}
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func cmdForLog(command string, args ...string) string {
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