fix(git): Two behavior fixes for Sort. (#20)

- Move the default branch up top.
  - Handle branches that point to the same commit correctly.

git/git/git.go

@@ -161,12 +161,13 @@ func (repo *gitRepo) Sort(workUnits []string) error {
 		return nil
 	}
 
-	workUnitsByHash, err := repo.keyByHash(workUnits)
+	branchesByHash, err := repo.keyBranchByHash(workUnits)
 	if err != nil {
 		return err
 	}
+	slog.Debug("Found hashes for branches.", "hashes", branchesByHash)
 
-	args := []string{"rev-list", "--topo-order", "--format=format:%H", "--reverse"}
+	args := []string{"rev-list", "--topo-order", "--reverse"}
 	// We're reversing the output of rev-list, which will use its command line for
 	// tie breakers. So reverse the order of our work units so that they'll be
 	// sorted correctly in the output.
@@ -182,12 +183,12 @@ func (repo *gitRepo) Sort(workUnits []string) error {
 	}
 	var i int
 	r := bufio.NewReader(stdout)
-	for i < len(workUnitsByHash) {
+	for i < len(workUnits) {
 		hash, err := r.ReadString('\n')
 		if hash != "" {
 			hash = strings.TrimSuffix(hash, "\n")
-			if wu := workUnitsByHash[hash]; wu != "" {
-				workUnits[i] = wu
+			for _, b := range branchesByHash[hash] {
+				workUnits[i] = b
 				i++
 			}
 		}
@@ -199,38 +200,53 @@ func (repo *gitRepo) Sort(workUnits []string) error {
 			return err
 		}
 	}
-	if i != len(workUnitsByHash) {
+	if n := len(workUnits); i != n {
 		found := make(map[string]bool)
 		for _, wu := range workUnits[:i] {
 			found[wu] = true
 		}
 		var missing []string
-		for wu := range workUnitsByHash {
-			if !found[wu] {
-				missing = append(missing, wu)
+		for _, branches := range branchesByHash {
+			for _, b := range branches {
+				if !found[b] {
+					missing = append(missing, b)
+				}
 			}
 		}
-		return fmt.Errorf("only able to topologically sort %d of %d branches: unsortable branches: %q", i, len(workUnitsByHash), missing)
+		return fmt.Errorf("only able to topologically sort %d of %d branches: unsortable branches: %q", i, n, missing)
 	}
 	if err := cmd.Process.Kill(); err != nil {
 		slog.Warn("Problem killing rev-list command early.", "error", err)
 	}
+
+	// Move the default branch up top.
+	defaultBranch, err := repo.defaultBranchName()
+	if err != nil {
+		return err
+	}
+	isDefault := func(name string) bool { return name == defaultBranch }
+	slices.SortStableFunc(workUnits, morecmp.ComparingFunc(isDefault, morecmp.TrueFirst()))
+
 	return nil
 }
 
-func (repo *gitRepo) keyByHash(objects []string) (map[string]string, error) {
-	if len(objects) == 0 {
+func (repo *gitRepo) keyBranchByHash(branches []string) (map[string][]string, error) {
+	if len(branches) == 0 {
 		return nil, nil
 	}
-	args := []string{"rev-list", "--no-walk=unsorted"}
-	args = append(args, objects...)
+	args := []string{"branch", "--list", "--format=%(refname:short) %(objectname)"}
+	args = append(args, branches...)
 	stdout, err := repo.Command(args...).RunStdout()
 	if err != nil {
-		return nil, fmt.Errorf("could not get object hashes: %w", err)
+		return nil, fmt.Errorf("could not get branch hashes: %w", err)
 	}
-	ret := make(map[string]string)
-	for i, hash := range strings.Split(stdout, "\n") {
-		ret[hash] = objects[i]
+	ret := make(map[string][]string)
+	for _, line := range strings.Split(stdout, "\n") {
+		if line == "" {
+			break
+		}
+		sp := strings.Split(line, " ")
+		ret[sp[1]] = append(ret[sp[1]], sp[0])
 	}
 	return ret, nil
 }
@@ -252,6 +268,7 @@ func (repo *gitRepo) defaultBranchName() (string, error) {
 	}
 	for _, n := range slices.Compact([]string{def, "master"}) {
 		if repo.branchExists(n) {
+			slog.Debug("Found default branch name.", "name", n)
 			return n, nil
 		}
 	}

git/git/git_test.go

@@ -5,13 +5,15 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"slices"
 	"strings"
 	"testing"
 
 	"github.com/JeffFaer/tmux-vcs-sync/api"
 	"github.com/JeffFaer/tmux-vcs-sync/api/exec"
 	"github.com/JeffFaer/tmux-vcs-sync/api/exec/exectest"
 	"github.com/JeffFaer/tmux-vcs-sync/api/repotest"
+	"github.com/google/go-cmp/cmp"
 	"github.com/kballard/go-shellquote"
 )
 
@@ -50,6 +52,7 @@ func (git testGit) newRepo(dir string, name string) (*testGitRepo, error) {
 		return nil, err
 	}
 	gitRepo := &testGitRepo{repo.(*gitRepo)}
+	gitRepo.gitRepo.git = git.git
 	if err := gitRepo.addEmptyCommit("Initial commit."); err != nil {
 		return nil, err
 	}
@@ -241,6 +244,31 @@ func TestCurrent(t *testing.T) {
 	}
 }
 
+func TestSort_DuplicateBranch(t *testing.T) {
+	git := newGit(t)
+	repo, err := git.newRepo(t.TempDir(), t.Name())
+	if err != nil {
+		t.Fatalf("Could not create repo: %v", err)
+	}
+	addBranch := func(name string) initStep {
+		return repoCommand{args: []string{"branch", name}}
+	}
+	commit := func(name string) initStep {
+		return apiCommand{"commit " + name, func(repo *testGitRepo) error { return repo.Commit(name) }}
+	}
+
+	initializeRepo(t, repo, []initStep{addBranch("foo"), commit("bar")})
+
+	branches := []string{"foo", defaultBranchName, "bar"}
+	got := slices.Clone(branches)
+	if err := repo.Sort(got); err != nil {
+		t.Errorf("repo.Sort(%q) = %v", branches, err)
+	}
+	if diff := cmp.Diff([]string{"main", "foo", "bar"}, got); diff != "" {
+		t.Errorf("repo.Sort(%q) diff (-want +got)\n%s", branches, diff)
+	}
+}
+
 type initStep interface {
 	Run(*testGitRepo) error
 	String() string
@@ -282,6 +310,19 @@ func (cmd newFile) String() string {
 	return fmt.Sprintf("echo %q > %q", cmd.content, cmd.path)
 }
 
+type apiCommand struct {
+	name string
+	cmd  func(*testGitRepo) error
+}
+
+func (cmd apiCommand) Run(repo *testGitRepo) error {
+	return cmd.cmd(repo)
+}
+
+func (cmd apiCommand) String() string {
+	return cmd.name
+}
+
 func initializeRepo(t *testing.T, repo *testGitRepo, init []initStep) {
 	t.Helper()
 	for i, step := range init {

git/go.mod

@@ -5,12 +5,12 @@ go 1.22.0
 require (
 	github.com/JeffFaer/go-stdlib-ext v0.2.0
 	github.com/JeffFaer/tmux-vcs-sync/api v0.0.0-20240314045224-4f466c92bafd
+	github.com/google/go-cmp v0.6.0
 	github.com/kballard/go-shellquote v0.0.0-20180428030007-95032a82bc51
 )
 
 require (
 	github.com/adrg/xdg v0.4.0 // indirect
-	github.com/google/go-cmp v0.6.0 // indirect
 	github.com/magefile/mage v1.15.0 // indirect
 	golang.org/x/sys v0.0.0-20211025201205-69cdffdb9359 // indirect
 )

git/go.sum

@@ -1,5 +1,5 @@
-github.com/JeffFaer/go-stdlib-ext v0.1.1 h1:M8JFdsiV9Uyi8CFSTZr/TCAoE8bdVYuDlGvudxVkgHw=
-github.com/JeffFaer/go-stdlib-ext v0.1.1/go.mod h1:+ipHu7aPnk5LuKfU1dda8+eIEfXNF2m7bC4porFJKXs=
+github.com/JeffFaer/go-stdlib-ext v0.2.0 h1:jUNUFurbzFdh1XtENCrb+QIaHeWUe8YneHvUs81hW5M=
+github.com/JeffFaer/go-stdlib-ext v0.2.0/go.mod h1:+ipHu7aPnk5LuKfU1dda8+eIEfXNF2m7bC4porFJKXs=
 github.com/JeffFaer/tmux-vcs-sync/api v0.0.0-20240314045224-4f466c92bafd h1:WJgnYObOv3BnL+AV+mUCIzGthpypB5xb3bHAvJxvbCs=
 github.com/JeffFaer/tmux-vcs-sync/api v0.0.0-20240314045224-4f466c92bafd/go.mod h1:3hqch0mjY8h884063yZLPulFxvxbsoB9Pir02j3ubt4=
 github.com/adrg/xdg v0.4.0 h1:RzRqFcjH4nE5C6oTAxhBtoE2IRyjBSa62SCbyPidvls=