Improve performance of showDivergenceFromBaseBranch (#5536)

### PR Description Instead of manually figuring out how much ahead each branch is from it's upstream branch, use [for-each-ref ahead-behind](https://git-scm.com/docs/git-for-each-ref/2.41.0#Documentation/git-for-each-ref.txt-ahead-behindcommittish) if supported by the git binary. On my Windows machine, using the lazygit repo with all 61 branches created locally, it goes from ~8.5s to ~200ms. It was also able to find a base branch for `assets` which the previous iteration did not. Fixes #5532
2026-05-22 10:15:43 +02:00 · 2026-04-27 07:11:36 +02:00
parent 01b617ea18 3d14881f05
commit b4f79851db
2 changed files with 502 additions and 1 deletions
@@ -155,6 +155,17 @@ func (self *BranchLoader) GetBehindBaseBranchValuesForAllBranches(
 		return nil
 	}

+	if self.version.IsAtLeast(2, 41, 0) {
+		return self.getBehindBaseBranchValuesFast(branches, mainBranchRefs, renderFunc)
+	}
+	return self.getBehindBaseBranchValuesLegacy(branches, mainBranches, renderFunc)
+}
+
+func (self *BranchLoader) getBehindBaseBranchValuesLegacy(
+	branches []*models.Branch,
+	mainBranches *MainBranches,
+	renderFunc func(),
+) error {
 	t := time.Now()
 	errg := errgroup.Group{}

@@ -190,11 +201,134 @@ func (self *BranchLoader) GetBehindBaseBranchValuesForAllBranches(
 	}

 	err := errg.Wait()
-	self.Log.Debugf("time to get behind base branch values for all branches: %s", time.Since(t))
+	self.Log.Debugf("time to get behind base branch values for all branches (legacy): %s", time.Since(t))
 	renderFunc()
 	return err
 }

+// Holds parsed values from a single %(ahead-behind:<base>) field.
+type aheadBehind struct {
+	ahead, behind int
+}
+
+type branchAheadBehind struct {
+	refName      string
+	aheadBehinds []aheadBehind
+}
+
+// Parses output produced by:
+//
+//	git for-each-ref --format='%(refname)\x00%(ahead-behind:<base1>)\x00...' refs/heads
+//
+// Lines whose NUL-split column count doesn't match (1 + numBases) are dropped.
+// Blank lines are ignored.
+// Individual malformed ahead-behind fields produce {valid: false} entries
+func parseAheadBehindForEachRefOutput(
+	output string,
+	numBases int, // number of %(ahead-behind:...) tokens
+) []branchAheadBehind {
+	if output == "" {
+		return nil
+	}
+	lines := strings.Split(output, "\n")
+	result := make([]branchAheadBehind, 0, len(lines))
+	for _, line := range lines {
+		cols := strings.Split(line, "\x00")
+		if len(cols) != numBases+1 {
+			continue
+		}
+		refName := cols[0]
+		aheadBehinds := lo.FilterMap(cols[1:], func(col string, _ int) (aheadBehind, bool) {
+			return parseAheadBehindField(col)
+		})
+		entry := branchAheadBehind{
+			refName:      refName,
+			aheadBehinds: aheadBehinds,
+		}
+		result = append(result, entry)
+	}
+	return result
+}
+
+func parseAheadBehindField(s string) (aheadBehind, bool) {
+	parts := strings.Fields(s)
+	if len(parts) != 2 {
+		return aheadBehind{}, false
+	}
+	ahead, err1 := strconv.Atoi(parts[0])
+	behind, err2 := strconv.Atoi(parts[1])
+	if err1 != nil || err2 != nil {
+		return aheadBehind{}, false
+	}
+	return aheadBehind{ahead: ahead, behind: behind}, true
+}
+
+// Picks the "closest" base by smallest ahead value (commits the branch
+// has that the base doesn't = roughly "since fork point") and returns
+// its behind value.
+// Ties are broken by index order
+func selectBehindForBranch(aheadBehinds []aheadBehind) int {
+	return lo.MinBy(aheadBehinds, func(a, b aheadBehind) bool {
+		return a.ahead < b.ahead
+	}).behind
+}
+
+// The output format is:
+//
+//	<refname>\x00<ahead> <behind>\x00<ahead> <behind>...\n
+//
+// with one ahead-behind field per base, in the same order as mainBranchRefs.
+//
+// Requires git >= 2.41 (when %(ahead-behind:...) was added).
+func buildAheadBehindForEachRefArgs(mainBranchRefs []string) []string {
+	formatParts := make([]string, 0, 1+len(mainBranchRefs))
+	formatParts = append(formatParts, "%(refname)")
+	for _, ref := range mainBranchRefs {
+		formatParts = append(formatParts, "%(ahead-behind:"+ref+")")
+	}
+	format := strings.Join(formatParts, "%00")
+
+	return NewGitCmd("for-each-ref").
+		Arg("--format=" + format).
+		Arg("refs/heads").
+		ToArgv()
+}
+
+func (self *BranchLoader) getBehindBaseBranchValuesFast(
+	branches []*models.Branch,
+	mainBranchRefs []string,
+	renderFunc func(),
+) error {
+	t := time.Now()
+
+	output, err := self.cmd.New(
+		buildAheadBehindForEachRefArgs(mainBranchRefs),
+	).DontLog().RunWithOutput()
+	if err != nil {
+		return err
+	}
+
+	parsed := parseAheadBehindForEachRefOutput(output, len(mainBranchRefs))
+	branchByRef := lo.KeyBy(branches, (*models.Branch).FullRefName)
+
+	for _, p := range parsed {
+		if branch, ok := branchByRef[p.refName]; ok {
+			behind := selectBehindForBranch(p.aheadBehinds)
+			branch.BehindBaseBranch.Store(int32(behind))
+			delete(branchByRef, p.refName)
+		}
+	}
+
+	// Branches not in parse are default to 0
+	for _, branch := range branchByRef {
+		branch.BehindBaseBranch.Store(0)
+	}
+
+	self.Log.Debugf("time to get behind base branch values for all branches (fast): %s", time.Since(t))
+	renderFunc()
+	return nil
+}
+
 // Find the base branch for the given branch (i.e. the main branch that the
 // given branch was forked off of)
 //
@@ -7,6 +7,7 @@ import (
 	"time"

 	"github.com/jesseduffield/lazygit/pkg/commands/models"
+	"github.com/jesseduffield/lazygit/pkg/commands/oscommands"
 	"github.com/stretchr/testify/assert"
 )

@@ -124,3 +125,369 @@ func TestObtainBranch(t *testing.T) {
 		})
 	}
 }
+
+func TestParseAheadBehindForEachRefOutput(t *testing.T) {
+	type scenario struct {
+		testName string
+		input    string
+		numBases int
+		expected []branchAheadBehind
+	}
+
+	scenarios := []scenario{
+		{
+			testName: "single branch single base",
+			input:    "refs/heads/feat\x002 5\n",
+			numBases: 1,
+			expected: []branchAheadBehind{
+				{
+					refName:      "refs/heads/feat",
+					aheadBehinds: []aheadBehind{{ahead: 2, behind: 5}},
+				},
+			},
+		},
+		{
+			testName: "multiple branches multiple bases",
+			input: "refs/heads/feat\x002 5\x0010 1\n" +
+				"refs/heads/main\x000 0\x000 0\n",
+			numBases: 2,
+			expected: []branchAheadBehind{
+				{
+					refName: "refs/heads/feat",
+					aheadBehinds: []aheadBehind{
+						{ahead: 2, behind: 5},
+						{ahead: 10, behind: 1},
+					},
+				},
+				{
+					refName: "refs/heads/main",
+					aheadBehinds: []aheadBehind{
+						{ahead: 0, behind: 0},
+						{ahead: 0, behind: 0},
+					},
+				},
+			},
+		},
+		{
+			testName: "empty ahead-behind field for unreachable base",
+			input:    "refs/heads/feat\x00\x002 5\n",
+			numBases: 2,
+			expected: []branchAheadBehind{
+				{
+					refName: "refs/heads/feat",
+					aheadBehinds: []aheadBehind{
+						{ahead: 2, behind: 5},
+					},
+				},
+			},
+		},
+		{
+			testName: "ref name containing slashes and dashes",
+			input:    "refs/heads/feat/foo-bar\x001 2\n",
+			numBases: 1,
+			expected: []branchAheadBehind{
+				{
+					refName:      "refs/heads/feat/foo-bar",
+					aheadBehinds: []aheadBehind{{ahead: 1, behind: 2}},
+				},
+			},
+		},
+		{
+			testName: "trailing newline and blank lines are ignored",
+			input:    "refs/heads/feat\x001 2\n\n",
+			numBases: 1,
+			expected: []branchAheadBehind{
+				{
+					refName:      "refs/heads/feat",
+					aheadBehinds: []aheadBehind{{ahead: 1, behind: 2}},
+				},
+			},
+		},
+		{
+			testName: "line with wrong column count is skipped",
+			input: "refs/heads/good\x001 2\n" +
+				"refs/heads/bad\n" +
+				"refs/heads/also_good\x003 4\n",
+			numBases: 1,
+			expected: []branchAheadBehind{
+				{
+					refName:      "refs/heads/good",
+					aheadBehinds: []aheadBehind{{ahead: 1, behind: 2}},
+				},
+				{
+					refName:      "refs/heads/also_good",
+					aheadBehinds: []aheadBehind{{ahead: 3, behind: 4}},
+				},
+			},
+		},
+		{
+			testName: "malformed ahead-behind field becomes invalid but line is kept",
+			input:    "refs/heads/feat\x00not_a_number\n",
+			numBases: 1,
+			expected: []branchAheadBehind{
+				{
+					refName:      "refs/heads/feat",
+					aheadBehinds: []aheadBehind{},
+				},
+			},
+		},
+		{
+			testName: "empty input",
+			input:    "",
+			numBases: 1,
+			expected: nil,
+		},
+	}
+
+	for _, s := range scenarios {
+		t.Run(s.testName, func(t *testing.T) {
+			result := parseAheadBehindForEachRefOutput(s.input, s.numBases)
+			assert.Equal(t, s.expected, result)
+		})
+	}
+}
+
+func TestSelectBehindForBranch(t *testing.T) {
+	type scenario struct {
+		testName     string
+		aheadBehinds []aheadBehind
+		expected     int
+	}
+
+	scenarios := []scenario{
+		{
+			testName:     "single base, valid value",
+			aheadBehinds: []aheadBehind{{ahead: 3, behind: 7}},
+			expected:     7,
+		},
+		{
+			testName: "multi-base, clear winner by ahead",
+			aheadBehinds: []aheadBehind{
+				{ahead: 50, behind: 10}, // master
+				{ahead: 5, behind: 2},   // develop  ← smallest ahead
+			},
+			expected: 2,
+		},
+		{
+			testName: "develop forked from master case (ancestor-of-each-other)",
+			// feat-x has 5 commits since fork from develop.
+			// develop is 50 commits ahead of master.
+			// ahead vs master = 5 + 50 = 55; behind vs master = 0
+			// ahead vs develop = 5;          behind vs develop = 5
+			aheadBehinds: []aheadBehind{
+				{ahead: 55, behind: 0}, // master
+				{ahead: 5, behind: 5},  // develop  ← smallest ahead
+			},
+			expected: 5,
+		},
+		{
+			testName: "tie on ahead - first base wins (config order)",
+			aheadBehinds: []aheadBehind{
+				{ahead: 5, behind: 10}, // first
+				{ahead: 5, behind: 99}, // second, same ahead
+			},
+			expected: 10,
+		},
+		{
+			testName: "first base invalid, second valid",
+			aheadBehinds: []aheadBehind{
+				{ahead: 3, behind: 8},
+			},
+			expected: 8,
+		},
+		{
+			testName:     "all invalid - returns 0",
+			aheadBehinds: []aheadBehind{},
+			expected:     0,
+		},
+		{
+			testName:     "empty - returns 0",
+			aheadBehinds: nil,
+			expected:     0,
+		},
+	}
+
+	for _, s := range scenarios {
+		t.Run(s.testName, func(t *testing.T) {
+			result := selectBehindForBranch(s.aheadBehinds)
+			assert.Equal(t, s.expected, result)
+		})
+	}
+}
+
+func TestBuildAheadBehindForEachRefArgs(t *testing.T) {
+	type scenario struct {
+		testName       string
+		mainBranchRefs []string
+		expected       []string
+	}
+
+	scenarios := []scenario{
+		{
+			testName:       "single base",
+			mainBranchRefs: []string{"refs/heads/master"},
+			expected: []string{
+				"git",
+				"for-each-ref",
+				"--format=%(refname)%00%(ahead-behind:refs/heads/master)",
+				"refs/heads",
+			},
+		},
+		{
+			testName:       "two bases",
+			mainBranchRefs: []string{"refs/heads/master", "refs/remotes/origin/develop"},
+			expected: []string{
+				"git",
+				"for-each-ref",
+				"--format=%(refname)%00%(ahead-behind:refs/heads/master)%00%(ahead-behind:refs/remotes/origin/develop)",
+				"refs/heads",
+			},
+		},
+		{
+			testName:       "four bases",
+			mainBranchRefs: []string{"refs/heads/a", "refs/heads/b", "refs/heads/c", "refs/heads/d"},
+			expected: []string{
+				"git",
+				"for-each-ref",
+				"--format=%(refname)%00%(ahead-behind:refs/heads/a)%00%(ahead-behind:refs/heads/b)%00%(ahead-behind:refs/heads/c)%00%(ahead-behind:refs/heads/d)",
+				"refs/heads",
+			},
+		},
+	}
+
+	for _, s := range scenarios {
+		t.Run(s.testName, func(t *testing.T) {
+			result := buildAheadBehindForEachRefArgs(s.mainBranchRefs)
+			assert.Equal(t, s.expected, result)
+		})
+	}
+}
+
+func TestGetBehindBaseBranchValuesForAllBranches_FastPath(t *testing.T) {
+	mainBranchRefs := []string{"refs/heads/master", "refs/remotes/origin/develop"}
+
+	// Two branches: feat-x has clear divergence from develop; main matches master exactly.
+	branches := []*models.Branch{
+		{Name: "feat-x"},
+		{Name: "main"},
+	}
+
+	expectedFormat := "%(refname)%00%(ahead-behind:refs/heads/master)%00%(ahead-behind:refs/remotes/origin/develop)"
+	output := "refs/heads/feat-x\x0055 0\x005 5\n" + // picks develop (ahead=5 < 55), behind=5
+		"refs/heads/main\x000 0\x000 0\n" // picks master (first, tie), behind=0
+
+	runner := oscommands.NewFakeRunner(t).
+		ExpectGitArgs([]string{"for-each-ref", "--format=" + expectedFormat, "refs/heads"}, output, nil)
+
+	gitCommon := buildGitCommon(commonDeps{
+		runner:     runner,
+		gitVersion: &GitVersion{2, 41, 0, ""},
+	})
+
+	loader := &BranchLoader{
+		Common:    gitCommon.Common,
+		GitCommon: gitCommon,
+		cmd:       gitCommon.cmd,
+	}
+
+	mainBranches := &MainBranches{
+		c:                    gitCommon.Common,
+		cmd:                  gitCommon.cmd,
+		existingMainBranches: mainBranchRefs,
+		previousMainBranches: gitCommon.Common.UserConfig().Git.MainBranches,
+	}
+
+	rendered := false
+	err := loader.GetBehindBaseBranchValuesForAllBranches(branches, mainBranches, func() { rendered = true })
+	assert.NoError(t, err)
+	assert.True(t, rendered, "renderFunc should have been called")
+
+	assert.Equal(t, int32(5), branches[0].BehindBaseBranch.Load(), "feat-x should be behind develop by 5")
+	assert.Equal(t, int32(0), branches[1].BehindBaseBranch.Load(), "main should be behind master by 0")
+
+	runner.CheckForMissingCalls()
+}
+
+// edge case where a failure would leave artifacts from prior load
+func TestGetBehindBaseBranchValuesForAllBranches_FastPath_ClearsStaleValueWhenBranchMissingFromOutput(t *testing.T) {
+	mainBranchRefs := []string{"refs/heads/master"}
+
+	feat := &models.Branch{Name: "feat-x"}
+	feat.BehindBaseBranch.Store(99) // stale value from a prior load
+	ghost := &models.Branch{Name: "ghost"}
+	ghost.BehindBaseBranch.Store(42) // stale value from a prior load
+
+	expectedFormat := "%(refname)%00%(ahead-behind:refs/heads/master)"
+	output := "refs/heads/feat-x\x003 5\n" // ghost is intentionally absent
+
+	runner := oscommands.NewFakeRunner(t).
+		ExpectGitArgs([]string{"for-each-ref", "--format=" + expectedFormat, "refs/heads"}, output, nil)
+
+	gitCommon := buildGitCommon(commonDeps{
+		runner:     runner,
+		gitVersion: &GitVersion{2, 41, 0, ""},
+	})
+
+	loader := &BranchLoader{
+		Common:    gitCommon.Common,
+		GitCommon: gitCommon,
+		cmd:       gitCommon.cmd,
+	}
+
+	mainBranches := &MainBranches{
+		c:                    gitCommon.Common,
+		cmd:                  gitCommon.cmd,
+		existingMainBranches: mainBranchRefs,
+		previousMainBranches: gitCommon.Common.UserConfig().Git.MainBranches,
+	}
+
+	err := loader.GetBehindBaseBranchValuesForAllBranches(
+		[]*models.Branch{feat, ghost}, mainBranches, func() {})
+	assert.NoError(t, err)
+
+	assert.Equal(t, int32(5), feat.BehindBaseBranch.Load(), "feat-x should be updated to fresh value")
+	assert.Equal(t, int32(0), ghost.BehindBaseBranch.Load(), "ghost should be reset to 0 since it has no fresh data")
+
+	runner.CheckForMissingCalls()
+}
+
+func TestGetBehindBaseBranchValuesForAllBranches_LegacyPath(t *testing.T) {
+	mainBranchRefs := []string{"refs/heads/master"}
+
+	branches := []*models.Branch{
+		{Name: "feat-x"},
+	}
+
+	// In legacy path: per-branch GetBaseBranch (merge-base + for-each-ref --contains)
+	// then rev-list --left-right --count.
+	runner := oscommands.NewFakeRunner(t).
+		ExpectGitArgs([]string{"merge-base", "refs/heads/feat-x", "refs/heads/master"}, "abc123\n", nil).
+		ExpectGitArgs([]string{"for-each-ref", "--contains", "abc123", "--format=%(refname)", "refs/heads/master"}, "refs/heads/master\n", nil).
+		ExpectGitArgs([]string{"rev-list", "--left-right", "--count", "refs/heads/feat-x...refs/heads/master"}, "5\t7\n", nil)
+
+	gitCommon := buildGitCommon(commonDeps{
+		runner:     runner,
+		gitVersion: &GitVersion{2, 34, 0, ""}, // pre-2.41, forces legacy
+	})
+
+	loader := &BranchLoader{
+		Common:    gitCommon.Common,
+		GitCommon: gitCommon,
+		cmd:       gitCommon.cmd,
+	}
+
+	mainBranches := &MainBranches{
+		c:                    gitCommon.Common,
+		cmd:                  gitCommon.cmd,
+		existingMainBranches: mainBranchRefs,
+		previousMainBranches: gitCommon.Common.UserConfig().Git.MainBranches,
+	}
+
+	rendered := false
+	err := loader.GetBehindBaseBranchValuesForAllBranches(branches, mainBranches, func() { rendered = true })
+	assert.NoError(t, err)
+	assert.True(t, rendered)
+	assert.Equal(t, int32(7), branches[0].BehindBaseBranch.Load())
+
+	runner.CheckForMissingCalls()
+}