fix: checkout out commits fails during bisect

pkg/commands/git_commands/bisect.go

@@ -89,13 +89,27 @@ func (self *BisectCommands) GetInfoForGitDir(gitDir string) *BisectInfo {
 		info.statusMap[hash] = status
 	}
 
-	currentContent, err := os.ReadFile(filepath.Join(gitDir, "BISECT_EXPECTED_REV"))
+	// Only set current when BISECT_EXPECTED_REV exists, which indicates that git has
+	// started the narrowing process (both good and bad commits have been marked).
+	// We use HEAD instead of BISECT_EXPECTED_REV because we want to show where HEAD
+	// actually is, not where git bisect expects you to be. This way, if the user manually
+	// checks out a different commit during bisect, the UI will correctly show that commit
+	// as "current" instead of the bisect-expected commit.
+	bisectExpectedRevPath := filepath.Join(gitDir, "BISECT_EXPECTED_REV")
+	exists, err = self.os.FileExists(bisectExpectedRevPath)
 	if err != nil {
 		self.Log.Infof("error getting git bisect info: %s", err.Error())
 		return info
 	}
-	currentHash := strings.TrimSpace(string(currentContent))
-	info.current = currentHash
+	if exists {
+		cmdArgs := NewGitCmd("rev-parse").Arg("HEAD").ToArgv()
+		output, err := self.cmd.New(cmdArgs).DontLog().RunWithOutput()
+		if err != nil {
+			self.Log.Infof("error getting git bisect info: %s", err.Error())
+			return info
+		}
+		info.current = strings.TrimSpace(output)
+	}
 
 	return info
 }

pkg/integration/tests/bisect/checkout.go

@@ -0,0 +1,78 @@
+package bisect
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var Checkout = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Start a git bisect and checkout a different commit within the bisect range",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	SetupRepo: func(shell *Shell) {
+		shell.
+			CreateNCommits(10)
+	},
+	SetupConfig: func(cfg *config.AppConfig) {
+		cfg.GetUserConfig().Git.Log.ShowGraph = "never"
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Commits().
+			Focus().
+			SelectedLine(Contains("commit 10")).
+			Press(keys.Commits.ViewBisectOptions).
+			Tap(func() {
+				t.ExpectPopup().Menu().Title(Equals("Bisect")).Select(MatchesRegexp(`Mark .* as bad`)).Confirm()
+			}).
+			NavigateToLine(Contains("commit 01")).
+			Press(keys.Commits.ViewBisectOptions).
+			Tap(func() {
+				t.ExpectPopup().Menu().Title(Equals("Bisect")).Select(MatchesRegexp(`Mark .* as good`)).Confirm()
+				t.Views().Information().Content(Contains("Bisecting"))
+			}).
+			// Verify we're at the bisect-selected commit (commit 05)
+			Lines(
+				Contains("CI commit 10").Contains("<-- bad"),
+				Contains("CI commit 09").DoesNotContain("<--"),
+				Contains("CI commit 08").DoesNotContain("<--"),
+				Contains("CI commit 07").DoesNotContain("<--"),
+				Contains("CI commit 06").DoesNotContain("<--"),
+				Contains("CI commit 05").Contains("<-- current").IsSelected(),
+				Contains("CI commit 04").DoesNotContain("<--"),
+				Contains("CI commit 03").DoesNotContain("<--"),
+				Contains("CI commit 02").DoesNotContain("<--"),
+				Contains("CI commit 01").Contains("<-- good"),
+			).
+			// Navigate to a different commit and checkout
+			NavigateToLine(Contains("commit 07")).
+			PressPrimaryAction()
+
+		// Confirm the checkout menu and select detached head checkout
+		t.ExpectPopup().Menu().
+			Title(Contains("Checkout branch or commit")).
+			Select(MatchesRegexp("Checkout commit .* as detached head")).
+			Confirm()
+
+		// After checkout, focus switches to branches panel - just verify it's focused
+		t.Views().Branches().
+			IsFocused()
+
+		// Switch back to commits panel and verify the current marker moved
+		t.Views().Commits().
+			Focus().
+			Lines(
+				Contains("CI commit 10").Contains("<-- bad"),
+				Contains("CI commit 09").DoesNotContain("<--"),
+				Contains("CI commit 08").DoesNotContain("<--"),
+				// The current marker should now be on commit 07 (where HEAD is),
+				// not on commit 05 (where bisect expected us to be)
+				Contains("CI commit 07").Contains("<-- current"),
+				Contains("CI commit 06").DoesNotContain("<--"),
+				Contains("CI commit 05").DoesNotContain("<--"),
+				Contains("CI commit 04").DoesNotContain("<--"),
+				Contains("CI commit 03").DoesNotContain("<--"),
+				Contains("CI commit 02").DoesNotContain("<--"),
+				Contains("CI commit 01").Contains("<-- good"),
+			)
+	},
+})

pkg/integration/tests/test_list.go

@@ -36,6 +36,7 @@ import (
 
 var tests = []*components.IntegrationTest{
 	bisect.Basic,
+	bisect.Checkout,
 	bisect.ChooseTerms,
 	bisect.FromOtherBranch,
 	bisect.Skip,