Use the squash merge message when committing a squash merge

After "Squash merge and leave uncommitted", the commit panel opens
empty, or with the commit prefix of the branch. Users have to type a
message for the squash merge themselves. "git commit" from the terminal
suggests the message in SQUASH_MSG instead.

Show the message in SQUASH_MSG in the commit panel, unless there is a
preserved message. It takes precedence over the commit prefix, like the
message of "Squash merge and commit" does.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

pkg/commands/git_commands/status.go

@@ -73,6 +73,16 @@ func (self *StatusCommands) IsInSquashMerge() (bool, error) {
 	return self.os.FileExists(filepath.Join(self.repoPaths.WorktreeGitDirPath(), "SQUASH_MSG"))
 }
 
+// SquashMergeMessage returns the message in SQUASH_MSG (see IsInSquashMerge), or
+// an empty string if there is no squash merge in progress
+func (self *StatusCommands) SquashMergeMessage() string {
+	content, err := os.ReadFile(filepath.Join(self.repoPaths.WorktreeGitDirPath(), "SQUASH_MSG"))
+	if err != nil {
+		return ""
+	}
+	return strings.TrimSpace(string(content))
+}
+
 func (self *StatusCommands) IsInCherryPick() (bool, error) {
 	hasCherryPickHead, err := self.hasCherryPickHead()
 	if err != nil || hasCherryPickHead {

pkg/gui/context/commit_message_context.go

@@ -131,6 +131,10 @@ func (self *CommitMessageContext) GetInitialMessage() string {
 	return self.viewModel.initialMessage
 }
 
+func (self *CommitMessageContext) SetInitialMessage(message string) {
+	self.viewModel.initialMessage = message
+}
+
 func (self *CommitMessageContext) GetHistoryMessage() string {
 	return self.viewModel.historyMessage
 }
@@ -148,7 +152,6 @@ func (self *CommitMessageContext) SetPanelState(
 	summaryTitle string,
 	descriptionTitle string,
 	preserveMessage bool,
-	initialMessage string,
 	onConfirm func(string, string) error,
 	onSwitchToEditor func(string) error,
 	forceSkipHooks bool,
@@ -156,7 +159,6 @@ func (self *CommitMessageContext) SetPanelState(
 ) {
 	self.viewModel.selectedindex = index
 	self.viewModel.preserveMessage = preserveMessage
-	self.viewModel.initialMessage = initialMessage
 	self.viewModel.onConfirm = onConfirm
 	self.viewModel.onSwitchToEditor = onSwitchToEditor
 	self.viewModel.forceSkipHooks = forceSkipHooks

pkg/gui/controllers/helpers/commits_helper.go

@@ -143,10 +143,7 @@ func (self *CommitsHelper) OpenCommitMessagePanel(opts *OpenCommitMessagePanelOp
 	}
 
 	// When there's no explicit initial message but we're in a preservation
-	// context, fall back to any previously preserved message. This is stored as
-	// the "initial" value so the unchanged-message check on close still works
-	// correctly (in particular, clearing the panel then escaping will notice
-	// the difference and delete the preserved file).
+	// context, fall back to any previously preserved message.
 	initialMessage := opts.InitialMessage
 	initialMessageIsPreserved := false
 	if opts.PreserveMessage && initialMessage == "" {
@@ -159,7 +156,6 @@ func (self *CommitsHelper) OpenCommitMessagePanel(opts *OpenCommitMessagePanelOp
 		opts.SummaryTitle,
 		opts.DescriptionTitle,
 		opts.PreserveMessage,
-		initialMessage,
 		onConfirm,
 		opts.OnSwitchToEditor,
 		opts.ForceSkipHooks,
@@ -172,6 +168,14 @@ func (self *CommitsHelper) OpenCommitMessagePanel(opts *OpenCommitMessagePanelOp
 		self.SetMessageAndDescriptionInView(initialMessage)
 	}
 
+	// PreserveCommitMessage compares the message in the panel with this when the
+	// panel closes, so that it preserves the message only if the user changed it
+	// (in particular, clearing the panel then escaping will notice the
+	// difference and delete the preserved file). Take it from the panel, because
+	// a message with a blank line after the summary comes out of the panel
+	// without it.
+	self.c.Contexts().CommitMessage.SetInitialMessage(self.JoinCommitMessageAndUnwrappedDescription())
+
 	self.c.Context().Push(self.c.Contexts().CommitMessage, types.OnFocusOpts{})
 }
 

pkg/gui/controllers/helpers/working_tree_helper.go

@@ -237,6 +237,9 @@ func (self *WorkingTreeHelper) HandleCommitPress() error {
 	var initialMessage string
 	preservedMessage := self.c.Contexts().CommitMessage.GetPreservedMessageAndLogError()
 	if preservedMessage == "" {
+		initialMessage = self.c.Git().Status.SquashMergeMessage()
+	}
+	if preservedMessage == "" && initialMessage == "" {
 		commitPrefixConfigs := self.commitPrefixConfigsForRepo()
 		for _, commitPrefixConfig := range commitPrefixConfigs {
 			prefixPattern := commitPrefixConfig.Pattern

pkg/integration/tests/commit/cancel_commit_during_squash_merge.go

@@ -0,0 +1,35 @@
+package commit
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var CancelCommitDuringSquashMerge = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Open the commit panel during a squash merge started outside lazygit, and close it without changing git's message",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	SetupConfig:  func(cfg *config.AppConfig) {},
+	SetupRepo: func(shell *Shell) {
+		shell.EmptyCommit("one").
+			NewBranch("feature-branch").
+			CreateFileAndAdd("feature-file", "content").
+			Commit("feature").
+			Checkout("master").
+			RunCommand([]string{"git", "merge", "--squash", "feature-branch"})
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Files().
+			Focus().
+			Lines(
+				Equals("A  feature-file"),
+			).
+			Press(keys.Files.CommitChanges)
+
+		t.ExpectPopup().CommitMessagePanel().
+			InitialText(Equals("Squashed commit of the following:")).
+			Cancel()
+
+		t.FileSystem().PathNotPresent(".git/LAZYGIT_PENDING_COMMIT")
+	},
+})

pkg/integration/tests/commit/commit_during_squash_merge.go

@@ -0,0 +1,58 @@
+package commit
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var CommitDuringSquashMerge = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Commit the changes of a squash merge that was left uncommitted, using the squash merge message",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	SetupConfig: func(cfg *config.AppConfig) {
+		cfg.GetUserConfig().Git.CommitPrefix = []config.CommitPrefixConfig{{Pattern: "^(\\w+)-branch$", Replace: "[$1] "}}
+	},
+	SetupRepo: func(shell *Shell) {
+		shell.NewBranch("original-branch").
+			EmptyCommit("one").
+			NewBranch("feature-branch").
+			CreateFileAndAdd("feature-file", "content").
+			Commit("feature").
+			Checkout("original-branch")
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Branches().
+			Focus().
+			Lines(
+				Contains("original-branch").IsSelected(),
+				Contains("feature-branch"),
+			).
+			SelectNextItem().
+			Press(keys.Branches.MergeIntoCurrentBranch)
+
+		t.ExpectPopup().Menu().
+			Title(Equals("Merge")).
+			Select(Contains("Squash merge and leave uncommitted")).
+			Confirm()
+
+		t.Views().Files().
+			Focus().
+			Lines(
+				Equals("A  feature-file"),
+			).
+			Press(keys.Files.CommitChanges)
+
+		t.ExpectPopup().CommitMessagePanel().
+			Title(Equals("Commit summary")).
+			InitialText(Equals("Squash merge feature-branch into original-branch")).
+			Confirm()
+
+		t.Views().Status().Content(Equals("repo → original-branch"))
+
+		t.Views().Commits().
+			Lines(
+				Contains("Squash merge feature-branch into original-branch"),
+				Contains("one"),
+			)
+	},
+})

pkg/integration/tests/test_list.go

@@ -137,12 +137,14 @@ var tests = []*components.IntegrationTest{
 	commit.AmendWhenThereAreConflictsAndCancel,
 	commit.AmendWhenThereAreConflictsAndContinue,
 	commit.AutoWrapMessage,
+	commit.CancelCommitDuringSquashMerge,
 	commit.Checkout,
 	commit.CheckoutFileFromCommit,
 	commit.CheckoutFileFromRangeSelectionOfCommits,
 	commit.CheckoutFileWithLocalModifications,
 	commit.Commit,
 	commit.CommitAllWithNestedRepository,
+	commit.CommitDuringSquashMerge,
 	commit.CommitMultiline,
 	commit.CommitSkipHooks,
 	commit.CommitSwitchToEditor,