Non-sticky range selection diff (#3869)

- **PR Description**

When selecting a range of commits, show the combined diff for them.

Along the way, fix a few minor issues with the current implementation of
diffing mode; see the individual commit messages for details.

Fixes #3862.

- **Please check if the PR fulfills these requirements**

* [x] Cheatsheets are up-to-date (run `go generate ./...`)
* [x] Code has been formatted (see
[here](https://github.com/jesseduffield/lazygit/blob/master/CONTRIBUTING.md#code-formatting))
* [x] Tests have been added/updated (see
[here](https://github.com/jesseduffield/lazygit/blob/master/pkg/integration/README.md)
for the integration test guide)
* [x] Text is internationalised (see
[here](https://github.com/jesseduffield/lazygit/blob/master/CONTRIBUTING.md#internationalisation))
* [ ] If a new UserConfig entry was added, make sure it can be
hot-reloaded (see
[here](https://github.com/jesseduffield/lazygit/blob/master/docs/dev/Codebase_Guide.md#using-userconfig))
* [ ] Docs have been updated if necessary
* [x] You've read through your own file changes for silly mistakes etc

pkg/commands/models/branch.go

@@ -53,6 +53,10 @@ func (b *Branch) RefName() string {
 	return b.Name
 }
 
+func (b *Branch) ShortRefName() string {
+	return b.RefName()
+}
+
 func (b *Branch) ParentRefName() string {
 	return b.RefName() + "^"
 }

pkg/commands/models/commit.go

@@ -70,6 +70,10 @@ func (c *Commit) RefName() string {
 	return c.Hash
 }
 
+func (c *Commit) ShortRefName() string {
+	return c.Hash[:7]
+}
+
 func (c *Commit) ParentRefName() string {
 	if c.IsFirstCommit() {
 		return EmptyTreeCommitHash

pkg/commands/models/remote_branch.go

@@ -18,6 +18,10 @@ func (r *RemoteBranch) RefName() string {
 	return r.FullName()
 }
 
+func (r *RemoteBranch) ShortRefName() string {
+	return r.RefName()
+}
+
 func (r *RemoteBranch) ParentRefName() string {
 	return r.RefName() + "^"
 }

pkg/commands/models/stash_entry.go

@@ -17,6 +17,10 @@ func (s *StashEntry) RefName() string {
 	return fmt.Sprintf("stash@{%d}", s.Index)
 }
 
+func (s *StashEntry) ShortRefName() string {
+	return s.RefName()
+}
+
 func (s *StashEntry) ParentRefName() string {
 	return s.RefName() + "^"
 }

pkg/commands/models/tag.go

@@ -16,6 +16,10 @@ func (t *Tag) RefName() string {
 	return t.Name
 }
 
+func (t *Tag) ShortRefName() string {
+	return t.RefName()
+}
+
 func (t *Tag) ParentRefName() string {
 	return t.RefName() + "^"
 }

pkg/gui/context/commit_files_context.go

@@ -1,6 +1,8 @@
 package context
 
 import (
+	"fmt"
+
 	"github.com/jesseduffield/gocui"
 	"github.com/jesseduffield/lazygit/pkg/commands/models"
 	"github.com/jesseduffield/lazygit/pkg/gui/filetree"
@@ -75,6 +77,25 @@ func (self *CommitFilesContext) GetDiffTerminals() []string {
 	return []string{self.GetRef().RefName()}
 }
 
+func (self *CommitFilesContext) GetFromAndToForDiff() (string, string) {
+	if refs := self.GetRefRange(); refs != nil {
+		return refs.From.ParentRefName(), refs.To.RefName()
+	}
+	ref := self.GetRef()
+	return ref.ParentRefName(), ref.RefName()
+}
+
 func (self *CommitFilesContext) ModelSearchResults(searchStr string, caseSensitive bool) []gocui.SearchPosition {
 	return nil
 }
+
+func (self *CommitFilesContext) ReInit(ref types.Ref, refRange *types.RefRange) {
+	self.SetRef(ref)
+	self.SetRefRange(refRange)
+	if refRange != nil {
+		self.SetTitleRef(fmt.Sprintf("%s-%s", refRange.From.ShortRefName(), refRange.To.ShortRefName()))
+	} else {
+		self.SetTitleRef(ref.Description())
+	}
+	self.GetView().Title = self.Title()
+}

pkg/gui/context/local_commits_context.go

@@ -128,6 +128,19 @@ func (self *LocalCommitsContext) GetSelectedRef() types.Ref {
 	return commit
 }
 
+func (self *LocalCommitsContext) GetSelectedRefRangeForDiffFiles() *types.RefRange {
+	commits, startIdx, endIdx := self.GetSelectedItems()
+	if commits == nil || startIdx == endIdx {
+		return nil
+	}
+	from := commits[len(commits)-1]
+	to := commits[0]
+	if from.IsTODO() || to.IsTODO() {
+		return nil
+	}
+	return &types.RefRange{From: from, To: to}
+}
+
 // Returns the commit hash of the selected commit, or an empty string if no
 // commit is selected
 func (self *LocalCommitsContext) GetSelectedCommitHash() string {

pkg/gui/context/reflog_commits_context.go

@@ -71,6 +71,11 @@ func (self *ReflogCommitsContext) GetSelectedRef() types.Ref {
 	return commit
 }
 
+func (self *ReflogCommitsContext) GetSelectedRefRangeForDiffFiles() *types.RefRange {
+	// It doesn't make much sense to show a range diff between two reflog entries.
+	return nil
+}
+
 func (self *ReflogCommitsContext) GetCommits() []*models.Commit {
 	return self.getModel()
 }

pkg/gui/context/stash_context.go

@@ -61,6 +61,11 @@ func (self *StashContext) GetSelectedRef() types.Ref {
 	return stash
 }
 
+func (self *StashContext) GetSelectedRefRangeForDiffFiles() *types.RefRange {
+	// It doesn't make much sense to show a range diff between two stash entries.
+	return nil
+}
+
 func (self *StashContext) GetDiffTerminals() []string {
 	itemId := self.GetSelectedItemId()
 

pkg/gui/context/sub_commits_context.go

@@ -186,6 +186,19 @@ func (self *SubCommitsContext) GetSelectedRef() types.Ref {
 	return commit
 }
 
+func (self *SubCommitsContext) GetSelectedRefRangeForDiffFiles() *types.RefRange {
+	commits, startIdx, endIdx := self.GetSelectedItems()
+	if commits == nil || startIdx == endIdx {
+		return nil
+	}
+	from := commits[len(commits)-1]
+	to := commits[0]
+	if from.Divergence != to.Divergence {
+		return nil
+	}
+	return &types.RefRange{From: from, To: to}
+}
+
 func (self *SubCommitsContext) GetCommits() []*models.Commit {
 	return self.getModel()
 }

pkg/gui/controllers.go

@@ -259,7 +259,7 @@ func (gui *Gui) resetHelpersAndControllers() {
 		gui.State.Contexts.Stash,
 	} {
 		controllers.AttachControllers(context, controllers.NewSwitchToDiffFilesController(
-			common, context, gui.State.Contexts.CommitFiles,
+			common, context,
 		))
 	}
 

pkg/gui/controllers/commits_files_controller.go

@@ -136,9 +136,8 @@ func (self *CommitFilesController) GetOnRenderToMain() func() error {
 			return nil
 		}
 
-		ref := self.context().GetRef()
-		to := ref.RefName()
-		from, reverse := self.c.Modes().Diffing.GetFromAndReverseArgsForDiff(ref.ParentRefName())
+		from, to := self.context().GetFromAndToForDiff()
+		from, reverse := self.c.Modes().Diffing.GetFromAndReverseArgsForDiff(from)
 
 		cmdObj := self.c.Git().WorkingTree.ShowFileDiffCmdObj(from, to, reverse, node.GetPath(), false)
 		task := types.NewRunPtyTask(cmdObj.GetCmd())
@@ -250,9 +249,8 @@ func (self *CommitFilesController) canEditFiles(nodes []*filetree.CommitFileNode
 }
 
 func (self *CommitFilesController) openDiffTool(node *filetree.CommitFileNode) error {
-	ref := self.context().GetRef()
-	to := ref.RefName()
-	from, reverse := self.c.Modes().Diffing.GetFromAndReverseArgsForDiff(ref.ParentRefName())
+	from, to := self.context().GetFromAndToForDiff()
+	from, reverse := self.c.Modes().Diffing.GetFromAndReverseArgsForDiff(from)
 	_, err := self.c.RunSubprocess(self.c.Git().Diff.OpenDiffToolCmdObj(
 		git_commands.DiffToolCmdOptions{
 			Filepath:    node.GetPath(),
@@ -307,7 +305,8 @@ func (self *CommitFilesController) toggleForPatch(selectedNodes []*filetree.Comm
 		})
 	}
 
-	if self.c.Git().Patch.PatchBuilder.Active() && self.c.Git().Patch.PatchBuilder.To != self.context().GetRef().RefName() {
+	from, to, reverse := self.currentFromToReverseForPatchBuilding()
+	if self.c.Git().Patch.PatchBuilder.Active() && self.c.Git().Patch.PatchBuilder.NewPatchRequired(from, to, reverse) {
 		return self.c.Confirm(types.ConfirmOpts{
 			Title:  self.c.Tr.DiscardPatch,
 			Prompt: self.c.Tr.DiscardPatchConfirm,
@@ -330,14 +329,20 @@ func (self *CommitFilesController) startPatchBuilder() error {
 	commitFilesContext := self.context()
 
 	canRebase := commitFilesContext.GetCanRebase()
-	ref := commitFilesContext.GetRef()
-	to := ref.RefName()
-	from, reverse := self.c.Modes().Diffing.GetFromAndReverseArgsForDiff(ref.ParentRefName())
+	from, to, reverse := self.currentFromToReverseForPatchBuilding()
 
 	self.c.Git().Patch.PatchBuilder.Start(from, to, reverse, canRebase)
 	return nil
 }
 
+func (self *CommitFilesController) currentFromToReverseForPatchBuilding() (string, string, bool) {
+	commitFilesContext := self.context()
+
+	from, to := commitFilesContext.GetFromAndToForDiff()
+	from, reverse := self.c.Modes().Diffing.GetFromAndReverseArgsForDiff(from)
+	return from, to, reverse
+}
+
 func (self *CommitFilesController) enter(node *filetree.CommitFileNode) error {
 	return self.enterCommitFile(node, types.OnFocusOpts{ClickedWindowName: "", ClickedViewLineIdx: -1})
 }
@@ -357,7 +362,8 @@ func (self *CommitFilesController) enterCommitFile(node *filetree.CommitFileNode
 		return self.c.Context().Push(self.c.Contexts().CustomPatchBuilder, opts)
 	}
 
-	if self.c.Git().Patch.PatchBuilder.Active() && self.c.Git().Patch.PatchBuilder.To != self.context().GetRef().RefName() {
+	from, to, reverse := self.currentFromToReverseForPatchBuilding()
+	if self.c.Git().Patch.PatchBuilder.Active() && self.c.Git().Patch.PatchBuilder.NewPatchRequired(from, to, reverse) {
 		return self.c.Confirm(types.ConfirmOpts{
 			Title:  self.c.Tr.DiscardPatch,
 			Prompt: self.c.Tr.DiscardPatchConfirm,

pkg/gui/controllers/helpers/diff_helper.go

@@ -1,9 +1,13 @@
 package helpers
 
 import (
+	"strings"
+
 	"github.com/jesseduffield/lazygit/pkg/commands/git_commands"
+	"github.com/jesseduffield/lazygit/pkg/commands/models"
 	"github.com/jesseduffield/lazygit/pkg/gui/context"
 	"github.com/jesseduffield/lazygit/pkg/gui/modes/diffing"
+	"github.com/jesseduffield/lazygit/pkg/gui/style"
 	"github.com/jesseduffield/lazygit/pkg/gui/types"
 	"github.com/samber/lo"
 )
@@ -19,7 +23,7 @@ func NewDiffHelper(c *HelperCommon) *DiffHelper {
 }
 
 func (self *DiffHelper) DiffArgs() []string {
-	output := []string{self.c.Modes().Diffing.Ref}
+	output := []string{"--stat", "-p", self.c.Modes().Diffing.Ref}
 
 	right := self.currentDiffTerminal()
 	if right != "" {
@@ -46,14 +50,46 @@ func (self *DiffHelper) DiffArgs() []string {
 	return output
 }
 
+// Returns an update task that can be passed to RenderToMainViews to render a
+// diff for the selected commit(s). We need to pass both the selected commit
+// and the refRange for a range selection. If the refRange is nil (meaning that
+// either there's no range, or it can't be diffed for some reason), then we want
+// to fall back to rendering the diff for the single commit.
+func (self *DiffHelper) GetUpdateTaskForRenderingCommitsDiff(commit *models.Commit, refRange *types.RefRange) types.UpdateTask {
+	if refRange != nil {
+		from, to := refRange.From, refRange.To
+		args := []string{from.ParentRefName(), to.RefName(), "--stat", "-p"}
+		if self.c.GetAppState().IgnoreWhitespaceInDiffView {
+			args = append(args, "--ignore-all-space")
+		}
+		args = append(args, "--")
+		if path := self.c.Modes().Filtering.GetPath(); path != "" {
+			args = append(args, path)
+		}
+		cmdObj := self.c.Git().Diff.DiffCmdObj(args)
+		task := types.NewRunPtyTask(cmdObj.GetCmd())
+		task.Prefix = style.FgYellow.Sprintf("%s %s-%s\n\n", self.c.Tr.ShowingDiffForRange, from.ShortRefName(), to.ShortRefName())
+		return task
+	}
+
+	cmdObj := self.c.Git().Commit.ShowCmdObj(commit.Hash, self.c.Modes().Filtering.GetPath())
+	return types.NewRunPtyTask(cmdObj.GetCmd())
+}
+
 func (self *DiffHelper) ExitDiffMode() error {
 	self.c.Modes().Diffing = diffing.New()
 	return self.c.Refresh(types.RefreshOptions{Mode: types.ASYNC})
 }
 
 func (self *DiffHelper) RenderDiff() error {
-	cmdObj := self.c.Git().Diff.DiffCmdObj(self.DiffArgs())
+	args := self.DiffArgs()
+	cmdObj := self.c.Git().Diff.DiffCmdObj(args)
 	task := types.NewRunPtyTask(cmdObj.GetCmd())
+	task.Prefix = style.FgMagenta.Sprintf(
+		"%s %s\n\n",
+		self.c.Tr.ShowingGitDiff,
+		"git diff "+strings.Join(args, " "),
+	)
 
 	return self.c.RenderToMainViews(types.RefreshMainOpts{
 		Pair: self.c.MainViewPairs().Normal,

pkg/gui/controllers/helpers/patch_building_helper.go

@@ -73,9 +73,8 @@ func (self *PatchBuildingHelper) RefreshPatchBuildingPanel(opts types.OnFocusOpt
 		return nil
 	}
 
-	ref := self.c.Contexts().CommitFiles.CommitFileTreeViewModel.GetRef()
-	to := ref.RefName()
-	from, reverse := self.c.Modes().Diffing.GetFromAndReverseArgsForDiff(ref.ParentRefName())
+	from, to := self.c.Contexts().CommitFiles.GetFromAndToForDiff()
+	from, reverse := self.c.Modes().Diffing.GetFromAndReverseArgsForDiff(from)
 	diff, err := self.c.Git().WorkingTree.ShowFileDiff(from, to, reverse, path, true)
 	if err != nil {
 		return err

pkg/gui/controllers/helpers/refresh_helper.go

@@ -285,8 +285,8 @@ func (self *RefreshHelper) refreshCommitsAndCommitFiles() {
 		// For now the awkwardness remains.
 		commit := self.c.Contexts().LocalCommits.GetSelected()
 		if commit != nil && commit.RefName() != "" {
-			self.c.Contexts().CommitFiles.SetRef(commit)
-			self.c.Contexts().CommitFiles.SetTitleRef(commit.RefName())
+			refRange := self.c.Contexts().LocalCommits.GetSelectedRefRangeForDiffFiles()
+			self.c.Contexts().CommitFiles.ReInit(commit, refRange)
 			_ = self.refreshCommitFilesContext()
 		}
 	}
@@ -387,9 +387,8 @@ func (self *RefreshHelper) RefreshAuthors(commits []*models.Commit) {
 }
 
 func (self *RefreshHelper) refreshCommitFilesContext() error {
-	ref := self.c.Contexts().CommitFiles.GetRef()
-	to := ref.RefName()
-	from, reverse := self.c.Modes().Diffing.GetFromAndReverseArgsForDiff(ref.ParentRefName())
+	from, to := self.c.Contexts().CommitFiles.GetFromAndToForDiff()
+	from, reverse := self.c.Modes().Diffing.GetFromAndReverseArgsForDiff(from)
 
 	files, err := self.c.Git().Loaders.CommitFileLoader.GetFilesInDiff(from, to, reverse)
 	if err != nil {

pkg/gui/controllers/local_commits_controller.go

@@ -290,8 +290,8 @@ func (self *LocalCommitsController) GetOnRenderToMain() func() error {
 				task = types.NewRenderStringTask(
 					self.c.Tr.ExecCommandHere + "\n\n" + commit.Name)
 			} else {
-				cmdObj := self.c.Git().Commit.ShowCmdObj(commit.Hash, self.c.Modes().Filtering.GetPath())
-				task = types.NewRunPtyTask(cmdObj.GetCmd())
+				refRange := self.context().GetSelectedRefRangeForDiffFiles()
+				task = self.c.Helpers().Diff.GetUpdateTaskForRenderingCommitsDiff(commit, refRange)
 			}
 
 			return self.c.RenderToMainViews(types.RefreshMainOpts{

pkg/gui/controllers/sub_commits_controller.go

@@ -46,9 +46,8 @@ func (self *SubCommitsController) GetOnRenderToMain() func() error {
 			if commit == nil {
 				task = types.NewRenderStringTask("No commits")
 			} else {
-				cmdObj := self.c.Git().Commit.ShowCmdObj(commit.Hash, self.c.Modes().Filtering.GetPath())
-
-				task = types.NewRunPtyTask(cmdObj.GetCmd())
+				refRange := self.context().GetSelectedRefRangeForDiffFiles()
+				task = self.c.Helpers().Diff.GetUpdateTaskForRenderingCommitsDiff(commit, refRange)
 			}
 
 			return self.c.RenderToMainViews(types.RefreshMainOpts{