Extract a single helper for the paths a node's diff is limited to

The files and commit files panels each had their own copy of this, one of
which used to be missing the previous path of a rename. Growing them
apart again is the last thing we want, since the next commit needs to
teach both of them about renames that cross a directory boundary.

The files panel version only returned paths for the filtered case, and
left it to WorktreeFileDiffCmdObj to derive the rest from the node; now
that all callers pass the paths in, that command doesn't need to know
about renames at all.

pkg/commands/git_commands/working_tree.go

@@ -385,27 +385,22 @@ func (self *WorkingTreeCommands) Exclude(filename string) error {
 // WorktreeFileDiff returns the diff of a file
 func (self *WorkingTreeCommands) WorktreeFileDiff(file *models.File, plain bool, cached bool) string {
 	// for now we assume an error means the file was deleted
-	s, _ := self.WorktreeFileDiffCmdObj(file, plain, cached, nil).RunWithOutput()
+	s, _ := self.WorktreeFileDiffCmdObj(file, plain, cached, file.Names()).RunWithOutput()
 	return s
 }
 
-// WorktreeFileDiffCmdObj returns a command object for diffing a file or directory
-// in the working tree. When pathOverrides is non-empty, those paths are used instead of
-// the node's path (used to diff only filtered/visible files within a directory).
-func (self *WorkingTreeCommands) WorktreeFileDiffCmdObj(node models.IFile, plain bool, cached bool, pathOverrides []string) *oscommands.CmdObj {
+// WorktreeFileDiffCmdObj returns a command object for diffing the given paths
+// in the working tree. node is the item they belong to; all it decides is
+// whether git has to compare against /dev/null, which is the case for a file
+// that isn't in the index yet.
+func (self *WorkingTreeCommands) WorktreeFileDiffCmdObj(node models.IFile, plain bool, cached bool, paths []string) *oscommands.CmdObj {
 	colorArg := self.diffRendererConfigManager.GetColorArg()
 	if plain {
 		colorArg = "never"
 	}
 
-	prevPath := node.GetPreviousPath()
 	noIndex := !node.GetIsTracked() && !node.GetHasStagedChanges() && !cached && node.GetIsFile()
 
-	paths := pathOverrides
-	if len(paths) == 0 {
-		paths = []string{node.GetPath()}
-	}
-
 	cmdArgs := NewGitCmd("diff").
 		AddCommonDiffArgs(self.diffRendererConfigManager, self.UserConfig(), !plain).
 		Arg("--submodule").
@@ -415,7 +410,6 @@ func (self *WorkingTreeCommands) WorktreeFileDiffCmdObj(node models.IFile, plain
 		Arg("--").
 		ArgIf(noIndex, "/dev/null").
 		Arg(paths...).
-		ArgIf(prevPath != "", prevPath).
 		Dir(self.repoPaths.worktreePath).
 		ToArgv()
 

pkg/gui/controllers/commits_files_controller.go

@@ -175,7 +175,7 @@ func (self *CommitFilesController) GetOnRenderToMain() func() {
 		from, to := self.context().GetFromAndToForDiff()
 		from, reverse := self.c.Modes().Diffing.GetFromAndReverseArgsForDiff(from)
 
-		paths := self.pathsForDiff(node)
+		paths := pathsForDiff(node.Raw(), self.context().IsFiltering())
 		cmdObj := self.c.Git().WorkingTree.ShowFileDiffCmdObj(from, to, reverse, paths, false)
 		task := types.NewRunPtyTask(cmdObj.GetCmd())
 
@@ -263,7 +263,8 @@ func (self *CommitFilesController) openCopyMenu() error {
 	copyFileDiffItem := &types.MenuItem{
 		Label: self.c.Tr.CopySelectedDiff,
 		OnPress: func() error {
-			return self.copyDiffToClipboard(self.pathsForDiff(node), self.c.Tr.FileDiffCopiedToast)
+			paths := pathsForDiff(node.Raw(), self.context().IsFiltering())
+			return self.copyDiffToClipboard(paths, self.c.Tr.FileDiffCopiedToast)
 		},
 		DisabledReason: self.require(self.singleItemSelected())(),
 		Keys:           menuKey('s'),
@@ -616,26 +617,6 @@ func (self *CommitFilesController) GetOnClickFocusedMainView() func(mainViewName
 	}
 }
 
-// pathsForDiff returns the file paths to use for a diff command. When a text
-// filter is active and the node is a directory, only the visible (filtered)
-// file paths are returned so the diff reflects what the user sees.
-func (self *CommitFilesController) pathsForDiff(node *filetree.CommitFileNode) []string {
-	if !node.IsFile() && self.context().IsFiltering() {
-		var paths []string
-		_ = node.ForEachFile(func(file *models.CommitFile) error {
-			// For a rename we need to pass both paths so that git detects it as
-			// a rename rather than an unrelated delete and add.
-			paths = append(paths, file.Names()...)
-			return nil
-		})
-		return paths
-	}
-	if file := node.GetFile(); file != nil {
-		return file.Names()
-	}
-	return []string{node.GetPath()}
-}
-
 // NOTE: these functions are identical to those in files_controller.go (except for types) and
 // could also be cleaned up with some generics
 func normalisedSelectedCommitFileNodes(selectedNodes []*filetree.CommitFileNode) []*filetree.CommitFileNode {

pkg/gui/controllers/diff_paths.go

@@ -0,0 +1,35 @@
+package controllers
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/gui/filetree"
+)
+
+// Both models.File and models.CommitFile satisfy this. Names returns the file's
+// path, plus the path it was renamed from if it is a rename.
+type fileWithNames[T any] interface {
+	*T
+	Names() []string
+}
+
+// pathsForDiff returns the paths to limit a diff command to for showing the
+// changes of the given node. For a directory this is the directory itself,
+// unless a filter is active, in which case we list the files that are visible
+// under it.
+func pathsForDiff[T any, PT fileWithNames[T]](node *filetree.Node[T], isFiltering bool) []string {
+	if file := node.GetFile(); file != nil {
+		return PT(file).Names()
+	}
+
+	if isFiltering {
+		var paths []string
+		_ = node.ForEachFile(func(file *T) error {
+			// For a rename we need to pass both paths so that git detects it as
+			// a rename rather than an unrelated delete and add.
+			paths = append(paths, PT(file).Names()...)
+			return nil
+		})
+		return paths
+	}
+
+	return []string{node.GetPath()}
+}

pkg/gui/controllers/files_controller.go

@@ -369,8 +369,8 @@ func (self *FilesController) renderWorkingTreeDiff(node *filetree.FileNode) {
 	split := self.c.UserConfig().Gui.SplitDiff == "always" || (node.GetHasUnstagedChanges() && node.GetHasStagedChanges())
 	mainShowsStaged := !split && node.GetHasStagedChanges()
 
-	pathOverrides := self.pathOverridesForDiff(node)
-	cmdObj := self.c.Git().WorkingTree.WorktreeFileDiffCmdObj(node, false, mainShowsStaged, pathOverrides)
+	paths := pathsForDiff(node.Raw(), self.context().IsFiltering())
+	cmdObj := self.c.Git().WorkingTree.WorktreeFileDiffCmdObj(node, false, mainShowsStaged, paths)
 	title := self.c.Tr.UnstagedChanges
 	if mainShowsStaged {
 		title = self.c.Tr.StagedChanges
@@ -385,7 +385,7 @@ func (self *FilesController) renderWorkingTreeDiff(node *filetree.FileNode) {
 	}
 
 	if split {
-		cmdObj := self.c.Git().WorkingTree.WorktreeFileDiffCmdObj(node, false, true, pathOverrides)
+		cmdObj := self.c.Git().WorkingTree.WorktreeFileDiffCmdObj(node, false, true, paths)
 
 		title := self.c.Tr.StagedChanges
 		if mainShowsStaged {
@@ -643,23 +643,6 @@ func (self *FilesController) press(nodes []*filetree.FileNode) error {
 	return nil
 }
 
-// pathOverridesForDiff returns file paths to override the node's path in diff
-// commands when a text filter is active and the node is a directory. This
-// ensures the diff only shows filtered/visible files.
-func (self *FilesController) pathOverridesForDiff(node *filetree.FileNode) []string {
-	if !node.IsFile() && self.context().IsFiltering() {
-		var paths []string
-		_ = node.ForEachFile(func(file *models.File) error {
-			// For a rename we need to pass both paths so that git detects it as
-			// a rename rather than an unrelated delete and add.
-			paths = append(paths, file.Names()...)
-			return nil
-		})
-		return paths
-	}
-	return nil
-}
-
 // unstageFilteredFiles unstages only the visible (filtered) files from the
 // given nodes, correctly partitioning by tracked/untracked.
 func (self *FilesController) unstageFilteredFiles(nodes []*filetree.FileNode) error {

pkg/gui/controllers/submodules_controller.go

@@ -123,7 +123,7 @@ func (self *SubmodulesController) GetOnRenderToMain() func() {
 				if file == nil {
 					task = types.NewRenderStringTask(prefix)
 				} else {
-					cmdObj := self.c.Git().WorkingTree.WorktreeFileDiffCmdObj(file, false, !file.HasUnstagedChanges && file.HasStagedChanges, nil)
+					cmdObj := self.c.Git().WorkingTree.WorktreeFileDiffCmdObj(file, false, !file.HasUnstagedChanges && file.HasStagedChanges, file.Names())
 					task = types.NewRunCommandTaskWithPrefix(cmdObj.GetCmd(), prefix)
 				}
 			}