Show an error if the file of the selected diff lines can't be found

If the path in the diff header of a selected line doesn't name a file
of the files panel, staging or discarding the line does nothing. The
command log shows "Apply patch", but nothing else happens, so the user
has nothing to go on when reporting it. Adding a line of a commit's
diff to a custom patch fails in the same silent way if the path
doesn't name a file of that diff. A diff renderer that names files
differently can cause this, and so can a bug in how we read the path,
like the one we had with diff.mnemonicPrefix.

Show an error that names the path instead, and do nothing else. If a
selection spans several files, don't act on the files we did find,
because that would do only part of what the user asked for. Do the
same for opening a line of a diff in its pull request.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

pkg/gui/controllers/commit_diff_actions.go

@@ -108,9 +108,6 @@ func (self *CommitDiffActions) PrimaryAction(pane types.DiffPaneContext, firstBu
 	if err != nil {
 		return err
 	}
-	if len(selection.paths) == 0 {
-		return nil
-	}
 
 	patchBuilder := self.c.Git().Patch.PatchBuilder
 	from, reverse := self.patchEndpoints(target)
@@ -182,7 +179,7 @@ func (self *CommitDiffActions) removePatchLines(
 	for path, ordinals := range self.c.Helpers().DiffLine.ChangeLineOrdinals(self.customPatchDiff(), lines) {
 		filename := self.patchBuilderPath(path)
 		if filename == "" {
-			continue
+			return diffLinesFileNotFoundError(self.c, path)
 		}
 		included := patchBuilder.IncludedChangeLineIndices(filename)
 		indices := []int{}
@@ -243,9 +240,6 @@ func (self *CommitDiffActions) DiscardSelection(pane types.DiffPaneContext, firs
 	if err != nil {
 		return err
 	}
-	if len(selection.paths) == 0 {
-		return nil
-	}
 
 	patchBuilder := self.c.Git().Patch.PatchBuilder
 	prompt := lo.Ternary(patchBuilder.IsEmpty(),
@@ -353,7 +347,8 @@ type commitDiffSelection struct {
 }
 
 // selectionByFile groups the given lines of the commit's diff by the file they belong
-// to. A line whose path is no file of this repo is left out.
+// to. If a line belongs to no file of the diff, the diff on screen and the one the
+// patch is built from disagree, so this fails and we build nothing.
 func (self *CommitDiffActions) selectionByFile(lines []types.DiffLineInfo) (commitDiffSelection, error) {
 	files, err := self.filesInDiff()
 	if err != nil {
@@ -362,8 +357,8 @@ func (self *CommitDiffActions) selectionByFile(lines []types.DiffLineInfo) (comm
 	selection := commitDiffSelection{files: files, linesByPath: map[string][]patch.LineIdentity{}}
 	for _, line := range lines {
 		path := self.patchBuilderPath(line.Path)
-		if path == "" {
-			continue
+		if _, ok := files[path]; !ok {
+			return commitDiffSelection{}, diffLinesFileNotFoundError(self.c, line.Path)
 		}
 		if _, seen := selection.linesByPath[path]; !seen {
 			selection.paths = append(selection.paths, path)

pkg/gui/controllers/diff_paths.go

@@ -1,11 +1,13 @@
 package controllers
 
 import (
+	"errors"
 	"path"
 	"path/filepath"
 	"strings"
 
 	"github.com/jesseduffield/lazygit/pkg/gui/filetree"
+	"github.com/jesseduffield/lazygit/pkg/utils"
 	"github.com/samber/lo"
 )
 
@@ -132,6 +134,18 @@ func isInDir(path string, dir string) bool {
 	return dir == "." || strings.HasPrefix(path, dir+"/")
 }
 
+// diffLinesFileNotFoundError reports that the file selected diff lines belong to can't
+// be found. It names the file by its path in the repo, or by the path the diff line
+// carries for one outside of it.
+func diffLinesFileNotFoundError(c *ControllerCommon, absolutePath string) error {
+	path := repoRelativePath(c.Git().RepoPaths.WorktreePath(), absolutePath)
+	if path == "" {
+		path = absolutePath
+	}
+	return errors.New(utils.ResolvePlaceholderString(c.Tr.DiffLinesFileNotFound,
+		map[string]string{"path": path}))
+}
+
 // repoRelativePath turns the absolute path a diff line carries into the one git speaks
 // of the file: relative to the worktree, with forward slashes. It is "" for a path that
 // is no file of this repo, which a diff renderer's own naming of a line can produce.

pkg/gui/controllers/main_view_controller.go

@@ -1105,7 +1105,7 @@ func (self *MainViewController) openPullRequestAtSelectedLine() error {
 	}
 	relativePath := repoRelativePath(self.c.Git().RepoPaths.WorktreePath(), info.Path)
 	if relativePath == "" {
-		return nil
+		return diffLinesFileNotFoundError(self.c, info.Path)
 	}
 
 	self.c.LogAction(self.c.Tr.Actions.OpenPullRequest)

pkg/gui/controllers/working_tree_diff_actions.go

@@ -59,7 +59,10 @@ func (self *WorkingTreeDiffActions) PrimaryAction(pane types.DiffPaneContext, fi
 			self.c.UserConfig().Keybinding.Universal.IncreaseContextInDiffView)
 	}
 
-	linesByFile, onStagedSide := self.diffLineSelection(pane, firstBufferLine, lastBufferLine)
+	linesByFile, onStagedSide, err := self.diffLineSelection(pane, firstBufferLine, lastBufferLine)
+	if err != nil {
+		return err
+	}
 	if len(linesByFile) == 0 {
 		return nil
 	}
@@ -79,7 +82,10 @@ func (self *WorkingTreeDiffActions) DiscardSelection(pane types.DiffPaneContext,
 			self.c.UserConfig().Keybinding.Universal.IncreaseContextInDiffView)
 	}
 
-	linesByFile, onStagedSide := self.diffLineSelection(pane, firstBufferLine, lastBufferLine)
+	linesByFile, onStagedSide, err := self.diffLineSelection(pane, firstBufferLine, lastBufferLine)
+	if err != nil {
+		return err
+	}
 	if len(linesByFile) == 0 {
 		return nil
 	}
@@ -117,7 +123,10 @@ func (self *WorkingTreeDiffActions) DiscardSelectionDisabledReason(types.DiffPan
 func (self *WorkingTreeDiffActions) EditHunk(
 	pane types.DiffPaneContext, firstBufferLine int, lastBufferLine int,
 ) error {
-	linesByFile, onStagedSide := self.diffLineSelection(pane, firstBufferLine, lastBufferLine)
+	linesByFile, onStagedSide, err := self.diffLineSelection(pane, firstBufferLine, lastBufferLine)
+	if err != nil {
+		return err
+	}
 	if len(linesByFile) == 0 {
 		return nil
 	}
@@ -203,21 +212,23 @@ type fileDiffLines struct {
 // there is nothing to act on.
 //
 // A directory's diff spans several files, and a patch is of one file, so the lines are
-// grouped by the file they belong to, in the order the diff shows the files.
+// grouped by the file they belong to, in the order the diff shows the files. If a line
+// belongs to no file of the files panel, the diff and the panel disagree. Acting on the
+// other lines would do only part of what the user asked for, so this fails instead.
 func (self *WorkingTreeDiffActions) diffLineSelection(
 	pane types.DiffPaneContext, firstBufferLine int, lastBufferLine int,
-) (linesByFile []fileDiffLines, onStagedSide bool) {
+) (linesByFile []fileDiffLines, onStagedSide bool, err error) {
 	infos := self.c.Helpers().DiffLine.ChangeLinesInBufferRange(pane.GetView(), firstBufferLine, lastBufferLine)
 	infosByPath := lo.GroupBy(infos, func(info types.DiffLineInfo) string { return info.Path })
 	paths := lo.Uniq(lo.Map(infos, func(info types.DiffLineInfo, _ int) string { return info.Path }))
 	for _, path := range paths {
 		file := self.fileForDiffLinePath(path)
 		if file == nil {
-			continue
+			return nil, false, diffLinesFileNotFoundError(self.c, path)
 		}
 		linesByFile = append(linesByFile, fileDiffLines{file: file, lines: infosByPath[path]})
 	}
-	return linesByFile, self.showsStagedSide(pane)
+	return linesByFile, self.showsStagedSide(pane), nil
 }
 
 // applyDiffLineSelection applies the selected change lines, a patch per file, and

pkg/i18n/english.go

@@ -748,6 +748,7 @@ type TranslationSet struct {
 	CopySelectedDiffLinesToClipboard      string
 	SelectedDiffLinesCopiedToast          string
 	SelectionNotFoundInDiffToast          string
+	DiffLinesFileNotFound                 string
 	NoFilesStagedTitle                    string
 	NoFilesStagedPrompt                   string
 	BranchNotFoundTitle                   string
@@ -1938,6 +1939,7 @@ func EnglishTranslationSet() *TranslationSet {
 		CopySelectedDiffLinesToClipboard:         "Copy selected diff lines to clipboard",
 		SelectedDiffLinesCopiedToast:             "Selected diff lines copied to clipboard",
 		SelectionNotFoundInDiffToast:             "Nothing in the selection could be found in the diff",
+		DiffLinesFileNotFound:                    "Can't find the file '{{.path}}' that the selected lines belong to",
 		CommitPrefixPatternError:                 "Error in commitPrefix pattern",
 		NoFilesStagedTitle:                       "No files staged",
 		NoFilesStagedPrompt:                      "You have not staged any files. Commit all files?",

pkg/integration/tests/main_view/report_lines_of_a_file_missing_from_the_commits_diff.go

@@ -0,0 +1,51 @@
+package main_view
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var ReportLinesOfAFileMissingFromTheCommitsDiff = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Adding lines to a custom patch that the diff puts in a file the commit doesn't change shows an error",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	SetupConfig: func(cfg *config.AppConfig) {
+		cfg.GetUserConfig().Gui.UseHunkModeInDiffView = false
+		// A renderer that announces the metadata protocol and passes the diff through,
+		// except that its +++ line names a file in another directory.
+		cfg.GetUserConfig().Git.DiffRenderers = []config.DiffRendererConfig{
+			{Command: `printf '\033]1717;1\007'; sed 's#+++ b/#+++ b/elsewhere/#'`},
+		}
+	},
+	SetupRepo: func(shell *Shell) {
+		shell.CreateFileAndAdd("file1", "one\ntwo\nthree\n")
+		shell.Commit("one")
+
+		shell.UpdateFileAndAdd("file1", "one\nADD1\ntwo\nthree\n")
+		shell.Commit("two")
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Commits().
+			Focus().
+			Lines(
+				Contains("two").IsSelected(),
+				Contains("one"),
+			).
+			Press(keys.Universal.FocusMainView)
+
+		t.Views().Main().
+			IsFocused().
+			SelectedLines(
+				Contains("+ADD1"),
+			).
+			PressPrimaryAction()
+
+		t.ExpectPopup().Alert().
+			Title(Equals("Error")).
+			Content(Equals("Can't find the file 'elsewhere/file1' that the selected lines belong to")).
+			Confirm()
+
+		// No patch is left behind.
+		t.Views().Information().Content(DoesNotContain("Building patch"))
+	},
+})

pkg/integration/tests/main_view/report_lines_of_a_file_missing_from_the_files_panel.go

@@ -0,0 +1,50 @@
+package main_view
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var ReportLinesOfAFileMissingFromTheFilesPanel = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Staging lines that the diff puts in a file the files panel doesn't have shows an error",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	SetupConfig: func(cfg *config.AppConfig) {
+		cfg.GetUserConfig().Gui.UseHunkModeInDiffView = false
+		// A renderer that announces the metadata protocol and passes the diff through,
+		// except that its +++ line names a file in another directory.
+		cfg.GetUserConfig().Git.DiffRenderers = []config.DiffRendererConfig{
+			{Command: `printf '\033]1717;1\007'; sed 's#+++ b/#+++ b/elsewhere/#'`},
+		}
+	},
+	SetupRepo: func(shell *Shell) {
+		shell.CreateFileAndAdd("file1", "one\ntwo\nthree\n")
+		shell.Commit("one")
+
+		shell.UpdateFile("file1", "one\nADD1\ntwo\nthree\n")
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Files().
+			IsFocused().
+			Lines(
+				Contains(" M file1").IsSelected(),
+			).
+			Press(keys.Universal.FocusMainView)
+
+		t.Views().Main().
+			IsFocused().
+			SelectedLines(
+				Contains("+ADD1"),
+			).
+			PressPrimaryAction()
+
+		t.ExpectPopup().Alert().
+			Title(Equals("Error")).
+			Content(Equals("Can't find the file 'elsewhere/file1' that the selected lines belong to")).
+			Confirm()
+
+		t.Views().Files().Lines(
+			Contains(" M file1"),
+		)
+	},
+})

pkg/integration/tests/test_list.go

@@ -463,6 +463,8 @@ var tests = []*components.IntegrationTest{
 	main_view.RemovePartOfAddedFileFromCommit,
 	main_view.RemovePatchFromCommit,
 	main_view.RenderTheDiffBesideThePatchMarks,
+	main_view.ReportLinesOfAFileMissingFromTheCommitsDiff,
+	main_view.ReportLinesOfAFileMissingFromTheFilesPanel,
 	main_view.ResetAPatchBuiltFromACommitsDiff,
 	main_view.ResetPatchWithEscape,
 	main_view.ResetThePatchFromThePaneShowingIt,