Fix custom patch operations for added files (#3684)

- **PR Description**

Several custom patch commands on parts of an added file would fail with the
confusing error message "error: new file XXX depends on old contents".
These were dropping the custom patch from the original commit, moving the
patch to a new commit, moving it to a later commit, or moving it to the index.

We fix this by converting the patch header from an added file to a diff against
an empty file. We do this not just for the purpose of applying the patch, but
also for rendering it and copying it to the clip board. I'm not sure it matters
much in these cases, but it does feel more correct for a filtered patch to be
presented this way.

Fixes #3679.

- **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)
* [ ] Text is internationalised (see
[here](https://github.com/jesseduffield/lazygit/blob/master/CONTRIBUTING.md#internationalisation))
* [ ] Docs have been updated if necessary
* [x] You've read through your own file changes for silly mistakes etc

Author: stefanhaller

pkg/commands/git_commands/patch.go

@@ -47,8 +47,8 @@ type ApplyPatchOpts struct {
 	Reverse  bool
 }
 
-func (self *PatchCommands) ApplyCustomPatch(reverse bool) error {
-	patch := self.PatchBuilder.PatchToApply(reverse)
+func (self *PatchCommands) ApplyCustomPatch(reverse bool, turnAddedFilesIntoDiffAgainstEmptyFile bool) error {
+	patch := self.PatchBuilder.PatchToApply(reverse, turnAddedFilesIntoDiffAgainstEmptyFile)
 
 	return self.ApplyPatch(patch, ApplyPatchOpts{
 		Index:    true,
@@ -94,7 +94,7 @@ func (self *PatchCommands) DeletePatchesFromCommit(commits []*models.Commit, com
 	}
 
 	// apply each patch in reverse
-	if err := self.ApplyCustomPatch(true); err != nil {
+	if err := self.ApplyCustomPatch(true, true); err != nil {
 		_ = self.rebase.AbortRebase()
 		return err
 	}
@@ -123,7 +123,7 @@ func (self *PatchCommands) MovePatchToSelectedCommit(commits []*models.Commit, s
 		}
 
 		// apply each patch forward
-		if err := self.ApplyCustomPatch(false); err != nil {
+		if err := self.ApplyCustomPatch(false, false); err != nil {
 			// Don't abort the rebase here; this might cause conflicts, so give
 			// the user a chance to resolve them
 			return err
@@ -172,7 +172,7 @@ func (self *PatchCommands) MovePatchToSelectedCommit(commits []*models.Commit, s
 	}
 
 	// apply each patch in reverse
-	if err := self.ApplyCustomPatch(true); err != nil {
+	if err := self.ApplyCustomPatch(true, true); err != nil {
 		_ = self.rebase.AbortRebase()
 		return err
 	}
@@ -228,7 +228,7 @@ func (self *PatchCommands) MovePatchIntoIndex(commits []*models.Commit, commitId
 		return err
 	}
 
-	if err := self.ApplyCustomPatch(true); err != nil {
+	if err := self.ApplyCustomPatch(true, true); err != nil {
 		if self.status.WorkingTreeState() == enums.REBASE_MODE_REBASING {
 			_ = self.rebase.AbortRebase()
 		}
@@ -282,7 +282,7 @@ func (self *PatchCommands) PullPatchIntoNewCommit(
 		return err
 	}
 
-	if err := self.ApplyCustomPatch(true); err != nil {
+	if err := self.ApplyCustomPatch(true, true); err != nil {
 		_ = self.rebase.AbortRebase()
 		return err
 	}

pkg/commands/patch/patch_builder.go

@@ -65,15 +65,20 @@ func (p *PatchBuilder) Start(from, to string, reverse bool, canRebase bool) {
 	p.fileInfoMap = map[string]*fileInfo{}
 }
 
-func (p *PatchBuilder) PatchToApply(reverse bool) string {
+func (p *PatchBuilder) PatchToApply(reverse bool, turnAddedFilesIntoDiffAgainstEmptyFile bool) string {
 	patch := ""
 
 	for filename, info := range p.fileInfoMap {
 		if info.mode == UNSELECTED {
 			continue
 		}
 
-		patch += p.RenderPatchForFile(filename, true, reverse)
+		patch += p.RenderPatchForFile(RenderPatchForFileOpts{
+			Filename:                               filename,
+			Plain:                                  true,
+			Reverse:                                reverse,
+			TurnAddedFilesIntoDiffAgainstEmptyFile: turnAddedFilesIntoDiffAgainstEmptyFile,
+		})
 	}
 
 	return patch
@@ -172,8 +177,15 @@ func (p *PatchBuilder) RemoveFileLineRange(filename string, firstLineIdx, lastLi
 	return nil
 }
 
-func (p *PatchBuilder) RenderPatchForFile(filename string, plain bool, reverse bool) string {
-	info, err := p.getFileInfo(filename)
+type RenderPatchForFileOpts struct {
+	Filename                               string
+	Plain                                  bool
+	Reverse                                bool
+	TurnAddedFilesIntoDiffAgainstEmptyFile bool
+}
+
+func (p *PatchBuilder) RenderPatchForFile(opts RenderPatchForFileOpts) string {
+	info, err := p.getFileInfo(opts.Filename)
 	if err != nil {
 		p.Log.Error(err)
 		return ""
@@ -183,7 +195,7 @@ func (p *PatchBuilder) RenderPatchForFile(filename string, plain bool, reverse b
 		return ""
 	}
 
-	if info.mode == WHOLE && plain {
+	if info.mode == WHOLE && opts.Plain {
 		// Use the whole diff (spares us parsing it and then formatting it).
 		// TODO: see if this is actually noticeably faster.
 		// The reverse flag is only for part patches so we're ignoring it here.
@@ -192,11 +204,12 @@ func (p *PatchBuilder) RenderPatchForFile(filename string, plain bool, reverse b
 
 	patch := Parse(info.diff).
 		Transform(TransformOpts{
-			Reverse:             reverse,
-			IncludedLineIndices: info.includedLineIndices,
+			Reverse:                                opts.Reverse,
+			TurnAddedFilesIntoDiffAgainstEmptyFile: opts.TurnAddedFilesIntoDiffAgainstEmptyFile,
+			IncludedLineIndices:                    info.includedLineIndices,
 		})
 
-	if plain {
+	if opts.Plain {
 		return patch.FormatPlain()
 	} else {
 		return patch.FormatView(FormatViewOpts{})
@@ -209,7 +222,12 @@ func (p *PatchBuilder) renderEachFilePatch(plain bool) []string {
 
 	sort.Strings(filenames)
 	patches := lo.Map(filenames, func(filename string, _ int) string {
-		return p.RenderPatchForFile(filename, plain, false)
+		return p.RenderPatchForFile(RenderPatchForFileOpts{
+			Filename:                               filename,
+			Plain:                                  plain,
+			Reverse:                                false,
+			TurnAddedFilesIntoDiffAgainstEmptyFile: true,
+		})
 	})
 	output := lo.Filter(patches, func(patch string, _ int) bool {
 		return patch != ""

pkg/commands/patch/transform.go

@@ -1,6 +1,10 @@
 package patch
 
-import "github.com/samber/lo"
+import (
+	"strings"
+
+	"github.com/samber/lo"
+)
 
 type patchTransformer struct {
 	patch *Patch
@@ -22,6 +26,13 @@ type TransformOpts struct {
 	// information it needs to cleanly apply patches
 	FileNameOverride string
 
+	// Custom patches tend to work better when treating new files as diffs
+	// against an empty file. The only case where we need this to be false is
+	// when moving a custom patch to an earlier commit; in that case the patch
+	// command would fail with the error "file does not exist in index" if we
+	// treat it as a diff against an empty file.
+	TurnAddedFilesIntoDiffAgainstEmptyFile bool
+
 	// The indices of lines that should be included in the patch.
 	IncludedLineIndices []int
 }
@@ -61,6 +72,18 @@ func (self *patchTransformer) transformHeader() []string {
 			"--- a/" + self.opts.FileNameOverride,
 			"+++ b/" + self.opts.FileNameOverride,
 		}
+	} else if self.opts.TurnAddedFilesIntoDiffAgainstEmptyFile {
+		result := make([]string, 0, len(self.patch.header))
+		for idx, line := range self.patch.header {
+			if strings.HasPrefix(line, "new file mode") {
+				continue
+			}
+			if line == "--- /dev/null" && strings.HasPrefix(self.patch.header[idx+1], "+++ b/") {
+				line = "--- a/" + self.patch.header[idx+1][6:]
+			}
+			result = append(result, line)
+		}
+		return result
 	} else {
 		return self.patch.header
 	}

pkg/gui/controllers/custom_patch_options_menu_action.go

@@ -237,7 +237,7 @@ func (self *CustomPatchOptionsMenuAction) handleApplyPatch(reverse bool) error {
 		action = "Apply patch in reverse"
 	}
 	self.c.LogAction(action)
-	if err := self.c.Git().Patch.ApplyCustomPatch(reverse); err != nil {
+	if err := self.c.Git().Patch.ApplyCustomPatch(reverse, true); err != nil {
 		return err
 	}
 	return self.c.Refresh(types.RefreshOptions{Mode: types.ASYNC})

pkg/gui/controllers/helpers/patch_building_helper.go

@@ -3,6 +3,7 @@ package helpers
 import (
 	"errors"
 
+	"github.com/jesseduffield/lazygit/pkg/commands/patch"
 	"github.com/jesseduffield/lazygit/pkg/commands/types/enums"
 	"github.com/jesseduffield/lazygit/pkg/gui/patch_exploring"
 	"github.com/jesseduffield/lazygit/pkg/gui/types"
@@ -80,7 +81,12 @@ func (self *PatchBuildingHelper) RefreshPatchBuildingPanel(opts types.OnFocusOpt
 		return err
 	}
 
-	secondaryDiff := self.c.Git().Patch.PatchBuilder.RenderPatchForFile(path, false, false)
+	secondaryDiff := self.c.Git().Patch.PatchBuilder.RenderPatchForFile(patch.RenderPatchForFileOpts{
+		Filename:                               path,
+		Plain:                                  false,
+		Reverse:                                false,
+		TurnAddedFilesIntoDiffAgainstEmptyFile: true,
+	})
 
 	context := self.c.Contexts().CustomPatchBuilder
 

pkg/integration/tests/patch_building/move_to_earlier_commit_from_added_file.go

@@ -0,0 +1,115 @@
+package patch_building
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var MoveToEarlierCommitFromAddedFile = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Move a patch from a file that was added in a commit to an earlier commit",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	SetupConfig:  func(config *config.AppConfig) {},
+	SetupRepo: func(shell *Shell) {
+		shell.EmptyCommit("first commit")
+		shell.EmptyCommit("destination commit")
+		shell.CreateFileAndAdd("file1", "1st line\n2nd line\n3rd line\n")
+		shell.Commit("commit to move from")
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Commits().
+			Focus().
+			Lines(
+				Contains("commit to move from").IsSelected(),
+				Contains("destination commit"),
+				Contains("first commit"),
+			).
+			PressEnter()
+
+		t.Views().CommitFiles().
+			IsFocused().
+			Lines(
+				Contains("A file").IsSelected(),
+			).
+			PressEnter()
+
+		t.Views().PatchBuilding().
+			IsFocused().
+			SelectNextItem().
+			PressPrimaryAction()
+
+		t.Views().Information().Content(Contains("Building patch"))
+
+		t.Views().Commits().
+			Focus().
+			SelectNextItem()
+
+		t.Common().SelectPatchOption(Contains("Move patch to selected commit"))
+
+		// This results in a conflict at the commit we're moving from, because
+		// it tries to add a file that already exists
+		t.Common().AcknowledgeConflicts()
+
+		t.Views().Files().
+			IsFocused().
+			Lines(
+				Contains("AA").Contains("file"),
+			).
+			PressEnter()
+
+		t.Views().MergeConflicts().
+			IsFocused().
+			TopLines(
+				Contains("<<<<<<< HEAD"),
+				Contains("2nd line"),
+				Contains("======="),
+				Contains("1st line"),
+				Contains("2nd line"),
+				Contains("3rd line"),
+				Contains(">>>>>>>"),
+			).
+			SelectNextItem().
+			PressPrimaryAction() // choose the version with all three lines
+
+		t.Common().ContinueOnConflictsResolved()
+
+		t.Views().Commits().
+			Focus().
+			Lines(
+				Contains("commit to move from"),
+				Contains("destination commit").IsSelected(),
+				Contains("first commit"),
+			).
+			PressEnter()
+
+		t.Views().CommitFiles().
+			IsFocused().
+			Lines(
+				Contains("A file").IsSelected(),
+			).
+			Tap(func() {
+				t.Views().Main().ContainsLines(
+					Equals("+2nd line"),
+				)
+			}).
+			PressEscape()
+
+		t.Views().Commits().
+			IsFocused().
+			NavigateToLine(Contains("commit to move from")).
+			PressEnter()
+
+		t.Views().CommitFiles().
+			IsFocused().
+			Lines(
+				Contains("M file").IsSelected(),
+			).
+			Tap(func() {
+				t.Views().Main().ContainsLines(
+					Equals("+1st line"),
+					Equals(" 2nd line"),
+					Equals("+3rd line"),
+				)
+			})
+	},
+})