Adjust line number for working copy when editing a line

There are two ways to jump to the editor on a specific line: pressing `e` in the
staging or patch building panels, or clicking on a hyperlink in a delta diff. In
both cases, this works perfectly in the unstaged changes view, but in other
views (either staged changes, or an older commit) it can often jump to the wrong
line; this happens when there are further changes to the file being viewed in
later commits or in unstaged changes.

This commit fixes this so that you end up on the right line in these cases.

pkg/commands/patch/patch.go

@@ -154,3 +154,24 @@ func (self *Patch) LineCount() int {
 func (self *Patch) HunkCount() int {
 	return len(self.hunks)
 }
+
+// Adjust the given line number (one-based) according to the current patch. The
+// patch is supposed to be a diff of an old file state against the working
+// directory; the line number is a line number in that old file, and the
+// function returns the corresponding line number in the working directory file.
+func (self *Patch) AdjustLineNumber(lineNumber int) int {
+	adjustedLineNumber := lineNumber
+	for _, hunk := range self.hunks {
+		if hunk.oldStart >= lineNumber {
+			break
+		}
+
+		if hunk.oldStart+hunk.oldLength() > lineNumber {
+			return hunk.newStart
+		}
+
+		adjustedLineNumber += hunk.newLength() - hunk.oldLength()
+	}
+
+	return adjustedLineNumber
+}

pkg/commands/patch/patch_test.go

@@ -639,3 +639,59 @@ func TestGetNextStageableLineIndex(t *testing.T) {
 		})
 	}
 }
+
+func TestAdjustLineNumber(t *testing.T) {
+	type scenario struct {
+		oldLineNumbers  []int
+		expectedResults []int
+	}
+	scenarios := []scenario{
+		{
+			oldLineNumbers:  []int{1, 2, 3, 4, 5, 6, 7},
+			expectedResults: []int{1, 2, 2, 3, 4, 7, 8},
+		},
+	}
+
+	// The following diff was generated from old.txt:
+	//   1
+	//   2a
+	//   2b
+	//   3
+	//   4
+	//   7
+	//   8
+	// against new.txt:
+	//   1
+	//   2
+	//   3
+	//   4
+	//   5
+	//   6
+	//   7
+	//   8
+
+	// This test setup makes the test easy to understand, because the resulting
+	// adjusted line numbers are the same as the content of the lines in new.txt.
+
+	diff := `--- old.txt	2024-12-16 18:04:29
++++ new.txt	2024-12-16 18:04:27
+@@ -2,2 +2 @@
+-2a
+-2b
++2
+@@ -5,0 +5,2 @@
++5
++6
+`
+
+	patch := Parse(diff)
+
+	for _, s := range scenarios {
+		t.Run("TestAdjustLineNumber", func(t *testing.T) {
+			for idx, oldLineNumber := range s.oldLineNumbers {
+				result := patch.AdjustLineNumber(oldLineNumber)
+				assert.Equal(t, s.expectedResults[idx], result)
+			}
+		})
+	}
+}

pkg/gui/context/branches_context.go

@@ -80,6 +80,14 @@ func (self *BranchesContext) GetDiffTerminals() []string {
 	return nil
 }
 
+func (self *BranchesContext) RefForAdjustingLineNumberInDiff() string {
+	branch := self.GetSelected()
+	if branch != nil {
+		return branch.ID()
+	}
+	return ""
+}
+
 func (self *BranchesContext) ShowBranchHeadsInSubCommits() bool {
 	return true
 }

pkg/gui/context/commit_files_context.go

@@ -77,6 +77,13 @@ func (self *CommitFilesContext) GetDiffTerminals() []string {
 	return []string{self.GetRef().RefName()}
 }
 
+func (self *CommitFilesContext) RefForAdjustingLineNumberInDiff() string {
+	if refs := self.GetRefRange(); refs != nil {
+		return refs.To.RefName()
+	}
+	return self.GetRef().RefName()
+}
+
 func (self *CommitFilesContext) GetFromAndToForDiff() (string, string) {
 	if refs := self.GetRefRange(); refs != nil {
 		return refs.From.ParentRefName(), refs.To.RefName()

pkg/gui/context/local_commits_context.go

@@ -170,6 +170,14 @@ func (self *LocalCommitsContext) GetDiffTerminals() []string {
 	return []string{itemId}
 }
 
+func (self *LocalCommitsContext) RefForAdjustingLineNumberInDiff() string {
+	commits, _, _ := self.GetSelectedItems()
+	if commits == nil {
+		return ""
+	}
+	return commits[0].Hash
+}
+
 func (self *LocalCommitsContext) ModelSearchResults(searchStr string, caseSensitive bool) []gocui.SearchPosition {
 	return searchModelCommits(caseSensitive, self.GetCommits(), self.ColumnPositions(), searchStr)
 }

pkg/gui/context/reflog_commits_context.go

@@ -86,6 +86,10 @@ func (self *ReflogCommitsContext) GetDiffTerminals() []string {
 	return []string{itemId}
 }
 
+func (self *ReflogCommitsContext) RefForAdjustingLineNumberInDiff() string {
+	return self.GetSelectedItemId()
+}
+
 func (self *ReflogCommitsContext) ShowBranchHeadsInSubCommits() bool {
 	return false
 }

pkg/gui/context/remote_branches_context.go

@@ -78,6 +78,10 @@ func (self *RemoteBranchesContext) GetDiffTerminals() []string {
 	return []string{itemId}
 }
 
+func (self *RemoteBranchesContext) RefForAdjustingLineNumberInDiff() string {
+	return self.GetSelectedItemId()
+}
+
 func (self *RemoteBranchesContext) ShowBranchHeadsInSubCommits() bool {
 	return true
 }

pkg/gui/context/remotes_context.go

@@ -53,3 +53,7 @@ func (self *RemotesContext) GetDiffTerminals() []string {
 
 	return []string{itemId}
 }
+
+func (self *RemotesContext) RefForAdjustingLineNumberInDiff() string {
+	return ""
+}

pkg/gui/context/stash_context.go

@@ -71,3 +71,7 @@ func (self *StashContext) GetDiffTerminals() []string {
 
 	return []string{itemId}
 }
+
+func (self *StashContext) RefForAdjustingLineNumberInDiff() string {
+	return self.GetSelectedItemId()
+}

pkg/gui/context/sub_commits_context.go

@@ -217,6 +217,14 @@ func (self *SubCommitsContext) GetDiffTerminals() []string {
 	return []string{itemId}
 }
 
+func (self *SubCommitsContext) RefForAdjustingLineNumberInDiff() string {
+	commits, _, _ := self.GetSelectedItems()
+	if commits == nil {
+		return ""
+	}
+	return commits[0].Hash
+}
+
 func (self *SubCommitsContext) ModelSearchResults(searchStr string, caseSensitive bool) []gocui.SearchPosition {
 	return searchModelCommits(caseSensitive, self.GetCommits(), self.ColumnPositions(), searchStr)
 }

pkg/gui/context/tags_context.go

@@ -66,6 +66,10 @@ func (self *TagsContext) GetDiffTerminals() []string {
 	return []string{itemId}
 }
 
+func (self *TagsContext) RefForAdjustingLineNumberInDiff() string {
+	return self.GetSelectedItemId()
+}
+
 func (self *TagsContext) ShowBranchHeadsInSubCommits() bool {
 	return true
 }

pkg/gui/controllers/helpers/diff_helper.go

@@ -5,6 +5,7 @@ import (
 
 	"github.com/jesseduffield/lazygit/pkg/commands/git_commands"
 	"github.com/jesseduffield/lazygit/pkg/commands/models"
+	"github.com/jesseduffield/lazygit/pkg/commands/patch"
 	"github.com/jesseduffield/lazygit/pkg/gui/context"
 	"github.com/jesseduffield/lazygit/pkg/gui/modes/diffing"
 	"github.com/jesseduffield/lazygit/pkg/gui/style"
@@ -164,3 +165,45 @@ func (self *DiffHelper) OpenDiffToolForRef(selectedRef types.Ref) error {
 		}))
 	return err
 }
+
+// AdjustLineNumber is used to adjust a line number in the diff that's currently
+// being viewed, so that it corresponds to the line number in the actual working
+// copy state of the file. It is used when clicking on a delta hyperlink in a
+// diff, or when pressing `e` in the staging or patch building panels. It works
+// by getting a diff of what's being viewed in the main view against the working
+// copy, and then using that diff to adjust the line number.
+// path is the file path of the file being viewed
+// linenumber is the line number to adjust (one-based)
+// viewname is the name of the view that shows the diff. We need to pass it
+// because the diff adjustment is slightly different depending on which view is
+// showing the diff.
+func (self *DiffHelper) AdjustLineNumber(path string, linenumber int, viewname string) int {
+	switch viewname {
+
+	case "main", "patchBuilding":
+		if diffableContext, ok := self.c.Context().CurrentSide().(types.DiffableContext); ok {
+			ref := diffableContext.RefForAdjustingLineNumberInDiff()
+			if len(ref) != 0 {
+				return self.adjustLineNumber(linenumber, ref, "--", path)
+			}
+		}
+		// if the type cast to DiffableContext returns false, we are in the
+		// unstaged changes view of the Files panel; no need to adjust line
+		// numbers in this case
+
+	case "secondary", "stagingSecondary":
+		return self.adjustLineNumber(linenumber, "--", path)
+	}
+
+	return linenumber
+}
+
+func (self *DiffHelper) adjustLineNumber(linenumber int, diffArgs ...string) int {
+	args := append([]string{"--unified=0"}, diffArgs...)
+	diff, err := self.c.Git().Diff.GetDiff(false, args...)
+	if err != nil {
+		return linenumber
+	}
+	patch := patch.Parse(diff)
+	return patch.AdjustLineNumber(linenumber)
+}

pkg/gui/controllers/patch_building_controller.go

@@ -105,6 +105,7 @@ func (self *PatchBuildingController) EditFile() error {
 	}
 
 	lineNumber := self.context().GetState().CurrentLineNumber()
+	lineNumber = self.c.Helpers().Diff.AdjustLineNumber(path, lineNumber, self.context().GetViewName())
 	return self.c.Helpers().Files.EditFileAtLine(path, lineNumber)
 }
 

pkg/gui/controllers/staging_controller.go

@@ -160,6 +160,7 @@ func (self *StagingController) EditFile() error {
 	}
 
 	lineNumber := self.context.GetState().CurrentLineNumber()
+	lineNumber = self.c.Helpers().Diff.AdjustLineNumber(path, lineNumber, self.context.GetViewName())
 	return self.c.Helpers().Files.EditFileAtLine(path, lineNumber)
 }
 

pkg/gui/gui.go

@@ -368,6 +368,7 @@ func (gui *Gui) onNewRepo(startArgs appTypes.StartArgs, contextKey types.Context
 			filepath := matches[1]
 			if matches[2] != "" {
 				lineNumber := utils.MustConvertToInt(matches[2])
+				lineNumber = gui.helpers.Diff.AdjustLineNumber(filepath, lineNumber, viewname)
 				return gui.helpers.Files.EditFileAtLine(filepath, lineNumber)
 			}
 			return gui.helpers.Files.EditFiles([]string{filepath})

pkg/gui/types/context.go

@@ -152,6 +152,14 @@ type DiffableContext interface {
 	// which becomes an option when you bring up the diff menu, but when you're just
 	// flicking through branches it will be using the local branch name.
 	GetDiffTerminals() []string
+
+	// Returns the ref that should be used for creating a diff of what's
+	// currently shown in the main view against the working directory, in order
+	// to adjust line numbers in the diff to match the current state of the
+	// shown file. For example, if the main view shows a range diff of commits,
+	// we need to pass the first commit of the range. This is used by
+	// DiffHelper.AdjustLineNumber.
+	RefForAdjustingLineNumberInDiff() string
 }
 
 type IListContext interface {

pkg/integration/tests/patch_building/edit_line_in_patch_building_panel.go

@@ -42,9 +42,6 @@ var EditLineInPatchBuildingPanel = NewIntegrationTest(NewIntegrationTestArgs{
 			NavigateToLine(Contains("+5")).
 			Press(keys.Universal.Edit)
 
-		/* EXPECTED:
 		t.FileSystem().FileContent("edit-command", Contains("file.txt:5\n"))
-		ACTUAL: */
-		t.FileSystem().FileContent("edit-command", Contains("file.txt:2\n"))
 	},
 })