Take a diff renderer at its word about a diff line

Where a renderer states which line of which file it is rendering, take
that as the line's identity. The renderer knows, and for a rendering
that no longer looks like a diff nothing else does. Reading the rendered
text stays the way for the renderings that keep a diff's structure, and
for the renderers that say nothing at all.

Which of the two is used is settled for the rendering as a whole, not
row by row. A rendering with records is not parsed at all, not even for
the rows the renderer says nothing about. Its text is no unified diff,
and a row of it can read like one. Under delta, a commit that adds a
test whose input is a diff shows the test's "diff --git a/img.png
b/img.png" line as a row of its own; parsed, that row opens a file
section that runs to the end of the rendering, and every row delta puts
between hunks and files comes out as a header of a file called img.png.
So the untagged rows of such a rendering stay unresolved, as the
protocol has it (spec section 6.4).

Header records are accepted too. This lets a renderer point at a file
with no content lines, such as a pure rename, a mode change or a binary
file: for those files the header is the only row in the diff.

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

pkg/gui/controllers/helpers/diff_line_helper.go

@@ -18,10 +18,16 @@ func NewDiffLineHelper(c *HelperCommon) *DiffLineHelper {
 // GetDiffLineInfo recovers the identity — file, kind, and old/new line number —
 // of the diff row at the given (wrapped) view line of the given view. It is the
 // seam every consumer of a diff row goes through, so that how we recover that
-// identity can change without them noticing: today the only way is to parse the
-// view's contents as a unified diff, which works for the renderings that keep a
-// diff's structure (no renderer, `git diff --color`, a renderer that only
-// colorizes) and fails for the ones that restructure it.
+// identity can change without them noticing.
+//
+// There are two ways, and which one is used is settled for the rendering as a
+// whole (see renderingStatesDiffLines). A diff renderer that speaks the OSC 1717
+// protocol states the identity of each line it renders. That is the only way to
+// recover it from a rendering that doesn't look like a diff any more (columns, or
+// +/- markers replaced by colour), and a row such a renderer says nothing about
+// has no identity. Otherwise we parse the view's contents as a unified diff; this
+// works for the renderings that keep a diff's structure (no renderer, `git diff
+// --color`, a renderer that only colorizes) and fails for the rest.
 //
 // ok is false when the row's identity can't be recovered, in which case the
 // caller must not act on the line at all.
@@ -33,19 +39,42 @@ func (self *DiffLineHelper) GetDiffLineInfo(view *gocui.View, viewLineIdx int) (
 		return types.DiffLineInfo{}, false
 	}
 
-	parsed, ok := parseDiffLineFromBuffer(diffLineTexts(view.DiffLineContents()), bufferLineIdx)
+	contents := view.DiffLineContents()
+	if bufferLineIdx >= len(contents) {
+		return types.DiffLineInfo{}, false
+	}
+
+	if renderingStatesDiffLines(contents) {
+		// A row can carry more than one record, when the rendering puts two diff
+		// lines on it; the first one is the row's identity, and the leftmost record
+		// is the one a reader would call the row's own.
+		if metadata := contents[bufferLineIdx].Metadata; len(metadata) > 0 {
+			if parsed, ok := parseDiffLineMetadata(metadata[0]); ok {
+				return self.diffLineInfo(parsed), true
+			}
+		}
+		return types.DiffLineInfo{}, false
+	}
+
+	parsed, ok := parseDiffLineFromBuffer(diffLineTexts(contents), bufferLineIdx)
 	if !ok {
 		return types.DiffLineInfo{}, false
 	}
 
-	return self.diffLineInfoFromParsed(parsed), true
+	return self.diffLineInfo(parsed), true
 }
 
-// diffLineInfoFromParsed turns the parser's repo-relative result into the
-// absolute-path identity consumers work with.
-func (self *DiffLineHelper) diffLineInfoFromParsed(parsed parsedDiffLine) types.DiffLineInfo {
+// diffLineInfo turns a parser's result into the absolute-path identity consumers
+// work with. The path arrives repo-relative from the diff header, but a renderer
+// states it however it likes, absolute paths included.
+func (self *DiffLineHelper) diffLineInfo(parsed parsedDiffLine) types.DiffLineInfo {
+	path := parsed.Path
+	if !filepath.IsAbs(path) {
+		path = filepath.Join(self.c.Git().RepoPaths.WorktreePath(), path)
+	}
+
 	return types.DiffLineInfo{
-		Path:    filepath.Join(self.c.Git().RepoPaths.WorktreePath(), parsed.Path),
+		Path:    path,
 		Type:    parsed.Type,
 		NewLine: parsed.NewLine,
 		OldLine: parsed.OldLine,

pkg/gui/controllers/helpers/diff_line_parser.go

@@ -2,6 +2,7 @@ package helpers
 
 import (
 	"regexp"
+	"slices"
 	"strconv"
 	"strings"
 
@@ -103,6 +104,27 @@ func diffLineTexts(contents []gocui.DiffLineContent) []string {
 	return texts
 }
 
+// renderingStatesDiffLines reports whether the renderer stated, for at least one row
+// of the rendering, which diff line it shows. The version-only record a renderer
+// announces the protocol with names no line, and doesn't count.
+//
+// The answer settles how the whole rendering is read. A renderer that states its
+// lines lays the diff out as it likes, so its text is no unified diff and must not be
+// parsed as one, not even for the rows it says nothing about. Such a row can read
+// like a diff header when the file being diffed is itself a diff; the parser would
+// take that for the start of a file section and place every untagged row below it
+// in a file the diff doesn't have. So the rows a renderer leaves untagged (dividers,
+// padding) have no identity, as the protocol has it. A rendering without any record
+// is a diff that describes itself, and is parsed as one.
+func renderingStatesDiffLines(contents []gocui.DiffLineContent) bool {
+	return slices.ContainsFunc(contents, func(content gocui.DiffLineContent) bool {
+		return slices.ContainsFunc(content.Metadata, func(record string) bool {
+			_, ok := parseDiffLineMetadata(record)
+			return ok
+		})
+	})
+}
+
 // fileSectionBounds returns the half-open range [start, end) of the file section
 // containing targetIdx: the nearest line starting a section at or above it, up to
 // where that section ends. start is -1 when targetIdx is above the first file
@@ -313,6 +335,67 @@ func stripDiffPathPrefix(path string) string {
 	return path
 }
 
+// parseDiffLineMetadata parses the payload of an OSC 1717 record, in which a
+// diff renderer states which line of which file it is rendering. The v1 payload
+// is positional and ';'-delimited:
+//
+//	version;type;new-line;old-line;file
+//
+// The file comes last so that it may itself contain a ';'. The old-file line is
+// empty unless the line is a deletion, the only kind that needs it, and the
+// new-file line is empty on a file header, the one kind that has no line.
+//
+// ok is false for a payload of an unknown version or shape, so that the caller
+// can fall back to reading the rendered text.
+func parseDiffLineMetadata(payload string) (parsedDiffLine, bool) {
+	fields := strings.SplitN(payload, ";", 5)
+	if len(fields) < 5 || fields[0] != "1" {
+		return parsedDiffLine{}, false
+	}
+
+	lineType, ok := diffLineTypeFromMetadata(fields[1])
+	if !ok {
+		return parsedDiffLine{}, false
+	}
+
+	newLine := 0
+	if fields[2] != "" {
+		var err error
+		if newLine, err = strconv.Atoi(fields[2]); err != nil {
+			return parsedDiffLine{}, false
+		}
+	} else if lineType != types.DiffLineFileHeader {
+		return parsedDiffLine{}, false
+	}
+
+	oldLine := 0
+	if fields[3] != "" {
+		var err error
+		if oldLine, err = strconv.Atoi(fields[3]); err != nil {
+			return parsedDiffLine{}, false
+		}
+	}
+
+	return parsedDiffLine{Path: fields[4], Type: lineType, NewLine: newLine, OldLine: oldLine}, true
+}
+
+func diffLineTypeFromMetadata(typeField string) (types.DiffLineType, bool) {
+	switch typeField {
+	case "c":
+		return types.DiffLineContext, true
+	case "a":
+		return types.DiffLineAdded, true
+	case "d":
+		return types.DiffLineDeleted, true
+	case "f":
+		return types.DiffLineFileHeader, true
+	case "h":
+		return types.DiffLineHunkHeader, true
+	default:
+		return types.DiffLineOther, false
+	}
+}
+
 // pathFromDiffGitLine extracts the new-file path from a "diff --git a/X b/X"
 // line, where the two paths are separated by a space and either may be quoted.
 // A path containing " b/" (or ` "b/`) would defeat this, but the +++/--- lines

pkg/gui/controllers/helpers/diff_line_parser_test.go

@@ -5,6 +5,7 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/jesseduffield/lazygit/pkg/gocui"
 	"github.com/jesseduffield/lazygit/pkg/gui/types"
 	"github.com/stretchr/testify/assert"
 )
@@ -320,3 +321,102 @@ func TestParseAllDiffLinesFromBuffer(t *testing.T) {
 	}
 	assert.True(t, all[6].ok)
 }
+
+func TestParseDiffLineMetadata(t *testing.T) {
+	scenarios := []struct {
+		name     string
+		payload  string
+		expected parsedDiffLine
+		expectOk bool
+	}{
+		{"context", "1;c;1;;foo.txt", parsedDiffLine{Path: "foo.txt", Type: types.DiffLineContext, NewLine: 1}, true},
+		{"added", "1;a;3;;foo.txt", parsedDiffLine{Path: "foo.txt", Type: types.DiffLineAdded, NewLine: 3}, true},
+		// A deletion carries both numbers; two consecutive deletions share the
+		// new-file line and differ only in the old-file one.
+		{"first deletion", "1;d;2;2;foo.txt", parsedDiffLine{Path: "foo.txt", Type: types.DiffLineDeleted, NewLine: 2, OldLine: 2}, true},
+		{"second deletion", "1;d;2;3;foo.txt", parsedDiffLine{Path: "foo.txt", Type: types.DiffLineDeleted, NewLine: 2, OldLine: 3}, true},
+		// A whole-file deletion has new-file position 0 and the old path.
+		{"deleted file", "1;d;0;1;gone.txt", parsedDiffLine{Path: "gone.txt", Type: types.DiffLineDeleted, NewLine: 0, OldLine: 1}, true},
+		// The path is the last field, so a ';' within it survives.
+		{"path with semicolon", "1;c;5;;weird;name.txt", parsedDiffLine{Path: "weird;name.txt", Type: types.DiffLineContext, NewLine: 5}, true},
+		// A renderer may state the path absolutely; the parser keeps it verbatim
+		// and leaves resolving it to the caller.
+		{"absolute path", "1;a;7;;/abs/foo.txt", parsedDiffLine{Path: "/abs/foo.txt", Type: types.DiffLineAdded, NewLine: 7}, true},
+		// A file header has no line number; a hunk header carries the new-file
+		// line of the hunk's first line (0 for a whole-file deletion, mirroring
+		// `@@ -1,N +0,0 @@`).
+		{"file header", "1;f;;;foo.txt", parsedDiffLine{Path: "foo.txt", Type: types.DiffLineFileHeader}, true},
+		{"hunk header", "1;h;10;;foo.txt", parsedDiffLine{Path: "foo.txt", Type: types.DiffLineHunkHeader, NewLine: 10}, true},
+		{"hunk header of a deleted file", "1;h;0;;gone.txt", parsedDiffLine{Path: "gone.txt", Type: types.DiffLineHunkHeader, NewLine: 0}, true},
+		// A file header's line number is always empty, but a renderer that fills
+		// it in anyway is taken at its word rather than rejected.
+		{"file header with a line number", "1;f;10;;foo.txt", parsedDiffLine{Path: "foo.txt", Type: types.DiffLineFileHeader, NewLine: 10}, true},
+
+		{"unknown version", "2;c;1;;foo.txt", parsedDiffLine{}, false},
+		{"unknown type", "1;x;1;;foo.txt", parsedDiffLine{}, false},
+		{"too few fields", "1;c;1", parsedDiffLine{}, false},
+		{"non-numeric new-line", "1;c;x;;foo.txt", parsedDiffLine{}, false},
+		{"non-numeric old-line", "1;d;2;y;foo.txt", parsedDiffLine{}, false},
+		// Only a file header may omit the new-file line; on any other kind the
+		// record is malformed, and rejecting it falls the row back to the diff
+		// text rather than acting on a line number we don't have.
+		{"empty new-line on a content line", "1;c;;;foo.txt", parsedDiffLine{}, false},
+		{"empty new-line on a hunk header", "1;h;;;foo.txt", parsedDiffLine{}, false},
+	}
+
+	for _, s := range scenarios {
+		t.Run(s.name, func(t *testing.T) {
+			result, ok := parseDiffLineMetadata(s.payload)
+			assert.Equal(t, s.expectOk, ok)
+			if s.expectOk {
+				assert.Equal(t, s.expected, result)
+			}
+		})
+	}
+}
+
+func TestRenderingStatesDiffLines(t *testing.T) {
+	row := func(text string, records ...string) gocui.DiffLineContent {
+		return gocui.DiffLineContent{Text: text, Metadata: records}
+	}
+
+	scenarios := []struct {
+		name     string
+		contents []gocui.DiffLineContent
+		expected bool
+	}{
+		{
+			name:     "a rendering without records is read as a diff",
+			contents: []gocui.DiffLineContent{row("diff --git a/foo.txt b/foo.txt"), row("+one")},
+			expected: false,
+		},
+		{
+			name:     "a record on any row makes the records the source",
+			contents: []gocui.DiffLineContent{row("foo.txt"), row("one", "1;c;1;;foo.txt"), row("")},
+			expected: true,
+		},
+		{
+			// A renderer announces the protocol with a record that names no line; a
+			// rendering with nothing but that one says nothing about its rows.
+			name:     "the version-only handshake record doesn't count",
+			contents: []gocui.DiffLineContent{row("foo.txt", "1"), row("one")},
+			expected: false,
+		},
+		{
+			name:     "records of a version we don't understand don't count",
+			contents: []gocui.DiffLineContent{row("one", "2;c;1;;foo.txt")},
+			expected: false,
+		},
+		{
+			name:     "an empty rendering states nothing",
+			contents: nil,
+			expected: false,
+		},
+	}
+
+	for _, s := range scenarios {
+		t.Run(s.name, func(t *testing.T) {
+			assert.Equal(t, s.expected, renderingStatesDiffLines(s.contents))
+		})
+	}
+}