kovidgoyal/kitty · error

Right side line mismatch %d != %d

Error message

Right side line mismatch %d != %d

What it means

The companion check to the left-side check in Patch.finalize: the last chunk's right_start+right_count must equal the patch's right_start+right_count. It verifies the right side of every hunk tiles the file contiguously; failure indicates malformed or mis-parsed diff output rather than a user input problem.

Source

Thrown at kittens/diff/patch.go:329

	self.removed_count++
}

func (self *Hunk) context_line() {
	self.ensure_context_chunk()
	self.current_chunk.context_line()
}

func (self *Hunk) finalize(left_lines, right_lines []string) error {
	if self.current_chunk != nil {
		self.chunks = append(self.chunks, self.current_chunk)
	}
	// Sanity check
	c := self.chunks[len(self.chunks)-1]
	if c.left_start+c.left_count != self.left_start+self.left_count {
		return fmt.Errorf("Left side line mismatch %d != %d", c.left_start+c.left_count, self.left_start+self.left_count)
	}
	if c.right_start+c.right_count != self.right_start+self.right_count {
		return fmt.Errorf("Right side line mismatch %d != %d", c.right_start+c.right_count, self.right_start+self.right_count)
	}
	for _, c := range self.chunks {
		c.finalize(left_lines, right_lines)
	}
	return nil
}

type Patch struct {
	all_hunks                                       []*Hunk
	largest_line_number, added_count, removed_count int
	left_moved_lines, right_moved_lines             *utils.Set[int]
}

func (self *Patch) Len() int { return len(self.all_hunks) }

func splitlines_like_git(raw string, strip_trailing_lines bool, process_line func(string)) {
	sz := len(raw)
	if strip_trailing_lines {

View on GitHub (pinned to 6d5d0c4406)

Solutions

1. Revert `diff_cmd` to the default and retry to isolate the cause.
2. Validate your diff tool's output with `your-diff-cmd a b | diff - a.patch` style checks or feed it to `patch --dry-run` to confirm it's well-formed unified diff.
3. If the default setup fails, file a kitty issue including both files and the generated diff.

Example fix

# before
diff_cmd custom-wrapper.sh

# after
# use default diff
# (delete the diff_cmd line in kitty.conf)

# shell: verify hunk arithmetic of your diff tool's output
# GNU diff is the reference; compare hunk headers
your-diff-cmd a b > /tmp/xd
diff a b > /tmp/gd
head -100 /tmp/xd   # inspect @@ start,count @@ headers vs /tmp/gd

Wrap finalize results; on a right/left side line mismatch, retry the whole diff with the default diff command, else report the malformed output to the user with the raw diff attached.

When it happens

Trigger: Same as the left-side check: a custom diff_cmd emitting hunks whose right-side line counts don't sum correctly; diffs with headers claiming more/fewer lines than the hunk bodies contain; rename-only or binary hunks handled inconsistently by an external diff tool.

Common situations: Custom `diff_cmd` wrappers (delta, difftastic, custom scripts) in kitty.conf; diffs produced with unusual options (--unified=0 combined with word-diff, etc.); kitty version regressions in the patch parser.

Related errors

• Left side line mismatch %d != %d
• You must specify exactly two files/directories to compare
• The items to be diffed should both be either directories or
• This terminal does not support the kitty keyboard protocol,
• Failed to compile word_regex %q: %w

AI-assisted analysis of kovidgoyal/kitty@6d5d0c4406 (2026-08-27). Data as JSON: /api/errors/ae301109b5a0876b. Report an issue: GitHub.