+++
title = "nbd update diff output"
priority = 5
status = "todo"
ticket_type = "feature"
dependencies = []
+++
Show a git-diff-style +/- summary of what changed when `nbd update` is run without `--json`.

## Motivation

Currently `nbd update` prints the full ticket after the change, making it hard to see at a glance what actually changed. A diff view — showing only changed fields — is more informative.

## Approach

### display.rs
Add `format_diff(old: &Ticket, new: &Ticket) -> String`:
- Compare each field between `old` and `new`.
- For each field that changed, emit two lines:
  ```
  - status:   todo
  + status:   in_progress
  ```
- If no fields changed, emit `(no changes)`.
- Fields compared: `title`, `body`, `priority`, `status`, `ticket_type`, `dependencies`.
- `id` is never shown (it cannot change).
- Label width matches `format_ticket` (LABEL_WIDTH).

Add `print_diff(old: &Ticket, new: &Ticket)` that calls `println!("{}" format_diff(...))`.

### main.rs
In `cmd_update`:
- Before applying changes: `let old = ticket.clone();`
- After `write_ticket`:
  - If `json`: current behaviour (print new ticket as JSON).
  - Else: `display::print_diff(&old, &ticket)`.

## Tests

Unit tests in `src/tests.rs`:
- `format_diff` shows changed fields only.
- `format_diff` with identical tickets outputs `(no changes)`.
- Changed dependencies are shown as comma-separated lists on each line.

Integration test:
- `nbd update <id> --status in_progress` (no `--json`) prints `- status:` and `+ status:` lines.
- `nbd update <id> --json` still prints full JSON (no diff).

## Files touched
- `src/display.rs` — `format_diff`, `print_diff`
- `src/main.rs` — `cmd_update` uses `print_diff`
- `src/tests.rs` — unit tests for `format_diff`
- `tests/integration.rs` — integration tests