# Format the frontend with Prettier

Branch: `frontend-format` → `main`

PR 11 of the review fixes plan (`docs/review-fixes-plan.md`), a readability PR: no behaviour change, no version change.

## What changed

The PR has three commits, so the large mechanical one can be skipped in review:

1. **Add Prettier to the frontend (R2).**
   - **Dev dependencies:** `prettier` 3.9.10 (published 2026-10-10) and `prettier-plugin-svelte` 4.1.1 (2026-06-15). Both are the current releases `min-release-age=7` allows, and the lockfile is updated: npm added only these two packages.
   - **`frontend/.prettierrc`:** `printWidth` 120, double quotes, semicolons, trailing commas, and the Svelte plugin. Everything else is Prettier's default, which already matched the code: two-space indents, `<script>` and `<style>` content indented, blocks in script–markup–style order.
   - **`frontend/.prettierignore`:** `dist`, `bindings` and `node_modules`.
   - **npm scripts:** `format` (`prettier --write .`) and `format:check` (`prettier --check .`) in `frontend/package.json`.
2. **Reformat the frontend with Prettier.**
   - The output of `npm run format` and nothing else, across 11 files, all under `frontend/`.
   - Besides `src`, Prettier touched three config files: `index.html` (`<!DOCTYPE html>` became `<!doctype html>`, which HTML treats the same), `svelte.config.js` (single quotes to double, semicolons added) and `tsconfig.json` (a trailing comma removed).
3. **Name the variables in `SequencePanel.svelte`'s `save()` and `remove()` (R3).**
   - `s`, `n`, `b` and `l` become `slot`, `newName`, `newBpm` and `newBars`.
   - The local `slot` shadows the component's `slot` prop on purpose: it is copied from `seq.slot` before the `await`, because props are live. A comment now says so.

**Long lines:** 30 lines under `frontend/src` were over 120 characters, the longest 250. Now 5 are, and Prettier cannot break any of them:

| Line | Length | Why Prettier leaves it |
| --- | --- | --- |
| `src/lib/AboutModal.svelte:28` | 192 | A `svelte-ignore` comment, which must stay on one line. |
| `src/lib/SequencePanel.svelte:28` | 159 | A template literal: the "Shorten a sequence with notes?" message. |
| `src/App.svelte:73` | 143 | A template literal: a pad's screen-reader label. |
| `src/App.svelte:52` | 124 | A string literal: the "Export is disabled…" tooltip. |
| `src/App.svelte:236` | 122 | Text with a `{st.limits.maxSequences}` expression in the sequence grid's hint. |

## Notes

- **Whitespace that could show on screen.** I compiled every component with the Svelte compiler before and after the reformat and compared the output. The compiler keeps rendered whitespace and reprints the script code, so any difference is one the page could show.
  - **The result:** 7 of 8 components compile to identical output. The one difference is in `App.svelte`: Prettier wrapped the pads tab's help paragraph ("Click a pad to select and hear it. … Drop a WAV file on any pad to assign it.") onto two lines. In the compiled template, that turns one space into a newline plus indentation inside the text.
  - **Why it cannot show:** that paragraph (`.hint.grid-hint`) uses normal whitespace handling, which collapses it back to a single space. The only `white-space: pre-line` rule in the app is on the error banner.
  - **No ignore comments added:** none was needed.
  - **After the rename:** `SequencePanel.svelte` differs from the reformatted version only in the renamed variables and the two comments.
- **Left out on purpose:** `add()` in `SequencePanel.svelte` also uses `const s = slot`. The plan names only `save()` and `remove()`, so I left `add()` as it is. Say if it should be renamed too.
- **The checks list in the plan** already includes `npm run format:check` from this PR on.

## Testing

**On the server, every command with `GOTOOLCHAIN=go1.27.4`:**
- `go test ./...` passes; no test changed.
- `go vet ./...` and `staticcheck ./...` are clean, and `govulncheck ./...` reports "No vulnerabilities found."
- In `frontend`:
  - `npm ci` installs from the lockfile ("added 53 packages");
  - `npm run check` reports 0 errors and 0 warnings;
  - `npm run build` builds;
  - `npm run format:check` reports "All matched files use Prettier code style!".
- `wails3 build` builds and the app starts under Xvfb.
- **Exports are byte-identical.** Before the first commit (`main`) and after the last, I ran `go run ./cmd/mpckit-cli -load testdata/device/DemoFile.xpj -out <dir>`. `cmp` finds the two `DemoFile.xpj` identical, and `diff -r` finds the two data folders identical.
- **No bound method changed:** `TestBoundMethods` passes untouched. `git diff origin/main` shows no change in `frontend/bindings`, in any Go file, or anywhere outside `frontend/`.

**On the laptop (PowerShell, in the repo).** Compare each screen with the current `main` build; nothing should look different.
1. `git fetch; git checkout frontend-format`
2. `cd frontend; npm ci; npm run check; npm run format:check; cd ..`: 0 errors and 0 warnings; "All matched files use Prettier code style!".
3. `wails3 dev`, then load `testdata\device\DemoFile.xpj`. **Pads tab:**
   - **Grid and help:** the pad grid, the bank bar and the help paragraph under the grid read as one paragraph, with normal spacing.
   - **Pad panel:** select A1, then A3 and B2. The panel shows the name, file, tune and mute group.
   - **Edits:** change a tune and a mute group, and the badges on the pads update.
4. **Move/Copy to pad:**
   - From the pad panel, open Move to pad and Copy to pad. Check the picker's title, its bank and pad lists, and its hint lines ("… has a sample: the two pads will swap.", "… will be replaced.").
   - Close the picker with Escape, then with Cancel.
5. **Notes warning:** drag A1 onto A5. The notes warning dialog shows its message and items. Cancel.
6. **Sequences tab:** select Intro and Sequence 02. The panel shows the name, BPM and length, and the help line under the grid reads normally.
   - **Shorten:** set Sequence 02's length to 1 bar. The "Shorten a sequence with notes?" dialog shows its message. Cancel.
   - **Add:** add a sequence in an empty slot (B5).
   - **Remove:** remove that new sequence, which shows the "Remove …?" dialog with "The sequence has no recorded notes.". Confirm.
7. **Export:**
   - Export to a new folder. The notice shows where it went.
   - Export there again: "Replace existing files?" lists the items. Cancel.
   - Export a zip.
8. **Missing files:** load a copy of DemoFile with one WAV deleted from its data folder.
   - The missing-file badge and the footer line ("1 sample file missing: export is disabled") show.
   - Hovering the disabled Export buttons shows the "Export is disabled…" tooltip.
9. **About, New and close:**
   - About: the dialog's text, links and Close button.
   - New with unsaved changes: the "unsaved changes" confirm dialog shows.
   - Close the window with unsaved changes: the close prompt shows.