redefined-designs/docs/superpowers/specs/2026-08-19-eslint-design.md

ESLint — Design

Issue: #60 — No ESLint anywhere Date: 2026-08-19 Status: Approved

Goal

Put a linter in front of the code that catches, at authoring time, the classes of defect this project has already shipped and then fixed by hand. Two workspaces, one CI job, green on the day it lands.

The issue's own framing is the target: TypeScript's strict: true checks types and nothing else, so rules-of-hooks, exhaustive-deps, no-floating-promises and the SonarJS rules currently run either never or on a server after the fact.

What the code actually reports

Every number below comes from running the candidate rule set against backend/src and frontend/src before writing any config, rather than from estimating. A full-strength config — typescript-eslint recommendedTypeChecked, sonarjs, react-hooks v7, jsx-a11y — reports 435 violations across 50 files.

Rule family	Count	Disposition
@typescript-eslint/no-unsafe-* (5 rules)	325	Deferred to #65
no-floating-promises	30	Error — fix here
no-misused-promises	28	Error, but 25 disappear under checksVoidReturn: { attributes: false }
sonarjs/prefer-read-only-props	16	Warn
react-hooks compiler rules (set-state-in-effect, purity)	9	Warn
no-explicit-any, no-unnecessary-type-assertion	11	Warn
sonarjs/no-nested-conditional, cognitive-complexity	7	Warn
react-hooks/exhaustive-deps	2	Error — fix here
jsx-a11y/alt-text	2	Error — fix here
rules-of-hooks	0	Error (nothing to fix)
Remaining singles	5	Warn

Two of the issue's premises do not survive measurement

exhaustive-deps flags 2, not 10. The issue inferred ten suspects from ten empty dependency arrays. The rule's own analysis clears eight of them — an empty array is only wrong when the effect closes over something that changes, and most of these genuinely do not. The two real ones are Admin.tsx:62 (missing load) and Cart.tsx:132 (missing refreshCartContext). The "decide case by case rather than blanket-autofix" instinct in the issue is still right; it applies to two cases.

The backend is already clean on the defect rules. #59 wrapped every async route, and it shows: zero floating promises in backend/src. Its three no-misused-promises hits are all benign, and each was read rather than assumed — asyncRoute.ts:13 is the wrapper performing its entire purpose, and the two server.ts scheduled jobs (setInterval cart sweep, cron.schedule reminder emails) already try/catch internally, so no rejection escapes.

Decisions

Area	Decision
Config format	Flat config (eslint.config.js), one per workspace
Config location	backend/ and frontend/ separately — not a root config
Type-aware linting	On, but narrowly: recommended, not recommendedTypeChecked
no-unsafe-* family	Deferred to #65
no-misused-promises	checksVoidReturn: { attributes: false }
React Compiler rules	Warn
CI	New lint job in tests.yml
Fail/warn split	Defect rules error; stylistic and advisory rules warn

Why not recommendedTypeChecked

It is the obvious choice and it is the wrong one here. Its no-unsafe-* family accounts for 325 of the 435 findings — 75% — and every one of them traces back to two untyped boundaries: pool.query() returning any rows on the backend, and fetch(...).json() on the frontend. Fixing them means typing those boundaries, which is the entire content of #65.

Turning them on here would produce a lint run whose output is 75% another issue's backlog, which is the reliable way to teach everyone to ignore lint output. Instead this issue enables recommended plus the two type-aware rules that catch defects rather than describe type debt:

'@typescript-eslint/no-floating-promises': 'error',
'@typescript-eslint/no-misused-promises': ['error', { checksVoidReturn: { attributes: false } }],

Both need type information, so parserOptions.projectService is still required — the cost of type-aware linting is paid either way. This is a choice about which findings to surface, not about whether to run the type-aware engine.

#65 turns the no-unsafe-* rules on as it types those boundaries. That is the change that makes them green, so that is the change that should own them.

Why checksVoidReturn: { attributes: false }

Left at its default, no-misused-promises flags every onClick={async () => …} — 25 of its 28 hits, all antd buttons in the admin screens. Passing an async function to a React event handler is idiomatic and safe when the function handles its own errors, which these do. typescript-eslint's own documentation recommends this option for React codebases. Without it the rule is 89% noise and would be switched off within a week; with it, the three remaining hits are all real signal.

Why the React Compiler rules only warn

eslint-plugin-react-hooks v7 ships the React Compiler rule set — set-state-in-effect, purity, static-components and others — alongside the two classic rules. This is React 18 with no compiler in the build, so those rules are advising on a stricter model than the code is written against.

They are not worthless: purity correctly flags Date.now() being called during render in Cart.tsx:160. That is a genuine render-purity smell worth seeing. It is not worth failing a build over in a codebase that never opted into the model, and fixing all nine would mean restructuring effects that behave correctly today — behaviour change well outside what #60 asked for.

Warn keeps the finding visible and the build honest.

Why per-workspace configs rather than one at the root

CI already runs npm install separately in backend and frontend, and the two have genuinely different rule needs — React and a11y rules are meaningless in backend/src, and each workspace has its own tsconfig.json that type-aware linting must point at. A root config would need file-pattern overrides to express a split the directory structure already expresses, and would put React plugins in the backend's dependency tree for no reason.

The cost is a small amount of duplication between the two config files. That is cheaper than the alternative, and the files are short.

Fail/warn split

The issue asks whether to fail CI on day one or start as warnings, and names the middle path: fail on the rules with real defect-catching value, warn on the rest. That is what this does.

Error — build fails (≈37 sites to fix):

Rule	Sites	Fix
no-floating-promises	30	void load()
no-misused-promises	3	Targeted disable with a reason
exhaustive-deps	2	Triage individually
jsx-a11y/alt-text	2	Add alt
rules-of-hooks	0	—

Warn — visible, does not block (≈73 sites): SonarJS complexity and style, remaining jsx-a11y, React Compiler rules, no-explicit-any.

No --max-warnings flag is needed: ESLint exits non-zero on errors and zero on warnings, so the split falls out of rule severity alone.

On void load() being a real fix rather than a disguised suppression

Thirty floating promises sounds like thirty bugs; it is not, and the distinction matters because void can be either an honest annotation or a way to silence a rule without thinking.

These are fire-and-forget calls to load()-style useCallbacks in effects and event handlers. The callbacks were read before choosing this fix: each one sets its own error state — App.tsx's load calls setFailed(true) — so a rejection is already handled inside, and nothing is being swallowed. void states "deliberately not awaited," which is exactly true here.

Had any of them lacked internal handling, the fix for that one would be a .catch, not a void. The implementation plan checks each site rather than applying void mechanically.

Files

File	Change
backend/eslint.config.js	New
frontend/eslint.config.js	New
backend/package.json	lint script, devDependencies
frontend/package.json	lint script, devDependencies
.gitea/workflows/tests.yml	New lint job
frontend/src/** (10 files)	≈37 violation fixes
backend/src/asyncRoute.ts, server.ts	3 targeted disables
.claude/project-context.md	Record the linter and the deferral to #65

Testing

The linter is its own test: npm run lint in each workspace must exit 0. Success criteria:

1. npm run lint passes in both workspaces with zero errors.
2. The warning count is reported, not zero, and that is expected.
3. npm run build still passes in both workspaces.
4. Backend unit and integration suites still pass — the void and disable edits touch frontend files almost exclusively, but server.ts and asyncRoute.ts are on the backend.
5. Playwright e2e passes, since ≈37 edits land in rendered components.
6. The lint job runs in CI and fails the build when a rule in the error set is violated.

Point 6 is verified by deliberately introducing a violation locally and confirming a non-zero exit, not by assuming the job's configuration is correct.

Out of scope

• The no-unsafe-* family and the any backlog — #65.
• Prettier or any formatting tool. The issue asks for defect detection. Formatting is a separate argument with separate churn.
• Linting tests/ and Playwright specs. Worth doing; a second step once the source is green, so that this change's error count stays the measured one.
• Replacing SonarQube. The CI scan stays. This puts the same rule families in the editor, where they are cheaper to act on.

Follow-ups this creates

• #65 owns turning on no-unsafe-* as it types pool.query results and fetch responses.
• routesAreWrapped.test.ts can retire once no-misused-promises runs on the backend in CI. The test predates the linter and covers the same ground by scanning source; it is more targeted and its failure message is better, so this is a judgement call for whoever next touches either. Recorded here so the duplication is deliberate rather than forgotten.