Eslint: upgrade to version 8.0.0

See:

- https://eslint.org/blog/2021/10/eslint-v8.0.0-released
- https://eslint.org/docs/user-guide/migrating-to-8.0.0

Known unresolved issues (with low impact )that we decided to accept:

- mysticatea/eslint-plugin-node#301

Known issues that need to be fixed first:

- [x] wait for import-js/eslint-plugin-import#2191 to be released and merged here
- [x] wait for gajus/eslint-plugin-flowtype#496 to be released and merged here
- [x] wait for testing-library/eslint-plugin-testing-library#462 to be released and merged here
- [ ] ~wait for mysticatea/eslint-plugin-node#294 to be released and merged here~ replaced (probably temporarily) with `eslint-plugin-n` which supports Eslint 8
- [x] wait for facebook/react#22248 to be released and merged here
- [x] release minor/patch version of Adeira Eslint Config before merging this breaking change
- [x] switch `NEXT_VERSION_ERROR` to `ERROR` (adeira/universe#3625)

adeira-source-id: b194be7e4f2fc10d51a10ed8753c440414e36b4d

CHANGELOG.md

@@ -2,7 +2,8 @@
 
 **Breaking changes ahead!**
 
-- New rules enabled: `fb-flow/use-indexed-access-type` ([more info](https://flow.org/en/docs/types/indexed-access/)) and `ft-flow/enforce-suppression-code` (warnings or errors in strict mode).
+- Eslint version 8 is now required (visit https://eslint.org/blog/2021/10/eslint-v8.0.0-released and other related blog posts for more info).
+- New rules enabled: `fb-flow/use-indexed-access-type` ([more info](https://flow.org/en/docs/types/indexed-access/)), `ft-flow/enforce-suppression-code` and `no-unused-private-class-members`.
 - Many rules that were showing warnings in normal mode but errors in strict mode were converted to normal errors (so there is no difference between normal and strict mode). The best way how to migrate is to temporarily switch to the strict mode and address all the errors before upgrading to this major version.
 - Switched from [`eslint-plugin-flowtype`](https://github.com/gajus/eslint-plugin-flowtype/tree/449cb99f1b6d3bbbb66f5be55f497667f5b2cb31) to [`eslint-plugin-ft-flow`](https://github.com/flow-typed/eslint-plugin-ft-flow/tree/820e631ce491cdf45821744d4e29f348cf776392) which contains the same set of rules but should be more up to date and maintained. We are going to enable additional rules later. There is a possible minor breaking change (with very simple fix) when suppressing the rules manually, for example:
 

__tests__/__fixtures__/valid-eslint-examples/node/process-exit-as-throw.js

@@ -7,6 +7,11 @@ class Bar {}
 // Normally, Eslint would complain because of `consistent-return` error, however,
 // rule `node/process-exit-as-throw` makes sure this is not the case.
 // See: https://github.com/mysticatea/eslint-plugin-node/blob/master/docs/rules/process-exit-as-throw.md
+
+// TODO: the following `consistent-return` error is incorrect and should be removed once the following
+//       issue is resolved: https://github.com/mysticatea/eslint-plugin-node/issues/301. We decided to
+//       accept the low risk for now to ease migration to Eslint 8.
+// eslint-disable-next-line consistent-return
 export function foo(a: boolean): ?Bar {
   if (a) {
     return new Bar();

__tests__/__snapshots__/index.test.js.snap

@@ -711,6 +711,7 @@ Object {
     "no-unsafe-optional-chaining": 2,
     "no-unused-expressions": 0,
     "no-unused-labels": 1,
+    "no-unused-private-class-members": 2,
     "no-unused-vars": Array [
       2,
       Object {
@@ -763,6 +764,7 @@ Object {
     "prefer-exponentiation-operator": 2,
     "prefer-named-capture-group": 2,
     "prefer-numeric-literals": 0,
+    "prefer-object-has-own": 0,
     "prefer-object-spread": 2,
     "prefer-promise-reject-errors": 1,
     "prefer-regex-literals": 2,

__tests__/__snapshots__/presets.test.js.snap

@@ -416,6 +416,7 @@ Object {
     "no-unsafe-optional-chaining": 2,
     "no-unused-expressions": 0,
     "no-unused-labels": 1,
+    "no-unused-private-class-members": 2,
     "no-unused-vars": Array [
       2,
       Object {
@@ -459,6 +460,7 @@ Object {
     "prefer-exponentiation-operator": 2,
     "prefer-named-capture-group": 2,
     "prefer-numeric-literals": 0,
+    "prefer-object-has-own": 0,
     "prefer-object-spread": 2,
     "prefer-promise-reject-errors": 1,
     "prefer-regex-literals": 2,

package.json

@@ -42,6 +42,6 @@
     "snapshot-diff": "^0.9.0"
   },
   "peerDependencies": {
-    "eslint": ">=7.24.0 <8.0.0"
+    "eslint": ">=8.0.0"
   }
 }

src/presets/base.js

@@ -55,6 +55,7 @@ module.exports = ({
     'no-unsafe-finally': ERROR,
     'no-unsafe-negation': ERROR,
     'no-unsafe-optional-chaining': ERROR,
+    'no-unused-private-class-members': ERROR,
     'require-atomic-updates': ERROR,
     'use-isnan': [ERROR, { enforceForSwitchCase: true }],
     'valid-jsdoc': OFF,
@@ -268,6 +269,7 @@ module.exports = ({
     'prefer-const': [ERROR, { destructuring: 'all' }],
     'prefer-destructuring': OFF,
     'prefer-numeric-literals': OFF,
+    'prefer-object-has-own': OFF, // TODO: NEXT_VERSION_ERROR (?) (https://eslint.org/docs/rules/prefer-object-has-own)
     'prefer-rest-params': WARN,
     'prefer-spread': WARN,
     'prefer-template': ERROR,

src/presets/flowtype.js

@@ -11,7 +11,9 @@ import type { EslintConfig } from '../EslintConfig.flow';
 module.exports = ({
   plugins: ['eslint-plugin-ft-flow', 'eslint-plugin-fb-flow'],
   rules: {
-    // flowtype (https://github.com/gajus/eslint-plugin-flowtype)
+    // Flow:
+    //  - https://github.com/flow-typed/eslint-plugin-ft-flow
+    //  - https://github.com/gajus/eslint-plugin-flowtype
     'ft-flow/array-style-complex-type': OFF,
     'ft-flow/array-style-simple-type': OFF,
     'ft-flow/arrow-parens': OFF,