feat(unbound-method): create rule (#765)

* feat(unbound-method): add original `unbound-method` rule

* feat(unbound-method): modify rule for `jest`

* refactor(unbound-method): extend base rule

* docs(readme): add section about type-based rules

* chore: add `@typescript-eslint/eslint-plugin` as an optional peer dep

* fix(unbound-method): re-throw errors that are not `MODULE_NOT_FOUND`

* chore(unbound-method): use early return instead of empty string

* test(unbound-method): adjust test

* build: ignore test fixtures

* test: add end of file newline to fixture

* docs(unbound-method): mention `@typescript-eslint/eslint-plugin` dep

* refactor(unbound-method): improve method & variable name

.eslintignore

@@ -1,3 +1,4 @@
 coverage/
 lib/
 !.eslintrc.js
+src/rules/__tests__/fixtures/

README.md

@@ -128,7 +128,7 @@ installations requiring long-term consistency.
 
 ## Rules
 
-<!-- begin rules list -->
+<!-- begin base rules list -->
 
 | Rule                                                                         | Description                                                     | Configurations   | Fixable      |
 | ---------------------------------------------------------------------------- | --------------------------------------------------------------- | ---------------- | ------------ |
@@ -173,7 +173,32 @@ installations requiring long-term consistency.
 | [valid-expect-in-promise](docs/rules/valid-expect-in-promise.md)             | Enforce having return statement when testing with promises      | ![recommended][] |              |
 | [valid-title](docs/rules/valid-title.md)                                     | Enforce valid titles                                            | ![recommended][] | ![fixable][] |
 
-<!-- end rules list -->
+<!-- end base rules list -->
+
+## TypeScript Rules
+
+In addition to the above rules, this plugin also includes a few advanced rules
+that are powered by type-checking information provided by TypeScript.
+
+In order to use these rules, you must be using `@typescript-eslint/parser` &
+adjust your eslint config as outlined
+[here](https://github.com/typescript-eslint/typescript-eslint/blob/master/docs/getting-started/linting/TYPED_LINTING.md)
+
+Note that unlike the type-checking rules in `@typescript-eslint/eslint-plugin`,
+the rules here will fallback to doing nothing if type information is not
+available, meaning its safe to include them in shared configs that could be used
+on JavaScript and TypeScript projects.
+
+Also note that `unbound-method` depends on `@typescript-eslint/eslint-plugin`,
+as it extends the original `unbound-method` rule from that plugin.
+
+<!-- begin type rules list -->
+
+| Rule                                           | Description                                                   | Configurations | Fixable |
+| ---------------------------------------------- | ------------------------------------------------------------- | -------------- | ------- |
+| [unbound-method](docs/rules/unbound-method.md) | Enforces unbound methods are called with their expected scope |                |         |
+
+<!-- end type rules list -->
 
 ## Credit
 

babel.config.js

@@ -7,4 +7,5 @@ module.exports = {
     '@babel/preset-typescript',
     ['@babel/preset-env', { targets: { node: 10 } }],
   ],
+  ignore: ['src/**/__tests__/fixtures/**'],
 };

docs/rules/unbound-method.md

@@ -0,0 +1,54 @@
+# Enforces unbound methods are called with their expected scope (`unbound-method`)
+
+## Rule Details
+
+This rule extends the base [`@typescript-eslint/unbound-method`][original-rule]
+rule, meaning you must depend on `@typescript-eslint/eslint-plugin` for it to
+work. It adds support for understanding when it's ok to pass an unbound method
+to `expect` calls.
+
+See the [`@typescript-eslint` documentation][original-rule] for more details on
+the `unbound-method` rule.
+
+Note that while this rule requires type information to work, it will fail
+silently when not available allowing you to safely enable it on projects that
+are not using TypeScript.
+
+## How to use
+
+```json5
+{
+  parser: '@typescript-eslint/parser',
+  parserOptions: {
+    project: 'tsconfig.json',
+    ecmaVersion: 2020,
+    sourceType: 'module',
+  },
+  overrides: [
+    {
+      files: ['test/**'],
+      extends: ['jest'],
+      rules: {
+        // you should turn the original rule off *only* for test files
+        '@typescript-eslint/unbound-method': 'off',
+        'jest/unbound-method': 'error',
+      },
+    },
+  ],
+  rules: {
+    '@typescript-eslint/unbound-method': 'error',
+  },
+}
+```
+
+This rule should be applied to your test files in place of the original rule,
+which should be applied to the rest of your codebase.
+
+## Options
+
+See [`@typescript-eslint/unbound-method`][original-rule] options.
+
+<sup>Taken with ❤️ [from `@typescript-eslint` core][original-rule]</sup>
+
+[original-rule]:
+  https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/unbound-method.md

package.json

@@ -62,7 +62,8 @@
         "displayName": "test",
         "testEnvironment": "node",
         "testPathIgnorePatterns": [
-          "<rootDir>/lib/.*"
+          "<rootDir>/lib/.*",
+          "<rootDir>/src/rules/__tests__/fixtures/*"
         ]
       },
       {
@@ -121,8 +122,14 @@
     "typescript": "^4.0.0"
   },
   "peerDependencies": {
+    "@typescript-eslint/eslint-plugin": ">= 4",
     "eslint": ">=5"
   },
+  "peerDependenciesMeta": {
+    "@typescript-eslint/eslint-plugin": {
+      "optional": true
+    }
+  },
   "engines": {
     "node": ">=10"
   },

src/__tests__/__snapshots__/rules.test.ts.snap

@@ -46,6 +46,7 @@ Object {
       "jest/prefer-todo": "error",
       "jest/require-to-throw-message": "error",
       "jest/require-top-level-describe": "error",
+      "jest/unbound-method": "error",
       "jest/valid-describe": "error",
       "jest/valid-expect": "error",
       "jest/valid-expect-in-promise": "error",

src/__tests__/rules.test.ts

@@ -2,7 +2,7 @@ import { existsSync } from 'fs';
 import { resolve } from 'path';
 import plugin from '../';
 
-const numberOfRules = 44;
+const numberOfRules = 45;
 const ruleNames = Object.keys(plugin.rules);
 const deprecatedRules = Object.entries(plugin.rules)
   .filter(([, rule]) => rule.meta.deprecated)

src/rules/__tests__/fixtures/class.ts

@@ -0,0 +1,13 @@
+// used by no-throw-literal test case to validate custom error
+export class Error {}
+
+// used by unbound-method test case to test imports
+export const console = { log() {} };
+
+// used by prefer-reduce-type-parameter to test native vs userland check
+export class Reducable {
+  reduce() {}
+}
+
+// used by no-implied-eval test function imports
+export class Function {}

src/rules/__tests__/fixtures/foo.ts

@@ -0,0 +1 @@
+export type T = number;