docs: add readme

typescript-eslint · Feb 7, 2020 · 6eaa9f3 · 6eaa9f3
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diff --git a/packages/eslint-plugin/README.md b/packages/eslint-plugin/README.md
@@ -141,7 +141,7 @@ Pro Tip: For larger codebases you may want to consider splitting our linting int
 | [`@typescript-eslint/prefer-nullish-coalescing`](./docs/rules/prefer-nullish-coalescing.md)                           | Enforce the usage of the nullish coalescing operator instead of logical chaining                                        |                    | :wrench: | :thought_balloon: |
 | [`@typescript-eslint/prefer-optional-chain`](./docs/rules/prefer-optional-chain.md)                                   | Prefer using concise optional chain expressions instead of chained logical ands                                         |                    | :wrench: |                   |
 | [`@typescript-eslint/prefer-readonly`](./docs/rules/prefer-readonly.md)                                               | Requires that private members are marked as `readonly` if they're never modified outside of the constructor             |                    | :wrench: | :thought_balloon: |
-| [`@typescript-eslint/prefer-readonly-parameter-types`](./docs/rules/prefer-readonly-parameter-types.md)               | TODO                                                                                                                    |                    |          | :thought_balloon: |
+| [`@typescript-eslint/prefer-readonly-parameter-types`](./docs/rules/prefer-readonly-parameter-types.md)               | Requires that function parameters are typed as readonly to prevent accidental mutation of inputs                        |                    |          | :thought_balloon: |
 | [`@typescript-eslint/prefer-regexp-exec`](./docs/rules/prefer-regexp-exec.md)                                         | Enforce that `RegExp#exec` is used instead of `String#match` if no global flag is provided                              | :heavy_check_mark: |          | :thought_balloon: |
 | [`@typescript-eslint/prefer-string-starts-ends-with`](./docs/rules/prefer-string-starts-ends-with.md)                 | Enforce the use of `String#startsWith` and `String#endsWith` instead of other equivalent methods of checking substrings | :heavy_check_mark: | :wrench: | :thought_balloon: |
 | [`@typescript-eslint/promise-function-async`](./docs/rules/promise-function-async.md)                                 | Requires any function or method that returns a Promise to be marked async                                               |                    |          | :thought_balloon: |

diff --git a/packages/eslint-plugin/src/configs/all.json b/packages/eslint-plugin/src/configs/all.json
@@ -78,6 +78,7 @@
     "@typescript-eslint/prefer-nullish-coalescing": "error",
     "@typescript-eslint/prefer-optional-chain": "error",
     "@typescript-eslint/prefer-readonly": "error",
+    "@typescript-eslint/prefer-readonly-parameter-types": "error",
     "@typescript-eslint/prefer-regexp-exec": "error",
     "@typescript-eslint/prefer-string-starts-ends-with": "error",
     "@typescript-eslint/promise-function-async": "error",

diff --git a/packages/eslint-plugin/src/rules/prefer-readonly-parameter-types.ts b/packages/eslint-plugin/src/rules/prefer-readonly-parameter-types.ts
@@ -9,7 +9,8 @@ export default util.createRule({
   meta: {
     type: 'suggestion',
     docs: {
-      description: 'TODO',
+      description:
+        'Requires that function parameters are typed as readonly to prevent accidental mutation of inputs',
       category: 'Possible Errors',
       recommended: false,
       requiresTypeChecking: true,

diff --git a/packages/eslint-plugin/tests/rules/prefer-readonly-parameter-types.test.ts b/packages/eslint-plugin/tests/rules/prefer-readonly-parameter-types.test.ts
@@ -26,6 +26,7 @@ const primitives = [
   "'a'",
   'number',
   '1',
+  'symbol',
   'any',
   'unknown',
   'never',
@@ -62,11 +63,18 @@ const weirdIntersections = [
 
 ruleTester.run('prefer-readonly-parameter-types', rule, {
   valid: [
-    'function foo(arg: { readonly a: string }) {}',
     'function foo() {}',
 
     // primitives
     ...primitives.map(type => `function foo(arg: ${type}) {}`),
+    `
+      const symb = Symbol('a');
+      function foo(arg: typeof symb) {}
+    `,
+    `
+      enum Enum { a, b }
+      function foo(arg: Enum) {}
+    `,
 
     // arrays
     ...arrays.map(type => `function foo(arg: ${type}) {}`),