feat(eslint-plugin): add no-extra-non-null-assertion (#1183)

Co-authored-by: Brad Zacher <brad.zacher@gmail.com>

packages/eslint-plugin/README.md

@@ -164,6 +164,7 @@ Then you should add `airbnb` (or `airbnb-base`) to your `extends` section of `.e
 | [`@typescript-eslint/no-empty-function`](./docs/rules/no-empty-function.md)                               | Disallow empty functions                                                                                                                            | :heavy_check_mark: |          |                   |
 | [`@typescript-eslint/no-empty-interface`](./docs/rules/no-empty-interface.md)                             | Disallow the declaration of empty interfaces                                                                                                        | :heavy_check_mark: |          |                   |
 | [`@typescript-eslint/no-explicit-any`](./docs/rules/no-explicit-any.md)                                   | Disallow usage of the `any` type                                                                                                                    | :heavy_check_mark: | :wrench: |                   |
+| [`@typescript-eslint/no-extra-non-null-assertion`](./docs/rules/no-extra-non-null-assertion.md)                           | Disallow extra non-null assertion                                                                                                            |                    |          |                   |
 | [`@typescript-eslint/no-extra-parens`](./docs/rules/no-extra-parens.md)                                   | Disallow unnecessary parentheses                                                                                                                    |                    | :wrench: |                   |
 | [`@typescript-eslint/no-extraneous-class`](./docs/rules/no-extraneous-class.md)                           | Forbids the use of classes as namespaces                                                                                                            |                    |          |                   |
 | [`@typescript-eslint/no-floating-promises`](./docs/rules/no-floating-promises.md)                         | Requires Promise-like values to be handled appropriately.                                                                                           |                    |          | :thought_balloon: |

packages/eslint-plugin/docs/rules/no-extra-non-null-assertion.md

@@ -0,0 +1,37 @@
+# Disallow extra non-null assertion
+
+## Rule Details
+
+Examples of **incorrect** code for this rule:
+
+```ts
+const foo: { bar: number } | null = null;
+const bar = foo!!!.bar;
+```
+
+```ts
+function foo(bar: number | undefined) {
+  const bar: number = bar!!!;
+}
+```
+
+Examples of **correct** code for this rule:
+
+```ts
+const foo: { bar: number } | null = null;
+const bar = foo!.bar;
+```
+
+```ts
+function foo(bar: number | undefined) {
+  const bar: number = bar!;
+}
+```
+
+## How to use
+
+```json
+{
+  "@typescript-eslint/no-extra-non-null-assertion": ["error"]
+}
+```

packages/eslint-plugin/src/configs/all.json

@@ -32,6 +32,7 @@
     "@typescript-eslint/no-empty-interface": "error",
     "@typescript-eslint/no-explicit-any": "error",
     "no-extra-parens": "off",
+    "@typescript-eslint/no-extra-non-null-assertion": "error",
     "@typescript-eslint/no-extra-parens": "error",
     "@typescript-eslint/no-extraneous-class": "error",
     "@typescript-eslint/no-floating-promises": "error",

packages/eslint-plugin/src/rules/index.ts

@@ -22,6 +22,7 @@ import noDynamicDelete from './no-dynamic-delete';
 import noEmptyFunction from './no-empty-function';
 import noEmptyInterface from './no-empty-interface';
 import noExplicitAny from './no-explicit-any';
+import noExtraNonNullAssertion from './no-extra-non-null-assertion';
 import noExtraParens from './no-extra-parens';
 import noExtraneousClass from './no-extraneous-class';
 import noFloatingPromises from './no-floating-promises';
@@ -93,6 +94,7 @@ export default {
   'no-empty-function': noEmptyFunction,
   'no-empty-interface': noEmptyInterface,
   'no-explicit-any': noExplicitAny,
+  'no-extra-non-null-assertion': noExtraNonNullAssertion,
   'no-extra-parens': noExtraParens,
   'no-extraneous-class': noExtraneousClass,
   'no-floating-promises': noFloatingPromises,

packages/eslint-plugin/src/rules/no-extra-non-null-assertion.ts

@@ -0,0 +1,25 @@
+import * as util from '../util';
+
+export default util.createRule({
+  name: 'no-extra-non-null-assertion',
+  meta: {
+    type: 'problem',
+    docs: {
+      description: 'Disallow extra non-null assertion',
+      category: 'Stylistic Issues',
+      recommended: false,
+    },
+    schema: [],
+    messages: {
+      noExtraNonNullAssertion: 'Forbidden extra non-null assertion.',
+    },
+  },
+  defaultOptions: [],
+  create(context) {
+    return {
+      'TSNonNullExpression > TSNonNullExpression'(node): void {
+        context.report({ messageId: 'noExtraNonNullAssertion', node });
+      },
+    };
+  },
+});

packages/eslint-plugin/tests/rules/no-extra-non-null-assertion.test.ts

@@ -0,0 +1,66 @@
+import rule from '../../src/rules/no-extra-non-null-assertion';
+import { RuleTester } from '../RuleTester';
+
+const ruleTester = new RuleTester({
+  parser: '@typescript-eslint/parser',
+});
+
+ruleTester.run('no-extra-non-null-assertion', rule, {
+  valid: [
+    {
+      code: `
+const foo: { bar: number } | null = null;
+const bar = foo!.bar;
+      `,
+    },
+    {
+      code: `
+function foo(bar: number | undefined) {
+  const bar: number = bar!;
+}      `,
+    },
+  ],
+  invalid: [
+    {
+      code: `
+const foo: { bar: number } | null = null;
+const bar = foo!!!!.bar;
+      `,
+      errors: [
+        {
+          messageId: 'noExtraNonNullAssertion',
+          endColumn: 19,
+          column: 13,
+          line: 3,
+        },
+        {
+          messageId: 'noExtraNonNullAssertion',
+          endColumn: 18,
+          column: 13,
+          line: 3,
+        },
+        {
+          messageId: 'noExtraNonNullAssertion',
+          endColumn: 17,
+          column: 13,
+          line: 3,
+        },
+      ],
+    },
+    {
+      code: `
+function foo(bar: number | undefined) {
+  const bar: number = bar!!;
+}
+      `,
+      errors: [
+        {
+          messageId: 'noExtraNonNullAssertion',
+          endColumn: 27,
+          column: 23,
+          line: 3,
+        },
+      ],
+    },
+  ],
+});