typescript-eslint · bradzacher · Jan 18, 2020 · Jan 18, 2020 · Jan 18, 2020
diff --git a/packages/eslint-plugin/README.md b/packages/eslint-plugin/README.md
diff --git a/packages/eslint-plugin/docs/rules/no-non-null-asserted-optional-chain.md b/packages/eslint-plugin/docs/rules/no-non-null-asserted-optional-chain.md
@@ -0,0 +1,39 @@
+# Disallows using a non-null assertion after an optional chain expression (`no-non-null-asserted-optional-chain`)
+
+## Rule Details
+
+Optional chain expressions are designed to return `undefined` if the optional property is nullish.
+Using non-null assertions after an optional chain expression is wrong, and introduces a serious type safety hole into your code.
+
+Examples of **incorrect** code for this rule:
+
+```ts
+/* eslint @typescript-eslint/no-non-null-asserted-optional-chain: "error" */
+
+foo?.bar!;
+foo?.bar!.baz;
+foo?.bar()!;
+foo?.bar!();
+foo?.bar!().baz;
+```
+
+Examples of **correct** code for this rule:
+
+```ts
+/* eslint @typescript-eslint/no-non-null-asserted-optional-chain: "error" */
+
+foo?.bar;
+(foo?.bar).baz;
+foo?.bar();
+foo?.bar();
+foo?.bar().baz;
+```
+
+## When Not To Use It
+
+If you are not using TypeScript 3.7 (or greater), then you will not need to use this rule, as the operator is not supported.
+
+## Further Reading
+
+- [TypeScript 3.7 Release Notes](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html)
+- [Optional Chaining Proposal](https://github.com/tc39/proposal-optional-chaining/)
diff --git a/packages/eslint-plugin/src/configs/all.json b/packages/eslint-plugin/src/configs/all.json
@@ -44,6 +44,7 @@
     "@typescript-eslint/no-misused-new": "error",
     "@typescript-eslint/no-misused-promises": "error",
     "@typescript-eslint/no-namespace": "error",
+    "@typescript-eslint/no-non-null-asserted-optional-chain": "error",
     "@typescript-eslint/no-non-null-assertion": "error",
     "@typescript-eslint/no-parameter-properties": "error",
     "@typescript-eslint/no-require-imports": "error",

diff --git a/packages/eslint-plugin/src/rules/index.ts b/packages/eslint-plugin/src/rules/index.ts
@@ -38,6 +38,7 @@ import noMisusedNew from './no-misused-new';
 import noMisusedPromises from './no-misused-promises';
 import noNamespace from './no-namespace';
 import noNonNullAssertion from './no-non-null-assertion';
+import noNonNullAssertedOptionalChain from './no-non-null-asserted-optional-chain';
 import noParameterProperties from './no-parameter-properties';
 import noRequireImports from './no-require-imports';
 import noThisAlias from './no-this-alias';
@@ -120,6 +121,7 @@ export default {
   'no-misused-promises': noMisusedPromises,
   'no-namespace': noNamespace,
   'no-non-null-assertion': noNonNullAssertion,
+  'no-non-null-asserted-optional-chain': noNonNullAssertedOptionalChain,
   'no-parameter-properties': noParameterProperties,
   'no-require-imports': noRequireImports,
   'no-this-alias': noThisAlias,

diff --git a/packages/eslint-plugin/src/rules/no-non-null-asserted-optional-chain.ts b/packages/eslint-plugin/src/rules/no-non-null-asserted-optional-chain.ts
@@ -0,0 +1,52 @@
+import { TSESTree, TSESLint } from '@typescript-eslint/experimental-utils';
+import * as util from '../util';
+
+type MessageIds = 'noNonNullOptionalChain' | 'suggestRemovingNonNull';
+
+export default util.createRule<[], MessageIds>({
+  name: 'no-non-null-asserted-optional-chain',
+  meta: {
+    type: 'problem',
+    docs: {
+      description:
+        'Disallows using a non-null assertion after an optional chain expression',
+      category: 'Possible Errors',
+      recommended: false,
+    },
+    messages: {
+      noNonNullOptionalChain:
+        'Optional chain expressions can return undefined by design - using a non-null assertion is unsafe and wrong.',
+      suggestRemovingNonNull: 'You should remove the non-null assertion.',
+    },
+    schema: [],
+  },
+  defaultOptions: [],
+  create(context) {
+    return {
+      'TSNonNullExpression > :matches(OptionalMemberExpression, OptionalCallExpression)'(
+        node:
+          | TSESTree.OptionalCallExpression
+          | TSESTree.OptionalMemberExpression,
+      ): void {
+        // selector guarantees this assertion
+        const parent = node.parent as TSESTree.TSNonNullExpression;
+        context.report({
+          node,
+          messageId: 'noNonNullOptionalChain',
+          // use a suggestion instead of a fixer, because this can obviously break type checks
+          suggest: [
+            {
+              messageId: 'suggestRemovingNonNull',
+              fix(fixer): TSESLint.RuleFix {
+                return fixer.removeRange([
+                  parent.range[1] - 1,
+                  parent.range[1],
+                ]);
+              },
+            },
+          ],
+        });
+      },
+    };
+  },
+});
diff --git a/packages/eslint-plugin/tests/rules/no-non-null-asserted-optional-chain.test.ts b/packages/eslint-plugin/tests/rules/no-non-null-asserted-optional-chain.test.ts
@@ -0,0 +1,187 @@
+import rule from '../../src/rules/no-non-null-asserted-optional-chain';
+import { RuleTester } from '../RuleTester';
+
+const ruleTester = new RuleTester({
+  parser: '@typescript-eslint/parser',
+});
+
+ruleTester.run('no-non-null-asserted-optional-chain', rule, {
+  valid: [
+    'foo.bar!',
+    'foo.bar()!',
+    'foo?.bar',
+    'foo?.bar()',
+    '(foo?.bar).baz!',
+    '(foo?.bar()).baz!',
+  ],
+  invalid: [
+    {
+      code: 'foo?.bar!',
+      errors: [
+        {
+          messageId: 'noNonNullOptionalChain',
+          suggestions: [
+            {
+              messageId: 'suggestRemovingNonNull',
+              output: 'foo?.bar',
+            },
+          ],
+        },
+      ],
+    },
+    {
+      code: 'foo?.["bar"]!',
+      errors: [
+        {
+          messageId: 'noNonNullOptionalChain',
+          suggestions: [
+            {
+              messageId: 'suggestRemovingNonNull',
+              output: 'foo?.["bar"]',
+            },
+          ],
+        },
+      ],
+    },
+    {
+      code: 'foo?.bar()!',
+      errors: [
+        {
+          messageId: 'noNonNullOptionalChain',
+          suggestions: [
+            {
+              messageId: 'suggestRemovingNonNull',
+              output: 'foo?.bar()',
+            },
+          ],
+        },
+      ],
+    },
+    {
+      code: 'foo.bar?.()!',
+      errors: [
+        {
+          messageId: 'noNonNullOptionalChain',
+          suggestions: [
+            {
+              messageId: 'suggestRemovingNonNull',
+              output: 'foo.bar?.()',
+            },
+          ],
+        },
+      ],
+    },
+    {
+      code: 'foo?.bar!()',
+      errors: [
+        {
+          messageId: 'noNonNullOptionalChain',
+          suggestions: [
+            {
+              messageId: 'suggestRemovingNonNull',
+              output: 'foo?.bar()',
+            },
+          ],
+        },
+      ],
+    },
+    {
+      code: '(foo?.bar)!.baz',
+      errors: [
+        {
+          messageId: 'noNonNullOptionalChain',
+          suggestions: [
+            {
+              messageId: 'suggestRemovingNonNull',
+              output: '(foo?.bar).baz',
+            },
+          ],
+        },
+      ],
+    },
+    {
+      code: 'foo?.["bar"]!.baz',
+      errors: [
+        {
+          messageId: 'noNonNullOptionalChain',
+          suggestions: [
+            {
+              messageId: 'suggestRemovingNonNull',
+              output: 'foo?.["bar"].baz',
+            },
+          ],
+        },
+      ],
+    },
+    {
+      code: '(foo?.bar)!().baz',
+      errors: [
+        {
+          messageId: 'noNonNullOptionalChain',
+          suggestions: [
+            {
+              messageId: 'suggestRemovingNonNull',
+              output: '(foo?.bar)().baz',
+            },
+          ],
+        },
+      ],
+    },
+    {
+      code: '(foo?.bar)!',
+      errors: [
+        {
+          messageId: 'noNonNullOptionalChain',
+          suggestions: [
+            {
+              messageId: 'suggestRemovingNonNull',
+              output: '(foo?.bar)',
+            },
+          ],
+        },
+      ],
+    },
+    {
+      code: '(foo?.bar)!()',
+      errors: [
+        {
+          messageId: 'noNonNullOptionalChain',
+          suggestions: [
+            {
+              messageId: 'suggestRemovingNonNull',
+              output: '(foo?.bar)()',
+            },
+          ],
+        },
+      ],
+    },
+    {
+      code: '(foo?.bar!)',
+      errors: [
+        {
+          messageId: 'noNonNullOptionalChain',
+          suggestions: [
+            {
+              messageId: 'suggestRemovingNonNull',
+              output: '(foo?.bar)',
+            },
+          ],
+        },
+      ],
+    },
+    {
+      code: '(foo?.bar!)()',
+      errors: [
+        {
+          messageId: 'noNonNullOptionalChain',
+          suggestions: [
+            {
+              messageId: 'suggestRemovingNonNull',
+              output: '(foo?.bar)()',
+            },
+          ],
+        },
+      ],
+    },
+  ],
+});
diff --git a/packages/eslint-plugin/tools/generate-configs.ts b/packages/eslint-plugin/tools/generate-configs.ts
@@ -19,7 +19,10 @@ interface LinterConfig extends TSESLint.Linter.Config {
 }
 
 const RULE_NAME_PREFIX = '@typescript-eslint/';
-const MAX_RULE_NAME_LENGTH = 32;
+const MAX_RULE_NAME_LENGTH = Object.keys(rules).reduce(
+  (acc, name) => Math.max(acc, name.length),
+  0,
+);
 const DEFAULT_RULE_SETTING = 'warn';
 const BASE_RULES_TO_BE_OVERRIDDEN = new Map(
   Object.entries(rules)