typescript-eslint · JoshuaKGoldberg · Nov 11, 2024 · Oct 22, 2024 · Nov 4, 2024 · Nov 4, 2024
diff --git a/packages/eslint-plugin/docs/rules/related-getter-setter-pairs.mdx b/packages/eslint-plugin/docs/rules/related-getter-setter-pairs.mdx
@@ -0,0 +1,61 @@
+---
+description: 'Enforce that `get()` types should be assignable to their equivalent `set()` type.'
+---
+
+import Tabs from '@theme/Tabs';
+import TabItem from '@theme/TabItem';
+
+> 🛑 This file is source code, not the primary documentation location! 🛑
+>
+> See **https://typescript-eslint.io/rules/related-getter-setter-pairs** for documentation.
+
+TypeScript allows defining different types for a `get` parameter and its corresponding `set` return.
+Prior to TypeScript 4.3, the types had to be identical.
+From TypeScript 4.3 to 5.0, the `get` type had to be a subtype of the `set` type.
+As of TypeScript 5.1, the types may be completely unrelated as long as there is an explicit type annotation.
+
+Defining drastically different types for a `get` and `set` pair can be confusing.
+It means that assigning a property to itself would not work:
+
+```ts
+// Assumes box.value's get() return is assignable to its set() parameter
+box.value = box.value;
+```
+
+This rule reports cases where a `get()` and `set()` have the same name, but the `get()`'s type is not assignable to the `set()`'s.
+
+## Examples
+
+<Tabs>
+<TabItem value="❌ Incorrect">
+
+```ts
+interface Box {
+  get value(): string;
+  set value(newValue: number);
+}
+```
+
+</TabItem>
+<TabItem value="✅ Correct">
+
+```ts
+interface Box {
+  get value(): string;
+  set value(newValue: string);
+}
+```
+
+</TabItem>
+</Tabs>
+
+## When Not To Use It
+
+If your project needs to model unusual relationships between data, such as older DOM types, this rule may not be useful for you.
+You might consider using [ESLint disable comments](https://eslint.org/docs/latest/use/configure/rules#using-configuration-comments-1) for those specific situations instead of completely disabling this rule.
+
+## Further Reading
+
+- [MDN documentation on `get`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/get)
+- [MDN documentation on `set`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/set)
+- [TypeScript 5.1 Release Notes > Unrelated Types for Getters and Setters](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-5-1.html#unrelated-types-for-getters-and-setters)
diff --git a/packages/eslint-plugin/src/configs/all.ts b/packages/eslint-plugin/src/configs/all.ts
@@ -142,6 +142,7 @@ export = {
     '@typescript-eslint/prefer-return-this-type': 'error',
     '@typescript-eslint/prefer-string-starts-ends-with': 'error',
     '@typescript-eslint/promise-function-async': 'error',
+    '@typescript-eslint/related-getter-setter-pairs': 'error',
     '@typescript-eslint/require-array-sort-compare': 'error',
     'require-await': 'off',
     '@typescript-eslint/require-await': 'error',

diff --git a/packages/eslint-plugin/src/configs/disable-type-checked.ts b/packages/eslint-plugin/src/configs/disable-type-checked.ts
@@ -56,6 +56,7 @@ export = {
     '@typescript-eslint/prefer-return-this-type': 'off',
     '@typescript-eslint/prefer-string-starts-ends-with': 'off',
     '@typescript-eslint/promise-function-async': 'off',
+    '@typescript-eslint/related-getter-setter-pairs': 'off',
     '@typescript-eslint/require-array-sort-compare': 'off',
     '@typescript-eslint/require-await': 'off',
     '@typescript-eslint/restrict-plus-operands': 'off',

diff --git a/packages/eslint-plugin/src/configs/strict-type-checked-only.ts b/packages/eslint-plugin/src/configs/strict-type-checked-only.ts
@@ -43,6 +43,7 @@ export = {
     '@typescript-eslint/prefer-promise-reject-errors': 'error',
     '@typescript-eslint/prefer-reduce-type-parameter': 'error',
     '@typescript-eslint/prefer-return-this-type': 'error',
+    '@typescript-eslint/related-getter-setter-pairs': 'error',
     'require-await': 'off',
     '@typescript-eslint/require-await': 'error',
     '@typescript-eslint/restrict-plus-operands': [

diff --git a/packages/eslint-plugin/src/configs/strict-type-checked.ts b/packages/eslint-plugin/src/configs/strict-type-checked.ts
@@ -76,6 +76,7 @@ export = {
     '@typescript-eslint/prefer-promise-reject-errors': 'error',
     '@typescript-eslint/prefer-reduce-type-parameter': 'error',
     '@typescript-eslint/prefer-return-this-type': 'error',
+    '@typescript-eslint/related-getter-setter-pairs': 'error',
     'require-await': 'off',
     '@typescript-eslint/require-await': 'error',
     '@typescript-eslint/restrict-plus-operands': [
@@ -93,10 +94,10 @@ export = {
       {
         allowAny: false,
         allowBoolean: false,
+        allowNever: false,
         allowNullish: false,
         allowNumber: false,
         allowRegExp: false,
-        allowNever: false,
       },
     ],
     'no-return-await': 'off',

diff --git a/packages/eslint-plugin/src/rules/index.ts b/packages/eslint-plugin/src/rules/index.ts
@@ -114,6 +114,7 @@ import preferReturnThisType from './prefer-return-this-type';
 import preferStringStartsEndsWith from './prefer-string-starts-ends-with';
 import preferTsExpectError from './prefer-ts-expect-error';
 import promiseFunctionAsync from './promise-function-async';
+import relatedGetterSetterPairs from './related-getter-setter-pairs';
 import requireArraySortCompare from './require-array-sort-compare';
 import requireAwait from './require-await';
 import restrictPlusOperands from './restrict-plus-operands';
@@ -244,6 +245,7 @@ const rules = {
   'prefer-string-starts-ends-with': preferStringStartsEndsWith,
   'prefer-ts-expect-error': preferTsExpectError,
   'promise-function-async': promiseFunctionAsync,
+  'related-getter-setter-pairs': relatedGetterSetterPairs,
   'require-array-sort-compare': requireArraySortCompare,
   'require-await': requireAwait,
   'restrict-plus-operands': restrictPlusOperands,

diff --git a/packages/eslint-plugin/src/rules/related-getter-setter-pairs.ts b/packages/eslint-plugin/src/rules/related-getter-setter-pairs.ts
@@ -0,0 +1,113 @@
+import type { TSESTree } from '@typescript-eslint/utils';
+
+import { AST_NODE_TYPES } from '@typescript-eslint/utils';
+
+import { createRule, getNameFromMember, getParserServices } from '../util';
+
+type Method = TSESTree.MethodDefinition | TSESTree.TSMethodSignature;
+
+type GetMethod = {
+  kind: 'get';
+  returnType: TSESTree.TSTypeAnnotation;
+} & Method;
+
+type GetMethodRaw = {
+  returnType: TSESTree.TSTypeAnnotation | undefined;
+} & GetMethod;
+
+type SetMethod = { kind: 'set'; params: [TSESTree.Node] } & Method;
+
+interface MethodPair {
+  get?: GetMethod;
+  set?: SetMethod;
+}
+
+export default createRule({
+  name: 'related-getter-setter-pairs',
+  meta: {
+    type: 'problem',
+    docs: {
+      description:
+        'Enforce that `get()` types should be assignable to their equivalent `set()` type',
+      recommended: 'strict',
+      requiresTypeChecking: true,
+    },
+    messages: {
+      mismatch:
+        '`get()` type should be assignable to its equivalent `set()` type.',
+    },
+    schema: [],
+  },
+  defaultOptions: [],
+  create(context) {
+    const services = getParserServices(context);
+    const checker = services.program.getTypeChecker();
+    const methodPairsStack: Map<string, MethodPair>[] = [];
+
+    function addPropertyNode(
+      member: GetMethod | SetMethod,
+      inner: TSESTree.Node,
+      kind: 'get' | 'set',
+    ): void {
+      const methodPairs = methodPairsStack[methodPairsStack.length - 1];
+      const { name } = getNameFromMember(member, context.sourceCode);
+
+      methodPairs.set(name, {
+        ...methodPairs.get(name),
+        [kind]: inner,
+      });
+    }
+
+    return {
+      ':matches(ClassBody, TSInterfaceBody, TSTypeLiteral):exit'(): void {
+        const methodPairs = methodPairsStack[methodPairsStack.length - 1];
+
+        for (const pair of methodPairs.values()) {
+          if (!pair.get || !pair.set) {
+            continue;
+          }
+
+          const getter = pair.get;
+
+          const getType = services.getTypeAtLocation(getter);
+          const setType = services.getTypeAtLocation(pair.set.params[0]);
+
+          if (!checker.isTypeAssignableTo(getType, setType)) {
+            context.report({
+              node: getter.returnType.typeAnnotation,
+              messageId: 'mismatch',
+            });
+          }
+        }
+
+        methodPairsStack.pop();
+      },
+      ':matches(MethodDefinition, TSMethodSignature)[kind=get]'(
+        node: GetMethodRaw,
+      ): void {
+        const getter = getMethodFromNode(node);
+
+        if (getter.returnType) {
+          addPropertyNode(node, getter, 'get');
+        }
+      },
+      ':matches(MethodDefinition, TSMethodSignature)[kind=set]'(
+        node: SetMethod,
+      ): void {
+        const setter = getMethodFromNode(node);
+
+        if (setter.params.length === 1) {
+          addPropertyNode(node, setter, 'set');
+        }
+      },
+
+      'ClassBody, TSInterfaceBody, TSTypeLiteral'(): void {
+        methodPairsStack.push(new Map());
+      },
+    };
+  },
+});
+
+function getMethodFromNode(node: GetMethodRaw | SetMethod) {
+  return node.type === AST_NODE_TYPES.TSMethodSignature ? node : node.value;
+}
diff --git a/packages/eslint-plugin/tests/docs-eslint-output-snapshots/related-getter-setter-pairs.shot b/packages/eslint-plugin/tests/docs-eslint-output-snapshots/related-getter-setter-pairs.shot