114 lines
3.1 KiB
Plaintext
114 lines
3.1 KiB
Plaintext
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---
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description: 'Disallow returning a value with type `any` from a function.'
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---
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> 🛑 This file is source code, not the primary documentation location! 🛑
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>
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> See **https://typescript-eslint.io/rules/no-unsafe-return** for documentation.
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The `any` type in TypeScript is a dangerous "escape hatch" from the type system.
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Using `any` disables many type checking rules and is generally best used only as a last resort or when prototyping code.
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Despite your best intentions, the `any` type can sometimes leak into your codebase.
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Returning an an `any`-typed value from a function creates a potential type safety hole and source of bugs in your codebase.
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This rule disallows returning `any` or `any[]` from a function.
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This rule also compares generic type argument types to ensure you don't return an unsafe `any` in a generic position to a function that's expecting a specific type.
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For example, it will error if you return `Set<any>` from a function declared as returning `Set<string>`.
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## Examples
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<!--tabs-->
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### ❌ Incorrect
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```ts
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function foo1() {
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return 1 as any;
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}
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function foo2() {
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return Object.create(null);
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}
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const foo3 = () => {
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return 1 as any;
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};
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const foo4 = () => Object.create(null);
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function foo5() {
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return [] as any[];
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}
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function foo6() {
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return [] as Array<any>;
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}
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function foo7() {
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return [] as readonly any[];
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}
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function foo8() {
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return [] as Readonly<any[]>;
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}
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const foo9 = () => {
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return [] as any[];
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};
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const foo10 = () => [] as any[];
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const foo11 = (): string[] => [1, 2, 3] as any[];
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// generic position examples
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function assignability1(): Set<string> {
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return new Set<any>([1]);
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}
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type TAssign = () => Set<string>;
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const assignability2: TAssign = () => new Set<any>([true]);
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```
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### ✅ Correct
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```ts
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function foo1() {
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return 1;
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}
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function foo2() {
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return Object.create(null) as Record<string, unknown>;
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}
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const foo3 = () => [];
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const foo4 = () => ['a'];
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function assignability1(): Set<string> {
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return new Set<string>(['foo']);
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}
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type TAssign = () => Set<string>;
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const assignability2: TAssign = () => new Set(['foo']);
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```
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<!--/tabs-->
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There are cases where the rule allows to return `any` to `unknown`.
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Examples of `any` to `unknown` return that are allowed:
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```ts showPlaygroundButton
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function foo1(): unknown {
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return JSON.parse(singleObjString); // Return type for JSON.parse is any.
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}
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function foo2(): unknown[] {
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return [] as any[];
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}
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```
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## When Not To Use It
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If your codebase has many existing `any`s or areas of unsafe code, it may be difficult to enable this rule.
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It may be easier to skip the `no-unsafe-*` rules pending increasing type safety in unsafe areas of your project.
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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.
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## Related To
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- [`no-explicit-any`](./no-explicit-any.md)
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- [`no-unsafe-argument`](./no-unsafe-argument.md)
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- [`no-unsafe-assignment`](./no-unsafe-assignment.md)
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- [`no-unsafe-call`](./no-unsafe-call.md)
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- [`no-unsafe-member-access`](./no-unsafe-member-access.md)
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