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feat: update docs, and config
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‎packages/eslint-plugin/docs/rules/ban-types.md

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@@ -31,17 +31,34 @@ class Foo<F = string> extends Bar<string> implements Baz<string> {
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## Options
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The banned type can either be a type name literal (`Foo`), a type name with generic parameter instantiations(s) (`Foo<Bar>`), or the empty object literal (`{}`).
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```ts
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type Options = {
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types: {
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[typeName: string]:
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| string
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| {
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message: string;
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fixWith?: string;
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};
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};
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};
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```
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The rule accepts a single object as options, with the key `types`.
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```CJSON
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- The keys should match the types you want to ban. The type can either be a type name literal (`Foo`), a type name with generic parameter instantiations(s) (`Foo<Bar>`), or the empty object literal (`{}`).
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- The value can be an object with the following properties:
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- `message: string` - the message to display when the type is matched.
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- `fixWith?: string` - a string to replace the banned type with when the fixer is run. If this is omitted, no fix will be done.
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### Example config
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```JSONC
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{
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"@typescript-eslint/ban-types": ["error", {
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"types": {
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// report usages of the type using the default error message
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"Foo": null,
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// add a custom message to help explain why not to use it
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"Bar": "Don't use bar!",
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"Foo": "Don't use bar!",
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// add a custom message, AND tell the plugin how to fix it
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"String": {
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}
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```
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### Example
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### Default Options
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```json
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{
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"@typescript-eslint/ban-types": [
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"error",
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{
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"types": {
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"Array": null,
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"Object": "Use {} instead",
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"String": {
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"message": "Use string instead",
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"fixWith": "string"
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}
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}
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}
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]
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}
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```
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The default options provides a set of "best practices", intended to provide safety and standardization in your codebase:
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- Don't use the upper case primitive types, you should use the lower-case types for consistency.
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- Avoid the `Function` type, as it provides little safety for the following reasons:
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- It provides no type-safety when calling the value, which means it's easy to provide the wrong arguments.
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- It accepts class declarations, which will fail when called, as they are called without the `new` keyword.
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- Avoid the `Object` and `{}` types, as they means "any non-nullish value".
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- This is a point of confusion for many developers, who think it means "any object type".
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- Avoid the `object`, as it is currently hard to use due to not being able to assert that keys exist.
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- See [microsoft/TypeScript#21732](https://github.com/microsoft/TypeScript/issues/21732).
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**_Important note:_** the default options suggests using `Record<string, unknown>`; this was a stylistic decision, as the built-in `Record` type is considered to look cleaner.
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## Compatibility
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‎packages/eslint-plugin/src/rules/ban-types.ts

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defaultOptions: [
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{
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types: {
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// use lower-case instead
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String: {
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message: 'Use string instead',
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fixWith: 'string',
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message: 'Use number instead',
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fixWith: 'number',
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},
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Object: {
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message:
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'The Object type is mostly the same as unknown, you probably want Record<string, unknown> instead'
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},
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object: {
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message:
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'The object type is hard to use, use Record<string, unknown> instead',
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fixWith: 'Record<string, unknown>'
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},
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Symbol: {
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message: 'Use symbol instead',
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fixWith: 'symbol',
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},
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Function: {
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message: [
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'The `Function` type accepts any function-like value.',
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'It provides no type-safety when calling the function, which can be a common source of bugs.',
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'It also accepts things like class declarations, which will throw at runtime as they will not be called with `new`.',
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'If you are expecting the function to accept certain arguments, you should explicitly define function shape.',
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].join('\n'),
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},
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// object typing
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Object: {
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message: [
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'The `Object` type actually means "any non-nullish value", so it is marginally better than `unknown`.',
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'- If you want a type meaning "any object", you probably want `Record<string, unknown>` instead.',
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'- If you want a type meaning "any value", you probably want `unknown` instead.',
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].join('\n'),
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},
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'{}': {
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message: [
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'`{}` actually means "any non-nullish value".',
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'- If you want a type meaning "any object", you probably want `Record<string, unknown>` instead.',
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'- If you want a type meaning "any value", you probably want `unknown` instead.',
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].join('\n'),
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},
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object: {
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message: [
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'The `object` type is currently hard to use (see https://github.com/microsoft/TypeScript/issues/21732).',
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'Consider using `Record<string, unknown>` instead, as it allows you to more easily inspect and use the keys.',
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].join('\n'),
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},
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},
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},
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],

‎packages/eslint-plugin/tests/rules/ban-types.test.ts

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ruleTester.run('ban-types', rule, {
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valid: [
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'let f = Object();', // Should not fail if there is no options set
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'let f: {} = {};',
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'let f = Object();', // Should not fail, as it is not a type position
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'let f: { x: number, y: number } = { x: 1, y: 1 };',
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{
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code: 'let f = Object();',

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