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Rebecca Stevens
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Merge pull request #29 from jonaskello/rule/prefer-readonly-types
prefer-readonly-types
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‎.eslintrc

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@@ -34,8 +34,10 @@
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// Our rules.
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"ts-immutable/immutable-data": "error",
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"ts-immutable/no-let": "error",
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"ts-immutable/readonly-array": ["error", { "ignoreReturnType": true }],
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"ts-immutable/readonly-keyword": "error",
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"ts-immutable/prefer-readonly-types": [
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"error",
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{ "ignoreReturnType": true }
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],
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"ts-immutable/no-method-signature": "error",
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"ts-immutable/no-this": "error",
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"ts-immutable/no-class": "error",

‎README.md

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@@ -99,13 +99,12 @@ In addition to immutable rules this project also contains a few rules for enforc
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### Immutability rules
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| Name | Description | <span title="Recommended">:see_no_evil:</span> | <span title="Functional Lite">:hear_no_evil:</span> | <span title="Functional">:speak_no_evil:</span> | :wrench: | :blue_heart: |
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| ------------------------------------------------------------ | -------------------------------------------------------------------------- | :--------------------------------------------: | :-------------------------------------------------: | :---------------------------------------------: | :------: | :---------------: |
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| [`readonly-keyword`](./docs/rules/readonly-keyword.md) | Enforce readonly modifiers are used where possible | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: | :wrench: | :thought_balloon: |
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| [`readonly-array`](./docs/rules/readonly-array.md) | Enforce readonly array over mutable arrays | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: | :wrench: | :thought_balloon: |
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| [`no-let`](./docs/rules/no-let.md) | Disallow mutable variables | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: | | |
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| [`immutable-data`](./docs/rules/immutable-data.md) | Disallow mutating objects and arrays | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: | | :blue_heart: |
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| [`no-method-signature`](./docs/rules/no-method-signature.md) | Enforce property signatures with readonly modifiers over method signatures | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: | | :thought_balloon: |
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| Name | Description | <span title="Recommended">:see_no_evil:</span> | <span title="Functional Lite">:hear_no_evil:</span> | <span title="Functional">:speak_no_evil:</span> | :wrench: | :blue_heart: |
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| ---------------------------------------------------------------- | -------------------------------------------------------------------------- | :--------------------------------------------: | :-------------------------------------------------: | :---------------------------------------------: | :------: | :---------------: |
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| [`prefer-readonly-types`](./docs/rules/prefer-readonly-types.md) | Use readonly types and readonly modifiers where possible | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: | :wrench: | :thought_balloon: |
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| [`no-let`](./docs/rules/no-let.md) | Disallow mutable variables | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: | | |
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| [`immutable-data`](./docs/rules/immutable-data.md) | Disallow mutating objects and arrays | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: | | :blue_heart: |
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| [`no-method-signature`](./docs/rules/no-method-signature.md) | Enforce property signatures with readonly modifiers over method signatures | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: | | :thought_balloon: |
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### Functional style rules
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‎docs/rules/readonly-keyword.md renamed to ‎docs/rules/prefer-readonly-types.md

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@@ -1,10 +1,14 @@
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# Enforce readonly modifiers are used where possible (readonly-keyword)
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# Prefer readonly types over mutable types (prefer-readonly-types)
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This rule enforces use of the `readonly` modifier. The `readonly` modifier can appear on property signatures in interfaces, property declarations in classes, and index signatures.
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This rule enforces use of the readonly modifier and readonly types.
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## Rule Details
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Below is some information about the `readonly` modifier and the benefits of using it:
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This rule enforces use of `readonly T[]` (`ReadonlyArray<T>`) over `T[]` (`Array<T>`).
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The readonly modifier must appear on property signatures in interfaces, property declarations in classes, and index signatures.
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### Benefits of using the `readonly` modifier
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You might think that using `const` would eliminate mutation from your TypeScript code. **Wrong.** Turns out that there's a pretty big loophole in `const`.
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@@ -52,25 +56,66 @@ const foo: { readonly [key: string]: number } = { a: 1, b: 2 };
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foo["a"] = 3; // Error: Index signature only permits reading
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```
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### Benefits of using `readonly T[]`
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Even if an array is declared with `const` it is still possible to mutate the contents of the array.
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```typescript
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interface Point {
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readonly x: number;
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readonly y: number;
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}
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const points: Array<Point> = [{ x: 23, y: 44 }];
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points.push({ x: 1, y: 2 }); // This is legal
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```
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Using the `ReadonlyArray<T>` type or `readonly T[]` will stop this mutation:
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```typescript
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interface Point {
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readonly x: number;
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readonly y: number;
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}
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const points: ReadonlyArray<Point> = [{ x: 23, y: 44 }];
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// const points: readonly Point[] = [{ x: 23, y: 44 }]; // This is the alternative syntax for the line above
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points.push({ x: 1, y: 2 }); // Unresolved method push()
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```
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## Options
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The rule accepts an options object with the following properties:
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```typescript
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type Options = {
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readonly checkImplicit: boolean
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readonly ignoreClass?: boolean;
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readonly ignoreInterface?: boolean;
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readonly ignoreLocal?: boolean;
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readonly ignorePattern?: string | Array<string>;
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readonly ignoreReturnType?: boolean;
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};
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const defaults = {
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checkImplicit: false,
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ignoreClass: false,
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ignoreInterface: false,
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ignoreLocal: false
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ignoreLocal: false,
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ignoreReturnType: false
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};
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```
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### `checkImplicit`
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By default, this function only checks explicit types. Enabling this option will make the rule also check implicit types.
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Note: Checking implicit types is more expensive (slow).
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### `ignoreReturnType`
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Doesn't check the return type of functions.
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### `ignoreClass`
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A boolean to specify if checking for `readonly` should apply to classes. `false` by default.

‎docs/rules/readonly-array.md

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This file was deleted.

‎src/configs/all.ts

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@@ -17,8 +17,7 @@ const config = {
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rules: {
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"ts-immutable/no-method-signature": "error",
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"ts-immutable/no-mixed-interface": "error",
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"ts-immutable/readonly-array": "error",
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"ts-immutable/readonly-keyword": "error"
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"ts-immutable/prefer-readonly-types": "error"
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}
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}
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]

‎src/configs/immutable.ts

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@@ -14,8 +14,7 @@ const config = deepMerge([
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files: ["*.ts", "*.tsx"],
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rules: {
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"ts-immutable/no-method-signature": "warn",
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"ts-immutable/readonly-array": "error",
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"ts-immutable/readonly-keyword": "error"
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"ts-immutable/prefer-readonly-types": "error"
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}
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}
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]

‎src/rules/index.ts

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@@ -37,13 +37,9 @@ import { name as noThisRuleName, rule as noThisRule } from "./no-this";
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import { name as noThrowRuleName, rule as noThrowRule } from "./no-throw";
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import { name as noTryRuleName, rule as noTryRule } from "./no-try";
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import {
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name as readonlyArrayRuleName,
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rule as readonlyArrayRule
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} from "./readonly-array";
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import {
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name as readonlyKeywordRuleName,
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rule as readonlyKeywordRule
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} from "./readonly-keyword";
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name as preferReadonlyTypesRuleName,
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rule as preferReadonlyTypesRule
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} from "./prefer-readonly-types";
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/**
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* All of the custom rules.
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[noThisRuleName]: noThisRule,
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[noThrowRuleName]: noThrowRule,
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[noTryRuleName]: noTryRule,
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[readonlyArrayRuleName]: readonlyArrayRule,
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[readonlyKeywordRuleName]: readonlyKeywordRule
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[preferReadonlyTypesRuleName]: preferReadonlyTypesRule
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};

‎src/rules/readonly-array.ts renamed to ‎src/rules/prefer-readonly-types.ts

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isFunctionLike,
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isIdentifier,
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isTSArrayType,
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isTSIndexSignature,
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isTSParameterProperty,
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isTSTupleType,
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isTSTypeOperator
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} from "../util/typeguard";
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// The name of this rule.
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export const name = "readonly-array" as const;
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export const name = "prefer-readonly-types" as const;
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// The options this rule can take.
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type Options = ignore.IgnoreLocalOption &
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ignore.IgnorePatternOption &
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ignore.IgnoreClassOption &
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ignore.IgnoreInterfaceOption &
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ignore.IgnoreReturnTypeOption & {
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readonly checkImplicit: boolean;
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};
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deepMerge([
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ignore.ignoreLocalOptionSchema,
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ignore.ignorePatternOptionSchema,
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ignore.ignoreClassOptionSchema,
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ignore.ignoreInterfaceOptionSchema,
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ignore.ignoreReturnTypeOptionSchema,
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{
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type: "object",
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// The default options for the rule.
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const defaultOptions: Options = {
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checkImplicit: false,
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ignoreClass: false,
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ignoreInterface: false,
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ignoreLocal: false,
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ignoreReturnType: false,
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checkImplicit: false
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ignoreReturnType: false
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};
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// The possible error messages.
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const errorMessages = {
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generic: "Only readonly arrays allowed.",
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implicit: "Implicitly a mutable array. Only readonly arrays allowed."
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array: "Only readonly arrays allowed.",
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tuple: "Only readonly tuples allowed.",
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implicit: "Implicitly a mutable array. Only readonly arrays allowed.",
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property: "A readonly modifier is required."
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} as const;
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// The meta data for this rule.
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? [
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{
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node,
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messageId: "generic",
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messageId: isTSTupleType(node) ? "tuple" : "array",
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fix:
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node.parent && isTSArrayType(node.parent)
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? fixer => [
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? [
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{
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node,
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messageId: "generic",
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messageId: "array",
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fix: fixer => fixer.insertTextBefore(node, "Readonly")
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}
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]
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: []
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};
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}
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149+
/**
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* Check if the given property/signature node violates this rule.
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*/
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function checkProperty(
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node:
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| TSESTree.ClassProperty
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| TSESTree.TSIndexSignature
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| TSESTree.TSParameterProperty
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| TSESTree.TSPropertySignature,
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context: RuleContext<keyof typeof errorMessages, Options>
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): RuleResult<keyof typeof errorMessages, Options> {
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return {
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context,
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descriptors: node.readonly
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? []
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: [
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{
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node,
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messageId: "property",
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fix: isTSIndexSignature(node)
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? fixer => fixer.insertTextBefore(node, "readonly ")
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: isTSParameterProperty(node)
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? fixer => fixer.insertTextBefore(node.parameter, "readonly ")
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: fixer => fixer.insertTextBefore(node.key, "readonly ")
173+
}
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]
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};
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}
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/**
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* Check if the given TypeReference violates this rule.
140180
*/
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options
204244
);
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const _checkTypeReference = checkNode(checkTypeReference, context, options);
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const _checkProperty = checkNode(checkProperty, context, options);
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const _checkImplicitType = checkNode(checkImplicitType, context, options);
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208249
return {
209250
TSArrayType: _checkArrayOrTupleType,
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TSTupleType: _checkArrayOrTupleType,
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TSTypeReference: _checkTypeReference,
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ClassProperty: _checkProperty,
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TSIndexSignature: _checkProperty,
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TSParameterProperty: _checkProperty,
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TSPropertySignature: _checkProperty,
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...(options.checkImplicit
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? {
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VariableDeclaration: _checkImplicitType,

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