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feat(eslint-plugin): add default-param-last rule
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# Enforce default parameters to be last (`default-param-last`) | ||
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## Rule Details | ||
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This rule enforces default or optional parameters to be the last of parameters. | ||
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Examples of **incorrect** code for this rule: | ||
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```ts | ||
/* eslint @typescript-eslint/default-param-last: ["error"] */ | ||
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function f(a = 0, b: number) {} | ||
function f(a: number, b = 0, c: number) {} | ||
function f(a: number, b?: number, c: number) {} | ||
``` | ||
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Examples of **correct** code for this rule: | ||
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```ts | ||
/* eslint @typescript-eslint/default-param-last: ["error"] */ | ||
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function f(a: number, b = 0) {} | ||
function f(a: number, b?: number) {} | ||
function f(a: number, b?: number, c = 0) {} | ||
``` | ||
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<sup>Taken with ❤️ [from ESLint core](https://github.com/eslint/eslint/blob/master/docs/rules/default-param-last.md)</sup> |
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import { createRule } from '../util'; | ||
import { | ||
TSESTree, | ||
AST_NODE_TYPES, | ||
} from '@typescript-eslint/experimental-utils'; | ||
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export default createRule({ | ||
name: 'default-param-last', | ||
meta: { | ||
type: 'suggestion', | ||
docs: { | ||
description: 'Enforce default parameters to be last', | ||
category: 'Best Practices', | ||
recommended: false, | ||
}, | ||
schema: [], | ||
messages: { | ||
shouldBeLast: 'Default parameters should be last.', | ||
}, | ||
}, | ||
defaultOptions: [], | ||
create(context) { | ||
/** | ||
* checks if node is optional parameter | ||
* @param {ASTNode} node node to evaluate | ||
* @returns {boolean} | ||
* @private | ||
*/ | ||
function isOptionalParam(node: TSESTree.Node): boolean { | ||
return node.type === AST_NODE_TYPES.Identifier && node.optional === true; | ||
} | ||
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/** | ||
* checks if node is plain parameter | ||
* @param {ASTNode} node node to evaluate | ||
* @returns {boolean} | ||
* @private | ||
*/ | ||
function isPlainParam(node: TSESTree.Node): boolean { | ||
return !( | ||
node.type === AST_NODE_TYPES.AssignmentPattern || | ||
node.type === AST_NODE_TYPES.RestElement || | ||
isOptionalParam(node) | ||
); | ||
} | ||
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function checkDefaultParamLast( | ||
node: | ||
| TSESTree.ArrowFunctionExpression | ||
| TSESTree.FunctionDeclaration | ||
| TSESTree.FunctionExpression, | ||
): void { | ||
let hasSeenPlainParam = false; | ||
for (let i = node.params.length - 1; i >= 0; i--) { | ||
const param = node.params[i]; | ||
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if (isPlainParam(param)) { | ||
hasSeenPlainParam = true; | ||
continue; | ||
} | ||
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if ( | ||
hasSeenPlainParam && | ||
(isOptionalParam(param) || | ||
param.type === AST_NODE_TYPES.AssignmentPattern) | ||
) { | ||
context.report({ node: param, messageId: 'shouldBeLast' }); | ||
} | ||
} | ||
} | ||
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return { | ||
ArrowFunctionExpression: checkDefaultParamLast, | ||
FunctionDeclaration: checkDefaultParamLast, | ||
FunctionExpression: checkDefaultParamLast, | ||
}; | ||
}, | ||
}); |
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