/**
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* @fileoverview A rule to disallow unnecessary `.call()` and `.apply()`.
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* @author Toru Nagashima
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*/
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"use strict";
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const astUtils = require("./utils/ast-utils");
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//------------------------------------------------------------------------------
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// Helpers
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//------------------------------------------------------------------------------
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/**
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* Checks whether or not a node is a `.call()`/`.apply()`.
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* @param {ASTNode} node A CallExpression node to check.
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* @returns {boolean} Whether or not the node is a `.call()`/`.apply()`.
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*/
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function isCallOrNonVariadicApply(node) {
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const callee = astUtils.skipChainExpression(node.callee);
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return (
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callee.type === "MemberExpression" &&
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callee.property.type === "Identifier" &&
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callee.computed === false &&
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(
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(callee.property.name === "call" && node.arguments.length >= 1) ||
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(callee.property.name === "apply" && node.arguments.length === 2 && node.arguments[1].type === "ArrayExpression")
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)
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);
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}
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/**
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* Checks whether or not `thisArg` is not changed by `.call()`/`.apply()`.
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* @param {ASTNode|null} expectedThis The node that is the owner of the applied function.
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* @param {ASTNode} thisArg The node that is given to the first argument of the `.call()`/`.apply()`.
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* @param {SourceCode} sourceCode The ESLint source code object.
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* @returns {boolean} Whether or not `thisArg` is not changed by `.call()`/`.apply()`.
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*/
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function isValidThisArg(expectedThis, thisArg, sourceCode) {
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if (!expectedThis) {
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return astUtils.isNullOrUndefined(thisArg);
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}
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return astUtils.equalTokens(expectedThis, thisArg, sourceCode);
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}
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//------------------------------------------------------------------------------
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// Rule Definition
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//------------------------------------------------------------------------------
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module.exports = {
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meta: {
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type: "suggestion",
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docs: {
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description: "disallow unnecessary calls to `.call()` and `.apply()`",
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category: "Best Practices",
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recommended: false,
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url: "https://eslint.org/docs/rules/no-useless-call"
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},
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schema: [],
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messages: {
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unnecessaryCall: "Unnecessary '.{{name}}()'."
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}
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},
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create(context) {
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const sourceCode = context.getSourceCode();
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return {
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CallExpression(node) {
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if (!isCallOrNonVariadicApply(node)) {
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return;
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}
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const callee = astUtils.skipChainExpression(node.callee);
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const applied = astUtils.skipChainExpression(callee.object);
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const expectedThis = (applied.type === "MemberExpression") ? applied.object : null;
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const thisArg = node.arguments[0];
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if (isValidThisArg(expectedThis, thisArg, sourceCode)) {
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context.report({ node, messageId: "unnecessaryCall", data: { name: callee.property.name } });
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}
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}
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};
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}
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};
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