oikos/web/node_modules/eslint/lib/rules/no-self-assign.js

/**
 * @fileoverview Rule to disallow assignments where both sides are exactly the same
 * @author Toru Nagashima
 */

"use strict";

//------------------------------------------------------------------------------
// Requirements
//------------------------------------------------------------------------------

const astUtils = require("./utils/ast-utils");

//------------------------------------------------------------------------------
// Helpers
//------------------------------------------------------------------------------

const SPACES = /\s+/gu;

/**
 * Traverses 2 Pattern nodes in parallel, then reports self-assignments.
 * @param {ASTNode|null} left A left node to traverse. This is a Pattern or
 *      a Property.
 * @param {ASTNode|null} right A right node to traverse. This is a Pattern or
 *      a Property.
 * @param {boolean} props The flag to check member expressions as well.
 * @param {Function} report A callback function to report.
 * @returns {void}
 */
function eachSelfAssignment(left, right, props, report) {
	if (!left || !right) {
		// do nothing
	} else if (
		left.type === "Identifier" &&
		right.type === "Identifier" &&
		left.name === right.name
	) {
		report(right);
	} else if (
		left.type === "ArrayPattern" &&
		right.type === "ArrayExpression"
	) {
		const end = Math.min(left.elements.length, right.elements.length);

		for (let i = 0; i < end; ++i) {
			const leftElement = left.elements[i];
			const rightElement = right.elements[i];

			// Avoid cases such as [...a] = [...a, 1]
			if (
				leftElement &&
				leftElement.type === "RestElement" &&
				i < right.elements.length - 1
			) {
				break;
			}

			eachSelfAssignment(leftElement, rightElement, props, report);

			// After a spread element, those indices are unknown.
			if (rightElement && rightElement.type === "SpreadElement") {
				break;
			}
		}
	} else if (left.type === "RestElement" && right.type === "SpreadElement") {
		eachSelfAssignment(left.argument, right.argument, props, report);
	} else if (
		left.type === "ObjectPattern" &&
		right.type === "ObjectExpression" &&
		right.properties.length >= 1
	) {
		/*
		 * Gets the index of the last spread property.
		 * It's possible to overwrite properties followed by it.
		 */
		let startJ = 0;

		for (let i = right.properties.length - 1; i >= 0; --i) {
			const propType = right.properties[i].type;

			if (
				propType === "SpreadElement" ||
				propType === "ExperimentalSpreadProperty"
			) {
				startJ = i + 1;
				break;
			}
		}

		for (let i = 0; i < left.properties.length; ++i) {
			for (let j = startJ; j < right.properties.length; ++j) {
				eachSelfAssignment(
					left.properties[i],
					right.properties[j],
					props,
					report,
				);
			}
		}
	} else if (
		left.type === "Property" &&
		right.type === "Property" &&
		right.kind === "init" &&
		!right.method
	) {
		const leftName = astUtils.getStaticPropertyName(left);

		if (
			leftName !== null &&
			leftName === astUtils.getStaticPropertyName(right)
		) {
			eachSelfAssignment(left.value, right.value, props, report);
		}
	} else if (
		props &&
		astUtils.skipChainExpression(left).type === "MemberExpression" &&
		astUtils.skipChainExpression(right).type === "MemberExpression" &&
		astUtils.isSameReference(left, right)
	) {
		report(right);
	}
}

//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------

/** @type {import('../types').Rule.RuleModule} */
module.exports = {
	meta: {
		type: "problem",

		defaultOptions: [{ props: true }],

		docs: {
			description:
				"Disallow assignments where both sides are exactly the same",
			recommended: true,
			url: "https://eslint.org/docs/latest/rules/no-self-assign",
		},

		schema: [
			{
				type: "object",
				properties: {
					props: {
						type: "boolean",
					},
				},
				additionalProperties: false,
			},
		],

		messages: {
			selfAssignment: "'{{name}}' is assigned to itself.",
		},
	},

	create(context) {
		const sourceCode = context.sourceCode;
		const [{ props }] = context.options;

		/**
		 * Reports a given node as self assignments.
		 * @param {ASTNode} node A node to report. This is an Identifier node.
		 * @returns {void}
		 */
		function report(node) {
			context.report({
				node,
				messageId: "selfAssignment",
				data: {
					name: sourceCode.getText(node).replace(SPACES, ""),
				},
			});
		}

		return {
			AssignmentExpression(node) {
				if (["=", "&&=", "||=", "??="].includes(node.operator)) {
					eachSelfAssignment(node.left, node.right, props, report);
				}
			},
		};
	},
};