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app_vue/node_modules/eslint/lib/rules/no-useless-constructor.js

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+/**
+ * @fileoverview Rule to flag the use of redundant constructors in classes.
+ * @author Alberto Rodríguez
+ */
+"use strict";
+
+//------------------------------------------------------------------------------
+// Helpers
+//------------------------------------------------------------------------------
+
+/**
+ * Checks whether a given array of statements is a single call of `super`.
+ * @param {ASTNode[]} body An array of statements to check.
+ * @returns {boolean} `true` if the body is a single call of `super`.
+ */
+function isSingleSuperCall(body) {
+    return (
+        body.length === 1 &&
+        body[0].type === "ExpressionStatement" &&
+        body[0].expression.type === "CallExpression" &&
+        body[0].expression.callee.type === "Super"
+    );
+}
+
+/**
+ * Checks whether a given node is a pattern which doesn't have any side effects.
+ * Default parameters and Destructuring parameters can have side effects.
+ * @param {ASTNode} node A pattern node.
+ * @returns {boolean} `true` if the node doesn't have any side effects.
+ */
+function isSimple(node) {
+    return node.type === "Identifier" || node.type === "RestElement";
+}
+
+/**
+ * Checks whether a given array of expressions is `...arguments` or not.
+ * `super(...arguments)` passes all arguments through.
+ * @param {ASTNode[]} superArgs An array of expressions to check.
+ * @returns {boolean} `true` if the superArgs is `...arguments`.
+ */
+function isSpreadArguments(superArgs) {
+    return (
+        superArgs.length === 1 &&
+        superArgs[0].type === "SpreadElement" &&
+        superArgs[0].argument.type === "Identifier" &&
+        superArgs[0].argument.name === "arguments"
+    );
+}
+
+/**
+ * Checks whether given 2 nodes are identifiers which have the same name or not.
+ * @param {ASTNode} ctorParam A node to check.
+ * @param {ASTNode} superArg A node to check.
+ * @returns {boolean} `true` if the nodes are identifiers which have the same
+ *      name.
+ */
+function isValidIdentifierPair(ctorParam, superArg) {
+    return (
+        ctorParam.type === "Identifier" &&
+        superArg.type === "Identifier" &&
+        ctorParam.name === superArg.name
+    );
+}
+
+/**
+ * Checks whether given 2 nodes are a rest/spread pair which has the same values.
+ * @param {ASTNode} ctorParam A node to check.
+ * @param {ASTNode} superArg A node to check.
+ * @returns {boolean} `true` if the nodes are a rest/spread pair which has the
+ *      same values.
+ */
+function isValidRestSpreadPair(ctorParam, superArg) {
+    return (
+        ctorParam.type === "RestElement" &&
+        superArg.type === "SpreadElement" &&
+        isValidIdentifierPair(ctorParam.argument, superArg.argument)
+    );
+}
+
+/**
+ * Checks whether given 2 nodes have the same value or not.
+ * @param {ASTNode} ctorParam A node to check.
+ * @param {ASTNode} superArg A node to check.
+ * @returns {boolean} `true` if the nodes have the same value or not.
+ */
+function isValidPair(ctorParam, superArg) {
+    return (
+        isValidIdentifierPair(ctorParam, superArg) ||
+        isValidRestSpreadPair(ctorParam, superArg)
+    );
+}
+
+/**
+ * Checks whether the parameters of a constructor and the arguments of `super()`
+ * have the same values or not.
+ * @param {ASTNode} ctorParams The parameters of a constructor to check.
+ * @param {ASTNode} superArgs The arguments of `super()` to check.
+ * @returns {boolean} `true` if those have the same values.
+ */
+function isPassingThrough(ctorParams, superArgs) {
+    if (ctorParams.length !== superArgs.length) {
+        return false;
+    }
+
+    for (let i = 0; i < ctorParams.length; ++i) {
+        if (!isValidPair(ctorParams[i], superArgs[i])) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
+/**
+ * Checks whether the constructor body is a redundant super call.
+ * @param {Array} body constructor body content.
+ * @param {Array} ctorParams The params to check against super call.
+ * @returns {boolean} true if the constructor body is redundant
+ */
+function isRedundantSuperCall(body, ctorParams) {
+    return (
+        isSingleSuperCall(body) &&
+        ctorParams.every(isSimple) &&
+        (
+            isSpreadArguments(body[0].expression.arguments) ||
+            isPassingThrough(ctorParams, body[0].expression.arguments)
+        )
+    );
+}
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+    meta: {
+        type: "suggestion",
+
+        docs: {
+            description: "disallow unnecessary constructors",
+            category: "ECMAScript 6",
+            recommended: false,
+            url: "https://eslint.org/docs/rules/no-useless-constructor"
+        },
+
+        schema: [],
+
+        messages: {
+            noUselessConstructor: "Useless constructor."
+        }
+    },
+
+    create(context) {
+
+        /**
+         * Checks whether a node is a redundant constructor
+         * @param {ASTNode} node node to check
+         * @returns {void}
+         */
+        function checkForConstructor(node) {
+            if (node.kind !== "constructor") {
+                return;
+            }
+
+            /*
+             * Prevent crashing on parsers which do not require class constructor
+             * to have a body, e.g. typescript and flow
+             */
+            if (!node.value.body) {
+                return;
+            }
+
+            const body = node.value.body.body;
+            const ctorParams = node.value.params;
+            const superClass = node.parent.parent.superClass;
+
+            if (superClass ? isRedundantSuperCall(body, ctorParams) : (body.length === 0)) {
+                context.report({
+                    node,
+                    messageId: "noUselessConstructor"
+                });
+            }
+        }
+
+        return {
+            MethodDefinition: checkForConstructor
+        };
+    }
+};