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app_vue/node_modules/eslint/lib/rules/prefer-const.js

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+/**
+ * @fileoverview A rule to suggest using of const declaration for variables that are never reassigned after declared.
+ * @author Toru Nagashima
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+const FixTracker = require("./utils/fix-tracker");
+const astUtils = require("./utils/ast-utils");
+
+//------------------------------------------------------------------------------
+// Helpers
+//------------------------------------------------------------------------------
+
+const PATTERN_TYPE = /^(?:.+?Pattern|RestElement|SpreadProperty|ExperimentalRestProperty|Property)$/u;
+const DECLARATION_HOST_TYPE = /^(?:Program|BlockStatement|SwitchCase)$/u;
+const DESTRUCTURING_HOST_TYPE = /^(?:VariableDeclarator|AssignmentExpression)$/u;
+
+/**
+ * Checks whether a given node is located at `ForStatement.init` or not.
+ * @param {ASTNode} node A node to check.
+ * @returns {boolean} `true` if the node is located at `ForStatement.init`.
+ */
+function isInitOfForStatement(node) {
+    return node.parent.type === "ForStatement" && node.parent.init === node;
+}
+
+/**
+ * Checks whether a given Identifier node becomes a VariableDeclaration or not.
+ * @param {ASTNode} identifier An Identifier node to check.
+ * @returns {boolean} `true` if the node can become a VariableDeclaration.
+ */
+function canBecomeVariableDeclaration(identifier) {
+    let node = identifier.parent;
+
+    while (PATTERN_TYPE.test(node.type)) {
+        node = node.parent;
+    }
+
+    return (
+        node.type === "VariableDeclarator" ||
+        (
+            node.type === "AssignmentExpression" &&
+            node.parent.type === "ExpressionStatement" &&
+            DECLARATION_HOST_TYPE.test(node.parent.parent.type)
+        )
+    );
+}
+
+/**
+ * Checks if an property or element is from outer scope or function parameters
+ * in destructing pattern.
+ * @param {string} name A variable name to be checked.
+ * @param {eslint-scope.Scope} initScope A scope to start find.
+ * @returns {boolean} Indicates if the variable is from outer scope or function parameters.
+ */
+function isOuterVariableInDestructing(name, initScope) {
+
+    if (initScope.through.find(ref => ref.resolved && ref.resolved.name === name)) {
+        return true;
+    }
+
+    const variable = astUtils.getVariableByName(initScope, name);
+
+    if (variable !== null) {
+        return variable.defs.some(def => def.type === "Parameter");
+    }
+
+    return false;
+}
+
+/**
+ * Gets the VariableDeclarator/AssignmentExpression node that a given reference
+ * belongs to.
+ * This is used to detect a mix of reassigned and never reassigned in a
+ * destructuring.
+ * @param {eslint-scope.Reference} reference A reference to get.
+ * @returns {ASTNode|null} A VariableDeclarator/AssignmentExpression node or
+ *      null.
+ */
+function getDestructuringHost(reference) {
+    if (!reference.isWrite()) {
+        return null;
+    }
+    let node = reference.identifier.parent;
+
+    while (PATTERN_TYPE.test(node.type)) {
+        node = node.parent;
+    }
+
+    if (!DESTRUCTURING_HOST_TYPE.test(node.type)) {
+        return null;
+    }
+    return node;
+}
+
+/**
+ * Determines if a destructuring assignment node contains
+ * any MemberExpression nodes. This is used to determine if a
+ * variable that is only written once using destructuring can be
+ * safely converted into a const declaration.
+ * @param {ASTNode} node The ObjectPattern or ArrayPattern node to check.
+ * @returns {boolean} True if the destructuring pattern contains
+ *      a MemberExpression, false if not.
+ */
+function hasMemberExpressionAssignment(node) {
+    switch (node.type) {
+        case "ObjectPattern":
+            return node.properties.some(prop => {
+                if (prop) {
+
+                    /*
+                     * Spread elements have an argument property while
+                     * others have a value property. Because different
+                     * parsers use different node types for spread elements,
+                     * we just check if there is an argument property.
+                     */
+                    return hasMemberExpressionAssignment(prop.argument || prop.value);
+                }
+
+                return false;
+            });
+
+        case "ArrayPattern":
+            return node.elements.some(element => {
+                if (element) {
+                    return hasMemberExpressionAssignment(element);
+                }
+
+                return false;
+            });
+
+        case "AssignmentPattern":
+            return hasMemberExpressionAssignment(node.left);
+
+        case "MemberExpression":
+            return true;
+
+        // no default
+    }
+
+    return false;
+}
+
+/**
+ * Gets an identifier node of a given variable.
+ *
+ * If the initialization exists or one or more reading references exist before
+ * the first assignment, the identifier node is the node of the declaration.
+ * Otherwise, the identifier node is the node of the first assignment.
+ *
+ * If the variable should not change to const, this function returns null.
+ * - If the variable is reassigned.
+ * - If the variable is never initialized nor assigned.
+ * - If the variable is initialized in a different scope from the declaration.
+ * - If the unique assignment of the variable cannot change to a declaration.
+ *   e.g. `if (a) b = 1` / `return (b = 1)`
+ * - If the variable is declared in the global scope and `eslintUsed` is `true`.
+ *   `/*exported foo` directive comment makes such variables. This rule does not
+ *   warn such variables because this rule cannot distinguish whether the
+ *   exported variables are reassigned or not.
+ * @param {eslint-scope.Variable} variable A variable to get.
+ * @param {boolean} ignoreReadBeforeAssign
+ *      The value of `ignoreReadBeforeAssign` option.
+ * @returns {ASTNode|null}
+ *      An Identifier node if the variable should change to const.
+ *      Otherwise, null.
+ */
+function getIdentifierIfShouldBeConst(variable, ignoreReadBeforeAssign) {
+    if (variable.eslintUsed && variable.scope.type === "global") {
+        return null;
+    }
+
+    // Finds the unique WriteReference.
+    let writer = null;
+    let isReadBeforeInit = false;
+    const references = variable.references;
+
+    for (let i = 0; i < references.length; ++i) {
+        const reference = references[i];
+
+        if (reference.isWrite()) {
+            const isReassigned = (
+                writer !== null &&
+                writer.identifier !== reference.identifier
+            );
+
+            if (isReassigned) {
+                return null;
+            }
+
+            const destructuringHost = getDestructuringHost(reference);
+
+            if (destructuringHost !== null && destructuringHost.left !== void 0) {
+                const leftNode = destructuringHost.left;
+                let hasOuterVariables = false,
+                    hasNonIdentifiers = false;
+
+                if (leftNode.type === "ObjectPattern") {
+                    const properties = leftNode.properties;
+
+                    hasOuterVariables = properties
+                        .filter(prop => prop.value)
+                        .map(prop => prop.value.name)
+                        .some(name => isOuterVariableInDestructing(name, variable.scope));
+
+                    hasNonIdentifiers = hasMemberExpressionAssignment(leftNode);
+
+                } else if (leftNode.type === "ArrayPattern") {
+                    const elements = leftNode.elements;
+
+                    hasOuterVariables = elements
+                        .map(element => element && element.name)
+                        .some(name => isOuterVariableInDestructing(name, variable.scope));
+
+                    hasNonIdentifiers = hasMemberExpressionAssignment(leftNode);
+                }
+
+                if (hasOuterVariables || hasNonIdentifiers) {
+                    return null;
+                }
+
+            }
+
+            writer = reference;
+
+        } else if (reference.isRead() && writer === null) {
+            if (ignoreReadBeforeAssign) {
+                return null;
+            }
+            isReadBeforeInit = true;
+        }
+    }
+
+    /*
+     * If the assignment is from a different scope, ignore it.
+     * If the assignment cannot change to a declaration, ignore it.
+     */
+    const shouldBeConst = (
+        writer !== null &&
+        writer.from === variable.scope &&
+        canBecomeVariableDeclaration(writer.identifier)
+    );
+
+    if (!shouldBeConst) {
+        return null;
+    }
+
+    if (isReadBeforeInit) {
+        return variable.defs[0].name;
+    }
+
+    return writer.identifier;
+}
+
+/**
+ * Groups by the VariableDeclarator/AssignmentExpression node that each
+ * reference of given variables belongs to.
+ * This is used to detect a mix of reassigned and never reassigned in a
+ * destructuring.
+ * @param {eslint-scope.Variable[]} variables Variables to group by destructuring.
+ * @param {boolean} ignoreReadBeforeAssign
+ *      The value of `ignoreReadBeforeAssign` option.
+ * @returns {Map<ASTNode, ASTNode[]>} Grouped identifier nodes.
+ */
+function groupByDestructuring(variables, ignoreReadBeforeAssign) {
+    const identifierMap = new Map();
+
+    for (let i = 0; i < variables.length; ++i) {
+        const variable = variables[i];
+        const references = variable.references;
+        const identifier = getIdentifierIfShouldBeConst(variable, ignoreReadBeforeAssign);
+        let prevId = null;
+
+        for (let j = 0; j < references.length; ++j) {
+            const reference = references[j];
+            const id = reference.identifier;
+
+            /*
+             * Avoid counting a reference twice or more for default values of
+             * destructuring.
+             */
+            if (id === prevId) {
+                continue;
+            }
+            prevId = id;
+
+            // Add the identifier node into the destructuring group.
+            const group = getDestructuringHost(reference);
+
+            if (group) {
+                if (identifierMap.has(group)) {
+                    identifierMap.get(group).push(identifier);
+                } else {
+                    identifierMap.set(group, [identifier]);
+                }
+            }
+        }
+    }
+
+    return identifierMap;
+}
+
+/**
+ * Finds the nearest parent of node with a given type.
+ * @param {ASTNode} node The node to search from.
+ * @param {string} type The type field of the parent node.
+ * @param {Function} shouldStop A predicate that returns true if the traversal should stop, and false otherwise.
+ * @returns {ASTNode} The closest ancestor with the specified type; null if no such ancestor exists.
+ */
+function findUp(node, type, shouldStop) {
+    if (!node || shouldStop(node)) {
+        return null;
+    }
+    if (node.type === type) {
+        return node;
+    }
+    return findUp(node.parent, type, shouldStop);
+}
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+    meta: {
+        type: "suggestion",
+
+        docs: {
+            description: "require `const` declarations for variables that are never reassigned after declared",
+            category: "ECMAScript 6",
+            recommended: false,
+            url: "https://eslint.org/docs/rules/prefer-const"
+        },
+
+        fixable: "code",
+
+        schema: [
+            {
+                type: "object",
+                properties: {
+                    destructuring: { enum: ["any", "all"], default: "any" },
+                    ignoreReadBeforeAssign: { type: "boolean", default: false }
+                },
+                additionalProperties: false
+            }
+        ],
+        messages: {
+            useConst: "'{{name}}' is never reassigned. Use 'const' instead."
+        }
+    },
+
+    create(context) {
+        const options = context.options[0] || {};
+        const sourceCode = context.getSourceCode();
+        const shouldMatchAnyDestructuredVariable = options.destructuring !== "all";
+        const ignoreReadBeforeAssign = options.ignoreReadBeforeAssign === true;
+        const variables = [];
+        let reportCount = 0;
+        let checkedId = null;
+        let checkedName = "";
+
+
+        /**
+         * Reports given identifier nodes if all of the nodes should be declared
+         * as const.
+         *
+         * The argument 'nodes' is an array of Identifier nodes.
+         * This node is the result of 'getIdentifierIfShouldBeConst()', so it's
+         * nullable. In simple declaration or assignment cases, the length of
+         * the array is 1. In destructuring cases, the length of the array can
+         * be 2 or more.
+         * @param {(eslint-scope.Reference|null)[]} nodes
+         *      References which are grouped by destructuring to report.
+         * @returns {void}
+         */
+        function checkGroup(nodes) {
+            const nodesToReport = nodes.filter(Boolean);
+
+            if (nodes.length && (shouldMatchAnyDestructuredVariable || nodesToReport.length === nodes.length)) {
+                const varDeclParent = findUp(nodes[0], "VariableDeclaration", parentNode => parentNode.type.endsWith("Statement"));
+                const isVarDecParentNull = varDeclParent === null;
+
+                if (!isVarDecParentNull && varDeclParent.declarations.length > 0) {
+                    const firstDeclaration = varDeclParent.declarations[0];
+
+                    if (firstDeclaration.init) {
+                        const firstDecParent = firstDeclaration.init.parent;
+
+                        /*
+                         * First we check the declaration type and then depending on
+                         * if the type is a "VariableDeclarator" or its an "ObjectPattern"
+                         * we compare the name and id from the first identifier, if the names are different
+                         * we assign the new name, id and reset the count of reportCount and nodeCount in
+                         * order to check each block for the number of reported errors and base our fix
+                         * based on comparing nodes.length and nodesToReport.length.
+                         */
+
+                        if (firstDecParent.type === "VariableDeclarator") {
+
+                            if (firstDecParent.id.name !== checkedName) {
+                                checkedName = firstDecParent.id.name;
+                                reportCount = 0;
+                            }
+
+                            if (firstDecParent.id.type === "ObjectPattern") {
+                                if (firstDecParent.init.name !== checkedName) {
+                                    checkedName = firstDecParent.init.name;
+                                    reportCount = 0;
+                                }
+                            }
+
+                            if (firstDecParent.id !== checkedId) {
+                                checkedId = firstDecParent.id;
+                                reportCount = 0;
+                            }
+                        }
+                    }
+                }
+
+                let shouldFix = varDeclParent &&
+
+                    // Don't do a fix unless all variables in the declarations are initialized (or it's in a for-in or for-of loop)
+                    (varDeclParent.parent.type === "ForInStatement" || varDeclParent.parent.type === "ForOfStatement" ||
+                        varDeclParent.declarations.every(declaration => declaration.init)) &&
+
+                    /*
+                     * If options.destructuring is "all", then this warning will not occur unless
+                     * every assignment in the destructuring should be const. In that case, it's safe
+                     * to apply the fix.
+                     */
+                    nodesToReport.length === nodes.length;
+
+                if (!isVarDecParentNull && varDeclParent.declarations && varDeclParent.declarations.length !== 1) {
+
+                    if (varDeclParent && varDeclParent.declarations && varDeclParent.declarations.length >= 1) {
+
+                        /*
+                         * Add nodesToReport.length to a count, then comparing the count to the length
+                         * of the declarations in the current block.
+                         */
+
+                        reportCount += nodesToReport.length;
+
+                        shouldFix = shouldFix && (reportCount === varDeclParent.declarations.length);
+                    }
+                }
+
+                nodesToReport.forEach(node => {
+                    context.report({
+                        node,
+                        messageId: "useConst",
+                        data: node,
+                        fix: shouldFix
+                            ? fixer => {
+                                const letKeywordToken = sourceCode.getFirstToken(varDeclParent, t => t.value === varDeclParent.kind);
+
+                                /**
+                                 * Extend the replacement range to the whole declaration,
+                                 * in order to prevent other fixes in the same pass
+                                 * https://github.com/eslint/eslint/issues/13899
+                                 */
+                                return new FixTracker(fixer, sourceCode)
+                                    .retainRange(varDeclParent.range)
+                                    .replaceTextRange(letKeywordToken.range, "const");
+                            }
+                            : null
+                    });
+                });
+            }
+        }
+
+        return {
+            "Program:exit"() {
+                groupByDestructuring(variables, ignoreReadBeforeAssign).forEach(checkGroup);
+            },
+
+            VariableDeclaration(node) {
+                if (node.kind === "let" && !isInitOfForStatement(node)) {
+                    variables.push(...context.getDeclaredVariables(node));
+                }
+            }
+        };
+    }
+};