Current Dev State

static/js/ketcher2/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";
+
+//------------------------------------------------------------------------------
+// Helpers
+//------------------------------------------------------------------------------
+
+const PATTERN_TYPE = /^(?:.+?Pattern|RestElement|SpreadProperty|ExperimentalRestProperty|Property)$/;
+const DECLARATION_HOST_TYPE = /^(?:Program|BlockStatement|SwitchCase)$/;
+const DESTRUCTURING_HOST_TYPE = /^(?:VariableDeclarator|AssignmentExpression)$/;
+
+/**
+ * Adds multiple items to the tail of an array.
+ *
+ * @param {any[]} array - A destination to add.
+ * @param {any[]} values - Items to be added.
+ * @returns {void}
+ */
+const pushAll = Function.apply.bind(Array.prototype.push);
+
+/**
+ * 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)
+        )
+    );
+}
+
+/**
+ * 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 {escope.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;
+    }
+
+    /*
+     * Due to a bug in acorn, code such as `let foo = 1; let foo = 2;` will not throw a syntax error. As a sanity
+     * check, make sure that the variable only has one declaration. After the parsing bug is fixed, this check
+     * will no longer be necessary, because variables declared with `let` or `const` should always have exactly one
+     * declaration.
+     * https://github.com/ternjs/acorn/issues/487
+     */
+    if (variable.defs.length > 1) {
+        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;
+            }
+            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;
+}
+
+/**
+ * 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 {escope.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;
+}
+
+/**
+ * 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 {escope.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: {
+        docs: {
+            description: "require `const` declarations for variables that are never reassigned after declared",
+            category: "ECMAScript 6",
+            recommended: false
+        },
+
+        fixable: "code",
+
+        schema: [
+            {
+                type: "object",
+                properties: {
+                    destructuring: { enum: ["any", "all"] },
+                    ignoreReadBeforeAssign: { type: "boolean" }
+                },
+                additionalProperties: false
+            }
+        ]
+    },
+
+    create(context) {
+        const options = context.options[0] || {};
+        const sourceCode = context.getSourceCode();
+        const checkingMixedDestructuring = options.destructuring !== "all";
+        const ignoreReadBeforeAssign = options.ignoreReadBeforeAssign === true;
+        const variables = [];
+
+        /**
+         * 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 {(escope.Reference|null)[]} nodes -
+         *      References which are grouped by destructuring to report.
+         * @returns {void}
+         */
+        function checkGroup(nodes) {
+            const nodesToReport = nodes.filter(Boolean);
+
+            if (nodes.length && (checkingMixedDestructuring || nodesToReport.length === nodes.length)) {
+                const varDeclParent = findUp(nodes[0], "VariableDeclaration", parentNode => parentNode.type.endsWith("Statement"));
+                const shouldFix = varDeclParent &&
+
+                    // If there are multiple variable declarations, like {let a = 1, b = 2}, then
+                    // do not attempt to fix if one of the declarations should be `const`. It's
+                    // too hard to know how the developer would want to automatically resolve the issue.
+                    varDeclParent.declarations.length === 1 &&
+
+                    // Don't do a fix unless the variable is initialized (or it's in a for-in or for-of loop)
+                    (varDeclParent.parent.type === "ForInStatement" || varDeclParent.parent.type === "ForOfStatement" || varDeclParent.declarations[0].init) &&
+
+                    // If options.destucturing 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;
+
+                nodesToReport.forEach(node => {
+                    context.report({
+                        node,
+                        message: "'{{name}}' is never reassigned. Use 'const' instead.",
+                        data: node,
+                        fix: shouldFix ? fixer => fixer.replaceText(sourceCode.getFirstToken(varDeclParent), "const") : null
+                    });
+                });
+            }
+        }
+
+        return {
+            "Program:exit"() {
+                groupByDestructuring(variables, ignoreReadBeforeAssign).forEach(checkGroup);
+            },
+
+            VariableDeclaration(node) {
+                if (node.kind === "let" && !isInitOfForStatement(node)) {
+                    pushAll(variables, context.getDeclaredVariables(node));
+                }
+            }
+        };
+    }
+};