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app_vue/node_modules/eslint/lib/rules/prefer-arrow-callback.js

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+/**
+ * @fileoverview A rule to suggest using arrow functions as callbacks.
+ * @author Toru Nagashima
+ */
+
+"use strict";
+
+const astUtils = require("./utils/ast-utils");
+
+//------------------------------------------------------------------------------
+// Helpers
+//------------------------------------------------------------------------------
+
+/**
+ * Checks whether or not a given variable is a function name.
+ * @param {eslint-scope.Variable} variable A variable to check.
+ * @returns {boolean} `true` if the variable is a function name.
+ */
+function isFunctionName(variable) {
+    return variable && variable.defs[0].type === "FunctionName";
+}
+
+/**
+ * Checks whether or not a given MetaProperty node equals to a given value.
+ * @param {ASTNode} node A MetaProperty node to check.
+ * @param {string} metaName The name of `MetaProperty.meta`.
+ * @param {string} propertyName The name of `MetaProperty.property`.
+ * @returns {boolean} `true` if the node is the specific value.
+ */
+function checkMetaProperty(node, metaName, propertyName) {
+    return node.meta.name === metaName && node.property.name === propertyName;
+}
+
+/**
+ * Gets the variable object of `arguments` which is defined implicitly.
+ * @param {eslint-scope.Scope} scope A scope to get.
+ * @returns {eslint-scope.Variable} The found variable object.
+ */
+function getVariableOfArguments(scope) {
+    const variables = scope.variables;
+
+    for (let i = 0; i < variables.length; ++i) {
+        const variable = variables[i];
+
+        if (variable.name === "arguments") {
+
+            /*
+             * If there was a parameter which is named "arguments", the
+             * implicit "arguments" is not defined.
+             * So does fast return with null.
+             */
+            return (variable.identifiers.length === 0) ? variable : null;
+        }
+    }
+
+    /* istanbul ignore next */
+    return null;
+}
+
+/**
+ * Checks whether or not a given node is a callback.
+ * @param {ASTNode} node A node to check.
+ * @returns {Object}
+ *   {boolean} retv.isCallback - `true` if the node is a callback.
+ *   {boolean} retv.isLexicalThis - `true` if the node is with `.bind(this)`.
+ */
+function getCallbackInfo(node) {
+    const retv = { isCallback: false, isLexicalThis: false };
+    let currentNode = node;
+    let parent = node.parent;
+    let bound = false;
+
+    while (currentNode) {
+        switch (parent.type) {
+
+            // Checks parents recursively.
+
+            case "LogicalExpression":
+            case "ChainExpression":
+            case "ConditionalExpression":
+                break;
+
+            // Checks whether the parent node is `.bind(this)` call.
+            case "MemberExpression":
+                if (
+                    parent.object === currentNode &&
+                    !parent.property.computed &&
+                    parent.property.type === "Identifier" &&
+                    parent.property.name === "bind"
+                ) {
+                    const maybeCallee = parent.parent.type === "ChainExpression"
+                        ? parent.parent
+                        : parent;
+
+                    if (astUtils.isCallee(maybeCallee)) {
+                        if (!bound) {
+                            bound = true; // Use only the first `.bind()` to make `isLexicalThis` value.
+                            retv.isLexicalThis = (
+                                maybeCallee.parent.arguments.length === 1 &&
+                                maybeCallee.parent.arguments[0].type === "ThisExpression"
+                            );
+                        }
+                        parent = maybeCallee.parent;
+                    } else {
+                        return retv;
+                    }
+                } else {
+                    return retv;
+                }
+                break;
+
+            // Checks whether the node is a callback.
+            case "CallExpression":
+            case "NewExpression":
+                if (parent.callee !== currentNode) {
+                    retv.isCallback = true;
+                }
+                return retv;
+
+            default:
+                return retv;
+        }
+
+        currentNode = parent;
+        parent = parent.parent;
+    }
+
+    /* istanbul ignore next */
+    throw new Error("unreachable");
+}
+
+/**
+ * Checks whether a simple list of parameters contains any duplicates. This does not handle complex
+ * parameter lists (e.g. with destructuring), since complex parameter lists are a SyntaxError with duplicate
+ * parameter names anyway. Instead, it always returns `false` for complex parameter lists.
+ * @param {ASTNode[]} paramsList The list of parameters for a function
+ * @returns {boolean} `true` if the list of parameters contains any duplicates
+ */
+function hasDuplicateParams(paramsList) {
+    return paramsList.every(param => param.type === "Identifier") && paramsList.length !== new Set(paramsList.map(param => param.name)).size;
+}
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+    meta: {
+        type: "suggestion",
+
+        docs: {
+            description: "require using arrow functions for callbacks",
+            category: "ECMAScript 6",
+            recommended: false,
+            url: "https://eslint.org/docs/rules/prefer-arrow-callback"
+        },
+
+        schema: [
+            {
+                type: "object",
+                properties: {
+                    allowNamedFunctions: {
+                        type: "boolean",
+                        default: false
+                    },
+                    allowUnboundThis: {
+                        type: "boolean",
+                        default: true
+                    }
+                },
+                additionalProperties: false
+            }
+        ],
+
+        fixable: "code",
+
+        messages: {
+            preferArrowCallback: "Unexpected function expression."
+        }
+    },
+
+    create(context) {
+        const options = context.options[0] || {};
+
+        const allowUnboundThis = options.allowUnboundThis !== false; // default to true
+        const allowNamedFunctions = options.allowNamedFunctions;
+        const sourceCode = context.getSourceCode();
+
+        /*
+         * {Array<{this: boolean, super: boolean, meta: boolean}>}
+         * - this - A flag which shows there are one or more ThisExpression.
+         * - super - A flag which shows there are one or more Super.
+         * - meta - A flag which shows there are one or more MethProperty.
+         */
+        let stack = [];
+
+        /**
+         * Pushes new function scope with all `false` flags.
+         * @returns {void}
+         */
+        function enterScope() {
+            stack.push({ this: false, super: false, meta: false });
+        }
+
+        /**
+         * Pops a function scope from the stack.
+         * @returns {{this: boolean, super: boolean, meta: boolean}} The information of the last scope.
+         */
+        function exitScope() {
+            return stack.pop();
+        }
+
+        return {
+
+            // Reset internal state.
+            Program() {
+                stack = [];
+            },
+
+            // If there are below, it cannot replace with arrow functions merely.
+            ThisExpression() {
+                const info = stack[stack.length - 1];
+
+                if (info) {
+                    info.this = true;
+                }
+            },
+
+            Super() {
+                const info = stack[stack.length - 1];
+
+                if (info) {
+                    info.super = true;
+                }
+            },
+
+            MetaProperty(node) {
+                const info = stack[stack.length - 1];
+
+                if (info && checkMetaProperty(node, "new", "target")) {
+                    info.meta = true;
+                }
+            },
+
+            // To skip nested scopes.
+            FunctionDeclaration: enterScope,
+            "FunctionDeclaration:exit": exitScope,
+
+            // Main.
+            FunctionExpression: enterScope,
+            "FunctionExpression:exit"(node) {
+                const scopeInfo = exitScope();
+
+                // Skip named function expressions
+                if (allowNamedFunctions && node.id && node.id.name) {
+                    return;
+                }
+
+                // Skip generators.
+                if (node.generator) {
+                    return;
+                }
+
+                // Skip recursive functions.
+                const nameVar = context.getDeclaredVariables(node)[0];
+
+                if (isFunctionName(nameVar) && nameVar.references.length > 0) {
+                    return;
+                }
+
+                // Skip if it's using arguments.
+                const variable = getVariableOfArguments(context.getScope());
+
+                if (variable && variable.references.length > 0) {
+                    return;
+                }
+
+                // Reports if it's a callback which can replace with arrows.
+                const callbackInfo = getCallbackInfo(node);
+
+                if (callbackInfo.isCallback &&
+                    (!allowUnboundThis || !scopeInfo.this || callbackInfo.isLexicalThis) &&
+                    !scopeInfo.super &&
+                    !scopeInfo.meta
+                ) {
+                    context.report({
+                        node,
+                        messageId: "preferArrowCallback",
+                        *fix(fixer) {
+                            if ((!callbackInfo.isLexicalThis && scopeInfo.this) || hasDuplicateParams(node.params)) {
+
+                                /*
+                                 * If the callback function does not have .bind(this) and contains a reference to `this`, there
+                                 * is no way to determine what `this` should be, so don't perform any fixes.
+                                 * If the callback function has duplicates in its list of parameters (possible in sloppy mode),
+                                 * don't replace it with an arrow function, because this is a SyntaxError with arrow functions.
+                                 */
+                                return;
+                            }
+
+                            // Remove `.bind(this)` if exists.
+                            if (callbackInfo.isLexicalThis) {
+                                const memberNode = node.parent;
+
+                                /*
+                                 * If `.bind(this)` exists but the parent is not `.bind(this)`, don't remove it automatically.
+                                 * E.g. `(foo || function(){}).bind(this)`
+                                 */
+                                if (memberNode.type !== "MemberExpression") {
+                                    return;
+                                }
+
+                                const callNode = memberNode.parent;
+                                const firstTokenToRemove = sourceCode.getTokenAfter(memberNode.object, astUtils.isNotClosingParenToken);
+                                const lastTokenToRemove = sourceCode.getLastToken(callNode);
+
+                                /*
+                                 * If the member expression is parenthesized, don't remove the right paren.
+                                 * E.g. `(function(){}.bind)(this)`
+                                 *                    ^^^^^^^^^^^^
+                                 */
+                                if (astUtils.isParenthesised(sourceCode, memberNode)) {
+                                    return;
+                                }
+
+                                // If comments exist in the `.bind(this)`, don't remove those.
+                                if (sourceCode.commentsExistBetween(firstTokenToRemove, lastTokenToRemove)) {
+                                    return;
+                                }
+
+                                yield fixer.removeRange([firstTokenToRemove.range[0], lastTokenToRemove.range[1]]);
+                            }
+
+                            // Convert the function expression to an arrow function.
+                            const functionToken = sourceCode.getFirstToken(node, node.async ? 1 : 0);
+                            const leftParenToken = sourceCode.getTokenAfter(functionToken, astUtils.isOpeningParenToken);
+
+                            if (sourceCode.commentsExistBetween(functionToken, leftParenToken)) {
+
+                                // Remove only extra tokens to keep comments.
+                                yield fixer.remove(functionToken);
+                                if (node.id) {
+                                    yield fixer.remove(node.id);
+                                }
+                            } else {
+
+                                // Remove extra tokens and spaces.
+                                yield fixer.removeRange([functionToken.range[0], leftParenToken.range[0]]);
+                            }
+                            yield fixer.insertTextBefore(node.body, "=> ");
+
+                            // Get the node that will become the new arrow function.
+                            let replacedNode = callbackInfo.isLexicalThis ? node.parent.parent : node;
+
+                            if (replacedNode.type === "ChainExpression") {
+                                replacedNode = replacedNode.parent;
+                            }
+
+                            /*
+                             * If the replaced node is part of a BinaryExpression, LogicalExpression, or MemberExpression, then
+                             * the arrow function needs to be parenthesized, because `foo || () => {}` is invalid syntax even
+                             * though `foo || function() {}` is valid.
+                             */
+                            if (
+                                replacedNode.parent.type !== "CallExpression" &&
+                                replacedNode.parent.type !== "ConditionalExpression" &&
+                                !astUtils.isParenthesised(sourceCode, replacedNode) &&
+                                !astUtils.isParenthesised(sourceCode, node)
+                            ) {
+                                yield fixer.insertTextBefore(replacedNode, "(");
+                                yield fixer.insertTextAfter(replacedNode, ")");
+                            }
+                        }
+                    });
+                }
+            }
+        };
+    }
+};