eslint/lib/rules/id-length.js

/**
 * @fileoverview Rule that warns when identifier names are shorter or longer
 * than the values provided in configuration.
 * @author Burak Yigit Kaya aka BYK
 */

"use strict";

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

module.exports = {
    meta: {
        type: "suggestion",

        docs: {
            description: "enforce minimum and maximum identifier lengths",
            category: "Stylistic Issues",
            recommended: false,
            url: "https://eslint.org/docs/rules/id-length"
        },

        schema: [
            {
                type: "object",
                properties: {
                    min: {
                        type: "integer",
                        default: 2
                    },
                    max: {
                        type: "integer"
                    },
                    exceptions: {
                        type: "array",
                        uniqueItems: true,
                        items: {
                            type: "string"
                        }
                    },
                    exceptionPatterns: {
                        type: "array",
                        uniqueItems: true,
                        items: {
                            type: "string"
                        }
                    },
                    properties: {
                        enum: ["always", "never"]
                    }
                },
                additionalProperties: false
            }
        ],
        messages: {
            tooShort: "Identifier name '{{name}}' is too short (< {{min}}).",
            tooLong: "Identifier name '{{name}}' is too long (> {{max}})."
        }
    },

    create(context) {
        const options = context.options[0] || {};
        const minLength = typeof options.min !== "undefined" ? options.min : 2;
        const maxLength = typeof options.max !== "undefined" ? options.max : Infinity;
        const properties = options.properties !== "never";
        const exceptions = new Set(options.exceptions);
        const exceptionPatterns = (options.exceptionPatterns || []).map(pattern => new RegExp(pattern, "u"));
        const reportedNode = new Set();

        /**
         * Checks if a string matches the provided exception patterns
         * @param {string} name The string to check.
         * @returns {boolean} if the string is a match
         * @private
         */
        function matchesExceptionPattern(name) {
            return exceptionPatterns.some(pattern => pattern.test(name));
        }

        const SUPPORTED_EXPRESSIONS = {
            MemberExpression: properties && function(parent) {
                return !parent.computed && (

                    // regular property assignment
                    (parent.parent.left === parent && parent.parent.type === "AssignmentExpression" ||

                    // or the last identifier in an ObjectPattern destructuring
                    parent.parent.type === "Property" && parent.parent.value === parent &&
                    parent.parent.parent.type === "ObjectPattern" && parent.parent.parent.parent.left === parent.parent.parent)
                );
            },
            AssignmentPattern(parent, node) {
                return parent.left === node;
            },
            VariableDeclarator(parent, node) {
                return parent.id === node;
            },
            Property(parent, node) {

                if (parent.parent.type === "ObjectPattern") {
                    return (
                        parent.value !== parent.key && parent.value === node ||
                        parent.value === parent.key && parent.key === node && properties
                    );
                }
                return properties && !parent.computed && parent.key === node;
            },
            ImportDefaultSpecifier: true,
            RestElement: true,
            FunctionExpression: true,
            ArrowFunctionExpression: true,
            ClassDeclaration: true,
            FunctionDeclaration: true,
            MethodDefinition: true,
            CatchClause: true,
            ArrayPattern: true
        };

        return {
            Identifier(node) {
                const name = node.name;
                const parent = node.parent;

                const isShort = name.length < minLength;
                const isLong = name.length > maxLength;

                if (!(isShort || isLong) || exceptions.has(name) || matchesExceptionPattern(name)) {
                    return; // Nothing to report
                }

                const isValidExpression = SUPPORTED_EXPRESSIONS[parent.type];

                if (isValidExpression && !reportedNode.has(node) && (isValidExpression === true || isValidExpression(parent, node))) {
                    reportedNode.add(node);
                    context.report({
                        node,
                        messageId: isShort ? "tooShort" : "tooLong",
                        data: { name, min: minLength, max: maxLength }
                    });
                }
            }
        };
    }
};