path: root/tools/eslint/lib/rules/curly.js

/**
 * @fileoverview Rule to flag statements without curly braces
 * @author Nicholas C. Zakas
 */
"use strict";

//------------------------------------------------------------------------------
// Requirements
//------------------------------------------------------------------------------

const astUtils = require("../ast-utils");

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

module.exports = {
    meta: {
        docs: {
            description: "enforce consistent brace style for all control statements",
            category: "Best Practices",
            recommended: false
        },

        schema: {
            anyOf: [
                {
                    type: "array",
                    items: [
                        {
                            enum: ["all"]
                        }
                    ],
                    minItems: 0,
                    maxItems: 1
                },
                {
                    type: "array",
                    items: [
                        {
                            enum: ["multi", "multi-line", "multi-or-nest"]
                        },
                        {
                            enum: ["consistent"]
                        }
                    ],
                    minItems: 0,
                    maxItems: 2
                }
            ]
        }
    },

    create: function(context) {

        const multiOnly = (context.options[0] === "multi");
        const multiLine = (context.options[0] === "multi-line");
        const multiOrNest = (context.options[0] === "multi-or-nest");
        const consistent = (context.options[1] === "consistent");

        const sourceCode = context.getSourceCode();

        //--------------------------------------------------------------------------
        // Helpers
        //--------------------------------------------------------------------------

        /**
         * Determines if a given node is a one-liner that's on the same line as it's preceding code.
         * @param {ASTNode} node The node to check.
         * @returns {boolean} True if the node is a one-liner that's on the same line as it's preceding code.
         * @private
         */
        function isCollapsedOneLiner(node) {
            const before = sourceCode.getTokenBefore(node),
                last = sourceCode.getLastToken(node);

            return before.loc.start.line === last.loc.end.line;
        }

        /**
         * Determines if a given node is a one-liner.
         * @param {ASTNode} node The node to check.
         * @returns {boolean} True if the node is a one-liner.
         * @private
         */
        function isOneLiner(node) {
            const first = sourceCode.getFirstToken(node),
                last = sourceCode.getLastToken(node);

            return first.loc.start.line === last.loc.end.line;
        }

        /**
         * Gets the `else` keyword token of a given `IfStatement` node.
         * @param {ASTNode} node - A `IfStatement` node to get.
         * @returns {Token} The `else` keyword token.
         */
        function getElseKeyword(node) {
            let token = sourceCode.getTokenAfter(node.consequent);

            while (token.type !== "Keyword" || token.value !== "else") {
                token = sourceCode.getTokenAfter(token);
            }

            return token;
        }

        /**
         * Checks a given IfStatement node requires braces of the consequent chunk.
         * This returns `true` when below:
         *
         * 1. The given node has the `alternate` node.
         * 2. There is a `IfStatement` which doesn't have `alternate` node in the
         *    trailing statement chain of the `consequent` node.
         *
         * @param {ASTNode} node - A IfStatement node to check.
         * @returns {boolean} `true` if the node requires braces of the consequent chunk.
         */
        function requiresBraceOfConsequent(node) {
            if (node.alternate && node.consequent.type === "BlockStatement") {
                if (node.consequent.body.length >= 2) {
                    return true;
                }

                node = node.consequent.body[0];
                while (node) {
                    if (node.type === "IfStatement" && !node.alternate) {
                        return true;
                    }
                    node = astUtils.getTrailingStatement(node);
                }
            }

            return false;
        }

        /**
         * Reports "Expected { after ..." error
         * @param {ASTNode} node The node to report.
         * @param {string} name The name to report.
         * @param {string} suffix Additional string to add to the end of a report.
         * @returns {void}
         * @private
         */
        function reportExpectedBraceError(node, name, suffix) {
            context.report({
                node: node,
                loc: (name !== "else" ? node : getElseKeyword(node)).loc.start,
                message: "Expected { after '{{name}}'{{suffix}}.",
                data: {
                    name: name,
                    suffix: (suffix ? " " + suffix : "")
                }
            });
        }

        /**
         * Reports "Unnecessary { after ..." error
         * @param {ASTNode} node The node to report.
         * @param {string} name The name to report.
         * @param {string} suffix Additional string to add to the end of a report.
         * @returns {void}
         * @private
         */
        function reportUnnecessaryBraceError(node, name, suffix) {
            context.report({
                node: node,
                loc: (name !== "else" ? node : getElseKeyword(node)).loc.start,
                message: "Unnecessary { after '{{name}}'{{suffix}}.",
                data: {
                    name: name,
                    suffix: (suffix ? " " + suffix : "")
                }
            });
        }

        /**
         * Prepares to check the body of a node to see if it's a block statement.
         * @param {ASTNode} node The node to report if there's a problem.
         * @param {ASTNode} body The body node to check for blocks.
         * @param {string} name The name to report if there's a problem.
         * @param {string} suffix Additional string to add to the end of a report.
         * @returns {Object} a prepared check object, with "actual", "expected", "check" properties.
         *   "actual" will be `true` or `false` whether the body is already a block statement.
         *   "expected" will be `true` or `false` if the body should be a block statement or not, or
         *   `null` if it doesn't matter, depending on the rule options. It can be modified to change
         *   the final behavior of "check".
         *   "check" will be a function reporting appropriate problems depending on the other
         *   properties.
         */
        function prepareCheck(node, body, name, suffix) {
            const hasBlock = (body.type === "BlockStatement");
            let expected = null;

            if (node.type === "IfStatement" && node.consequent === body && requiresBraceOfConsequent(node)) {
                expected = true;
            } else if (multiOnly) {
                if (hasBlock && body.body.length === 1) {
                    expected = false;
                }
            } else if (multiLine) {
                if (!isCollapsedOneLiner(body)) {
                    expected = true;
                }
            } else if (multiOrNest) {
                if (hasBlock && body.body.length === 1 && isOneLiner(body.body[0])) {
                    expected = false;
                } else if (!isOneLiner(body)) {
                    expected = true;
                }
            } else {
                expected = true;
            }

            return {
                actual: hasBlock,
                expected: expected,
                check: function() {
                    if (this.expected !== null && this.expected !== this.actual) {
                        if (this.expected) {
                            reportExpectedBraceError(node, name, suffix);
                        } else {
                            reportUnnecessaryBraceError(node, name, suffix);
                        }
                    }
                }
            };
        }

        /**
         * Prepares to check the bodies of a "if", "else if" and "else" chain.
         * @param {ASTNode} node The first IfStatement node of the chain.
         * @returns {Object[]} prepared checks for each body of the chain. See `prepareCheck` for more
         *   information.
         */
        function prepareIfChecks(node) {
            const preparedChecks = [];

            do {
                preparedChecks.push(prepareCheck(node, node.consequent, "if", "condition"));
                if (node.alternate && node.alternate.type !== "IfStatement") {
                    preparedChecks.push(prepareCheck(node, node.alternate, "else"));
                    break;
                }
                node = node.alternate;
            } while (node);

            if (consistent) {

                /*
                 * If any node should have or already have braces, make sure they
                 * all have braces.
                 * If all nodes shouldn't have braces, make sure they don't.
                 */
                const expected = preparedChecks.some(function(preparedCheck) {
                    if (preparedCheck.expected !== null) {
                        return preparedCheck.expected;
                    }
                    return preparedCheck.actual;
                });

                preparedChecks.forEach(function(preparedCheck) {
                    preparedCheck.expected = expected;
                });
            }

            return preparedChecks;
        }

        //--------------------------------------------------------------------------
        // Public
        //--------------------------------------------------------------------------

        return {
            IfStatement: function(node) {
                if (node.parent.type !== "IfStatement") {
                    prepareIfChecks(node).forEach(function(preparedCheck) {
                        preparedCheck.check();
                    });
                }
            },

            WhileStatement: function(node) {
                prepareCheck(node, node.body, "while", "condition").check();
            },

            DoWhileStatement: function(node) {
                prepareCheck(node, node.body, "do").check();
            },

            ForStatement: function(node) {
                prepareCheck(node, node.body, "for", "condition").check();
            },

            ForInStatement: function(node) {
                prepareCheck(node, node.body, "for-in").check();
            },

            ForOfStatement: function(node) {
                prepareCheck(node, node.body, "for-of").check();
            }
        };
    }
};