eslint/lib/rules/yield-star-spacing.js

/**
 * @fileoverview Rule to check the spacing around the * in yield* expressions.
 * @author Bryan Smith
 */

"use strict";

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

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

        docs: {
            description: "require or disallow spacing around the `*` in `yield*` expressions",
            category: "ECMAScript 6",
            recommended: false,
            url: "https://eslint.org/docs/rules/yield-star-spacing"
        },

        fixable: "whitespace",

        schema: [
            {
                oneOf: [
                    {
                        enum: ["before", "after", "both", "neither"]
                    },
                    {
                        type: "object",
                        properties: {
                            before: { type: "boolean" },
                            after: { type: "boolean" }
                        },
                        additionalProperties: false
                    }
                ]
            }
        ],
        messages: {
            missingBefore: "Missing space before *.",
            missingAfter: "Missing space after *.",
            unexpectedBefore: "Unexpected space before *.",
            unexpectedAfter: "Unexpected space after *."
        }
    },

    create(context) {
        const sourceCode = context.getSourceCode();

        const mode = (function(option) {
            if (!option || typeof option === "string") {
                return {
                    before: { before: true, after: false },
                    after: { before: false, after: true },
                    both: { before: true, after: true },
                    neither: { before: false, after: false }
                }[option || "after"];
            }
            return option;
        }(context.options[0]));

        /**
         * Checks the spacing between two tokens before or after the star token.
         * @param {string} side Either "before" or "after".
         * @param {Token} leftToken `function` keyword token if side is "before", or
         *     star token if side is "after".
         * @param {Token} rightToken Star token if side is "before", or identifier
         *     token if side is "after".
         * @returns {void}
         */
        function checkSpacing(side, leftToken, rightToken) {
            if (sourceCode.isSpaceBetweenTokens(leftToken, rightToken) !== mode[side]) {
                const after = leftToken.value === "*";
                const spaceRequired = mode[side];
                const node = after ? leftToken : rightToken;
                let messageId = "";

                if (spaceRequired) {
                    messageId = side === "before" ? "missingBefore" : "missingAfter";
                } else {
                    messageId = side === "before" ? "unexpectedBefore" : "unexpectedAfter";
                }

                context.report({
                    node,
                    messageId,
                    fix(fixer) {
                        if (spaceRequired) {
                            if (after) {
                                return fixer.insertTextAfter(node, " ");
                            }
                            return fixer.insertTextBefore(node, " ");
                        }
                        return fixer.removeRange([leftToken.range[1], rightToken.range[0]]);
                    }
                });
            }
        }

        /**
         * Enforces the spacing around the star if node is a yield* expression.
         * @param {ASTNode} node A yield expression node.
         * @returns {void}
         */
        function checkExpression(node) {
            if (!node.delegate) {
                return;
            }

            const tokens = sourceCode.getFirstTokens(node, 3);
            const yieldToken = tokens[0];
            const starToken = tokens[1];
            const nextToken = tokens[2];

            checkSpacing("before", yieldToken, starToken);
            checkSpacing("after", starToken, nextToken);
        }

        return {
            YieldExpression: checkExpression
        };

    }
};