node/tools/eslint/lib/rules/newline-after-var.js

/**
 * @fileoverview Rule to check empty newline after "var" statement
 * @author Gopal Venkatesan
 */

"use strict";

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

module.exports = {
    meta: {
        docs: {
            description: "require or disallow an empty line after `var` declarations",
            category: "Stylistic Issues",
            recommended: false
        },

        schema: [
            {
                enum: ["never", "always"]
            }
        ]
    },

    create(context) {

        const ALWAYS_MESSAGE = "Expected blank line after variable declarations.",
            NEVER_MESSAGE = "Unexpected blank line after variable declarations.";

        const sourceCode = context.getSourceCode();

        // Default `mode` to "always".
        const mode = context.options[0] === "never" ? "never" : "always";

        // Cache starting and ending line numbers of comments for faster lookup
        const commentEndLine = sourceCode.getAllComments().reduce(function(result, token) {
            result[token.loc.start.line] = token.loc.end.line;
            return result;
        }, {});


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

        /**
         * Gets a token from the given node to compare line to the next statement.
         *
         * In general, the token is the last token of the node. However, the token is the second last token if the following conditions satisfy.
         *
         * - The last token is semicolon.
         * - The semicolon is on a different line from the previous token of the semicolon.
         *
         * This behavior would address semicolon-less style code. e.g.:
         *
         *     var foo = 1
         *
         *     ;(a || b).doSomething()
         *
         * @param {ASTNode} node - The node to get.
         * @returns {Token} The token to compare line to the next statement.
         */
        function getLastToken(node) {
            const lastToken = sourceCode.getLastToken(node);

            if (lastToken.type === "Punctuator" && lastToken.value === ";") {
                const prevToken = sourceCode.getTokenBefore(lastToken);

                if (prevToken.loc.end.line !== lastToken.loc.start.line) {
                    return prevToken;
                }
            }

            return lastToken;
        }

        /**
         * Determine if provided keyword is a variable declaration
         * @private
         * @param {string} keyword - keyword to test
         * @returns {boolean} True if `keyword` is a type of var
         */
        function isVar(keyword) {
            return keyword === "var" || keyword === "let" || keyword === "const";
        }

        /**
         * Determine if provided keyword is a variant of for specifiers
         * @private
         * @param {string} keyword - keyword to test
         * @returns {boolean} True if `keyword` is a variant of for specifier
         */
        function isForTypeSpecifier(keyword) {
            return keyword === "ForStatement" || keyword === "ForInStatement" || keyword === "ForOfStatement";
        }

        /**
         * Determine if provided keyword is an export specifiers
         * @private
         * @param {string} nodeType - nodeType to test
         * @returns {boolean} True if `nodeType` is an export specifier
         */
        function isExportSpecifier(nodeType) {
            return nodeType === "ExportNamedDeclaration" || nodeType === "ExportSpecifier" ||
                nodeType === "ExportDefaultDeclaration" || nodeType === "ExportAllDeclaration";
        }

        /**
         * Determine if provided node is the last of their parent block.
         * @private
         * @param {ASTNode} node - node to test
         * @returns {boolean} True if `node` is last of their parent block.
         */
        function isLastNode(node) {
            const token = sourceCode.getTokenAfter(node);

            return !token || (token.type === "Punctuator" && token.value === "}");
        }

        /**
         * Determine if a token starts more than one line after a comment ends
         * @param  {token}   token            The token being checked
         * @param {integer}  commentStartLine The line number on which the comment starts
         * @returns {boolean}                 True if `token` does not start immediately after a comment
         */
        function hasBlankLineAfterComment(token, commentStartLine) {
            const commentEnd = commentEndLine[commentStartLine];

            // If there's another comment, repeat check for blank line
            if (commentEndLine[commentEnd + 1]) {
                return hasBlankLineAfterComment(token, commentEnd + 1);
            }

            return (token.loc.start.line > commentEndLine[commentStartLine] + 1);
        }

        /**
         * Checks that a blank line exists after a variable declaration when mode is
         * set to "always", or checks that there is no blank line when mode is set
         * to "never"
         * @private
         * @param {ASTNode} node - `VariableDeclaration` node to test
         * @returns {void}
         */
        function checkForBlankLine(node) {
            const lastToken = getLastToken(node),
                nextToken = sourceCode.getTokenAfter(node),
                nextLineNum = lastToken.loc.end.line + 1;

            // Ignore if there is no following statement
            if (!nextToken) {
                return;
            }

            // Ignore if parent of node is a for variant
            if (isForTypeSpecifier(node.parent.type)) {
                return;
            }

            // Ignore if parent of node is an export specifier
            if (isExportSpecifier(node.parent.type)) {
                return;
            }

            // Some coding styles use multiple `var` statements, so do nothing if
            // the next token is a `var` statement.
            if (nextToken.type === "Keyword" && isVar(nextToken.value)) {
                return;
            }

            // Ignore if it is last statement in a block
            if (isLastNode(node)) {
                return;
            }

            // Next statement is not a `var`...
            const noNextLineToken = nextToken.loc.start.line > nextLineNum;
            const hasNextLineComment = (typeof commentEndLine[nextLineNum] !== "undefined");

            if (mode === "never" && noNextLineToken && !hasNextLineComment) {
                context.report(node, NEVER_MESSAGE, { identifier: node.name });
            }

            // Token on the next line, or comment without blank line
            if (
                mode === "always" && (
                    !noNextLineToken ||
                    hasNextLineComment && !hasBlankLineAfterComment(nextToken, nextLineNum)
                )
            ) {
                context.report(node, ALWAYS_MESSAGE, { identifier: node.name });
            }
        }

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

        return {
            VariableDeclaration: checkForBlankLine
        };

    }
};