eslint/lib/rules/no-mixed-spaces-and-tabs.js

/**
 * @fileoverview Disallow mixed spaces and tabs for indentation
 * @author Jary Niebur
 */
"use strict";

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

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

        docs: {
            description: "disallow mixed spaces and tabs for indentation",
            category: "Stylistic Issues",
            recommended: true,
            url: "https://eslint.org/docs/rules/no-mixed-spaces-and-tabs"
        },

        schema: [
            {
                enum: ["smart-tabs", true, false]
            }
        ],

        messages: {
            mixedSpacesAndTabs: "Mixed spaces and tabs."
        }
    },

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

        let smartTabs;

        switch (context.options[0]) {
            case true: // Support old syntax, maybe add deprecation warning here
            case "smart-tabs":
                smartTabs = true;
                break;
            default:
                smartTabs = false;
        }

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

        return {

            "Program:exit"(node) {
                const lines = sourceCode.lines,
                    comments = sourceCode.getAllComments(),
                    ignoredCommentLines = new Set();

                // Add all lines except the first ones.
                comments.forEach(comment => {
                    for (let i = comment.loc.start.line + 1; i <= comment.loc.end.line; i++) {
                        ignoredCommentLines.add(i);
                    }
                });

                /*
                 * At least one space followed by a tab
                 * or the reverse before non-tab/-space
                 * characters begin.
                 */
                let regex = /^(?=( +|\t+))\1(?:\t| )/u;

                if (smartTabs) {

                    /*
                     * At least one space followed by a tab
                     * before non-tab/-space characters begin.
                     */
                    regex = /^(?=(\t*))\1(?=( +))\2\t/u;
                }

                lines.forEach((line, i) => {
                    const match = regex.exec(line);

                    if (match) {
                        const lineNumber = i + 1;
                        const loc = {
                            start: {
                                line: lineNumber,
                                column: match[0].length - 2
                            },
                            end: {
                                line: lineNumber,
                                column: match[0].length
                            }
                        };

                        if (!ignoredCommentLines.has(lineNumber)) {
                            const containingNode = sourceCode.getNodeByRangeIndex(sourceCode.getIndexFromLoc(loc.start));

                            if (!(containingNode && ["Literal", "TemplateElement"].includes(containingNode.type))) {
                                context.report({
                                    node,
                                    loc,
                                    messageId: "mixedSpacesAndTabs"
                                });
                            }
                        }
                    }
                });
            }
        };
    }
};