ember-template-lint/lib/rules/no-multiple-empty-lines.js

Linter for Ember or Handlebars templates.

'use strict';

const Rule = require('./base');

const CONFIG_ERROR_MESSAGE = 'Invalid rule configuration for `no-multiple-empty-lines` found';

module.exports = class NoMultipleEmptyLines extends Rule {
  parseConfig(config) {
    return parseConfig(config);
  }

  visitor() {
    // Swallow the final newline, as some editors add it automatically and we don't want it to cause an issue
    let allLines =
      this.source[this.source.length - 1] === '' ? this.source.slice(0, -1) : this.source;

    return {
      Template: {
        exit() {
          let max = 'max' in this.config ? this.config.max : 1;

          allLines

            // Given a list of lines, first get a list of line numbers that are non-empty.
            .reduce((nonEmptyLineNumbers, line, index) => {
              if (line.trim()) {
                nonEmptyLineNumbers.push(index + 1);
              }
              return nonEmptyLineNumbers;
            }, [])

            // Add a value at the end to allow trailing empty lines to be checked.
            .concat(allLines.length + 1) // eslint-disable-line unicorn/prefer-spread

            // Given two line numbers of non-empty lines, report the lines between if the difference is too large.
            .reduce((lastLineNumber, lineNumber) => {
              if (lineNumber - lastLineNumber - 1 > max) {
                let message = `More than ${max} blank ${max === 1 ? 'line' : 'lines'} not allowed.`;

                let loc = {
                  start: { line: lastLineNumber + max, column: 0 },
                  end: { line: lineNumber, column: 0 },
                };

                this.log({
                  message,
                  line: loc.start.line,
                  column: loc.start.column,
                  source: this.sourceForLoc(loc),
                });
              }

              return lineNumber;
            }, 0);
        },
      },
    };
  }
};

function parseConfig(config) {
  if (config === true) {
    return { max: 1 };
  }

  if (typeof config !== 'object' || config === null) {
    throw new Error(CONFIG_ERROR_MESSAGE);
  }

  let max = config.max;
  if (typeof max !== 'number') {
    throw new TypeError(CONFIG_ERROR_MESSAGE);
  }

  return { max };
}

module.exports.parseConfig = parseConfig;
module.exports.CONFIG_ERROR_MESSAGE = CONFIG_ERROR_MESSAGE;