import { Rule, RuleViolation } from './rule-interface';
/**
* MD009: Trailing spaces
*
* This rule is triggered when trailing spaces are found at the end of a line.
* Trailing spaces can cause unnecessary diffs in version control systems and
* can be confusing in a text editor.
*/
export const name = 'MD009';
export const description = 'Trailing spaces';
interface MD009Config {
br_spaces?: number;
list_item_empty_lines?: boolean;
strict?: boolean;
}
/**
* Validate lines for trailing spaces
* @param lines Array of string lines to validate
* @param config Rule configuration
* @returns Array of rule violations
*/
export function validate(lines: string[], config: MD009Config = {}): RuleViolation[] {
const violations: RuleViolation[] = [];
const brSpaces = config.br_spaces ?? 0;
const strictMode = config.strict === true;
for (let i = 0; i < lines.length; i++) {
const line = lines[i];
const trailingSpaceMatch = line.match(/[ \t]+$/);
if (trailingSpaceMatch) {
const trailingSpaces = trailingSpaceMatch[0];
// In strict mode, any trailing whitespace is a violation
if (strictMode) {
violations.push({
lineNumber: i + 1,
details: `Trailing spaces${trailingSpaces.length > 0 ? ` (${trailingSpaces.length})` : ''}`,
range: [line.length - trailingSpaces.length, trailingSpaces.length]
});
continue;
}
// Check if line is blank (only whitespace)
const isBlankLine = line.trim() === '';
// Check if this line has a valid line break (exactly br_spaces trailing spaces)
const hasContent = line.trim().length > 0;
const isLineBreak = brSpaces > 0 && hasContent && trailingSpaces.length === brSpaces;
// Report a violation if:
// 1. It's not a valid line break (and br_spaces is set)
// 2. It's a blank line with trailing spaces
// 3. Any trailing spaces when br_spaces is 0
if ((brSpaces > 0 && !isLineBreak && hasContent) ||
(isBlankLine && trailingSpaces.length > 0) ||
(brSpaces === 0)) {
violations.push({
lineNumber: i + 1,
details: `Trailing spaces${trailingSpaces.length > 0 ? ` (${trailingSpaces.length})` : ''}`,
range: [line.length - trailingSpaces.length, trailingSpaces.length]
});
}
}
}
return violations;
}
/**
* Fix trailing spaces by removing them from the end of each line
* @param lines Array of string lines to fix
* @param config Rule configuration
* @returns Fixed lines array with trailing spaces removed
*/
export function fix(lines: string[], config: MD009Config = {}): string[] {
const brSpaces = config.br_spaces ?? 0;
const strictMode = config.strict === true;
return lines.map(line => {
// Check if line has trailing spaces
const trailingSpaceMatch = line.match(/[ \t]+$/);
if (!trailingSpaceMatch) return line;
// Check if line is blank (only whitespace)
const isBlankLine = line.trim() === '';
// If it's a blank line, always remove all trailing whitespace
if (isBlankLine) {
return '';
}
// Handle strict mode differently
if (strictMode) {
// In strict mode, if br_spaces is set, normalize to exactly that many spaces
if (brSpaces > 0) {
const hasContent = line.trim().length > 0;
if (hasContent) {
// Example: Line with trailing spaces. -> Line with trailing spaces.
return line.replace(/[ \t]+$/, ' '.repeat(brSpaces));
} else {
// Empty lines should have no trailing spaces
return '';
}
} else {
// If br_spaces is not set, remove all trailing spaces
return line.replace(/[ \t]+$/, '');
}
}
// Non-strict mode handling
if (brSpaces > 0) {
// If trailing spaces are already exactly br_spaces, keep them
if (trailingSpaceMatch[0].length === brSpaces) {
return line;
}
// If trailing spaces are fewer than br_spaces, replace with br_spaces
if (trailingSpaceMatch[0].length < brSpaces) {
return line.replace(/[ \t]+$/, ' '.repeat(brSpaces));
}
// If trailing spaces are more than br_spaces, replace with br_spaces
return line.replace(/[ \t]+$/, ' '.repeat(brSpaces));
}
// If br_spaces is 0 or not specified, remove all trailing whitespace
return line.replace(/[ \t]+$/, '');
});
}
/**
* Rule implementation for MD009
*/
export const rule: Rule = {
name,
description,
validate,
fix
};
export default rule;
