rumdl_lib/rules/

md047_single_trailing_newline.rs

use crate::rule::{Fix, LintError, LintResult, LintWarning, Rule, RuleCategory, Severity};

/// Rule MD047: File should end with a single newline
///
/// See [docs/md047.md](../../docs/md047.md) for full documentation, configuration, and examples.

#[derive(Debug, Default, Clone)]
pub struct MD047SingleTrailingNewline;

impl Rule for MD047SingleTrailingNewline {
    fn name(&self) -> &'static str {
        "MD047"
    }

    fn description(&self) -> &'static str {
        "Files should end with a single newline character"
    }

    fn category(&self) -> RuleCategory {
        RuleCategory::Whitespace
    }

    fn should_skip(&self, ctx: &crate::lint_context::LintContext) -> bool {
        // Skip empty files - they don't need trailing newlines
        ctx.content.is_empty()
    }

    fn check(&self, ctx: &crate::lint_context::LintContext) -> LintResult {
        let content = ctx.content;
        let mut warnings = Vec::new();

        // Empty content is fine
        if content.is_empty() {
            return Ok(warnings);
        }

        // Content has been normalized to LF at I/O boundary
        // Check if file ends with newline
        let has_trailing_newline = content.ends_with('\n');

        // Check for missing trailing newline
        if !has_trailing_newline {
            let lines = &ctx.lines;
            let last_line_num = lines.len();
            let last_line_content = lines.last().map(|s| s.content(content)).unwrap_or("");

            // Calculate precise character range for the end of file
            // For missing newline, highlight the end of the last line
            let (start_line, start_col, end_line, end_col) = (
                last_line_num,
                last_line_content.len() + 1,
                last_line_num,
                last_line_content.len() + 1,
            );

            warnings.push(LintWarning {
                rule_name: Some(self.name().to_string()),
                message: String::from("File should end with a single newline character"),
                line: start_line,
                column: start_col,
                end_line,
                end_column: end_col,
                severity: Severity::Warning,
                fix: Some(Fix {
                    // For missing newline, insert at the end of the file
                    range: content.len()..content.len(),
                    // Always add LF - will be converted to CRLF at I/O boundary if needed
                    replacement: "\n".to_string(),
                }),
            });
        }

        Ok(warnings)
    }

    fn fix(&self, ctx: &crate::lint_context::LintContext) -> Result<String, LintError> {
        let content = ctx.content;

        // Empty content remains empty
        if content.is_empty() {
            return Ok(String::new());
        }

        // Content has been normalized to LF at I/O boundary
        // Check if file already ends with a newline
        let has_trailing_newline = content.ends_with('\n');

        if has_trailing_newline {
            return Ok(content.to_string());
        }

        // Check if the rule is disabled on the last line via inline config
        let last_line_num = ctx.lines.len();
        if ctx.inline_config().is_rule_disabled(self.name(), last_line_num) {
            return Ok(content.to_string());
        }

        // Content doesn't end with newline, add LF (will be converted at I/O boundary if needed)
        let mut result = String::with_capacity(content.len() + 1);
        result.push_str(content);
        result.push('\n');
        Ok(result)
    }

    fn as_any(&self) -> &dyn std::any::Any {
        self
    }

    fn from_config(_config: &crate::config::Config) -> Box<dyn Rule>
    where
        Self: Sized,
    {
        Box::new(MD047SingleTrailingNewline)
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::lint_context::LintContext;

    #[test]
    fn test_valid_trailing_newline() {
        let rule = MD047SingleTrailingNewline;
        let content = "Line 1\nLine 2\n";
        let ctx = LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();
        assert!(result.is_empty());
    }

    #[test]
    fn test_missing_trailing_newline() {
        let rule = MD047SingleTrailingNewline;
        let content = "Line 1\nLine 2";
        let ctx = LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();
        assert_eq!(result.len(), 1);
        let fixed = rule.fix(&ctx).unwrap();
        assert_eq!(fixed, "Line 1\nLine 2\n");
    }

    #[test]
    fn test_multiple_trailing_newlines() {
        // Should not trigger when file has trailing newlines
        let rule = MD047SingleTrailingNewline;
        let content = "Line 1\nLine 2\n\n\n";
        let ctx = LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();
        assert!(result.is_empty());
    }

    #[test]
    fn test_normalized_lf_content() {
        // In production, content is normalized to LF before rules see it
        // This test reflects the actual runtime behavior
        let rule = MD047SingleTrailingNewline;
        let content = "Line 1\nLine 2";
        let ctx = LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();
        assert_eq!(result.len(), 1);

        let fixed = rule.fix(&ctx).unwrap();
        // Rule always adds LF - I/O boundary converts to CRLF if needed
        assert_eq!(fixed, "Line 1\nLine 2\n");
        assert!(fixed.ends_with('\n'), "Should end with LF");
    }

    #[test]
    fn test_blank_file() {
        let rule = MD047SingleTrailingNewline;
        let content = "";
        let ctx = LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();
        assert!(result.is_empty());
    }

    #[test]
    fn test_file_with_only_newlines() {
        // Should not trigger when file contains only newlines
        let rule = MD047SingleTrailingNewline;
        let content = "\n\n\n";
        let ctx = LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();
        assert!(result.is_empty());
    }
}