feat(oxlint): add stylish formatter (#8607)

👋 This implements a reporter for `--format` on `oxlint` which aims to be
visually similar to
https://eslint.org/docs/latest/use/formatters/#stylish

Please note that this is my first time working with Rust and my
knowledge is very limited. I'm unlikely to understand best-practice or
best-pattern references outside of what clippy/cargo lint has already
had me change. If this needs modification, please help me out by making
code suggestions that can be merged to this PR.

Resolves #8422

---------

Co-authored-by: Cameron <cameron.clark@hey.com>

apps/oxlint/src/output_formatter/mod.rs

@@ -2,6 +2,7 @@ mod checkstyle;
 mod default;
 mod github;
 mod json;
+mod stylish;
 mod unix;
 
 use std::io::{BufWriter, Stdout, Write};
@@ -9,6 +10,7 @@ use std::str::FromStr;
 
 use checkstyle::CheckStyleOutputFormatter;
 use github::GithubOutputFormatter;
+use stylish::StylishOutputFormatter;
 use unix::UnixOutputFormatter;
 
 use oxc_diagnostics::reporter::DiagnosticReporter;
@@ -24,6 +26,7 @@ pub enum OutputFormat {
     Json,
     Unix,
     Checkstyle,
+    Stylish,
 }
 
 impl FromStr for OutputFormat {
@@ -36,13 +39,13 @@ impl FromStr for OutputFormat {
             "unix" => Ok(Self::Unix),
             "checkstyle" => Ok(Self::Checkstyle),
             "github" => Ok(Self::Github),
+            "stylish" => Ok(Self::Stylish),
             _ => Err(format!("'{s}' is not a known format")),
         }
     }
 }
 
 trait InternalFormatter {
-    // print all rules which are currently supported by oxlint
     fn all_rules(&mut self, writer: &mut dyn Write);
 
     fn get_diagnostic_reporter(&self) -> Box<dyn DiagnosticReporter>;
@@ -64,10 +67,10 @@ impl OutputFormatter {
             OutputFormat::Github => Box::new(GithubOutputFormatter),
             OutputFormat::Unix => Box::<UnixOutputFormatter>::default(),
             OutputFormat::Default => Box::new(DefaultOutputFormatter),
+            OutputFormat::Stylish => Box::<StylishOutputFormatter>::default(),
         }
     }
 
-    // print all rules which are currently supported by oxlint
     pub fn all_rules(&mut self, writer: &mut BufWriter<Stdout>) {
         self.internal_formatter.all_rules(writer);
     }

apps/oxlint/src/output_formatter/stylish.rs

@@ -0,0 +1,146 @@
+use std::io::Write;
+
+use oxc_diagnostics::{
+    reporter::{DiagnosticReporter, Info},
+    Error, Severity,
+};
+use rustc_hash::FxHashMap;
+
+use crate::output_formatter::InternalFormatter;
+
+#[derive(Debug, Default)]
+pub struct StylishOutputFormatter;
+
+impl InternalFormatter for StylishOutputFormatter {
+    fn all_rules(&mut self, writer: &mut dyn Write) {
+        writeln!(writer, "flag --rules with flag --format=stylish is not allowed").unwrap();
+    }
+
+    fn get_diagnostic_reporter(&self) -> Box<dyn DiagnosticReporter> {
+        Box::new(StylishReporter::default())
+    }
+}
+
+#[derive(Default)]
+struct StylishReporter {
+    diagnostics: Vec<Error>,
+}
+
+impl DiagnosticReporter for StylishReporter {
+    fn finish(&mut self) -> Option<String> {
+        Some(format_stylish(&self.diagnostics))
+    }
+
+    fn render_error(&mut self, error: Error) -> Option<String> {
+        self.diagnostics.push(error);
+        None
+    }
+}
+
+fn format_stylish(diagnostics: &[Error]) -> String {
+    if diagnostics.is_empty() {
+        return String::new();
+    }
+
+    let mut output = String::new();
+    let mut total_errors = 0;
+    let mut total_warnings = 0;
+
+    let mut grouped: FxHashMap<String, Vec<&Error>> = FxHashMap::default();
+    let mut sorted = diagnostics.iter().collect::<Vec<_>>();
+
+    sorted.sort_by_key(|diagnostic| Info::new(diagnostic).line);
+
+    for diagnostic in sorted {
+        let info = Info::new(diagnostic);
+        grouped.entry(info.filename).or_default().push(diagnostic);
+    }
+
+    for diagnostics in grouped.values() {
+        let diagnostic = diagnostics[0];
+        let info = Info::new(diagnostic);
+        let filename = info.filename;
+        let filename = if let Some(path) =
+            std::env::current_dir().ok().and_then(|d| d.join(&filename).canonicalize().ok())
+        {
+            path.display().to_string()
+        } else {
+            filename
+        };
+        let max_len_width = diagnostics
+            .iter()
+            .filter_map(|diagnostic| diagnostic.labels())
+            .flat_map(std::iter::Iterator::collect::<Vec<_>>)
+            .map(|label| format!("{}:{}", label.offset(), label.len()).len())
+            .max()
+            .unwrap_or(0);
+
+        output.push_str(&format!("\n\u{1b}[4m{filename}\u{1b}[0m\n"));
+
+        for diagnostic in diagnostics {
+            match diagnostic.severity() {
+                Some(Severity::Error) => total_errors += 1,
+                _ => total_warnings += 1,
+            }
+
+            let severity_str = if diagnostic.severity() == Some(Severity::Error) {
+                "\u{1b}[31merror\u{1b}[0m"
+            } else {
+                "\u{1b}[33mwarning\u{1b}[0m"
+            };
+
+            if let Some(label) = diagnostic.labels().expect("should have labels").next() {
+                let rule = diagnostic.code().map_or_else(String::new, |code| code.to_string());
+                let position = format!("{}:{}", label.offset(), label.len());
+                output.push_str(
+                    &format!("  \u{1b}[2m{position:max_len_width$}\u{1b}[0m  {severity_str}  {diagnostic}  \u{1b}[2m{rule}\u{1b}[0m\n"),
+                );
+            }
+        }
+    }
+
+    let total = total_errors + total_warnings;
+    if total > 0 {
+        let summary_color = if total_errors > 0 { "\u{1b}[31m" } else { "\u{1b}[33m" };
+        output.push_str(&format!(
+            "\n{summary_color}✖ {total} problem{} ({total_errors} error{}, {total_warnings} warning{})\u{1b}[0m\n",
+            if total == 1 { "" } else { "s" },
+            if total_errors == 1 { "" } else { "s" },
+            if total_warnings == 1 { "" } else { "s" }
+        ));
+    }
+
+    output
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use oxc_diagnostics::{NamedSource, OxcDiagnostic};
+    use oxc_span::Span;
+
+    #[test]
+    fn test_stylish_reporter() {
+        let mut reporter = StylishReporter::default();
+
+        let error = OxcDiagnostic::error("error message")
+            .with_label(Span::new(0, 8))
+            .with_source_code(NamedSource::new("file.js", "code"));
+
+        let warning = OxcDiagnostic::warn("warning message")
+            .with_label(Span::new(0, 8))
+            .with_source_code(NamedSource::new("file.js", "code"));
+
+        reporter.render_error(error);
+        reporter.render_error(warning);
+
+        let output = reporter.finish().unwrap();
+
+        assert!(output.contains("error message"), "Output should contain 'error message'");
+        assert!(output.contains("warning message"), "Output should contain 'warning message'");
+        assert!(output.contains("\u{2716}"), "Output should contain the ✖ character");
+        assert!(output.contains("2 problems"), "Output should mention total problems");
+        assert!(output.contains("1 error"), "Output should mention error count");
+        assert!(output.contains("1 warning"), "Output should mention warning count");
+    }
+}