[red-knot] Use colors to improve readability of mdtest output (#13725)

crates/red_knot_test/Cargo.toml

@@ -20,6 +20,7 @@ ruff_source_file = { workspace = true }
 ruff_text_size = { workspace = true }
 
 anyhow = { workspace = true }
+colored = { workspace = true }
 once_cell = { workspace = true }
 regex = { workspace = true }
 rustc-hash = { workspace = true }

crates/red_knot_test/src/lib.rs

@@ -1,3 +1,4 @@
+use colored::Colorize;
 use parser as test_parser;
 use red_knot_python_semantic::types::check_types;
 use ruff_db::files::system_path_to_file;
@@ -31,20 +32,23 @@ pub fn run(path: &PathBuf, title: &str) {
     for test in suite.tests() {
         if let Err(failures) = run_test(&test) {
             any_failures = true;
-            println!("{}", test.name());
+            println!("\n{}\n", test.name().bold().underline());
 
             for (path, by_line) in failures {
-                println!("  {path}");
-                for (line, failures) in by_line.iter() {
+                println!("{}", path.as_str().bold());
+                for (line_number, failures) in by_line.iter() {
                     for failure in failures {
-                        println!("    line {line}: {failure}");
+                        let line_info = format!("line {line_number}:").cyan();
+                        println!("    {line_info} {failure}");
                     }
                 }
                 println!();
             }
         }
     }
 
+    println!("{}\n", "-".repeat(50));
+
     assert!(!any_failures, "Some tests failed.");
 }
 

crates/red_knot_test/src/matcher.rs

@@ -3,6 +3,7 @@
 use crate::assertion::{Assertion, ErrorAssertion, InlineFileAssertions};
 use crate::db::Db;
 use crate::diagnostic::SortedDiagnostics;
+use colored::Colorize;
 use red_knot_python_semantic::types::TypeCheckDiagnostic;
 use ruff_db::files::File;
 use ruff_db::source::{line_index, source_text, SourceText};
@@ -155,7 +156,7 @@ trait UnmatchedWithColumn {
 
 impl Unmatched for Assertion<'_> {
     fn unmatched(&self) -> String {
-        format!("unmatched assertion: {self}")
+        format!("{} {self}", "unmatched assertion:".red())
     }
 }
 
@@ -165,11 +166,11 @@ fn maybe_add_undefined_reveal_clarification<T: Diagnostic>(
 ) -> String {
     if diagnostic.rule() == "undefined-reveal" {
         format!(
-            "used built-in `reveal_type`: add a `# revealed` assertion on this line \
-            (original diagnostic: {original})"
+            "{} add a `# revealed` assertion on this line (original diagnostic: {original})",
+            "used built-in `reveal_type`:".yellow()
         )
     } else {
-        format!("unexpected error: {original}")
+        format!("{} {original}", "unexpected error:".red())
     }
 }
 
@@ -232,7 +233,10 @@ impl Matcher {
                     ..
                 })
             ) {
-                failures.push("invalid assertion: no rule or message text".to_string());
+                failures.push(format!(
+                    "{} no rule or message text",
+                    "invalid assertion:".red()
+                ));
                 continue;
             }
             if !self.matches(assertion, &mut unmatched) {
@@ -360,6 +364,8 @@ mod tests {
     }
 
     fn get_result(source: &str, diagnostics: Vec<TestDiagnostic>) -> Result<(), FailuresByLine> {
+        colored::control::set_override(false);
+
         let mut db = crate::db::Db::setup(SystemPathBuf::from("/src"));
         db.write_file("/src/test.py", source).unwrap();
         let file = system_path_to_file(&db, "/src/test.py").unwrap();