--show-settings displays active settings in a far more readable for…

…mat (#9464)

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## Summary

Fixes #8334.

`Display` has been implemented for `ruff_workspace::Settings`, which
gives a much nicer and more readable output to `--show-settings`.

Internally, a `display_settings` utility macro has been implemented to
reduce the boilerplate of the display code.

### Work to be done

- [x] A lot of formatting for `Vec<_>` and `HashSet<_>` types have been
stubbed out, using `Debug` as a fallback. There should be a way to add
generic formatting support for these types as a modifier in
`display_settings`.
- [x] Several complex types were also stubbed out and need proper
`Display` implementations rather than falling back on `Debug`.
- [x] An open question needs to be answered: how important is it that
the output be valid TOML? Some types in settings, such as a hash-map
from a glob pattern to a multi-variant enum, will be hard to rework into
valid _and_ readable TOML.
- [x] Tests need to be implemented.

## Test Plan

Tests consist of a snapshot test for the default `--show-settings`
output and a doctest for `display_settings!`.

crates/ruff_cli/src/commands/show_settings.rs

@@ -35,7 +35,7 @@ pub(crate) fn show_settings(
     if let Some(settings_path) = pyproject_config.path.as_ref() {
         writeln!(writer, "Settings path: {settings_path:?}")?;
     }
-    writeln!(writer, "{settings:#?}")?;
+    write!(writer, "{settings}")?;
 
     Ok(())
 }

crates/ruff_cli/tests/show_settings.rs

@@ -0,0 +1,29 @@
+use insta_cmd::{assert_cmd_snapshot, get_cargo_bin};
+use std::path::Path;
+use std::process::Command;
+
+const BIN_NAME: &str = "ruff";
+
+#[cfg(not(target_os = "windows"))]
+const TEST_FILTERS: &[(&str, &str)] = &[
+    ("\"[^\\*\"]*/pyproject.toml", "\"[BASEPATH]/pyproject.toml"),
+    ("\".*/crates", "\"[BASEPATH]/crates"),
+    ("\".*/\\.ruff_cache", "\"[BASEPATH]/.ruff_cache"),
+    ("\".*/ruff\"", "\"[BASEPATH]\""),
+];
+#[cfg(target_os = "windows")]
+const TEST_FILTERS: &[(&str, &str)] = &[
+    (r#""[^\*"]*\\pyproject.toml"#, "\"[BASEPATH]/pyproject.toml"),
+    (r#"".*\\crates"#, "\"[BASEPATH]/crates"),
+    (r#"".*\\\.ruff_cache"#, "\"[BASEPATH]/.ruff_cache"),
+    (r#"".*\\ruff""#, "\"[BASEPATH]\""),
+    (r#"\\+(\w\w|\s|")"#, "/$1"),
+];
+
+#[test]
+fn display_default_settings() {
+    insta::with_settings!({ filters => TEST_FILTERS.to_vec() }, {
+        assert_cmd_snapshot!(Command::new(get_cargo_bin(BIN_NAME))
+            .args(["check", "--show-settings", "unformatted.py"]).current_dir(Path::new("./resources/test/fixtures")));
+    });
+}