update PartialOrd for StyleEdition::Edition2027

This was missed when the `Edition2027` variant was added.

src/config/options.rs

@@ -536,7 +536,14 @@ impl From<StyleEdition> for rustc_span::edition::Edition {
 
 impl PartialOrd for StyleEdition {
     fn partial_cmp(&self, other: &StyleEdition) -> Option<std::cmp::Ordering> {
-        rustc_span::edition::Edition::partial_cmp(&(*self).into(), &(*other).into())
+        // FIXME(ytmimi): Update the `StyleEdition::Edition2027` logic when the
+        // `Edition::Edition2027` becomes available in the compiler
+        match (self, other) {
+            (Self::Edition2027, Self::Edition2027) => Some(std::cmp::Ordering::Equal),
+            (_, Self::Edition2027) => Some(std::cmp::Ordering::Less),
+            (Self::Edition2027, _) => Some(std::cmp::Ordering::Greater),
+            _ => rustc_span::edition::Edition::partial_cmp(&(*self).into(), &(*other).into()),
+        }
     }
 }
 
@@ -684,3 +691,41 @@ config_option_with_style_edition_default!(
     MakeBackup, bool, _ => false;
     PrintMisformattedFileNames, bool, _ => false;
 );
+
+#[test]
+fn style_edition_comparisons() {
+    // Style Edition 2015
+    assert!(StyleEdition::Edition2015 == StyleEdition::Edition2015);
+    assert!(StyleEdition::Edition2015 < StyleEdition::Edition2018);
+    assert!(StyleEdition::Edition2015 < StyleEdition::Edition2021);
+    assert!(StyleEdition::Edition2015 < StyleEdition::Edition2024);
+    assert!(StyleEdition::Edition2015 < StyleEdition::Edition2027);
+
+    // Style Edition 2018
+    assert!(StyleEdition::Edition2018 > StyleEdition::Edition2015);
+    assert!(StyleEdition::Edition2018 == StyleEdition::Edition2018);
+    assert!(StyleEdition::Edition2018 < StyleEdition::Edition2021);
+    assert!(StyleEdition::Edition2018 < StyleEdition::Edition2024);
+    assert!(StyleEdition::Edition2018 < StyleEdition::Edition2027);
+
+    // Style Edition 2021
+    assert!(StyleEdition::Edition2021 > StyleEdition::Edition2015);
+    assert!(StyleEdition::Edition2021 > StyleEdition::Edition2018);
+    assert!(StyleEdition::Edition2021 == StyleEdition::Edition2021);
+    assert!(StyleEdition::Edition2021 < StyleEdition::Edition2024);
+    assert!(StyleEdition::Edition2021 < StyleEdition::Edition2027);
+
+    // Style Edition 2024
+    assert!(StyleEdition::Edition2024 > StyleEdition::Edition2015);
+    assert!(StyleEdition::Edition2024 > StyleEdition::Edition2018);
+    assert!(StyleEdition::Edition2024 > StyleEdition::Edition2021);
+    assert!(StyleEdition::Edition2024 == StyleEdition::Edition2024);
+    assert!(StyleEdition::Edition2024 < StyleEdition::Edition2027);
+
+    // Style Edition 2024
+    assert!(StyleEdition::Edition2027 > StyleEdition::Edition2015);
+    assert!(StyleEdition::Edition2027 > StyleEdition::Edition2018);
+    assert!(StyleEdition::Edition2027 > StyleEdition::Edition2021);
+    assert!(StyleEdition::Edition2027 > StyleEdition::Edition2024);
+    assert!(StyleEdition::Edition2027 == StyleEdition::Edition2027);
+}