Fix corrupted comments in trait generics

src/formatting/items.rs

@@ -1192,11 +1192,12 @@ pub(crate) fn format_trait(
             }
             result.push_str(&where_clause_str);
         }
-        let pre_block_span = if !generics.where_clause.predicates.is_empty() {
-            mk_sp(generics.where_clause.span.hi(), item.span.hi())
-        } else {
-            item.span
-        };
+        let pre_block_span =
+            if !generics.where_clause.predicates.is_empty() || !generics.params.is_empty() {
+                mk_sp(generics.where_clause.span.hi(), item.span.hi())
+            } else {
+                item.span
+            };
         let pre_block_snippet = context.snippet(pre_block_span);
         if let Some(lo) = pre_block_snippet.find('/') {
             // 1 = `{`

tests/source/issue-4643.rs

@@ -0,0 +1,22 @@
+pub trait Something<
+	A,
+	// some comment
+	B,
+	C
+> {
+    fn a(&self, x: A) -> i32;
+    fn b(&self, x: B) -> i32;
+    fn c(&self, x: C) -> i32;
+}
+
+pub trait Something<
+	A,
+	// some comment
+	B,
+        // Another comment
+	C
+> {
+    fn a(&self, x: A) -> i32;
+    fn b(&self, x: B) -> i32;
+    fn c(&self, x: C) -> i32;
+}

tests/target/issue-4643.rs

@@ -0,0 +1,24 @@
+pub trait Something<
+    A,
+    // some comment
+    B,
+    C,
+>
+{
+    fn a(&self, x: A) -> i32;
+    fn b(&self, x: B) -> i32;
+    fn c(&self, x: C) -> i32;
+}
+
+pub trait Something<
+    A,
+    // some comment
+    B,
+    // Another comment
+    C,
+>
+{
+    fn a(&self, x: A) -> i32;
+    fn b(&self, x: B) -> i32;
+    fn c(&self, x: C) -> i32;
+}