fix PathSegment grammar

crates/syntax/src/ast/node_ext.rs

@@ -361,6 +361,18 @@ impl ast::Impl {
     }
 }
 
+// for `PathSegment` '<i32 as core::ops::Add>', call `first_path_type` will get `i32` and `last_path_type` will get `core::ops::Add`
+// for '<&i32 as core::ops::Add>', call `first_path_type` and `last_path_type` will both get `core::ops::Add` cause `&i32` is `Type(RefType)`
+impl ast::PathSegment {
+    pub fn first_path_type(&self) -> Option<ast::PathType> {
+        self.syntax().children().find_map(ast::PathType::cast)
+    }
+
+    pub fn last_path_type(&self) -> Option<ast::PathType> {
+        self.syntax().children().filter_map(ast::PathType::cast).last()
+    }
+}
+
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum StructKind {
     Record(ast::RecordFieldList),