Add default type param in TypeParam Node

crates/ra_syntax/src/ast/generated.rs

@@ -4038,6 +4038,7 @@ impl ToOwned for TypeParam {
 impl ast::NameOwner for TypeParam {}
 impl ast::AttrsOwner for TypeParam {}
 impl ast::TypeBoundsOwner for TypeParam {}
+impl ast::DefaultTypeParamOwner for TypeParam {}
 impl TypeParam {}
 
 // TypeParamList

crates/ra_syntax/src/ast/traits.rs

@@ -152,3 +152,9 @@ impl<'a> Iterator for CommentIter<'a> {
         self.iter.by_ref().find_map(|el| el.as_token().and_then(ast::Comment::cast))
     }
 }
+
+pub trait DefaultTypeParamOwner: AstNode {
+    fn default_type(&self) -> Option<&ast::PathType> {
+        child_opt(self)
+    }
+}

crates/ra_syntax/src/grammar.ron

@@ -563,7 +563,7 @@ Grammar(
                 ["lifetime_params", "LifetimeParam" ],
             ]
         ),
-        "TypeParam": ( traits: ["NameOwner", "AttrsOwner", "TypeBoundsOwner"] ),
+        "TypeParam": ( traits: ["NameOwner", "AttrsOwner", "TypeBoundsOwner", "DefaultTypeParamOwner"] ),
         "LifetimeParam": (
             traits: ["AttrsOwner"],
         ),