Remove the custom impl of AttrsOwner for ImplItem

The default impl should have the same behaviour, and it can be generated
by codegen.
See also `ModuleItem` and `NominalDef`

crates/ra_syntax/src/ast/extensions.rs

@@ -2,7 +2,7 @@
 //! Extensions for various expressions live in a sibling `expr_extensions` module.
 
 use crate::{
-    ast::{self, child_opt, children, AstChildren, AstNode, AttrInput, SyntaxNode},
+    ast::{self, child_opt, children, AstNode, AttrInput, SyntaxNode},
     SmolStr, SyntaxElement,
     SyntaxKind::*,
     SyntaxToken, T,
@@ -176,16 +176,6 @@ impl ast::ImplBlock {
     }
 }
 
-impl ast::AttrsOwner for ast::ImplItem {
-    fn attrs(&self) -> AstChildren<ast::Attr> {
-        match self {
-            ast::ImplItem::FnDef(it) => it.attrs(),
-            ast::ImplItem::TypeAliasDef(it) => it.attrs(),
-            ast::ImplItem::ConstDef(it) => it.attrs(),
-        }
-    }
-}
-
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum StructKind {
     Tuple(ast::TupleFieldDefList),

crates/ra_syntax/src/ast/generated.rs

@@ -1298,6 +1298,7 @@ impl AstNode for ImplItem {
         }
     }
 }
+impl ast::AttrsOwner for ImplItem {}
 impl ImplItem {}
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct ImplTraitType {

crates/ra_syntax/src/grammar.ron

@@ -401,7 +401,8 @@ Grammar(
             traits: ["AttrsOwner"]
         ),
         "ImplItem": (
-            enum: ["FnDef", "TypeAliasDef", "ConstDef"]
+            enum: ["FnDef", "TypeAliasDef", "ConstDef"],
+            traits: ["AttrsOwner"]
         ),
 
         "TupleExpr": (