added fmt::Display as a supertrait for AstNode and changed generation.

crates/ra_syntax/src/ast.rs

@@ -30,7 +30,7 @@ pub use self::{
 /// conversion itself has zero runtime cost: ast and syntax nodes have exactly
 /// the same representation: a pointer to the tree root and a pointer to the
 /// node itself.
-pub trait AstNode {
+pub trait AstNode: std::fmt::Display {
     fn can_cast(kind: SyntaxKind) -> bool
     where
         Self: Sized;

xtask/src/codegen/gen_syntax.rs

@@ -68,6 +68,12 @@ fn generate_ast(grammar: AstSrc<'_>) -> Result<String> {
                 pub(crate) syntax: SyntaxNode,
             }
 
+            impl std::fmt::Display for #name {
+                fn fmt(..) -> std::fmt::Result {
+                    std::fmt::Display::fmt(self.syntax())
+                }
+            }
+
             impl AstNode for #name {
                 fn can_cast(kind: SyntaxKind) -> bool {
                     match kind {