ast: Introduce some traits to get AST node properties generically

And use them to avoid constructing some artificial `Nonterminal` tokens during expansion

Author: petrochenkov

src/attr.rs

@@ -1,7 +1,7 @@
 //! Format attributes and meta items.
 
 use rustc_ast::ast;
-use rustc_ast::AstLike;
+use rustc_ast::HasAttrs;
 use rustc_span::{symbol::sym, Span, Symbol};
 
 use self::doc_comment::DocCommentFormatter;

src/formatting.rs

@@ -5,7 +5,6 @@ use std::io::{self, Write};
 use std::time::{Duration, Instant};
 
 use rustc_ast::ast;
-use rustc_ast::AstLike;
 use rustc_span::Span;
 
 use self::newline_style::apply_newline_style;

src/modules.rs

@@ -4,7 +4,6 @@ use std::path::{Path, PathBuf};
 
 use rustc_ast::ast;
 use rustc_ast::visit::Visitor;
-use rustc_ast::AstLike;
 use rustc_span::symbol::{self, sym, Symbol};
 use rustc_span::Span;
 use thiserror::Error;
@@ -50,19 +49,10 @@ impl<'a> Module<'a> {
             ast_mod_kind,
         }
     }
-}
 
-impl<'a> AstLike for Module<'a> {
-    const SUPPORTS_CUSTOM_INNER_ATTRS: bool = true;
-    fn attrs(&self) -> &[ast::Attribute] {
+    pub(crate) fn attrs(&self) -> &[ast::Attribute] {
         &self.inner_attr
     }
-    fn visit_attrs(&mut self, f: impl FnOnce(&mut Vec<ast::Attribute>)) {
-        f(&mut self.inner_attr)
-    }
-    fn tokens_mut(&mut self) -> Option<&mut Option<rustc_ast::tokenstream::LazyTokenStream>> {
-        unimplemented!()
-    }
 }
 
 /// Maps each module to the corresponding file.

src/visitor.rs

@@ -1,7 +1,7 @@
 use std::cell::{Cell, RefCell};
 use std::rc::Rc;
 
-use rustc_ast::{ast, token::Delimiter, visit, AstLike};
+use rustc_ast::{ast, token::Delimiter, visit};
 use rustc_data_structures::sync::Lrc;
 use rustc_span::{symbol, BytePos, Pos, Span};