expand: Stop un-interpolating NtIdents before passing them to built-in macros

This was a big hack, and built-in macros should be able to deal with `NtIdents` in the input by themselves like any other parser code.

Author: petrochenkov

compiler/rustc_builtin_macros/src/concat_idents.rs

@@ -27,15 +27,15 @@ pub fn expand_concat_idents<'cx>(
                 }
             }
         } else {
-            match e {
-                TokenTree::Token(Token { kind: token::Ident(name, _), .. }) => {
-                    res_str.push_str(&name.as_str())
-                }
-                _ => {
-                    cx.span_err(sp, "concat_idents! requires ident args.");
-                    return DummyResult::any(sp);
+            if let TokenTree::Token(token) = e {
+                if let Some((ident, _)) = token.ident() {
+                    res_str.push_str(&ident.name.as_str());
+                    continue;
                 }
             }
+
+            cx.span_err(sp, "concat_idents! requires ident args.");
+            return DummyResult::any(sp);
         }
     }
 

compiler/rustc_expand/src/base.rs

@@ -1,10 +1,9 @@
 use crate::expand::{self, AstFragment, Invocation};
 use crate::module::DirectoryOwnership;
 
-use rustc_ast::mut_visit::{self, MutVisitor};
 use rustc_ast::ptr::P;
 use rustc_ast::token;
-use rustc_ast::tokenstream::{self, TokenStream};
+use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::visit::{AssocCtxt, Visitor};
 use rustc_ast::{self as ast, Attribute, NodeId, PatKind};
 use rustc_attr::{self as attr, Deprecation, HasAttrs, Stability};
@@ -364,30 +363,8 @@ where
         &self,
         ecx: &'cx mut ExtCtxt<'_>,
         span: Span,
-        mut input: TokenStream,
+        input: TokenStream,
     ) -> Box<dyn MacResult + 'cx> {
-        struct AvoidInterpolatedIdents;
-
-        impl MutVisitor for AvoidInterpolatedIdents {
-            fn visit_tt(&mut self, tt: &mut tokenstream::TokenTree) {
-                if let tokenstream::TokenTree::Token(token) = tt {
-                    if let token::Interpolated(nt) = &token.kind {
-                        if let token::NtIdent(ident, is_raw) = **nt {
-                            *tt = tokenstream::TokenTree::token(
-                                token::Ident(ident.name, is_raw),
-                                ident.span,
-                            );
-                        }
-                    }
-                }
-                mut_visit::noop_visit_tt(tt, self)
-            }
-
-            fn visit_mac(&mut self, mac: &mut ast::MacCall) {
-                mut_visit::noop_visit_mac(mac, self)
-            }
-        }
-        AvoidInterpolatedIdents.visit_tts(&mut input);
         (*self)(ecx, span, input)
     }
 }