Remove NtIdent and NtLifetime.

The extra span is now recorded in the new `TokenKind::NtIdent` and
`TokenKind::NtLifetime`. These both consist of a single token, and so
there's no operator precedence problems with inserting them directly
into the token stream.

The other way to do this would be to wrap the ident/lifetime in invisible
delimiters, but there's a lot of code that assumes an interpolated
ident/lifetime fits in a single token, and changing all that code to work with
invisible delimiters would have been a pain. (Maybe it could be done in a
follow-up.)

This change might not seem like much of a win, but it's a first step toward the
much bigger and long-desired removal of `Nonterminal` and
`TokenKind::Interpolated`. That change is big and complex enough that it's
worth doing this piece separately. (Indeed, this commit is based on part of a
late commit in #114647, a prior attempt at that big and complex change.)

compiler/rustc_expand/src/config.rs

@@ -201,10 +201,17 @@ impl<'a> StripUnconfigured<'a> {
                     inner = self.configure_tokens(&inner);
                     Some(AttrTokenTree::Delimited(sp, spacing, delim, inner)).into_iter()
                 }
-                AttrTokenTree::Token(ref token, _)
-                    if let TokenKind::Interpolated(nt) = &token.kind =>
-                {
-                    panic!("Nonterminal should have been flattened at {:?}: {:?}", token.span, nt);
+                AttrTokenTree::Token(
+                    Token {
+                        kind:
+                            TokenKind::NtIdent(..)
+                            | TokenKind::NtLifetime(..)
+                            | TokenKind::Interpolated(..),
+                        ..
+                    },
+                    _,
+                ) => {
+                    panic!("Nonterminal should have been flattened: {:?}", tree);
                 }
                 AttrTokenTree::Token(token, spacing) => {
                     Some(AttrTokenTree::Token(token, spacing)).into_iter()

compiler/rustc_expand/src/mbe/transcribe.rs

@@ -261,6 +261,16 @@ pub(super) fn transcribe<'a>(
                             // without wrapping them into groups.
                             maybe_use_metavar_location(cx, &stack, sp, tt, &mut marker)
                         }
+                        MatchedSingle(ParseNtResult::Ident(ident, is_raw)) => {
+                            marker.visit_span(&mut sp);
+                            let kind = token::NtIdent(*ident, *is_raw);
+                            TokenTree::token_alone(kind, sp)
+                        }
+                        MatchedSingle(ParseNtResult::Lifetime(ident)) => {
+                            marker.visit_span(&mut sp);
+                            let kind = token::NtLifetime(*ident);
+                            TokenTree::token_alone(kind, sp)
+                        }
                         MatchedSingle(ParseNtResult::Nt(nt)) => {
                             // Other variables are emitted into the output stream as groups with
                             // `Delimiter::Invisible` to maintain parsing priorities.

compiler/rustc_expand/src/proc_macro_server.rs

@@ -220,6 +220,12 @@ impl FromInternal<(TokenStream, &mut Rustc<'_, '_>)> for Vec<TokenTree<TokenStre
                 Ident(sym, is_raw) => {
                     trees.push(TokenTree::Ident(Ident { sym, is_raw: is_raw.into(), span }))
                 }
+                NtIdent(ident, is_raw) => trees.push(TokenTree::Ident(Ident {
+                    sym: ident.name,
+                    is_raw: is_raw.into(),
+                    span: ident.span,
+                })),
+
                 Lifetime(name) => {
                     let ident = symbol::Ident::new(name, span).without_first_quote();
                     trees.extend([
@@ -227,6 +233,15 @@ impl FromInternal<(TokenStream, &mut Rustc<'_, '_>)> for Vec<TokenTree<TokenStre
                         TokenTree::Ident(Ident { sym: ident.name, is_raw: false, span }),
                     ]);
                 }
+                NtLifetime(ident) => {
+                    let stream = TokenStream::token_alone(token::Lifetime(ident.name), ident.span);
+                    trees.push(TokenTree::Group(Group {
+                        delimiter: pm::Delimiter::None,
+                        stream: Some(stream),
+                        span: DelimSpan::from_single(span),
+                    }))
+                }
+
                 Literal(token::Lit { kind, symbol, suffix }) => {
                     trees.push(TokenTree::Literal(self::Literal {
                         kind: FromInternal::from_internal(kind),
@@ -259,14 +274,6 @@ impl FromInternal<(TokenStream, &mut Rustc<'_, '_>)> for Vec<TokenTree<TokenStre
                     }));
                 }
 
-                Interpolated(ref nt) if let NtIdent(ident, is_raw) = &**nt => {
-                    trees.push(TokenTree::Ident(Ident {
-                        sym: ident.name,
-                        is_raw: matches!(is_raw, IdentIsRaw::Yes),
-                        span: ident.span,
-                    }))
-                }
-
                 Interpolated(nt) => {
                     let stream = TokenStream::from_nonterminal_ast(&nt);
                     // A hack used to pass AST fragments to attribute and derive