Remove `NtTy`.

Notes about tests:

- tests/ui/parser/macro/trait-object-macro-matcher.rs: the syntax error
  is duplicated, because it occurs now when parsing the decl macro
  input, and also when parsing the expanded decl macro. But this won't
  show up for normal users due to error de-duplication.

- tests/ui/associated-consts/issue-93835.rs: similar, plus there are
  some additional errors about this very broken code.

- The changes to metavariable descriptions in #132629 are now visible in
  error message for several tests.

4 files changed, 51 insertions, 20 deletions

diff --git a/compiler/rustc_parse/src/parser/mod.rs b/compiler/rustc_parse/src/parser/mod.rs
index ecbc4e396ce..4b26100c46d 100644
--- a/compiler/rustc_parse/src/parser/mod.rs
+++ b/compiler/rustc_parse/src/parser/mod.rs
@@ -117,12 +117,16 @@ macro_rules! maybe_recover_from_interpolated_ty_qpath {
     ($self: expr, $allow_qpath_recovery: expr) => {
         if $allow_qpath_recovery
             && $self.may_recover()
-            && $self.look_ahead(1, |t| t == &token::PathSep)
-            && let token::Interpolated(nt) = &$self.token.kind
-            && let token::NtTy(ty) = &**nt
+            && let Some(token::MetaVarKind::Ty) = $self.token.is_metavar_seq()
+            && $self.check_noexpect_past_close_delim(&token::PathSep)
         {
-            let ty = ty.clone();
-            $self.bump();
+            // Reparse the type, then move to recovery.
+            let ty = $self
+                .eat_metavar_seq(token::MetaVarKind::Ty, |this| {
+                    this.parse_ty_no_question_mark_recover()
+                })
+                .expect("metavar seq ty");
+
             return $self.maybe_recover_from_bad_qpath_stage_2($self.prev_token.span, ty);
         }
     };
@@ -614,6 +618,24 @@ impl<'a> Parser<'a> {
         self.token == *tok
     }
 
+    // Check the first token after the delimiter that closes the current
+    // delimited sequence. (Panics if used in the outermost token stream, which
+    // has no delimiters.) It uses a clone of the relevant tree cursor to skip
+    // past the entire `TokenTree::Delimited` in a single step, avoiding the
+    // need for unbounded token lookahead.
+    //
+    // Primarily used when `self.token` matches
+    // `OpenDelim(Delimiter::Invisible(_))`, to look ahead through the current
+    // metavar expansion.
+    fn check_noexpect_past_close_delim(&self, tok: &TokenKind) -> bool {
+        let mut tree_cursor = self.token_cursor.stack.last().unwrap().clone();
+        tree_cursor.bump();
+        matches!(
+            tree_cursor.curr(),
+            Some(TokenTree::Token(token::Token { kind, .. }, _)) if kind == tok
+        )
+    }
+
     /// Consumes a token 'tok' if it exists. Returns whether the given token was present.
     ///
     /// the main purpose of this function is to reduce the cluttering of the suggestions list
@@ -1724,6 +1746,7 @@ pub enum ParseNtResult {
     Tt(TokenTree),
     Ident(Ident, IdentIsRaw),
     Lifetime(Ident, IdentIsRaw),
+    Ty(P<ast::Ty>),
     Vis(P<ast::Visibility>),
 
     /// This variant will eventually be removed, along with `Token::Interpolate`.
diff --git a/compiler/rustc_parse/src/parser/nonterminal.rs b/compiler/rustc_parse/src/parser/nonterminal.rs
index f102821adf7..e9cf8f1bbba 100644
--- a/compiler/rustc_parse/src/parser/nonterminal.rs
+++ b/compiler/rustc_parse/src/parser/nonterminal.rs
@@ -51,7 +51,6 @@ impl<'a> Parser<'a> {
                 NtStmt(_)
                 | NtPat(_)
                 | NtExpr(_)
-                | NtTy(_)
                 | NtLiteral(_) // `true`, `false`
                 | NtMeta(_)
                 | NtPath(_) => true,
@@ -100,7 +99,7 @@ impl<'a> Parser<'a> {
                 token::NtLifetime(..) => true,
                 token::Interpolated(nt) => match &**nt {
                     NtBlock(_) | NtStmt(_) | NtExpr(_) | NtLiteral(_) => true,
-                    NtItem(_) | NtPat(_) | NtTy(_) | NtMeta(_) | NtPath(_) => false,
+                    NtItem(_) | NtPat(_) | NtMeta(_) | NtPath(_) => false,
                 },
                 token::OpenDelim(Delimiter::Invisible(InvisibleOrigin::MetaVar(k))) => match k {
                     MetaVarKind::Block
@@ -187,7 +186,9 @@ impl<'a> Parser<'a> {
                 NtLiteral(self.collect_tokens_no_attrs(|this| this.parse_literal_maybe_minus())?)
             }
             NonterminalKind::Ty => {
-                NtTy(self.collect_tokens_no_attrs(|this| this.parse_ty_no_question_mark_recover())?)
+                return Ok(ParseNtResult::Ty(
+                    self.collect_tokens_no_attrs(|this| this.parse_ty_no_question_mark_recover())?,
+                ));
             }
             // this could be handled like a token, since it is one
             NonterminalKind::Ident => {
diff --git a/compiler/rustc_parse/src/parser/path.rs b/compiler/rustc_parse/src/parser/path.rs
index b241aa892db..b68eb9c99f5 100644
--- a/compiler/rustc_parse/src/parser/path.rs
+++ b/compiler/rustc_parse/src/parser/path.rs
@@ -2,7 +2,7 @@ use std::mem;
 
 use ast::token::IdentIsRaw;
 use rustc_ast::ptr::P;
-use rustc_ast::token::{self, Delimiter, Token, TokenKind};
+use rustc_ast::token::{self, Delimiter, MetaVarKind, Token, TokenKind};
 use rustc_ast::{
     self as ast, AngleBracketedArg, AngleBracketedArgs, AnonConst, AssocItemConstraint,
     AssocItemConstraintKind, BlockCheckMode, GenericArg, GenericArgs, Generics, ParenthesizedArgs,
@@ -196,13 +196,14 @@ impl<'a> Parser<'a> {
 
         maybe_whole!(self, NtPath, |path| reject_generics_if_mod_style(self, path.into_inner()));
 
-        if let token::Interpolated(nt) = &self.token.kind {
-            if let token::NtTy(ty) = &**nt {
-                if let ast::TyKind::Path(None, path) = &ty.kind {
-                    let path = path.clone();
-                    self.bump();
-                    return Ok(reject_generics_if_mod_style(self, path));
-                }
+        if let Some(MetaVarKind::Ty) = self.token.is_metavar_seq() {
+            let mut snapshot = self.create_snapshot_for_diagnostic();
+            let ty = snapshot
+                .eat_metavar_seq(MetaVarKind::Ty, |this| this.parse_ty_no_question_mark_recover())
+                .expect("metavar seq ty");
+            if let ast::TyKind::Path(None, path) = ty.into_inner().kind {
+                self.restore_snapshot(snapshot);
+                return Ok(reject_generics_if_mod_style(self, path));
             }
         }
 
diff --git a/compiler/rustc_parse/src/parser/ty.rs b/compiler/rustc_parse/src/parser/ty.rs
index dc5919b3630..c78c7bff9b5 100644
--- a/compiler/rustc_parse/src/parser/ty.rs
+++ b/compiler/rustc_parse/src/parser/ty.rs
@@ -1,5 +1,5 @@
 use rustc_ast::ptr::P;
-use rustc_ast::token::{self, BinOpToken, Delimiter, IdentIsRaw, Token, TokenKind};
+use rustc_ast::token::{self, BinOpToken, Delimiter, IdentIsRaw, MetaVarKind, Token, TokenKind};
 use rustc_ast::util::case::Case;
 use rustc_ast::{
     self as ast, BareFnTy, BoundAsyncness, BoundConstness, BoundPolarity, DUMMY_NODE_ID, FnRetTy,
@@ -18,7 +18,7 @@ use crate::errors::{
     HelpUseLatestEdition, InvalidDynKeyword, LifetimeAfterMut, NeedPlusAfterTraitObjectLifetime,
     NestedCVariadicType, ReturnTypesUseThinArrow,
 };
-use crate::{exp, maybe_recover_from_interpolated_ty_qpath, maybe_whole};
+use crate::{exp, maybe_recover_from_interpolated_ty_qpath};
 
 /// Signals whether parsing a type should allow `+`.
 ///
@@ -183,7 +183,8 @@ impl<'a> Parser<'a> {
         )
     }
 
-    /// Parse a type without recovering `:` as `->` to avoid breaking code such as `where fn() : for<'a>`
+    /// Parse a type without recovering `:` as `->` to avoid breaking code such
+    /// as `where fn() : for<'a>`.
     pub(super) fn parse_ty_for_where_clause(&mut self) -> PResult<'a, P<Ty>> {
         self.parse_ty_common(
             AllowPlus::Yes,
@@ -247,7 +248,12 @@ impl<'a> Parser<'a> {
     ) -> PResult<'a, P<Ty>> {
         let allow_qpath_recovery = recover_qpath == RecoverQPath::Yes;
         maybe_recover_from_interpolated_ty_qpath!(self, allow_qpath_recovery);
-        maybe_whole!(self, NtTy, |ty| ty);
+
+        if let Some(ty) =
+            self.eat_metavar_seq(MetaVarKind::Ty, |this| this.parse_ty_no_question_mark_recover())
+        {
+            return Ok(ty);
+        }
 
         let lo = self.token.span;
         let mut impl_dyn_multi = false;