Revert "Add expr_2021 nonterminal and feature flag"

This reverts commit ef6478b.

compiler/rustc_ast/src/token.rs

@@ -881,8 +881,6 @@ pub enum NonterminalKind {
     },
     PatWithOr,
     Expr,
-    /// Matches an expression using the rules from edition 2021 and earlier.
-    Expr2021,
     Ty,
     Ident,
     Lifetime,
@@ -912,7 +910,6 @@ impl NonterminalKind {
             },
             sym::pat_param => NonterminalKind::PatParam { inferred: false },
             sym::expr => NonterminalKind::Expr,
-            sym::expr_2021 if edition() >= Edition::Edition2024 => NonterminalKind::Expr2021,
             sym::ty => NonterminalKind::Ty,
             sym::ident => NonterminalKind::Ident,
             sym::lifetime => NonterminalKind::Lifetime,
@@ -932,7 +929,6 @@ impl NonterminalKind {
             NonterminalKind::PatParam { inferred: false } => sym::pat_param,
             NonterminalKind::PatParam { inferred: true } | NonterminalKind::PatWithOr => sym::pat,
             NonterminalKind::Expr => sym::expr,
-            NonterminalKind::Expr2021 => sym::expr_2021,
             NonterminalKind::Ty => sym::ty,
             NonterminalKind::Ident => sym::ident,
             NonterminalKind::Lifetime => sym::lifetime,

compiler/rustc_expand/messages.ftl

@@ -47,9 +47,6 @@ expand_explain_doc_comment_inner =
 expand_explain_doc_comment_outer =
     outer doc comments expand to `#[doc = "..."]`, which is what this macro attempted to match
 
-expand_expr_2021_is_experimental =
-    expr_2021 is experimental
-
 expand_expr_repeat_no_syntax_vars =
     attempted to repeat an expression containing no syntax variables matched as repeating at this depth
 

compiler/rustc_expand/src/mbe/macro_rules.rs

@@ -1293,7 +1293,7 @@ fn is_in_follow(tok: &mbe::TokenTree, kind: NonterminalKind) -> IsInFollow {
                 // maintain
                 IsInFollow::Yes
             }
-            NonterminalKind::Stmt | NonterminalKind::Expr | NonterminalKind::Expr2021 => {
+            NonterminalKind::Stmt | NonterminalKind::Expr => {
                 const TOKENS: &[&str] = &["`=>`", "`,`", "`;`"];
                 match tok {
                     TokenTree::Token(token) => match token.kind {

compiler/rustc_expand/src/mbe/quoted.rs

@@ -92,12 +92,6 @@ pub(super) fn parse(
                                                 token::NonterminalKind::Ident
                                             },
                                         );
-                                    if kind == token::NonterminalKind::Expr2021
-                                        && !features.expr_fragment_specifier_2024
-                                    {
-                                        sess.dcx()
-                                            .emit_err(errors::Expr2021IsExperimental { span });
-                                    }
                                     result.push(TokenTree::MetaVarDecl(span, ident, Some(kind)));
                                     continue;
                                 }

compiler/rustc_feature/src/unstable.rs

@@ -458,8 +458,6 @@ declare_features! (
     (unstable, exhaustive_patterns, "1.13.0", Some(51085)),
     /// Allows explicit tail calls via `become` expression.
     (incomplete, explicit_tail_calls, "1.72.0", Some(112788)),
-    /// Uses 2024 rules for matching `expr` fragments in macros. Also enables `expr_2021` fragment.
-    (incomplete, expr_fragment_specifier_2024, "CURRENT_RUSTC_VERSION", Some(123742)),
     /// Allows using `efiapi`, `sysv64` and `win64` as calling convention
     /// for functions with varargs.
     (unstable, extended_varargs_abi_support, "1.65.0", Some(100189)),

compiler/rustc_parse/src/parser/nonterminal.rs

@@ -36,7 +36,7 @@ impl<'a> Parser<'a> {
         }
 
         match kind {
-            NonterminalKind::Expr | NonterminalKind::Expr2021 => {
+            NonterminalKind::Expr => {
                 token.can_begin_expr()
                 // This exception is here for backwards compatibility.
                 && !token.is_keyword(kw::Let)
@@ -143,9 +143,7 @@ impl<'a> Parser<'a> {
                 })?)
             }
 
-            NonterminalKind::Expr | NonterminalKind::Expr2021 => {
-                NtExpr(self.parse_expr_force_collect()?)
-            }
+            NonterminalKind::Expr => NtExpr(self.parse_expr_force_collect()?),
             NonterminalKind::Literal => {
                 // The `:literal` matcher does not support attributes
                 NtLiteral(self.collect_tokens_no_attrs(|this| this.parse_literal_maybe_minus())?)

compiler/rustc_span/src/symbol.rs

@@ -782,8 +782,6 @@ symbols! {
         explicit_tail_calls,
         export_name,
         expr,
-        expr_2021,
-        expr_fragment_specifier_2024,
         extended_key_value_attributes,
         extended_varargs_abi_support,
         extern_absolute_paths,