Auto merge of #83312 - petrochenkov:noinner, r=Aaron1011

parser: Remove support for inner attributes on non-block expressions

Remove support for attributes like
```rust
fn attrs() {
    (#![print_target_and_args(fifth)] 1, 2);

    [#![print_target_and_args(sixth)] 1 , 2];
    [#![print_target_and_args(seventh)] true ; 5];

    match 0 {
        #![print_target_and_args(eighth)]
        _ => {}
    }

    MyStruct { #![print_target_and_args(ninth)] field: true };
}
```
They are
- useless
- unstable (modulo holes like https://github.com/rust-lang/rust/issues/65860)
- pessimize compiler performance, namely token collection for macros (cc https://github.com/rust-lang/rust/pull/82608)

I still want to run crater on this to check whether the stability holes are exploited in practice, and whether such attributes are used at all.

1 files changed, 4 insertions, 10 deletions

diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index e155b3fa773..56c97b59476 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -1216,10 +1216,9 @@ impl<'a> Parser<'a> {
         }
     }
 
-    fn parse_tuple_parens_expr(&mut self, mut attrs: AttrVec) -> PResult<'a, P<Expr>> {
+    fn parse_tuple_parens_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
         let lo = self.token.span;
         self.expect(&token::OpenDelim(token::Paren))?;
-        attrs.extend(self.parse_inner_attributes()?); // `(#![foo] a, b, ...)` is OK.
         let (es, trailing_comma) = match self.parse_seq_to_end(
             &token::CloseDelim(token::Paren),
             SeqSep::trailing_allowed(token::Comma),
@@ -1239,12 +1238,10 @@ impl<'a> Parser<'a> {
         self.maybe_recover_from_bad_qpath(expr, true)
     }
 
-    fn parse_array_or_repeat_expr(&mut self, mut attrs: AttrVec) -> PResult<'a, P<Expr>> {
+    fn parse_array_or_repeat_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
         let lo = self.token.span;
         self.bump(); // `[`
 
-        attrs.extend(self.parse_inner_attributes()?);
-
         let close = &token::CloseDelim(token::Bracket);
         let kind = if self.eat(close) {
             // Empty vector
@@ -1950,7 +1947,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses a `match ... { ... }` expression (`match` token already eaten).
-    fn parse_match_expr(&mut self, mut attrs: AttrVec) -> PResult<'a, P<Expr>> {
+    fn parse_match_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
         let match_span = self.prev_token.span;
         let lo = self.prev_token.span;
         let scrutinee = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
@@ -1965,7 +1962,6 @@ impl<'a> Parser<'a> {
             }
             return Err(e);
         }
-        attrs.extend(self.parse_inner_attributes()?);
 
         let mut arms: Vec<Arm> = Vec::new();
         while self.token != token::CloseDelim(token::Brace) {
@@ -2293,15 +2289,13 @@ impl<'a> Parser<'a> {
     pub(super) fn parse_struct_expr(
         &mut self,
         pth: ast::Path,
-        mut attrs: AttrVec,
+        attrs: AttrVec,
         recover: bool,
     ) -> PResult<'a, P<Expr>> {
         let mut fields = Vec::new();
         let mut base = ast::StructRest::None;
         let mut recover_async = false;
 
-        attrs.extend(self.parse_inner_attributes()?);
-
         let mut async_block_err = |e: &mut DiagnosticBuilder<'_>, span: Span| {
             recover_async = true;
             e.span_label(span, "`async` blocks are only allowed in Rust 2018 or later");