Re-add support for parsing (and pretty-printing) inner-attributes within body of a match.

In other words, we can do `match EXPR { #![inner_attr] ARM_1 ARM_2 ... }` again.

I believe this unbreaks the only four crates that crater flagged as broken by PR 83312.

(I am putting this up so that the lang-team can check it out and decide whether
it changes their mind about what to do regarding PR 83312.)

Author: pnkfelix

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -366,6 +366,10 @@ pub trait PrintState<'a>: std::ops::Deref<Target = pp::Printer> + std::ops::Dere
         self.print_either_attributes(attrs, ast::AttrStyle::Inner, false, true)
     }
 
+    fn print_inner_attributes_no_trailing_hardbreak(&mut self, attrs: &[ast::Attribute]) {
+        self.print_either_attributes(attrs, ast::AttrStyle::Inner, false, false)
+    }
+
     fn print_outer_attributes(&mut self, attrs: &[ast::Attribute]) {
         self.print_either_attributes(attrs, ast::AttrStyle::Outer, false, true)
     }
@@ -1940,6 +1944,7 @@ impl<'a> State<'a> {
                 self.print_expr_as_cond(expr);
                 self.s.space();
                 self.bopen();
+                self.print_inner_attributes_no_trailing_hardbreak(attrs);
                 for arm in arms {
                     self.print_arm(arm);
                 }

compiler/rustc_parse/src/parser/expr.rs

@@ -1947,7 +1947,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses a `match ... { ... }` expression (`match` token already eaten).
-    fn parse_match_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
+    fn parse_match_expr(&mut self, mut 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)?;
@@ -1962,6 +1962,7 @@ 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) {