Rollup merge of #94985 - dtolnay:constattr, r=pnkfelix

Parse inner attributes on inline const block

According to https://github.com/rust-lang/rust/pull/84414#issuecomment-826150936, inner attributes are intended to be supported *"in all containers for statements (or some subset of statements)"*.

This PR adds inner attribute parsing and pretty-printing for inline const blocks (https://github.com/rust-lang/rust/issues/76001), which contain statements just like an unsafe block or a loop body.

```rust
let _ = const {
    #![allow(...)]

    let x = ();
    x
};
```

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -959,7 +959,7 @@ pub fn print_assoc_constraint(&mut self, constraint: &ast::AssocConstraint) {
                 self.word_space("=");
                 match term {
                     Term::Ty(ty) => self.print_type(ty),
-                    Term::Const(c) => self.print_expr_anon_const(c),
+                    Term::Const(c) => self.print_expr_anon_const(c, &[]),
                 }
             }
             ast::AssocConstraintKind::Bound { bounds } => self.print_type_bounds(":", &*bounds),

compiler/rustc_ast_pretty/src/pprust/state/expr.rs

@@ -88,10 +88,21 @@ fn print_expr_vec(&mut self, exprs: &[P<ast::Expr>]) {
         self.end();
     }
 
-    pub(super) fn print_expr_anon_const(&mut self, expr: &ast::AnonConst) {
+    pub(super) fn print_expr_anon_const(
+        &mut self,
+        expr: &ast::AnonConst,
+        attrs: &[ast::Attribute],
+    ) {
         self.ibox(INDENT_UNIT);
         self.word("const");
-        self.print_expr(&expr.value);
+        self.nbsp();
+        if let ast::ExprKind::Block(block, None) = &expr.value.kind {
+            self.cbox(0);
+            self.ibox(0);
+            self.print_block_with_attrs(block, attrs);
+        } else {
+            self.print_expr(&expr.value);
+        }
         self.end();
     }
 
@@ -275,7 +286,7 @@ pub(super) fn print_expr_outer_attr_style(&mut self, expr: &ast::Expr, is_inline
                 self.print_expr_vec(exprs);
             }
             ast::ExprKind::ConstBlock(ref anon_const) => {
-                self.print_expr_anon_const(anon_const);
+                self.print_expr_anon_const(anon_const, attrs);
             }
             ast::ExprKind::Repeat(ref element, ref count) => {
                 self.print_expr_repeat(element, count);

compiler/rustc_parse/src/parser/mod.rs

@@ -1125,13 +1125,13 @@ fn parse_const_block(&mut self, span: Span, pat: bool) -> PResult<'a, P<Expr>> {
             self.sess.gated_spans.gate(sym::inline_const, span);
         }
         self.eat_keyword(kw::Const);
-        let blk = self.parse_block()?;
+        let (attrs, blk) = self.parse_inner_attrs_and_block()?;
         let anon_const = AnonConst {
             id: DUMMY_NODE_ID,
             value: self.mk_expr(blk.span, ExprKind::Block(blk, None), AttrVec::new()),
         };
         let blk_span = anon_const.value.span;
-        Ok(self.mk_expr(span.to(blk_span), ExprKind::ConstBlock(anon_const), AttrVec::new()))
+        Ok(self.mk_expr(span.to(blk_span), ExprKind::ConstBlock(anon_const), AttrVec::from(attrs)))
     }
 
     /// Parses mutability (`mut` or nothing).

src/test/pretty/stmt_expr_attributes.rs

@@ -1,6 +1,8 @@
 // pp-exact
 
 #![feature(box_syntax)]
+#![feature(inline_const)]
+#![feature(inline_const_pat)]
 #![feature(rustc_attrs)]
 #![feature(stmt_expr_attributes)]
 
@@ -16,6 +18,7 @@ fn _1() {
 
     #[rustc_dummy]
     unsafe {
+        #![rustc_dummy]
         // code
     }
 }
@@ -206,6 +209,12 @@ fn _11() {
             let _ = ();
             ()
         };
+    let const {
+                    #![rustc_dummy]
+                } =
+        #[rustc_dummy] const {
+                #![rustc_dummy]
+            };
     let mut x = 0;
     let _ = #[rustc_dummy] x = 15;
     let _ = #[rustc_dummy] x += 15;