Avoid double-collection for expression nonterminals

compiler/rustc_parse/src/parser/expr.rs

@@ -92,6 +92,21 @@ impl<'a> Parser<'a> {
         self.parse_expr_res(Restrictions::empty(), None)
     }
 
+    /// Parses an expression, forcing tokens to be collected
+    pub fn parse_expr_force_collect(&mut self) -> PResult<'a, P<Expr>> {
+        // If we have outer attributes, then the call to `collect_tokens_trailing_token`
+        // will be made for us.
+        if matches!(self.token.kind, TokenKind::Pound | TokenKind::DocComment(..)) {
+            self.parse_expr()
+        } else {
+            // If we don't have outer attributes, then we need to ensure
+            // that collection happens by using `collect_tokens_no_attrs`.
+            // Expression don't support custom inner attributes, so `parse_expr`
+            // will never try to collect tokens if we don't have outer attributes.
+            self.collect_tokens_no_attrs(|this| this.parse_expr())
+        }
+    }
+
     pub(super) fn parse_anon_const_expr(&mut self) -> PResult<'a, AnonConst> {
         self.parse_expr().map(|value| AnonConst { id: DUMMY_NODE_ID, value })
     }