Force token collection to run when parsing nonterminals

Fixes #81007

Previously, we would fail to collect tokens in the proper place when
only builtin attributes were present. As a result, we would end up with
attribute tokens in the collected `TokenStream`, leading to duplication
when we attempted to prepend the attributes from the AST node.

We now explicitly track when token collection must be performed due to
nomterminal parsing.

compiler/rustc_parse/src/parser/expr.rs

@@ -472,7 +472,11 @@ impl<'a> Parser<'a> {
     /// Parses a prefix-unary-operator expr.
     fn parse_prefix_expr(&mut self, attrs: Option<AttrVec>) -> PResult<'a, P<Expr>> {
         let attrs = self.parse_or_use_outer_attributes(attrs)?;
-        let needs_tokens = super::attr::maybe_needs_tokens(&attrs);
+        // FIXME: Use super::attr::maybe_needs_tokens(&attrs) once we come up
+        // with a good way of passing `force_tokens` through from `parse_nonterminal`.
+        // Checking !attrs.is_empty() is correct, but will cause us to unnecessarily
+        // capture tokens in some circumstances.
+        let needs_tokens = !attrs.is_empty();
         let do_parse = |this: &mut Parser<'a>| {
             let lo = this.token.span;
             // Note: when adding new unary operators, don't forget to adjust TokenKind::can_begin_expr()