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_expand/src/expand.rs

@@ -20,7 +20,7 @@ use rustc_data_structures::map_in_place::MapInPlace;
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_errors::{struct_span_err, Applicability, PResult};
 use rustc_feature::Features;
-use rustc_parse::parser::{AttemptLocalParseRecovery, Parser};
+use rustc_parse::parser::{AttemptLocalParseRecovery, ForceCollect, Parser};
 use rustc_parse::validate_attr;
 use rustc_session::lint::builtin::UNUSED_DOC_COMMENTS;
 use rustc_session::lint::BuiltinLintDiagnostics;
@@ -913,7 +913,7 @@ pub fn parse_ast_fragment<'a>(
     Ok(match kind {
         AstFragmentKind::Items => {
             let mut items = SmallVec::new();
-            while let Some(item) = this.parse_item()? {
+            while let Some(item) = this.parse_item(ForceCollect::No)? {
                 items.push(item);
             }
             AstFragment::Items(items)