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/proc_macro.rs

@@ -9,6 +9,7 @@ use rustc_data_structures::sync::Lrc;
 use rustc_errors::{struct_span_err, Applicability, ErrorReported};
 use rustc_lexer::is_ident;
 use rustc_parse::nt_to_tokenstream;
+use rustc_parse::parser::ForceCollect;
 use rustc_span::symbol::sym;
 use rustc_span::{Span, DUMMY_SP};
 
@@ -117,7 +118,7 @@ impl MultiItemModifier for ProcMacroDerive {
         let mut items = vec![];
 
         loop {
-            match parser.parse_item() {
+            match parser.parse_item(ForceCollect::No) {
                 Ok(None) => break,
                 Ok(Some(item)) => {
                     if is_stmt {