Clone entire TokenCursor when collecting tokens

Reverts PR #80830
Fixes taiki-e/pin-project#312

We can have an arbitrary number of `None`-delimited group frames pushed
on the stack due to proc-macro invocations, which can legally be exited.
Attempting to account for this would add a lot of complexity for a tiny
performance gain, so let's just use the original strategy.

Author: Aaron1011

compiler/rustc_parse/src/parser/mod.rs

@@ -1254,15 +1254,7 @@ impl<'a> Parser<'a> {
         f: impl FnOnce(&mut Self) -> PResult<'a, (R, TrailingToken)>,
     ) -> PResult<'a, R> {
         let start_token = (self.token.clone(), self.token_spacing);
-        let cursor_snapshot = TokenCursor {
-            frame: self.token_cursor.frame.clone(),
-            // We only ever capture tokens within our current frame,
-            // so we can just use an empty frame stack
-            stack: vec![],
-            desugar_doc_comments: self.token_cursor.desugar_doc_comments,
-            num_next_calls: self.token_cursor.num_next_calls,
-            append_unglued_token: self.token_cursor.append_unglued_token.clone(),
-        };
+        let cursor_snapshot = self.token_cursor.clone();
 
         let (mut ret, trailing_token) = f(self)?;
 

src/test/ui/proc-macro/auxiliary/nonterminal-recollect-attr.rs

@@ -0,0 +1,23 @@
+// force-host
+// no-prefer-dynamic
+
+#![crate_type = "proc-macro"]
+#![feature(proc_macro_quote)]
+
+extern crate proc_macro;
+use proc_macro::{TokenStream, quote};
+
+#[proc_macro_attribute]
+pub fn first_attr(_: TokenStream, input: TokenStream) -> TokenStream {
+    let recollected: TokenStream = input.into_iter().collect();
+    quote! {
+        #[second_attr]
+        $recollected
+    }
+}
+
+#[proc_macro_attribute]
+pub fn second_attr(_: TokenStream, input: TokenStream) -> TokenStream {
+    let _recollected: TokenStream = input.into_iter().collect();
+    TokenStream::new()
+}

src/test/ui/proc-macro/nonterminal-recollect-attr.rs

@@ -0,0 +1,17 @@
+// check-pass
+// aux-build:nonterminal-recollect-attr.rs
+
+extern crate nonterminal_recollect_attr;
+use nonterminal_recollect_attr::*;
+
+macro_rules! my_macro {
+    ($v:ident) => {
+        #[first_attr]
+        $v struct Foo {
+            field: u8
+        }
+    }
+}
+
+my_macro!(pub);
+fn main() {}