Confirm that fallback TokenStream can preserve jointness of last punct

Author: dtolnay

tests/test.rs

@@ -1,4 +1,4 @@
-use proc_macro2::{Ident, Literal, Spacing, Span, TokenStream, TokenTree};
+use proc_macro2::{Ident, Literal, Punct, Spacing, Span, TokenStream, TokenTree};
 use std::str::{self, FromStr};
 
 #[test]
@@ -304,6 +304,17 @@ fn punct_before_comment() {
     }
 }
 
+#[test]
+fn joint_last_token() {
+    let joint_punct = Punct::new(':', Spacing::Joint);
+    let stream = TokenStream::from(TokenTree::Punct(joint_punct));
+    let punct = match stream.into_iter().next().unwrap() {
+        TokenTree::Punct(punct) => punct,
+        _ => unreachable!(),
+    };
+    assert_eq!(punct.spacing(), Spacing::Joint);
+}
+
 #[test]
 fn raw_identifier() {
     let mut tts = TokenStream::from_str("r#dyn").unwrap().into_iter();