Remove the `Option` in `TokenStream`.

It means an allocation is required to create an empty `TokenStream`, but
all other operations are simpler and marginally faster due to not having
to check for `None`. Overall it simplifies the code for a negligible
performance effect.

The commit also removes `TokenStream::empty` by implementing `Default`,
which is now possible.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/libsyntax_ext/plugin_macro_defs.rs b/src/libsyntax_ext/plugin_macro_defs.rs
index 315babceae3..62c7e188eba 100644
--- a/src/libsyntax_ext/plugin_macro_defs.rs
+++ b/src/libsyntax_ext/plugin_macro_defs.rs
@@ -20,7 +20,7 @@ fn plugin_macro_def(name: Name, span: Span) -> P<Item> {
         attr::mk_word_item(Ident::new(sym::rustc_builtin_macro, span)));
 
     let parens: TreeAndJoint = TokenTree::Delimited(
-        DelimSpan::from_single(span), token::Paren, TokenStream::empty()
+        DelimSpan::from_single(span), token::Paren, TokenStream::default()
     ).into();
     let trees = vec![parens.clone(), TokenTree::token(token::FatArrow, span).into(), parens];