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.

4 files changed, 5 insertions, 5 deletions

diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index bbd8da2acef..ec87451edbd 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -671,12 +671,12 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                 }
             }
             Some(TokenTree::Token(..)) => {}
-            None => return TokenStream::empty(),
+            None => return TokenStream::default(),
         }
         self.cx.span_err(span, "custom attribute invocations must be \
             of the form `#[foo]` or `#[foo(..)]`, the macro name must only be \
             followed by a delimiter token");
-        TokenStream::empty()
+        TokenStream::default()
     }
 
     fn gate_proc_macro_attr_item(&self, span: Span, item: &Annotatable) {
diff --git a/src/libsyntax/ext/mbe/transcribe.rs b/src/libsyntax/ext/mbe/transcribe.rs
index ba818ebd35c..da930436d81 100644
--- a/src/libsyntax/ext/mbe/transcribe.rs
+++ b/src/libsyntax/ext/mbe/transcribe.rs
@@ -95,7 +95,7 @@ pub(super) fn transcribe(
 ) -> TokenStream {
     // Nothing for us to transcribe...
     if src.is_empty() {
-        return TokenStream::empty();
+        return TokenStream::default();
     }
 
     // We descend into the RHS (`src`), expanding things as we go. This stack contains the things
diff --git a/src/libsyntax/ext/placeholders.rs b/src/libsyntax/ext/placeholders.rs
index 8eecef1020d..43a49dbeb51 100644
--- a/src/libsyntax/ext/placeholders.rs
+++ b/src/libsyntax/ext/placeholders.rs
@@ -15,7 +15,7 @@ pub fn placeholder(kind: AstFragmentKind, id: ast::NodeId) -> AstFragment {
     fn mac_placeholder() -> ast::Mac {
         ast::Mac {
             path: ast::Path { span: DUMMY_SP, segments: Vec::new() },
-            tts: TokenStream::empty().into(),
+            tts: TokenStream::default().into(),
             delim: ast::MacDelimiter::Brace,
             span: DUMMY_SP,
             prior_type_ascription: None,
diff --git a/src/libsyntax/ext/proc_macro_server.rs b/src/libsyntax/ext/proc_macro_server.rs
index 021ec46d987..27ac8a2b78e 100644
--- a/src/libsyntax/ext/proc_macro_server.rs
+++ b/src/libsyntax/ext/proc_macro_server.rs
@@ -393,7 +393,7 @@ impl server::Types for Rustc<'_> {
 
 impl server::TokenStream for Rustc<'_> {
     fn new(&mut self) -> Self::TokenStream {
-        TokenStream::empty()
+        TokenStream::default()
     }
     fn is_empty(&mut self, stream: &Self::TokenStream) -> bool {
         stream.is_empty()