Remove `LazyTokenStream`.

It's present within `Token::Interpolated` as an optimization, so that if
a nonterminal is converted to a `TokenStream` multiple times, the
first-computed value is saved and reused.

But in practice it's not needed. `interpolated_to_tokenstream()` is a
cold function: it's only called a few dozen times while compiling rustc
itself, and a few hundred times across the entire `rustc-perf` suite.
Furthermore, when it is called, it is almost always the first
conversion, so no benefit is gained from it.

So this commit removes `LazyTokenStream`, along with the now-unnecessary
`Token::interpolated()`.

As well as a significant simplification, the removal speeds things up
slightly, mostly due to not having to `drop` the `LazyTokenStream`
instances.

1 files changed, 2 insertions, 1 deletions

diff --git a/src/libsyntax_ext/deriving/custom.rs b/src/libsyntax_ext/deriving/custom.rs
index 6aba4d83cd2..cfc3c931598 100644
--- a/src/libsyntax_ext/deriving/custom.rs
+++ b/src/libsyntax_ext/deriving/custom.rs
@@ -2,6 +2,7 @@ use crate::proc_macro_impl::EXEC_STRATEGY;
 use crate::proc_macro_server;
 
 use errors::FatalError;
+use rustc_data_structures::sync::Lrc;
 use syntax::ast::{self, ItemKind, Attribute, Mac};
 use syntax::attr::{mark_used, mark_known};
 use syntax::source_map::Span;
@@ -65,7 +66,7 @@ impl MultiItemModifier for ProcMacroDerive {
         // Mark attributes as known, and used.
         MarkAttrs(&self.attrs).visit_item(&item);
 
-        let token = Token::interpolated(token::NtItem(item));
+        let token = Token::Interpolated(Lrc::new(token::NtItem(item)));
         let input = tokenstream::TokenTree::Token(DUMMY_SP, token).into();
 
         let server = proc_macro_server::Rustc::new(ecx);