Rollup merge of #65455 - nnethercote:avoid-unnecessary-TokenTree-to-TokenStream-conversions, r=petrochenkov

Avoid unnecessary `TokenTree` to `TokenStream` conversions

A `TokenStream` contains any number of `TokenTrees`. Therefore, a single `TokenTree` can be promoted to a `TokenStream`. But doing so costs two allocations: one for the single-element `Vec`, and one for the `Lrc`. (An `IsJoint` value also must be added; the default is `NonJoint`.)

The current code converts `TokenTree`s to `TokenStream`s unnecessarily in a few places. This PR removes some of these unnecessary conversions, both simplifying the code and speeding it up.

r? @petrochenkov

1 files changed, 2 insertions, 2 deletions

diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index 9cb410a8ae3..6bbd8be0cb9 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -285,10 +285,10 @@ impl TokenCursor {
             token::NoDelim,
             &if doc_comment_style(&name.as_str()) == AttrStyle::Inner {
                 [TokenTree::token(token::Pound, sp), TokenTree::token(token::Not, sp), body]
-                    .iter().cloned().collect::<TokenStream>().into()
+                    .iter().cloned().collect::<TokenStream>()
             } else {
                 [TokenTree::token(token::Pound, sp), body]
-                    .iter().cloned().collect::<TokenStream>().into()
+                    .iter().cloned().collect::<TokenStream>()
             },
         )));