Remove `Peekable<TokenStreamIter>` uses.

Currently there are two ways to peek at a `TokenStreamIter`.
- Wrap it in a `Peekable` and use that traits `peek` method.
- Use `TokenStreamIter`'s inherent `peek` method.

Some code uses one, some use the other. This commit converts all places
to the inherent method. This eliminates mixing of `TokenStreamIter` and
`Peekable<TokenStreamIter>` and some use of `impl Iterator` and `dyn
Iterator`.

1 files changed, 4 insertions, 1 deletions

diff --git a/compiler/rustc_ast/src/tokenstream.rs b/compiler/rustc_ast/src/tokenstream.rs
index 9f7ba928692..9f7a583af09 100644
--- a/compiler/rustc_ast/src/tokenstream.rs
+++ b/compiler/rustc_ast/src/tokenstream.rs
@@ -676,7 +676,10 @@ impl<'t> TokenStreamIter<'t> {
         TokenStreamIter { stream, index: 0 }
     }
 
-    pub fn peek(&self) -> Option<&TokenTree> {
+    // Peeking could be done via `Peekable`, but most iterators need peeking,
+    // and this is simple and avoids the need to use `peekable` and `Peekable`
+    // at all the use sites.
+    pub fn peek(&self) -> Option<&'t TokenTree> {
         self.stream.0.get(self.index)
     }
 }