diff --git a/compiler/rustc_expand/src/proc_macro_server.rs b/compiler/rustc_expand/src/proc_macro_server.rs
index cc66eefac3e8..af0b5639d613 100644
--- a/compiler/rustc_expand/src/proc_macro_server.rs
+++ b/compiler/rustc_expand/src/proc_macro_server.rs
@@ -498,12 +498,13 @@ impl server::TokenStream for Rustc<'_, '_> {
         }
         builder.build()
     }
-    fn into_iter(
+    fn into_trees(
         &mut self,
         stream: Self::TokenStream,
     ) -> Vec<TokenTree<Self::Group, Self::Punct, Self::Ident, Self::Literal>> {
-        // FIXME: This is a raw port of the previous approach, and can probably
-        // be optimized.
+        // FIXME: This is a raw port of the previous approach (which had a
+        // `TokenStreamIter` server-side object with a single `next` method),
+        // and can probably be optimized (for bulk conversion).
         let mut cursor = stream.into_trees();
         let mut stack = Vec::new();
         let mut tts = Vec::new();
diff --git a/library/proc_macro/src/bridge/mod.rs b/library/proc_macro/src/bridge/mod.rs
index c6d0635df576..4e931569ef63 100644
--- a/library/proc_macro/src/bridge/mod.rs
+++ b/library/proc_macro/src/bridge/mod.rs
@@ -73,9 +73,9 @@ macro_rules! with_api {
                 ) -> $S::TokenStream;
                 fn concat_streams(
                     base: Option<$S::TokenStream>,
-                    trees: Vec<$S::TokenStream>,
+                    streams: Vec<$S::TokenStream>,
                 ) -> $S::TokenStream;
-                fn into_iter(
+                fn into_trees(
                     $self: $S::TokenStream
                 ) -> Vec<TokenTree<$S::Group, $S::Punct, $S::Ident, $S::Literal>>;
             },
@@ -307,32 +307,6 @@ impl<'a, T, M> Unmark for &'a mut Marked<T, M> {
     }
 }
 
-impl<T: Mark> Mark for Option<T> {
-    type Unmarked = Option<T::Unmarked>;
-    fn mark(unmarked: Self::Unmarked) -> Self {
-        unmarked.map(T::mark)
-    }
-}
-impl<T: Unmark> Unmark for Option<T> {
-    type Unmarked = Option<T::Unmarked>;
-    fn unmark(self) -> Self::Unmarked {
-        self.map(T::unmark)
-    }
-}
-
-impl<T: Mark, E: Mark> Mark for Result<T, E> {
-    type Unmarked = Result<T::Unmarked, E::Unmarked>;
-    fn mark(unmarked: Self::Unmarked) -> Self {
-        unmarked.map(T::mark).map_err(E::mark)
-    }
-}
-impl<T: Unmark, E: Unmark> Unmark for Result<T, E> {
-    type Unmarked = Result<T::Unmarked, E::Unmarked>;
-    fn unmark(self) -> Self::Unmarked {
-        self.map(T::unmark).map_err(E::unmark)
-    }
-}
-
 impl<T: Mark> Mark for Vec<T> {
     type Unmarked = Vec<T::Unmarked>;
     fn mark(unmarked: Self::Unmarked) -> Self {
@@ -378,7 +352,6 @@ mark_noop! {
     Level,
     LineColumn,
     Spacing,
-    Bound<usize>,
 }
 
 rpc_encode_decode!(
@@ -438,6 +411,28 @@ macro_rules! compound_traits {
     };
 }
 
+compound_traits!(
+    enum Bound<T> {
+        Included(x),
+        Excluded(x),
+        Unbounded,
+    }
+);
+
+compound_traits!(
+    enum Option<T> {
+        Some(t),
+        None,
+    }
+);
+
+compound_traits!(
+    enum Result<T, E> {
+        Ok(t),
+        Err(e),
+    }
+);
+
 #[derive(Clone)]
 pub enum TokenTree<G, P, I, L> {
     Group(G),
diff --git a/library/proc_macro/src/bridge/rpc.rs b/library/proc_macro/src/bridge/rpc.rs
index a94334e07362..e9d7a46c06f6 100644
--- a/library/proc_macro/src/bridge/rpc.rs
+++ b/library/proc_macro/src/bridge/rpc.rs
@@ -4,7 +4,6 @@ use std::any::Any;
 use std::char;
 use std::io::Write;
 use std::num::NonZeroU32;
-use std::ops::Bound;
 use std::str;
 
 pub(super) type Writer = super::buffer::Buffer;
@@ -186,28 +185,6 @@ impl<'a, S, A: for<'s> DecodeMut<'a, 's, S>, B: for<'s> DecodeMut<'a, 's, S>> De
     }
 }
 
-rpc_encode_decode!(
-    enum Bound<T> {
-        Included(x),
-        Excluded(x),
-        Unbounded,
-    }
-);
-
-rpc_encode_decode!(
-    enum Option<T> {
-        None,
-        Some(x),
-    }
-);
-
-rpc_encode_decode!(
-    enum Result<T, E> {
-        Ok(x),
-        Err(e),
-    }
-);
-
 impl<S> Encode<S> for &[u8] {
     fn encode(self, w: &mut Writer, s: &mut S) {
         self.len().encode(w, s);
diff --git a/library/proc_macro/src/lib.rs b/library/proc_macro/src/lib.rs
index 6e645216c8dd..5e1289ec79d3 100644
--- a/library/proc_macro/src/lib.rs
+++ b/library/proc_macro/src/lib.rs
@@ -235,7 +235,7 @@ impl From<TokenTree> for TokenStream {
 
 /// Non-generic helper for implementing `FromIterator<TokenTree>` and
 /// `Extend<TokenTree>` with less monomorphization in calling crates.
-struct ExtendStreamWithTreesHelper {
+struct ConcatTreesHelper {
     trees: Vec<
         bridge::TokenTree<
             bridge::client::Group,
@@ -246,9 +246,9 @@ struct ExtendStreamWithTreesHelper {
     >,
 }
 
-impl ExtendStreamWithTreesHelper {
+impl ConcatTreesHelper {
     fn new(capacity: usize) -> Self {
-        ExtendStreamWithTreesHelper { trees: Vec::with_capacity(capacity) }
+        ConcatTreesHelper { trees: Vec::with_capacity(capacity) }
     }
 
     fn push(&mut self, tree: TokenTree) {
@@ -263,7 +263,7 @@ impl ExtendStreamWithTreesHelper {
         }
     }
 
-    fn extend(self, stream: &mut TokenStream) {
+    fn append_to(self, stream: &mut TokenStream) {
         if self.trees.is_empty() {
             return;
         }
@@ -273,13 +273,13 @@ impl ExtendStreamWithTreesHelper {
 
 /// Non-generic helper for implementing `FromIterator<TokenStream>` and
 /// `Extend<TokenStream>` with less monomorphization in calling crates.
-struct ExtendStreamWithStreamsHelper {
+struct ConcatStreamsHelper {
     streams: Vec<bridge::client::TokenStream>,
 }
 
-impl ExtendStreamWithStreamsHelper {
+impl ConcatStreamsHelper {
     fn new(capacity: usize) -> Self {
-        ExtendStreamWithStreamsHelper { streams: Vec::with_capacity(capacity) }
+        ConcatStreamsHelper { streams: Vec::with_capacity(capacity) }
     }
 
     fn push(&mut self, stream: TokenStream) {
@@ -296,7 +296,7 @@ impl ExtendStreamWithStreamsHelper {
         }
     }
 
-    fn extend(mut self, stream: &mut TokenStream) {
+    fn append_to(mut self, stream: &mut TokenStream) {
         if self.streams.is_empty() {
             return;
         }
@@ -314,7 +314,7 @@ impl ExtendStreamWithStreamsHelper {
 impl iter::FromIterator<TokenTree> for TokenStream {
     fn from_iter<I: IntoIterator<Item = TokenTree>>(trees: I) -> Self {
         let iter = trees.into_iter();
-        let mut builder = ExtendStreamWithTreesHelper::new(iter.size_hint().0);
+        let mut builder = ConcatTreesHelper::new(iter.size_hint().0);
         iter.for_each(|tree| builder.push(tree));
         builder.build()
     }
@@ -326,7 +326,7 @@ impl iter::FromIterator<TokenTree> for TokenStream {
 impl iter::FromIterator<TokenStream> for TokenStream {
     fn from_iter<I: IntoIterator<Item = TokenStream>>(streams: I) -> Self {
         let iter = streams.into_iter();
-        let mut builder = ExtendStreamWithStreamsHelper::new(iter.size_hint().0);
+        let mut builder = ConcatStreamsHelper::new(iter.size_hint().0);
         iter.for_each(|stream| builder.push(stream));
         builder.build()
     }
@@ -336,9 +336,9 @@ impl iter::FromIterator<TokenStream> for TokenStream {
 impl Extend<TokenTree> for TokenStream {
     fn extend<I: IntoIterator<Item = TokenTree>>(&mut self, trees: I) {
         let iter = trees.into_iter();
-        let mut builder = ExtendStreamWithTreesHelper::new(iter.size_hint().0);
+        let mut builder = ConcatTreesHelper::new(iter.size_hint().0);
         iter.for_each(|tree| builder.push(tree));
-        builder.extend(self);
+        builder.append_to(self);
     }
 }
 
@@ -346,9 +346,9 @@ impl Extend<TokenTree> for TokenStream {
 impl Extend<TokenStream> for TokenStream {
     fn extend<I: IntoIterator<Item = TokenStream>>(&mut self, streams: I) {
         let iter = streams.into_iter();
-        let mut builder = ExtendStreamWithStreamsHelper::new(iter.size_hint().0);
+        let mut builder = ConcatStreamsHelper::new(iter.size_hint().0);
         iter.for_each(|stream| builder.push(stream));
-        builder.extend(self);
+        builder.append_to(self);
     }
 }
 
@@ -393,7 +393,7 @@ pub mod token_stream {
         type IntoIter = IntoIter;
 
         fn into_iter(self) -> IntoIter {
-            IntoIter(self.0.map(|v| v.into_iter()).unwrap_or_default().into_iter())
+            IntoIter(self.0.map(|v| v.into_trees()).unwrap_or_default().into_iter())
         }
     }
 }