From 21fb4ac0fb8341f490b094253d4c3649623d07e2 Mon Sep 17 00:00:00 2001
From: Nicholas Nethercote <n.nethercote@gmail.com>
Date: Thu, 10 Mar 2022 17:09:33 +1100
Subject: [PATCH 1/2] Remove two useless rules from `extension_trait!`.

They never run because they are subsumed by the two rules immediately
above.
---
 src/utils.rs | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/src/utils.rs b/src/utils.rs
index d8052444..a54d2525 100644
--- a/src/utils.rs
+++ b/src/utils.rs
@@ -309,14 +309,6 @@ macro_rules! extension_trait {
         extension_trait!(@ext ($($head)* -> $f) $($tail)*);
     };
 
-    // Parse the return type in an extension method.
-    (@doc ($($head:tt)*) -> impl Future<Output = $out:ty> + $lt:lifetime [$f:ty] $($tail:tt)*) => {
-        extension_trait!(@doc ($($head)* -> borrowed::ImplFuture<$lt, $out>) $($tail)*);
-    };
-    (@ext ($($head:tt)*) -> impl Future<Output = $out:ty> + $lt:lifetime [$f:ty] $($tail:tt)*) => {
-        extension_trait!(@ext ($($head)* -> $f) $($tail)*);
-    };
-
     // Parse a token.
     (@doc ($($head:tt)*) $token:tt $($tail:tt)*) => {
         extension_trait!(@doc ($($head)* $token) $($tail)*);

From db7c1946c89e119ea37966803735cdcc0601058e Mon Sep 17 00:00:00 2001
From: Nicholas Nethercote <n.nethercote@gmail.com>
Date: Thu, 10 Mar 2022 17:10:12 +1100
Subject: [PATCH 2/2] Move the `extension_trait!` accumulator to the end of the
 rules.

That way, when the `-> impl Future` rules fail (which is most of the
time), the cost of reparsing the accumulated tokens is avoided.
---
 src/utils.rs | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/src/utils.rs b/src/utils.rs
index a54d2525..6ae49115 100644
--- a/src/utils.rs
+++ b/src/utils.rs
@@ -281,7 +281,7 @@ macro_rules! extension_trait {
         #[cfg(feature = "docs")]
         #[doc = $doc]
         pub trait $name {
-            extension_trait!(@doc () $($body_base)* $($body_ext)*);
+            extension_trait!(@doc [$($body_base)* $($body_ext)*] -> []);
         }
 
         // When not rendering docs, re-export the base trait from the futures crate.
@@ -291,7 +291,7 @@ macro_rules! extension_trait {
         // The extension trait that adds methods to any type implementing the base trait.
         #[doc = $doc_ext]
         pub trait $ext: $name {
-            extension_trait!(@ext () $($body_ext)*);
+            extension_trait!(@ext [$($body_ext)*] -> []);
         }
 
         // Blanket implementation of the extension trait for any type implementing the base trait.
@@ -302,24 +302,24 @@ macro_rules! extension_trait {
     };
 
     // Parse the return type in an extension method.
-    (@doc ($($head:tt)*) -> impl Future<Output = $out:ty> $(+ $lt:lifetime)? [$f:ty] $($tail:tt)*) => {
-        extension_trait!(@doc ($($head)* -> owned::ImplFuture<$out>) $($tail)*);
+    (@doc [-> impl Future<Output = $out:ty> $(+ $lt:lifetime)? [$f:ty] $($tail:tt)*] -> [$($accum:tt)*]) => {
+        extension_trait!(@doc [$($tail)*] -> [$($accum)* -> owned::ImplFuture<$out>]);
     };
-    (@ext ($($head:tt)*) -> impl Future<Output = $out:ty> $(+ $lt:lifetime)? [$f:ty] $($tail:tt)*) => {
-        extension_trait!(@ext ($($head)* -> $f) $($tail)*);
+    (@ext [-> impl Future<Output = $out:ty> $(+ $lt:lifetime)? [$f:ty] $($tail:tt)*] -> [$($accum:tt)*]) => {
+        extension_trait!(@ext [$($tail)*] -> [$($accum)* -> $f]);
     };
 
     // Parse a token.
-    (@doc ($($head:tt)*) $token:tt $($tail:tt)*) => {
-        extension_trait!(@doc ($($head)* $token) $($tail)*);
+    (@doc [$token:tt $($tail:tt)*] -> [$($accum:tt)*]) => {
+        extension_trait!(@doc [$($tail)*] -> [$($accum)* $token]);
     };
-    (@ext ($($head:tt)*) $token:tt $($tail:tt)*) => {
-        extension_trait!(@ext ($($head)* $token) $($tail)*);
+    (@ext [$token:tt $($tail:tt)*] -> [$($accum:tt)*]) => {
+        extension_trait!(@ext [$($tail)*] -> [$($accum)* $token]);
     };
 
     // Handle the end of the token list.
-    (@doc ($($head:tt)*)) => { $($head)* };
-    (@ext ($($head:tt)*)) => { $($head)* };
+    (@doc [] -> [$($accum:tt)*]) => { $($accum)* };
+    (@ext [] -> [$($accum:tt)*]) => { $($accum)* };
 
     // Parse imports at the beginning of the macro.
     ($import:item $($tail:tt)*) => {