From d8bc17d9a7c90bb8954a397a1a3897a11b47c6f7 Mon Sep 17 00:00:00 2001
From: Christian Schwarz <christian@neon.tech>
Date: Thu, 24 Aug 2023 20:18:27 +0200
Subject: [PATCH] use auto-enums instead of hand-rolling the future

---
 Cargo.lock                                    | 24 ++++++++++++
 tokio-epoll-uring/Cargo.toml                  |  1 +
 .../src/system/submission/op_fut.rs           | 37 ++-----------------
 3 files changed, 28 insertions(+), 34 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 5f78f5a..6c55d59 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -119,6 +119,18 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "auto_enums"
+version = "0.8.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dd4ba50b181a898ce52142184e3a46641002b3b190bf5ef827eb3c578fad4b70"
+dependencies = [
+ "derive_utils",
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "autocfg"
 version = "1.1.0"
@@ -487,6 +499,17 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "derive_utils"
+version = "0.13.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9abcad25e9720609ccb3dcdb795d845e37d8ce34183330a9f48b03a1a71c8e21"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "either"
 version = "1.9.0"
@@ -1610,6 +1633,7 @@ name = "tokio-epoll-uring"
 version = "0.1.0"
 dependencies = [
  "assert-panic",
+ "auto_enums",
  "futures",
  "io-uring 0.6.0",
  "nix 0.26.2",
diff --git a/tokio-epoll-uring/Cargo.toml b/tokio-epoll-uring/Cargo.toml
index 8e96817..3155af6 100644
--- a/tokio-epoll-uring/Cargo.toml
+++ b/tokio-epoll-uring/Cargo.toml
@@ -8,6 +8,7 @@ repository = "https://github.com/neondatabase/tokio-epoll-uring"
 license = "MIT OR Apache-2.0"
 
 [dependencies]
+auto_enums = "0.8.2"
 futures = "0.3.28"
 io-uring = "0.6.0"
 once_cell = "1.18.0"
diff --git a/tokio-epoll-uring/src/system/submission/op_fut.rs b/tokio-epoll-uring/src/system/submission/op_fut.rs
index 3f5faa7..da5ddad 100644
--- a/tokio-epoll-uring/src/system/submission/op_fut.rs
+++ b/tokio-epoll-uring/src/system/submission/op_fut.rs
@@ -1,4 +1,4 @@
-use std::{fmt::Display, pin::Pin, sync::Arc};
+use std::{fmt::Display, sync::Arc};
 
 /// An io_uring operation and the resources it operates on.
 ///
@@ -156,42 +156,11 @@ where
 }
 
 // Used by `execute_op` to avoid boxing the future returned by the `with_submit_side` closure.
-enum Fut<Output, A, B, C, D, E>
-where
-    A: std::future::Future<Output = Output>,
-    B: std::future::Future<Output = Output>,
-    C: std::future::Future<Output = Output>,
-    D: std::future::Future<Output = Output>,
-    E: std::future::Future<Output = Output>,
-{
+#[auto_enums::enum_derive(Future)]
+enum Fut<A, B, C, D, E> {
     A(A),
     B(B),
     C(C),
     D(D),
     E(E),
 }
-impl<Output, A, B, C, D, E> std::future::Future for Fut<Output, A, B, C, D, E>
-where
-    A: std::future::Future<Output = Output>,
-    B: std::future::Future<Output = Output>,
-    C: std::future::Future<Output = Output>,
-    D: std::future::Future<Output = Output>,
-    E: std::future::Future<Output = Output>,
-{
-    type Output = Output;
-
-    fn poll(
-        self: std::pin::Pin<&mut Self>,
-        cx: &mut std::task::Context<'_>,
-    ) -> std::task::Poll<Self::Output> {
-        unsafe {
-            match self.get_unchecked_mut() {
-                Self::A(x) => Pin::new_unchecked(x).poll(cx),
-                Self::B(x) => Pin::new_unchecked(x).poll(cx),
-                Self::C(x) => Pin::new_unchecked(x).poll(cx),
-                Self::D(x) => Pin::new_unchecked(x).poll(cx),
-                Self::E(x) => Pin::new_unchecked(x).poll(cx),
-            }
-        }
-    }
-}