Drop support for Swift 5.2 and 5.3 (#581)

As outlined in a [Swift forums post in November ’21](https://forums.swift.org/t/swiftnio-swift-version-support/53232), SwiftNIO will only support the latest non-patch Swift release and the 2 immediately prior non-patch versions.

- drop support for Swift 5.2 and 5.3. 
- update CI for Swift 5.4 to run on bionic instead of focal to ensure that we still test bionic.

Author: fabianfett

.swiftformat

@@ -1,6 +1,6 @@
 # file options
 
---swiftversion 5.2
+--swiftversion 5.4
 --exclude .build
 
 # format options

CONTRIBUTING.md

@@ -57,7 +57,7 @@ A good AsyncHTTPClient patch is:
 3. Documented, adding API documentation as needed to cover new functions and properties.
 4. Accompanied by a great commit message, using our commit message template.
 
-*Note* as of version 1.5.0 AsyncHTTPClient requires Swift 5.2. Earlier versions support as far back as Swift 5.0.
+*Note* as of version 1.10.0 AsyncHTTPClient requires Swift 5.4. Earlier versions support as far back as Swift 5.0.
 
 ### Commit Message Template
 

Package.swift

@@ -1,4 +1,4 @@
-// swift-tools-version:5.2
+// swift-tools-version:5.4
 //===----------------------------------------------------------------------===//
 //
 // This source file is part of the AsyncHTTPClient open source project

docker/Dockerfile

@@ -1,4 +1,4 @@
-ARG swift_version=5.2
+ARG swift_version=5.4
 ARG ubuntu_version=bionic
 ARG base_image=swift:$swift_version-$ubuntu_version
 FROM $base_image

docker/docker-compose.1604.52.yaml

@@ -3,16 +3,16 @@ version: "3"
 services:
 
   runtime-setup:
-    image: async-http-client:18.04-5.3
+    image: async-http-client:18.04-5.4
     build:
       args:
         ubuntu_version: "bionic"
-        swift_version: "5.3"
+        swift_version: "5.4"
 
   test:
-    image: async-http-client:18.04-5.3
+    image: async-http-client:18.04-5.4
     environment: []
       #- SANITIZER_ARG=--sanitize=thread
 
   shell:
-    image: async-http-client:18.04-5.3
+    image: async-http-client:18.04-5.4

docker/docker-compose.1804.53.yaml renamed to docker/docker-compose.1804.54.yaml

@@ -3,7 +3,7 @@
 ##
 ## This source file is part of the AsyncHTTPClient open source project
 ##
-## Copyright (c) 2018-2019 Apple Inc. and the AsyncHTTPClient project authors
+## Copyright (c) 2018-2022 Apple Inc. and the AsyncHTTPClient project authors
 ## Licensed under Apache License v2.0
 ##
 ## See LICENSE.txt for license information
@@ -32,12 +32,12 @@ set -eu
 function usage() {
     echo >&2 "Usage: $0 REPO-GITHUB-URL NEW-VERSION OLD-VERSIONS..."
     echo >&2
-    echo >&2 "This script requires a Swift 5.2+ toolchain."
+    echo >&2 "This script requires a Swift 5.6+ toolchain."
     echo >&2
     echo >&2 "Examples:"
     echo >&2
-    echo >&2 "Check between main and tag 2.1.1 of swift-nio:"
-    echo >&2 "  $0 https://github.com/apple/swift-nio main 2.1.1"
+    echo >&2 "Check between main and tag 1.9.0 of async-http-client:"
+    echo >&2 "  $0 https://github.com/swift-server/async-http-client main 1.9.0"
     echo >&2
     echo >&2 "Check between HEAD and commit 64cf63d7 using the provided toolchain:"
     echo >&2 "  xcrun --toolchain org.swift.5120190702a $0 ../some-local-repo HEAD 64cf63d7"