Add script to check for API breaks (#258)

Co-authored-by: tomer doron <tomer@apple.com>

scripts/check_no_api_breakages.sh

@@ -0,0 +1,68 @@
+#!/bin/bash
+##===----------------------------------------------------------------------===##
+##
+## This source file is part of the SwiftAWSLambdaRuntime open source project
+##
+## Copyright (c) 2022 Apple Inc. and the SwiftAWSLambdaRuntime project authors
+## Licensed under Apache License v2.0
+##
+## See LICENSE.txt for license information
+## See CONTRIBUTORS.txt for the list of SwiftAWSLambdaRuntime project authors
+##
+## SPDX-License-Identifier: Apache-2.0
+##
+##===----------------------------------------------------------------------===##
+
+##===----------------------------------------------------------------------===##
+##
+## This source file is part of the SwiftNIO open source project
+##
+## Copyright (c) 2017-2020 Apple Inc. and the SwiftNIO project authors
+## Licensed under Apache License v2.0
+##
+## See LICENSE.txt for license information
+## See CONTRIBUTORS.txt for the list of SwiftNIO project authors
+##
+## SPDX-License-Identifier: Apache-2.0
+##
+##===----------------------------------------------------------------------===##
+
+set -eu
+
+function usage() {
+    echo >&2 "Usage: $0 REPO-GITHUB-URL NEW-VERSION OLD-VERSIONS..."
+    echo >&2
+    echo >&2 "This script requires a Swift 5.6+ 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
+    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"
+}
+
+if [[ $# -lt 3 ]]; then
+    usage
+    exit 1
+fi
+
+tmpdir=$(mktemp -d /tmp/.check-api_XXXXXX)
+repo_url=$1
+new_tag=$2
+shift 2
+
+repodir="$tmpdir/repo"
+git clone "$repo_url" "$repodir"
+git -C "$repodir" fetch -q origin '+refs/pull/*:refs/remotes/origin/pr/*'
+cd "$repodir"
+git checkout -q "$new_tag"
+
+for old_tag in "$@"; do
+    echo "Checking public API breakages from $old_tag to $new_tag"
+
+    swift package diagnose-api-breaking-changes "$old_tag"
+done
+
+echo done