Don't add c-ares/CMakeFiles dir to exclusion list if doesn't exist (#4)

Motivation:
`c-ares/CMakeFiles/` doesn't exist unless cmake is run locally. User reports that the exclude line causes SwiftPM warning about invalid exclude.

Modification:
Add `c-ares/CMakeFiles/` to exclude list iff it exists and is non-empty.

Author: yim-lee

Package.swift

@@ -1,6 +1,25 @@
 // swift-tools-version:5.0
+
+import class Foundation.FileManager
 import PackageDescription
 
+var caresExclude = [
+    "./c-ares/acountry.c",
+    "./c-ares/adig.c",
+    "./c-ares/ahost.c",
+    "./c-ares/ares_android.c",
+    "./c-ares/windows_port.c",
+    "./c-ares/test/",
+]
+
+do {
+    if !(try FileManager.default.contentsOfDirectory(atPath: "./Sources/CAsyncDNSResolver/c-ares/CMakeFiles").isEmpty) {
+        caresExclude.append("./c-ares/CMakeFiles/")
+    }
+} catch {
+    // Assume CMakeFiles does not exist so no need to exclude it
+}
+
 let package = Package(
     name: "swift-async-dns-resolver",
     products: [
@@ -12,15 +31,7 @@ let package = Package(
     targets: [
         .target(
             name: "CAsyncDNSResolver", dependencies: [],
-            exclude: [
-                "./c-ares/acountry.c",
-                "./c-ares/adig.c",
-                "./c-ares/ahost.c",
-                "./c-ares/ares_android.c",
-                "./c-ares/windows_port.c",
-                "./c-ares/CMakeFiles/",
-                "./c-ares/test/",
-            ],
+            exclude: caresExclude,
             sources: ["./c-ares"],
             cSettings: [
                 .headerSearchPath("./c-ares"),

docker/docker-compose.1804.54.yaml

@@ -0,0 +1,17 @@
+version: "3"
+
+services:
+
+  runtime-setup:
+    image: swift-async-dns-resolver:18.04-5.4
+    build:
+      args:
+        base_image: "swiftlang/swift:nightly-5.4-bionic"
+
+  test:
+    image: swift-async-dns-resolver:18.04-5.4
+    environment: []
+      #- SANITIZER_ARG=--sanitize=thread
+
+  shell:
+    image: swift-async-dns-resolver:18.04-5.4

docker/docker-compose.yaml

@@ -22,9 +22,9 @@ services:
       - CAP_NET_RAW
       - CAP_NET_BIND_SERVICE
 
-  sanity:
+  soundness:
     <<: *common
-    command: /bin/bash -xcl "./scripts/sanity.sh"
+    command: /bin/bash -xcl "./scripts/soundness.sh"
 
   test:
     <<: *common

scripts/sanity.sh renamed to scripts/soundness.sh

@@ -3,7 +3,7 @@
 ##
 ## This source file is part of the SwiftAsyncDNSResolver open source project
 ##
-## Copyright (c) 2020 Apple Inc. and the SwiftAsyncDNSResolver project authors
+## Copyright (c) 2020-2021 Apple Inc. and the SwiftAsyncDNSResolver project authors
 ## Licensed under Apache License v2.0
 ##
 ## See LICENSE.txt for license information
@@ -18,7 +18,7 @@ here="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
 
 function replace_acceptable_years() {
     # this needs to replace all acceptable forms with 'YEARS'
-    sed -e 's/2017-201[89]/YEARS/' -e 's/2019-2020/YEARS/' -e 's/2019/YEARS/' -e 's/2020/YEARS/'
+    sed -e 's/2020-2021/YEARS/' -e 's/2020/YEARS/' -e 's/2021/YEARS/'
 }
 
 printf "=> Checking format... "