Disable integration tests on macOS to unblock CI (#40)

* Add `Library` as a product of Snippets fixture library

SwiftPM now only makes product libraries available to Swift Snippets.

* Skip integration tests when Swift concurrency is not available

Author: ethan-kusters

IntegrationTests/Tests/DocCArchiveIndexGenerationTests.swift

@@ -8,7 +8,7 @@
 
 import XCTest
 
-final class DocCArchiveIndexGenerationTests: XCTestCase {
+final class DocCArchiveIndexGenerationTests: ConcurrencyRequiringTestCase {
     func testGenerateDocumentationWithIndexingEnabled() throws {
         let result = try swiftPackage(
             "generate-documentation",

IntegrationTests/Tests/Fixtures/PackageWithSnippets/Package.swift

@@ -13,6 +13,9 @@ import PackageDescription
 
 let package = Package(
     name: "PackageWithSnippets",
+    products: [
+        .library(name: "Library", targets: ["Library"])
+    ],
     targets: [
         .target(name: "Library"),
     ]

IntegrationTests/Tests/MixedTargetsTests.swift

@@ -8,7 +8,7 @@
 
 import XCTest
 
-final class MixedTargetsTests: XCTestCase {
+final class MixedTargetsTests: ConcurrencyRequiringTestCase {
     func testGenerateDocumentationForSpecificTarget() throws {
         let result = try swiftPackage(
             "generate-documentation", "--target", "Executable",

IntegrationTests/Tests/SingleExecutableTargetTests.swift

@@ -8,7 +8,7 @@
 
 import XCTest
 
-final class SingleExecutableTargetTests: XCTestCase {
+final class SingleExecutableTargetTests: ConcurrencyRequiringTestCase {
     func testGenerateDocumentation() throws {
         let result = try swiftPackage(
             "generate-documentation",

IntegrationTests/Tests/SingleLibraryTargetTests.swift

@@ -8,7 +8,7 @@
 
 import XCTest
 
-final class SingleLibraryTargetTests: XCTestCase {
+final class SingleLibraryTargetTests: ConcurrencyRequiringTestCase {
     func testGenerateDocumentation() throws {
         let result = try swiftPackage(
             "generate-documentation",

IntegrationTests/Tests/SingleTestTargetTests.swift

@@ -8,7 +8,7 @@
 
 import XCTest
 
-final class SingleTestTargetTests: XCTestCase {
+final class SingleTestTargetTests: ConcurrencyRequiringTestCase {
     func testDoesNotGenerateDocumentation() throws {
         let result = try swiftPackage(
             "generate-documentation",

IntegrationTests/Tests/SnippetDocumentationGenerationTests.swift

@@ -8,7 +8,7 @@
 
 import XCTest
 
-final class SnippetDocumentationGenerationTests: XCTestCase {
+final class SnippetDocumentationGenerationTests: ConcurrencyRequiringTestCase {
     func testGenerateDocumentationForPackageWithSnippets() throws {
         let result = try swiftPackage(
             "generate-documentation",

IntegrationTests/Tests/SwiftDocCPreviewTests.swift

@@ -9,7 +9,7 @@
 import Foundation
 import XCTest
 
-final class SwiftDocCPreview: XCTestCase {
+final class SwiftDocCPreview: ConcurrencyRequiringTestCase {
     func testRunPreviewServerOnSamePortRepeatedly() throws {
         // Because only a single server can bind to a given port at a time,
         // this test ensures that the preview server running in the `docc`

IntegrationTests/Tests/SwiftPMSandboxTests.swift

@@ -8,7 +8,7 @@
 
 import XCTest
 
-final class SwiftPMSandboxTests: XCTestCase {
+final class SwiftPMSandboxTests: ConcurrencyRequiringTestCase {
     func testEnableAdditionalSandboxedDirectories() throws {
         let outputDirectory = try temporaryDirectory()
 

IntegrationTests/Tests/TargetWithDocCCatalogTests.swift

@@ -8,7 +8,7 @@
 
 import XCTest
 
-final class TargetWithDocCCatalogTests: XCTestCase {
+final class TargetWithDocCCatalogTests: ConcurrencyRequiringTestCase {
     func testGenerateDocumentation() throws {
         let result = try swiftPackage(
             "generate-documentation",

IntegrationTests/Tests/Utility/ConcurrencyRequiringTestCase.swift

@@ -0,0 +1,87 @@
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2022 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for Swift project authors
+
+import Foundation
+import XCTest
+
+/// A test case that requires the host toolchain to support Swift concurrency in order
+/// to pass.
+///
+/// All SwiftPM command plugins depend on Swift concurrency so we don't expect to be able
+/// to run any integration test that actually invokes the Swift-DocC Plugin without
+/// the Swift concurrency libraries.
+class ConcurrencyRequiringTestCase: XCTestCase {
+    override func setUpWithError() throws {
+        try XCTSkipUnless(
+            supportsSwiftConcurrency(),
+            "The current SDK and/or OS do not support Swift concurrency."
+        )
+    }
+    
+    private static var _supportsSwiftConcurrency: Bool?
+    
+    // Adapted from https://github.com/apple/swift-package-manager/blob/dd7e9cc6/Sources/SPMTestSupport/Toolchain.swift#L55
+    private func supportsSwiftConcurrency() throws -> Bool {
+#if os(macOS)
+        if #available(macOS 12.0, *) {
+            // On macOS 12 and later, concurrency is assumed to work.
+            return true
+        } else {
+            if let _supportsSwiftConcurrency = Self._supportsSwiftConcurrency {
+                return _supportsSwiftConcurrency
+            }
+            
+            let temporaryDirectory = try temporaryDirectory()
+            
+            // On macOS 11 and earlier, we don't know if concurrency actually works because not all
+            // SDKs and toolchains have the right bits.  We could examine the SDK and the various
+            // libraries, but the most accurate test is to just try to compile and run a snippet of
+            // code that requires async/await support.  It doesn't have to actually do anything,
+            // it's enough that all the libraries can be found (but because the library reference
+            // is weak we do need the linkage reference to `_swift_task_create` and the like).
+            do {
+                let inputPath = temporaryDirectory.appendingPathComponent("foo.swift")
+                
+                try """
+                public func foo() async {}
+                
+                Task { await foo() }
+                """.write(to: inputPath, atomically: true, encoding: .utf8)
+                
+                let outputPath = temporaryDirectory.appendingPathComponent("foo")
+                let process = Process()
+                process.executableURL = try swiftExecutableURL
+                    .deletingLastPathComponent()
+                    .appendingPathComponent("swiftc")
+                
+                process.arguments = [inputPath.path, "-o", outputPath.path]
+                
+                try process.run()
+                process.waitUntilExit()
+                guard process.terminationStatus == EXIT_SUCCESS else {
+                    Self._supportsSwiftConcurrency = false
+                    return false
+                }
+            } catch {
+                // On any failure we assume false.
+                Self._supportsSwiftConcurrency = false
+                return false
+            }
+            // If we get this far we could compile and run a trivial executable that uses
+            // libConcurrency, so we can say that this toolchain supports concurrency on this host.
+            Self._supportsSwiftConcurrency = true
+            return true
+        }
+#else
+        // On other platforms, concurrency is assumed to work since with new enough versions
+        // of the toolchain.
+        return true
+#endif
+    }
+}
+

IntegrationTests/Tests/Utility/XCTestCase+swiftPackage.swift

@@ -110,7 +110,7 @@ extension XCTestCase {
         }
     }
 
-    private var swiftExecutableURL: URL {
+    var swiftExecutableURL: URL {
         get throws {
             let whichProcess = Process.shell("which swift")