added SpryMacroAvailable

Package.swift

@@ -21,6 +21,8 @@ let package = Package(
         .package(url: "https://github.com/apple/swift-syntax.git", exact: "600.0.0")
     ],
     targets: [
+        .target(name: "SpryMacroAvailable",
+                path: "VersionMarkerModule"),
         // internal
         .target(name: "SharedTypes",
                 dependencies: [
@@ -40,6 +42,7 @@ let package = Package(
         // public
         .target(name: "SpryKit",
                 dependencies: [
+                    "SpryMacroAvailable",
                     "SharedTypes",
                     "MacroAndCompilerPlugin",
                     "CwlPreconditionTesting",

README.md

@@ -24,6 +24,7 @@ __Table of Contents__
 * [SpryEquatable](#spryequatable)
 * [Argument](#Argument)
 * [ArgumentCaptor](#argumentcaptor)
+* [MacroAvailable](#MacroAvailable)
 
 ## Motivation
 
@@ -438,6 +439,20 @@ let secondArgFromFirstCall: String = captor[0]
 let secondArgFromSecondCall: String = captor[1]
 ```
 
+## MacroAvailable
+
+All the ideas described in the following apply to all packages that depend on SpryKit, not only macros.
+
+In order to handle breaking API changes, clients can wrap uses of such APIs in conditional compilation clauses that check MacroAvailable.
+
+```swift
+#if canImport(SpryMacroAvailable)
+// code to support @Spryable
+#else
+// code for SpryKit without Macro
+#endif
+```
+
 ## Contributing
 
 If you have an idea that can make SpryKit better, please don't hesitate to submit a pull request!

Tests/ThreadSafeTests.swift

@@ -27,7 +27,7 @@ final class ThreadSafeTests: XCTestCase {
             }
         }
 
-        wait(for: expectetions, timeout: 5)
+        wait(for: expectetions, timeout: 10)
         XCTAssertEqual(storage.values.count, expectetions.count)
     }
 }

VersionMarkerModule/Empty.swift

@@ -0,0 +1,3 @@
+// The SpryMacroAvailable module is intentionally empty.
+// It serves as an indicator of whether @Spryable-macro is available.
+// See the 'README -> #MacroAvailable' document for more information.