Add support for Swift 5.0 & 5.1 (#26)

* Add support for Swift 5.0 & 5.1

* try to compiler() guard the test

* try just compiler()

* try separate access

* Cannot support Swift 5.0 due to compiler bug #if

* Update .swiftformat

* Cannot support 5.0 due to compiler bug in #if preventing task-local access

* Apply suggestions from code review

* Update README.md

* formatting

Co-authored-by: Konrad `ktoso` Malawski <konrad_malawski@apple.com>
Co-authored-by: Konrad `ktoso` Malawski <konrad.malawski@project13.pl>

.swiftformat

@@ -1,6 +1,6 @@
 # file options
 
---swiftversion 5.2
+--swiftversion 5.1
 --exclude .build
 --exclude UseCases/.build
 --exclude Tests/LinuxMain.swift

Package@swift-5.1.swift

@@ -0,0 +1,27 @@
+// swift-tools-version:5.1
+import PackageDescription
+
+let package = Package(
+    name: "swift-distributed-tracing-baggage",
+    products: [
+        .library(
+            name: "InstrumentationBaggage",
+            targets: [
+                "InstrumentationBaggage",
+            ]
+        ),
+    ],
+    targets: [
+        .target(name: "InstrumentationBaggage"),
+
+        // ==== --------------------------------------------------------------------------------------------------------
+        // MARK: Tests
+
+        .testTarget(
+            name: "InstrumentationBaggageTests",
+            dependencies: [
+                .target(name: "InstrumentationBaggage"),
+            ]
+        ),
+    ]
+)

README.md

@@ -1,16 +1,20 @@
 # 🧳 Distributed Tracing: Baggage
 
+[![Swift 5.1](https://img.shields.io/badge/Swift-5.1-ED523F.svg?style=flat)](https://swift.org/download/)
 [![Swift 5.2](https://img.shields.io/badge/Swift-5.2-ED523F.svg?style=flat)](https://swift.org/download/)
 [![Swift 5.3](https://img.shields.io/badge/Swift-5.3-ED523F.svg?style=flat)](https://swift.org/download/)
 [![Swift 5.4](https://img.shields.io/badge/Swift-5.4-ED523F.svg?style=flat)](https://swift.org/download/)
 [![Swift 5.5](https://img.shields.io/badge/Swift-5.5-ED523F.svg?style=flat)](https://swift.org/download/)
+[![Swift 5.6](https://img.shields.io/badge/Swift-5.6-ED523F.svg?style=flat)](https://swift.org/download/)
+[![Swift 5.7](https://img.shields.io/badge/Swift-5.7-ED523F.svg?style=flat)](https://swift.org/download/)
 
-> ⚠️ Automatic propagation through task-locals only supported in Swift >= 5.5
+> **Warning**
+> Automatic propagation through task-locals only supported in Swift >= 5.5
 
 `Baggage` is a minimal (zero-dependency) context propagation container, intended to "carry" baggage items
 for purposes of cross-cutting tools to be built on top of it.
 
-It is modeled after the concepts explained in [W3C Baggage](https://w3c.github.io/baggage/) and the 
+It is modeled after the concepts explained in [W3C Baggage](https://w3c.github.io/baggage/) and the
 in the spirit of [Tracing Plane](https://cs.brown.edu/~jcmace/papers/mace18universal.pdf) 's "Baggage Context" type,
 although by itself it does not define a specific serialization format.
 
@@ -20,7 +24,7 @@ deploy various cross-cutting instruments all reusing the same baggage type. More
 
 ## Dependency
 
- In order to depend on this library you can use the Swift Package Manager, and add the following dependency to your `Package.swift`:
+In order to depend on this library you can use the Swift Package Manager, and add the following dependency to your `Package.swift`:
 
 ```swift
 dependencies: [
@@ -33,18 +37,18 @@ dependencies: [
 
 and depend on the module in your target:
 
-```swift 
+```swift
 targets: [
     .target(
         name: "MyAwesomeApp",
         dependencies: [
             .product(
-              name: "InstrumentationBaggage", 
+              name: "InstrumentationBaggage",
               package: "swift-distributed-tracing-baggage"
             ),
         ]
     ),
-    // ... 
+    // ...
 ]
 ```
 

Tests/InstrumentationBaggageTests/BaggageTests.swift

@@ -63,7 +63,7 @@ final class BaggageTests: XCTestCase {
     }
 
     func test_automaticPropagationThroughTaskLocal() throws {
-        #if swift(>=5.5) && canImport(_Concurrency)
+        #if compiler(>=5.5)
         guard #available(macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, *) else {
             throw XCTSkip("Task locals are not supported on this platform.")
         }
@@ -78,7 +78,8 @@ final class BaggageTests: XCTestCase {
             propagatedBaggage = Baggage.current
         }
 
-        Baggage.$current.withValue(baggage, operation: exampleFunction)
+        let c = Baggage.$current
+        c.withValue(baggage, operation: exampleFunction)
 
         XCTAssertEqual(propagatedBaggage?.count, 1)
         XCTAssertEqual(propagatedBaggage?[FirstTestKey.self], 42)

docker/docker-compose.1804.51.yaml

@@ -0,0 +1,16 @@
+version: "3"
+
+services:
+
+  runtime-setup:
+    image: swift-distributed-tracing-baggage:18.04-5.1
+    build:
+      args:
+        ubuntu_version: "bionic"
+        swift_version: "5.1"
+
+  test:
+    image: swift-distributed-tracing-baggage:18.04-5.1
+
+  shell:
+    image: swift-distributed-tracing-baggage:18.04-5.1