Fix compilation with older versions of swift

Author: Ignacio Bonafonte

Sources/OpenTelemetryApi/Context/ActivityContextManager.swift

@@ -16,9 +16,10 @@ private let OS_ACTIVITY_CURRENT = unsafeBitCast(dlsym(UnsafeMutableRawPointer(bi
 
 class ActivityContextManager: ContextManager {
     static let instance = ActivityContextManager()
-
+    #if swift(>=5.5)
     @available(macOS 12.0, iOS 15.0, tvOS 15.0, *)
     static let taskLocalContextManager = TaskLocalContextManager.instance
+    #endif
 
     let rlock = NSRecursiveLock()
 
@@ -37,12 +38,14 @@ class ActivityContextManager: ContextManager {
     var contextMap = [os_activity_id_t: [String: AnyObject]]()
 
     func getCurrentContextValue(forKey key: OpenTelemetryContextKeys) -> AnyObject? {
+        #if swift(>=5.5)
         if #available(macOS 12.0, iOS 15.0, tvOS 15.0, *) {
             // If running with task local, use first its stored value
             if let contextValue = ActivityContextManager.taskLocalContextManager.getCurrentContextValue(forKey: key) {
                 return contextValue
             }
         }
+        #endif
         var parentIdent: os_activity_id_t = 0
         let activityIdent = os_activity_get_identifier(OS_ACTIVITY_CURRENT, &parentIdent)
         var contextValue: AnyObject?
@@ -67,10 +70,12 @@ class ActivityContextManager: ContextManager {
             objectScope.setObject(ScopeElement(scope: scope), forKey: value)
         }
         contextMap[activityIdent]?[key.rawValue] = value
+        #if swift(>=5.5)
         if #available(macOS 12.0, iOS 15.0, tvOS 15.0, *) {
             // If running with task local, set the value after the activity, so activity is not empty
             ActivityContextManager.taskLocalContextManager.setCurrentContextValue(forKey: key, value: value)
         }
+        #endif
         rlock.unlock()
     }
 
@@ -89,12 +94,14 @@ class ActivityContextManager: ContextManager {
             os_activity_scope_leave(&scope)
             objectScope.removeObject(forKey: value)
         }
+        #if swift(>=5.5)
         if #available(macOS 12.0, iOS 15.0, tvOS 15.0, *) {
             // If there is a parent activity, set its content as the task local
             ActivityContextManager.taskLocalContextManager.removeContextValue(forKey: key, value: value)
             if let currentContext = self.getCurrentContextValue(forKey: key) {
                 ActivityContextManager.taskLocalContextManager.setCurrentContextValue(forKey: key, value: currentContext)
             }
         }
+        #endif
     }
 }

Sources/OpenTelemetryApi/Context/TaskLocalContextManager.swift

@@ -5,6 +5,7 @@
 
 import Foundation
 
+#if swift(>=5.5)
 @available(macOS 12.0, iOS 15.0, tvOS 15.0, *)
 enum ContextManagement {
     @TaskLocal
@@ -55,3 +56,4 @@ class TaskLocalContextManager: ContextManager {
         }
     }
 }
+#endif