[Concurrency] Fix init task group with flags availability

resolves rdar://112469076

Author: ktoso

include/swift/AST/ASTContext.h

@@ -892,6 +892,10 @@ class ASTContext final {
   /// Get the runtime availability of support for concurrency.
   AvailabilityContext getConcurrencyAvailability();
 
+  /// Get the runtime availability of the `DiscardingTaskGroup`,
+  /// and supporting runtime functions function
+  AvailabilityContext getConcurrencyDiscardingTaskGroupAvailability();
+
   /// Get the back-deployed availability for concurrency.
   AvailabilityContext getBackDeployedConcurrencyAvailability();
 

include/swift/Runtime/RuntimeFunctions.def

@@ -2217,7 +2217,7 @@ FUNCTION(TaskGroupInitialize,
 // void swift_taskGroup_initializeWithFlags(size_t flags, TaskGroup *group);
 FUNCTION(TaskGroupInitializeWithFlags,
          swift_taskGroup_initializeWithFlags, SwiftCC,
-         ConcurrencyAvailability,
+         ConcurrencyDiscardingTaskGroupAvailability,
          RETURNS(VoidTy),
          ARGS(SizeTy,           // flags
               Int8PtrTy,        // group

lib/AST/Availability.cpp

@@ -492,6 +492,10 @@ AvailabilityContext ASTContext::getConcurrencyAvailability() {
   return getSwift55Availability();
 }
 
+AvailabilityContext ASTContext::getConcurrencyDiscardingTaskGroupAvailability() {
+  return getSwift59Availability();
+}
+
 AvailabilityContext ASTContext::getBackDeployedConcurrencyAvailability() {
   return getSwift51Availability();
 }

lib/IRGen/IRGenModule.cpp

@@ -861,6 +861,15 @@ namespace RuntimeConstants {
     return RuntimeAvailability::AlwaysAvailable;
   }
 
+  RuntimeAvailability ConcurrencyDiscardingTaskGroupAvailability(ASTContext &context) {
+    auto featureAvailability =
+        context.getConcurrencyDiscardingTaskGroupAvailability();
+    if (!isDeploymentAvailabilityContainedIn(context, featureAvailability)) {
+      return RuntimeAvailability::ConditionallyAvailable;
+    }
+    return RuntimeAvailability::AlwaysAvailable;
+  }
+
   RuntimeAvailability DifferentiationAvailability(ASTContext &context) {
     auto featureAvailability = context.getDifferentiationAvailability();
     if (!isDeploymentAvailabilityContainedIn(context, featureAvailability)) {