Fix crash when back-deploying concurrency to iOS 15.0/15.1-era OSs

stdlib/toolchain/Compatibility56/Concurrency/Actor.cpp

@@ -8,6 +8,9 @@
 #include "swift/Runtime/Casting.h"
 #include "Runtime/Threading/ThreadLocal.h"
 
+#include <Availability.h>
+#include <TargetConditionals.h>
+
 #include <atomic>
 #include <new>
 
@@ -146,3 +149,47 @@ void swift::adoptTaskVoucher(AsyncTask *task) {
 void swift::restoreTaskVoucher(AsyncTask *task) {
   ExecutorTrackingInfo::current()->restoreVoucher(task);
 }
+
+static swift_once_t voucherDisableCheckOnce;
+static bool vouchersDisabled;
+
+namespace {
+  struct _SwiftNSOperatingSystemVersion{
+    intptr_t majorVersion;
+    intptr_t minorVersion;
+    intptr_t patchVersion;
+  };
+}
+
+extern "C"
+_SwiftNSOperatingSystemVersion
+_swift_stdlib_operatingSystemVersion() __attribute__((const));
+
+static void _initializeVouchersDisabled(void *ctxt) {
+  auto osVersion = _swift_stdlib_operatingSystemVersion();
+  #if TARGET_OS_WATCH
+  vouchersDisabled = (
+    osVersion.majorVersion == 8 &&
+    osVersion.minorVersion >= 0 && osVersion.minorVersion < 3
+  );
+  #elif TARGET_OS_IPHONE
+  vouchersDisabled = (
+    osVersion.majorVersion == 15 &&
+    osVersion.minorVersion >= 0 && osVersion.minorVersion < 2
+  );
+  #elif TARGET_OS_OSX
+  vouchersDisabled = (
+    osVersion.majorVersion == 12 &&
+    osVersion.minorVersion >= 0 && osVersion.minorVersion < 1
+  );
+  #else
+  vouchersDisabled = false;
+  #endif
+}
+
+bool VoucherManager::vouchersAreDisabled() {
+  swift_once(&voucherDisableCheckOnce,
+             &_initializeVouchersDisabled,
+             nullptr);
+  return vouchersDisabled;
+}

stdlib/toolchain/Compatibility56/include/Concurrency/VoucherSupport.h

@@ -31,6 +31,12 @@ class VoucherManager {
   /// async work.
   llvm::Optional<voucher_t> OriginalVoucher;
 
+  /// Determine whether vouchers are disabled entirely. This evaluates
+  /// true on platforms whose concurrency library does not support the
+  /// propagation of vouchers, in which case all of the operations of
+  /// this class must be no-ops.
+  static bool vouchersAreDisabled();
+
 public:
   VoucherManager() {
     SWIFT_TASK_DEBUG_LOG("[%p] Constructing VoucherManager", this);
@@ -41,6 +47,9 @@ class VoucherManager {
   /// VoucherManager object is destroyed. It may also be called in other
   /// places to restore the original voucher and reset the VoucherManager.
   void leave() {
+    if (vouchersAreDisabled())
+      return;
+
     if (OriginalVoucher) {
       SWIFT_TASK_DEBUG_LOG("[%p] Restoring original voucher %p", this,
                            *OriginalVoucher);
@@ -62,6 +71,9 @@ class VoucherManager {
   /// this is permanent. For Tasks, the voucher must be restored using
   /// restoreVoucher if the task suspends.
   void swapToJob(Job *job) {
+    if (vouchersAreDisabled())
+      return;
+
     SWIFT_TASK_DEBUG_LOG("[%p] Swapping jobs to %p", this, job);
     assert(job);
     assert(job->Voucher != SWIFT_DEAD_VOUCHER);
@@ -99,6 +111,9 @@ class VoucherManager {
   // Take the current thread's adopted voucher and place it back into the task
   // that previously owned it, re-adopting the thread's original voucher.
   void restoreVoucher(AsyncTask *task) {
+    if (vouchersAreDisabled())
+      return;
+
     SWIFT_TASK_DEBUG_LOG("[%p] Restoring %svoucher on task %p", this,
                          OriginalVoucher ? "" : "missing ", task);
     assert(OriginalVoucher);