Fix certain completion blocks not being dispatched on the main thread (…

…#4058)

Some completion blocks were not being dispatched to the main thread.
These include:

- Checking intro trial eligibility in SK1 and SK2
- Promo offer eligibility in SK1 and SK2
- Syncing/restoring purchases in SK2 when there are no transactions and
there is a cached customer info

### Checklist
- [ ] If applicable, unit tests
- [ ] If applicable, create follow-up issues for `purchases-android` and
hybrids

### Motivation
<!-- Why is this change required? What problem does it solve? -->
<!-- Please link to issues following this format: Resolves #999999 -->

### Description
<!-- Describe your changes in detail -->
<!-- Please describe in detail how you tested your changes -->

Sources/Purchasing/Purchases/PurchasesOrchestrator.swift

@@ -269,12 +269,16 @@ final class PurchasesOrchestrator {
                           product: StoreProductType,
                           completion: @escaping @Sendable (Result<PromotionalOffer, PurchasesError>) -> Void) {
         guard let discountIdentifier = productDiscount.offerIdentifier else {
-            completion(.failure(ErrorUtils.productDiscountMissingIdentifierError()))
+            self.operationDispatcher.dispatchOnMainActor {
+                completion(.failure(ErrorUtils.productDiscountMissingIdentifierError()))
+            }
             return
         }
 
         guard let subscriptionGroupIdentifier = product.subscriptionGroupIdentifier else {
-            completion(.failure(ErrorUtils.productDiscountMissingSubscriptionGroupIdentifierError()))
+            self.operationDispatcher.dispatchOnMainActor {
+                completion(.failure(ErrorUtils.productDiscountMissingSubscriptionGroupIdentifierError()))
+            }
             return
         }
 
@@ -284,14 +288,18 @@ final class PurchasesOrchestrator {
                                      discountIdentifier: discountIdentifier,
                                      product: product,
                                      subscriptionGroupIdentifier: subscriptionGroupIdentifier) { result in
-                completion(result)
+                self.operationDispatcher.dispatchOnMainActor {
+                    completion(result)
+                }
             }
         } else {
                 self.sk1PromotionalOffer(forProductDiscount: productDiscount,
                                          discountIdentifier: discountIdentifier,
                                          product: product,
                                          subscriptionGroupIdentifier: subscriptionGroupIdentifier) { result in
-                    completion(result)
+                    self.operationDispatcher.dispatchOnMainActor {
+                        completion(result)
+                    }
                 }
 
         }
@@ -1125,7 +1133,9 @@ private extension PurchasesOrchestrator {
                     if let cachedCustomerInfo,
                        cachedCustomerInfo.originalPurchaseDate != nil,
                        cachedCustomerInfo.originalApplicationVersion != nil {
-                        completion?(.success(cachedCustomerInfo))
+                        self.operationDispatcher.dispatchOnMainActor {
+                            completion?(.success(cachedCustomerInfo))
+                        }
                         return
                     }
 

Sources/Purchasing/TrialOrIntroPriceEligibilityChecker.swift

@@ -60,9 +60,18 @@ class TrialOrIntroPriceEligibilityChecker: TrialOrIntroPriceEligibilityCheckerTy
             return
         }
 
+        // Extracting and wrapping the completion block from the async call
+        // to avoid having to mark ReceiveIntroEligibilityBlock as @Sendable
+        // up to the public API thus making a breaking change.
+        let completionBlock: ReceiveIntroEligibilityBlock = { result in
+            self.operationDispatcher.dispatchOnMainActor {
+                completion(result)
+            }
+        }
+
         if #available(iOS 15.0, tvOS 15.0, watchOS 8.0, macOS 12.0, *),
            self.systemInfo.storeKitVersion.isStoreKit2EnabledAndAvailable {
-            Async.call(with: completion) {
+            Async.call(with: completionBlock) {
                 do {
                     return try await self.sk2CheckEligibility(productIdentifiers)
                 } catch {
@@ -74,7 +83,11 @@ class TrialOrIntroPriceEligibilityChecker: TrialOrIntroPriceEligibilityCheckerTy
                 }
             }
         } else {
-            self.sk1CheckEligibility(productIdentifiers, completion: completion)
+            self.sk1CheckEligibility(productIdentifiers) { result in
+                self.operationDispatcher.dispatchOnMainActor {
+                    completion(result)
+                }
+            }
         }
     }
 
@@ -85,12 +98,18 @@ class TrialOrIntroPriceEligibilityChecker: TrialOrIntroPriceEligibilityCheckerTy
         self.receiptFetcher.receiptData(refreshPolicy: .never) { data, _ in
             if let data = data {
                 self.sk1CheckEligibility(with: data,
-                                         productIdentifiers: productIdentifiers,
-                                         completion: completion)
+                                         productIdentifiers: productIdentifiers) { eligibility in
+                    self.operationDispatcher.dispatchOnMainActor {
+                        completion(eligibility)
+                    }
+                }
             } else {
                 self.getIntroEligibility(with: data ?? Data(),
-                                         productIdentifiers: productIdentifiers,
-                                         completion: completion)
+                                         productIdentifiers: productIdentifiers) { eligibility in
+                    self.operationDispatcher.dispatchOnMainActor {
+                        completion(eligibility)
+                    }
+                }
             }
         }
     }