[Swift6] Fix TSan race condition in Swift6 SynchronizedDictionary (#23091)

Problem

  SynchronizedDictionary is a struct held as a var property on shared singleton classes (URLSessionRequestBuilderConfiguration and AlamofireRequestBuilderConfiguration). When multiple concurrent network requests mutate credentialStore or managerStore from different
  threads, Swift's memory exclusivity rules treat each subscript mutation as a modifying access to the entire struct — causing a real ThreadSanitizer "Swift access race".

  Changes

  struct → class (SynchronizedDictionary.mustache + 13 sample files)

  Changing SynchronizedDictionary from a value type to a reference type makes mutations go through pointer indirection. Concurrent subscript writes now only touch the object's internal state (already protected by NSRecursiveLock), rather than triggering a modifying
  access on the owning class's stored property.

  var → let (URLSessionImplementations.mustache + 11 sample files, AlamofireImplementations.mustache + 2 sample files)

  Since SynchronizedDictionary is now a class, the properties credentialStore and managerStore only need to hold a stable reference — they never get reassigned. Declaring them as let makes this intent explicit and prevents any residual exclusivity issues on the property
   itself.

Author: biovolt

modules/openapi-generator/src/main/resources/swift6/SynchronizedDictionary.mustache

@@ -6,7 +6,7 @@
 
 import Foundation
 
-internal struct SynchronizedDictionary<K: Hashable, V> : @unchecked Sendable {
+internal class SynchronizedDictionary<K: Hashable, V> : @unchecked Sendable {
 
     private var dictionary = [K: V]()
     private let lock = NSRecursiveLock()

modules/openapi-generator/src/main/resources/swift6/libraries/alamofire/AlamofireImplementations.mustache

@@ -24,7 +24,7 @@ fileprivate class AlamofireRequestBuilderConfiguration: @unchecked Sendable {
     static let shared = AlamofireRequestBuilderConfiguration()
 
     // Store manager to retain its reference
-    var managerStore = SynchronizedDictionary<String, Alamofire.Session>()
+    let managerStore = SynchronizedDictionary<String, Alamofire.Session>()
 }
 
 {{#nonPublicApi}}internal{{/nonPublicApi}}{{^nonPublicApi}}open{{/nonPublicApi}} class AlamofireRequestBuilder<T: Sendable>: RequestBuilder<T>, @unchecked Sendable {

modules/openapi-generator/src/main/resources/swift6/libraries/urlsession/URLSessionImplementations.mustache

@@ -66,7 +66,7 @@ fileprivate class URLSessionRequestBuilderConfiguration: @unchecked Sendable {
     let defaultURLSession: URLSession
 
     // Store current URLCredential for every URLSessionTask
-    var credentialStore = SynchronizedDictionary<Int, URLCredential>()
+    let credentialStore = SynchronizedDictionary<Int, URLCredential>()
 }
 
 {{#nonPublicApi}}internal{{/nonPublicApi}}{{^nonPublicApi}}open{{/nonPublicApi}} class URLSessionRequestBuilder<T: Sendable>: RequestBuilder<T>, @unchecked Sendable {

samples/client/petstore/swift6/alamofireLibrary/Sources/PetstoreClient/Infrastructure/AlamofireImplementations.swift

@@ -24,7 +24,7 @@ fileprivate class AlamofireRequestBuilderConfiguration: @unchecked Sendable {
     static let shared = AlamofireRequestBuilderConfiguration()
 
     // Store manager to retain its reference
-    var managerStore = SynchronizedDictionary<String, Alamofire.Session>()
+    let managerStore = SynchronizedDictionary<String, Alamofire.Session>()
 }
 
 open class AlamofireRequestBuilder<T: Sendable>: RequestBuilder<T>, @unchecked Sendable {

samples/client/petstore/swift6/alamofireLibrary/Sources/PetstoreClient/Infrastructure/SynchronizedDictionary.swift

@@ -6,7 +6,7 @@
 
 import Foundation
 
-internal struct SynchronizedDictionary<K: Hashable, V> : @unchecked Sendable {
+internal class SynchronizedDictionary<K: Hashable, V> : @unchecked Sendable {
 
     private var dictionary = [K: V]()
     private let lock = NSRecursiveLock()

samples/client/petstore/swift6/apiNonStaticMethod/Sources/PetstoreClient/Infrastructure/AlamofireImplementations.swift

@@ -24,7 +24,7 @@ fileprivate class AlamofireRequestBuilderConfiguration: @unchecked Sendable {
     static let shared = AlamofireRequestBuilderConfiguration()
 
     // Store manager to retain its reference
-    var managerStore = SynchronizedDictionary<String, Alamofire.Session>()
+    let managerStore = SynchronizedDictionary<String, Alamofire.Session>()
 }
 
 open class AlamofireRequestBuilder<T: Sendable>: RequestBuilder<T>, @unchecked Sendable {

samples/client/petstore/swift6/apiNonStaticMethod/Sources/PetstoreClient/Infrastructure/SynchronizedDictionary.swift

@@ -6,7 +6,7 @@
 
 import Foundation
 
-internal struct SynchronizedDictionary<K: Hashable, V> : @unchecked Sendable {
+internal class SynchronizedDictionary<K: Hashable, V> : @unchecked Sendable {
 
     private var dictionary = [K: V]()
     private let lock = NSRecursiveLock()

samples/client/petstore/swift6/asyncAwaitLibrary/Sources/PetstoreClient/Infrastructure/SynchronizedDictionary.swift

@@ -6,7 +6,7 @@
 
 import Foundation
 
-internal struct SynchronizedDictionary<K: Hashable, V> : @unchecked Sendable {
+internal class SynchronizedDictionary<K: Hashable, V> : @unchecked Sendable {
 
     private var dictionary = [K: V]()
     private let lock = NSRecursiveLock()

samples/client/petstore/swift6/asyncAwaitLibrary/Sources/PetstoreClient/Infrastructure/URLSessionImplementations.swift

@@ -66,7 +66,7 @@ fileprivate class URLSessionRequestBuilderConfiguration: @unchecked Sendable {
     let defaultURLSession: URLSession
 
     // Store current URLCredential for every URLSessionTask
-    var credentialStore = SynchronizedDictionary<Int, URLCredential>()
+    let credentialStore = SynchronizedDictionary<Int, URLCredential>()
 }
 
 open class URLSessionRequestBuilder<T: Sendable>: RequestBuilder<T>, @unchecked Sendable {

samples/client/petstore/swift6/combineDeferredLibrary/PetstoreClient/Classes/OpenAPIs/Infrastructure/SynchronizedDictionary.swift

@@ -6,7 +6,7 @@
 
 import Foundation
 
-internal struct SynchronizedDictionary<K: Hashable, V> : @unchecked Sendable {
+internal class SynchronizedDictionary<K: Hashable, V> : @unchecked Sendable {
 
     private var dictionary = [K: V]()
     private let lock = NSRecursiveLock()