fix(apple): fix build issues discovered by stricter build flags (#1178)

Author: Saadnajmi

.changeset/modern-bugs-battle.md

@@ -0,0 +1,5 @@
+---
+"@react-native-async-storage/async-storage": patch
+---
+
+Mark some methods as nonnull

packages/default-storage/ios/RNCAsyncStorage.h

@@ -27,6 +27,9 @@
  *
  * Keys and values must always be strings or an error is returned.
  */
+
+NS_ASSUME_NONNULL_BEGIN
+
 @interface RNCAsyncStorage : NSObject <
 #ifdef RCT_NEW_ARCH_ENABLED
                                  NativeAsyncStorageModuleSpec
@@ -60,3 +63,5 @@
 - (void)getAllKeys:(RCTResponseSenderBlock)callback;
 
 @end
+
+NS_ASSUME_NONNULL_END

packages/default-storage/ios/RNCAsyncStorage.mm

@@ -302,7 +302,7 @@ static void RCTStorageDirectoryMigrate(NSString *oldDirectoryPath,
         // this folder and attempt folder copying again
         if (error != nil && error.code == 4 &&
             [newDirectoryPath isEqualToString:RCTGetStorageDirectory()]) {
-            NSError *error = nil;
+            error = nil;
             _createStorageDirectory(RCTCreateStorageDirectoryPath(@""), &error);
             if (error == nil) {
                 RCTStorageDirectoryMigrate(
@@ -559,7 +559,7 @@ - (NSDictionary *)_ensureSetup
     return nil;
 }
 
-- (NSDictionary *)_writeManifest:(NSMutableArray<NSDictionary *> **)errors
+- (NSDictionary *)_writeManifest:(NSMutableArray<NSDictionary *> *__autoreleasing *)errors
 {
     NSError *error;
     NSString *serialized = RCTJSONStringify(_manifest, &error);
@@ -587,7 +587,7 @@ - (NSDictionary *)_appendItemForKey:(NSString *)key
     return errorOut;
 }
 
-- (NSString *)_getValueForKey:(NSString *)key errorOut:(NSDictionary **)errorOut
+- (NSString *)_getValueForKey:(NSString *)key errorOut:(NSDictionary *__autoreleasing *)errorOut
 {
     NSString *value =
         _manifest[key];  // nil means missing, null means there may be a data file, else: NSString
@@ -699,14 +699,14 @@ - (BOOL)_passthroughDelegate
         }
     }
 
-    NSDictionary *errorOut = [self _ensureSetup];
-    if (errorOut) {
-        callback(@[@[errorOut], (id)kCFNull]);
+    NSDictionary *ensureSetupErrorOut = [self _ensureSetup];
+    if (ensureSetupErrorOut) {
+        callback(@[@[ensureSetupErrorOut], (id)kCFNull]);
         return;
     }
     [self _multiGet:keys
            callback:callback
-             getter:^(NSUInteger i, NSString *key, NSDictionary **errorOut) {
+             getter:^(__unused NSUInteger i, NSString *key, NSDictionary **errorOut) {
                return [self _getValueForKey:key errorOut:errorOut];
              }];
 }