Add macros for backward compatible nullability support.

Author: nlutsenko

ParseUI/Other/ParseUIConstants.h

@@ -19,19 +19,58 @@
  *
  */
 
+#import <Availability.h>
+#import <TargetConditionals.h>
+
 #ifndef ParseUI_ParseUIConstants_h
 #define ParseUI_ParseUIConstants_h
 
+///--------------------------------------
+/// @name Deprecated Macros
+///--------------------------------------
+
 #ifndef PARSE_UI_DEPRECATED
-    #ifdef __deprecated_msg
-        #define PARSE_UI_DEPRECATED(_MSG) (deprecated(_MSG))
-    #else
-        #ifdef __deprecated
-            #define PARSE_UI_DEPRECATED(_MSG) (deprecated)
-        #else
-            #define PARSE_UI_DEPRECATED(_MSG)
-        #endif
-    #endif
+#  ifdef __deprecated_msg
+#    define PARSE_UI_DEPRECATED(_MSG) (deprecated(_MSG))
+#  else
+#    ifdef __deprecated
+#      define PARSE_UI_DEPRECATED(_MSG) (deprecated)
+#    else
+#      define PARSE_UI_DEPRECATED(_MSG)
+#    endif
+#  endif
+#endif
+
+///--------------------------------------
+/// @name Nullability Support
+///--------------------------------------
+
+#if __has_feature(nullability)
+#  define PFUI_NULLABLE nullable
+#  define PFUI_NULLABLE_S __nullable
+#  define PFUI_NULL_UNSPECIFIED null_unspecified
+#  define PFUI_NULLABLE_PROPERTY nullable,
+#else
+#  define PFUI_NULLABLE
+#  define PFUI_NULLABLE_S
+#  define PFUI_NULL_UNSPECIFIED
+#  define PFUI_NULLABLE_PROPERTY
+#endif
+
+#if __has_feature(assume_nonnull)
+#  ifdef NS_ASSUME_NONNULL_BEGIN
+#    define PFUI_ASSUME_NONNULL_BEGIN NS_ASSUME_NONNULL_BEGIN
+#  else
+#    define PFUI_ASSUME_NONNULL_BEGIN _Pragma("clang assume_nonnull begin")
+#  endif
+#  ifdef NS_ASSUME_NONNULL_END
+#    define PFUI_ASSUME_NONNULL_END NS_ASSUME_NONNULL_END
+#  else
+#    define PFUI_ASSUME_NONNULL_END _Pragma("clang assume_nonnull end")
+#  endif
+#else
+#  define PFUI_ASSUME_NONNULL_BEGIN
+#  define PFUI_ASSUME_NONNULL_END
 #endif
 
 #endif