[nullsafe] Support @RecentlyNullable annotation

Summary: See comments for context.

Reviewed By: artempyanykh

Differential Revision: D18590948

fbshipit-source-id: 823b36660

infer/src/checkers/annotations.ml

@@ -95,6 +95,8 @@ let suppress_lint = "SuppressLint"
 
 let suppress_view_nullability = "SuppressViewNullability"
 
+let recently_nullable = "RecentlyNullable"
+
 let thread_confined = "ThreadConfined"
 
 let thread_safe = "ThreadSafe"
@@ -174,7 +176,17 @@ let ia_is_not_thread_safe ia = ia_ends_with ia not_thread_safe
 
 let ia_is_propagates_nullable ia = ia_ends_with ia propagates_nullable
 
-let ia_is_nullable ia = ia_ends_with ia nullable || ia_is_propagates_nullable ia
+let ia_is_nullable ia =
+  ia_ends_with ia nullable
+  (* @RecentlyNullable is a special annotation that was added to solve backward compatibility issues
+     for Android SDK migration.
+     See https://android-developers.googleblog.com/2018/08/android-pie-sdk-is-now-more-kotlin.html for details.
+     From nullsafe point of view, such annotations should be treated exactly as normal @Nullable annotation is treated.
+     (Actually, IDEs might even show it as @Nullable)
+  *)
+  || ia_ends_with ia recently_nullable
+  || ia_is_propagates_nullable ia
+
 
 let ia_is_nonnull ia = List.exists ~f:(ia_ends_with ia) [nonnull; notnull; camel_nonnull]