[threadsafety] Relax javaism of may_alias

Summary:
ThreadSafety.may_alias crashed on C++ code because it assumed Java
field names.

Reviewed By: sblackshear

Differential Revision: D5147284

fbshipit-source-id: d10841f

infer/src/IR/Fieldname.re

@@ -99,6 +99,16 @@ let java_get_field fn => {
 };
 
 
+/** Equality for field names ignoring the struct or class which contains the field. */
+let equal_modulo_parent x y =>
+  switch (x, y) {
+  | (Hidden, Hidden) => true
+  | (Clang a, Clang b) => Int.equal 0 (compare_clang_field_info a b)
+  | (Java _, Java _) => String.equal (java_get_field x) (java_get_field y)
+  | _ => false
+  };
+
+
 /** Check if the field is the synthetic this$n of a nested class, used to access the n-th outher instance. */
 let java_is_outer_instance fn => {
   let fn = to_string fn;

infer/src/IR/Fieldname.rei

@@ -17,6 +17,10 @@ type t [@@deriving compare];
 let equal: t => t => bool;
 
 
+/** Equality for field names ignoring the struct or class which contains the field. */
+let equal_modulo_parent: t => t => bool;
+
+
 /** Set for fieldnames */
 module Set: Caml.Set.S with type elt = t;
 

infer/src/checkers/ThreadSafety.ml

@@ -1219,8 +1219,7 @@ let may_alias p1 p2 =
   match List.last_exn (snd p1), List.last_exn (snd p2) with
   | FieldAccess _, ArrayAccess _ | ArrayAccess _, FieldAccess _ -> false
   (* fields in Infer contain class name *)
-  | FieldAccess f1, FieldAccess f2 ->
-      String.equal (Fieldname.java_get_field f1) (Fieldname.java_get_field f2)
+  | FieldAccess f1, FieldAccess f2 -> Fieldname.equal_modulo_parent f1 f2
   | ArrayAccess _, ArrayAccess _ -> true (*FIXME*)
 
 (* take a results table and quotient it by the may_alias relation *)