[pulse] Init struct fields with zero when a message is sent to nil

Summary:
By D26664187 (e4ff4b500a), it returns nil when a message is sent to nil.

On the other hand, when the return type is a struct type, the semantics should be different: it should return a struct with all fields are initialized with nil.

According to

https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/WorkingwithObjects/WorkingwithObjects.html#//apple_ref/doc/uid/TP40011210-CH4-SW28

> Note: If you expect a return value from a message sent to nil, the return value will be nil for object return types, 0 for numeric types, and NO for BOOL types. Returned structures have all members initialized to zero.

Reviewed By: jvillard

Differential Revision: D27289996

fbshipit-source-id: 1ddd9b088

infer/src/IR/Procdesc.ml

@@ -540,6 +540,8 @@ let get_ret_type pdesc = pdesc.attributes.ret_type
 
 let get_ret_var pdesc = Pvar.get_ret_pvar (get_proc_name pdesc)
 
+let get_ret_param_var pdesc = Pvar.get_ret_param_pvar (get_proc_name pdesc)
+
 let get_start_node pdesc = pdesc.start_node
 
 (** Return [true] iff the procedure is defined, and not just declared *)

infer/src/IR/Procdesc.mli

@@ -267,6 +267,8 @@ val is_ret_type_pod : t -> bool
 
 val get_ret_var : t -> Pvar.t
 
+val get_ret_param_var : t -> Pvar.t
+
 val get_start_node : t -> Node.t
 
 val get_static_callees : t -> Procname.t list

infer/src/pulse/PulseObjectiveCSummary.ml

@@ -6,6 +6,7 @@
  *)
 
 open! IStd
+open PulseDomainInterface
 open PulseOperations.Import
 
 let mk_objc_self_pvar proc_desc =
@@ -13,13 +14,43 @@ let mk_objc_self_pvar proc_desc =
   Pvar.mk Mangled.self proc_name
 
 
-let mk_objc_method_nil_summary_aux proc_desc astate =
+let init_fields_zero tenv location ~zero addr typ astate =
+  let get_fields typ =
+    match typ.Typ.desc with
+    | Tstruct struct_name ->
+        Tenv.lookup tenv struct_name |> Option.map ~f:(fun {Struct.fields} -> fields)
+    | _ ->
+        None
+  in
+  let rec init_fields_zero_helper addr typ astate =
+    match get_fields typ with
+    | Some fields ->
+        List.fold fields ~init:(Ok astate) ~f:(fun acc (field, field_typ, _) ->
+            let* acc = acc in
+            let acc, field_addr = Memory.eval_edge addr (FieldAccess field) acc in
+            init_fields_zero_helper field_addr field_typ acc )
+    | None ->
+        PulseOperations.write_deref location ~ref:addr ~obj:zero astate
+  in
+  init_fields_zero_helper addr typ astate
+
+
+let mk_objc_method_nil_summary_aux tenv proc_desc astate =
   (* Constructs summary {self = 0} {return = self}.
      This allows us to connect invalidation with invalid access in the trace *)
   let location = Procdesc.get_loc proc_desc in
   let self = mk_objc_self_pvar proc_desc in
   let* astate, self_value = PulseOperations.eval_deref location (Lvar self) astate in
   let* astate = PulseArithmetic.prune_eq_zero (fst self_value) astate in
+  match List.last (Procdesc.get_formals proc_desc) with
+  | Some (last_formal, {desc= Tptr (typ, _)}) when Mangled.equal last_formal Ident.name_return_param
+    ->
+      let ret_param_var = Procdesc.get_ret_param_var proc_desc in
+      let* astate, ret_param_var_addr_hist =
+        PulseOperations.eval_deref location (Lvar ret_param_var) astate
+      in
+      init_fields_zero tenv location ~zero:self_value ret_param_var_addr_hist typ astate
+  | _ ->
       let ret_var = Procdesc.get_ret_var proc_desc in
       let* astate, ret_var_addr_hist = PulseOperations.eval Write location (Lvar ret_var) astate in
       PulseOperations.write_deref location ~ref:ret_var_addr_hist ~obj:self_value astate
@@ -35,7 +66,7 @@ let mk_objc_method_nil_summary {InterproceduralAnalysis.tenv; proc_desc; err_log
          We create a nil summary to avoid reporting NPE in this case.
          However, there is an exception in the case where the return type is non-POD.
          In that case it's UB and we want to report an error. *)
-      let result = mk_objc_method_nil_summary_aux proc_desc astate in
+      let result = mk_objc_method_nil_summary_aux tenv proc_desc astate in
       Some (PulseReport.report_result tenv proc_desc err_log result)
   | ContinueProgram _, _
   | ExitProgram _, _

infer/tests/codetoanalyze/objc/pulse/uninit.m

@@ -9,6 +9,11 @@
 @interface Uninit : NSObject
 @end
 
+struct my_struct {
+  int x;
+  int y;
+};
+
 @implementation Uninit
 
 - (void)capture_in_closure_ok {
@@ -79,4 +84,16 @@
   return x;
 }
 
+- (struct my_struct)return_my_struct {
+  struct my_struct s;
+  s.x = 1;
+  s.y = 2;
+  return s;
+}
+
++ (int)call_return_my_struct_ok {
+  Uninit* o = nil;
+  return [o return_my_struct].x;
+}
+
 @end