[nullsafe] Make Trust list a closed type, and expose only emptiness.

Summary:
As artempyanykh pointed out, exposing trust list might encourage clients to
start writing business logic manipulating with trust lists outside of
NullsafeMode module, which we don't like to happen.

Reviewed By: artempyanykh

Differential Revision: D21230973

fbshipit-source-id: 39bd0b0d8

infer/src/nullsafe/ClassLevelAnalysis.ml

@@ -44,16 +44,18 @@ type meta_issue =
   ; severity: Exceptions.severity
   ; meta_issue_info: Jsonbug_t.nullsafe_meta_issue_info }
 
-let mode_to_json = function
+let mode_to_json mode =
-  | NullsafeMode.Default ->
+  let open NullsafeMode in
+  match mode with
+  | Default ->
       `Default
-  | NullsafeMode.Local NullsafeMode.Trust.All ->
+  | Local Trust.All ->
       `LocalTrustAll
-  | NullsafeMode.Local (NullsafeMode.Trust.Only names) when JavaClassName.Set.is_empty names ->
+  | Local (Trust.Only trust_list) when Trust.is_trust_none trust_list ->
       `LocalTrustNone
-  | NullsafeMode.Local (NullsafeMode.Trust.Only _) ->
+  | Local (Trust.Only _) ->
       `LocalTrustSome
-  | NullsafeMode.Strict ->
+  | Strict ->
       `Strict
 
 
@@ -105,8 +107,8 @@ let make_meta_issue all_issues current_mode class_name =
             match mode_to_promote_to with
             | NullsafeMode.Local NullsafeMode.Trust.All ->
                 trust_all_mode
-            | NullsafeMode.Local (NullsafeMode.Trust.Only names)
+            | NullsafeMode.Local (NullsafeMode.Trust.Only trust_list)
-              when JavaClassName.Set.is_empty names ->
+              when NullsafeMode.Trust.is_trust_none trust_list ->
                 trust_none_mode
             | NullsafeMode.Strict
             (* We don't recommend "strict" for now as it is harder to keep a class in strict mode than it "trust none" mode.

infer/src/nullsafe/Nullability.ml

@@ -49,13 +49,13 @@ let is_considered_nonnull ~nullsafe_mode nullability =
     match nullsafe_mode with
     | NullsafeMode.Strict ->
         StrictNonnull
-    | NullsafeMode.Local (NullsafeMode.Trust.Only classes) when JavaClassName.Set.is_empty classes
+    | NullsafeMode.Local (NullsafeMode.Trust.Only trust_list)
-      ->
+      when NullsafeMode.Trust.is_trust_none trust_list ->
         (* Though "trust none" is technically a subcase of trust some,
            we need this pattern to be different from the one below so we can detect possible
            promotions from "trust some" to "trust none" *)
         LocallyCheckedNonnull
-    | NullsafeMode.Local (NullsafeMode.Trust.Only _classes) ->
+    | NullsafeMode.Local (NullsafeMode.Trust.Only _) ->
         LocallyTrustedNonnull
     | NullsafeMode.Local NullsafeMode.Trust.All ->
         UncheckedNonnull

infer/src/nullsafe/NullsafeMode.ml

@@ -9,7 +9,11 @@ open! IStd
 module F = Format
 
 module Trust = struct
-  type t = All | Only of JavaClassName.Set.t [@@deriving compare, equal]
+  type trust_list = JavaClassName.Set.t [@@deriving compare, equal]
+
+  type t = All | Only of trust_list [@@deriving compare, equal]
+
+  let is_trust_none trust_list = JavaClassName.Set.is_empty trust_list
 
   let none = Only JavaClassName.Set.empty
 

infer/src/nullsafe/NullsafeMode.mli

@@ -12,7 +12,11 @@ open! IStd
 module Trust : sig
   [@@@warning "-32"]
 
-  type t = All | Only of JavaClassName.Set.t [@@deriving compare, equal]
+  type trust_list
+
+  val is_trust_none : trust_list -> bool
+
+  type t = All | Only of trust_list [@@deriving compare, equal]
 
   val none : t