[nullsafe] Consolidate logic specific to particular rules in dedicated modules

Summary:
Currently, we have NullsafeRules.ml responsible for detecting the
violation fact. All other logic: what should be the error type,
severity, and error message, is in TypeErr.ml.

In this diff, we move logic from NullsafeRules.ml and TypeErr.ml to
dedicated modules like AssignmentRule.ml etc.

Each such module is responsible for:
- detecting the violation fact (this is moved from NullsafeRules.ml)
- rendering the violation error (this is moved from TypeErr.ml).

This approach makes sense for two reasons:
1. The violation fact and the way we show error are logically related to
each other.
2. In future diffs, we will support more features guiding rule behavior,
such as a) decision whether to hide or show the error depending on type
information and mode; b) the way we render error depending on type
information and role.

Having dedicated modules incapsulating knowledge about rules is a natural way to support 2.

Reviewed By: artempyanykh

Differential Revision: D17977891

fbshipit-source-id: a53d916d3

infer/src/nullsafe/AssignmentRule.ml

@@ -0,0 +1,40 @@
+(*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *)
+open! IStd
+
+type violation = {lhs: Nullability.t; rhs: Nullability.t} [@@deriving compare]
+
+type assignment_type =
+  | PassingParamToFunction of
+      { param_description: string
+      ; param_position: int
+      ; function_procname: Typ.Procname.t }
+  | AssigningToField of Typ.Fieldname.t
+  | ReturningFromFunction of Typ.Procname.t
+[@@deriving compare]
+
+let check ~lhs ~rhs =
+  Result.ok_if_true (Nullability.is_subtype ~subtype:rhs ~supertype:lhs) ~error:{lhs; rhs}
+
+
+let violation_description _ assignment_type ~rhs_origin_descr =
+  let module MF = MarkupFormatter in
+  match assignment_type with
+  | PassingParamToFunction {param_description; param_position; function_procname} ->
+      Format.asprintf "%a needs a non-null value in parameter %d but argument %a can be null. %s"
+        MF.pp_monospaced
+        (Typ.Procname.to_simplified_string ~withclass:true function_procname)
+        param_position MF.pp_monospaced param_description rhs_origin_descr
+  | AssigningToField field_name ->
+      Format.asprintf "Field %a can be null but is not declared %a. %s" MF.pp_monospaced
+        (Typ.Fieldname.to_simplified_string field_name)
+        MF.pp_monospaced "@Nullable" rhs_origin_descr
+  | ReturningFromFunction function_proc_name ->
+      Format.asprintf "Method %a may return null but it is not annotated with %a. %s"
+        MF.pp_monospaced
+        (Typ.Procname.to_simplified_string function_proc_name)
+        MF.pp_monospaced "@Nullable" rhs_origin_descr

infer/src/nullsafe/AssignmentRule.mli

@@ -0,0 +1,27 @@
+(*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *)
+open! IStd
+
+(** Assignment rule should be checked when a value is assigned to a location.
+    Assignment can be explicit (lhs = rhs) or implicit (e.g. returning from a function).
+    This rule checks if null can be passed to a place that does not expect null.
+ *)
+
+type violation [@@deriving compare]
+
+val check : lhs:Nullability.t -> rhs:Nullability.t -> (unit, violation) result
+
+type assignment_type =
+  | PassingParamToFunction of
+      { param_description: string
+      ; param_position: int
+      ; function_procname: Typ.Procname.t }
+  | AssigningToField of Typ.Fieldname.t
+  | ReturningFromFunction of Typ.Procname.t
+[@@deriving compare]
+
+val violation_description : violation -> assignment_type -> rhs_origin_descr:string -> string

infer/src/nullsafe/DereferenceRule.ml

@@ -0,0 +1,58 @@
+(*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *)
+open! IStd
+
+type violation = Nullability.t [@@deriving compare]
+
+type dereference_type =
+  | MethodCall of Typ.Procname.t
+  | AccessToField of Typ.Fieldname.t
+  | AccessByIndex of {index_desc: string}
+  | ArrayLengthAccess
+[@@deriving compare]
+
+let check = function
+  | Nullability.Nullable as nullability ->
+      Error nullability
+  | Nullability.Nonnull ->
+      Ok ()
+
+
+let violation_description _ dereference_type ~nullable_object_descr ~origin_descr =
+  let module MF = MarkupFormatter in
+  let nullable_object_descr =
+    match dereference_type with
+    | MethodCall _ | AccessToField _ -> (
+      match nullable_object_descr with
+      | None ->
+          "Object"
+      (* Just describe an object itself *)
+      | Some descr ->
+          MF.monospaced_to_string descr )
+    | ArrayLengthAccess | AccessByIndex _ -> (
+      (* In Java, those operations can be applied only to arrays *)
+      match nullable_object_descr with
+      | None ->
+          "Array"
+      | Some descr ->
+          Format.sprintf "Array %s" (MF.monospaced_to_string descr) )
+  in
+  let action_descr =
+    match dereference_type with
+    | MethodCall method_name ->
+        Format.sprintf "calling %s"
+          (MF.monospaced_to_string (Typ.Procname.to_simplified_string method_name))
+    | AccessToField field_name ->
+        Format.sprintf "accessing field %s"
+          (MF.monospaced_to_string (Typ.Fieldname.to_simplified_string field_name))
+    | AccessByIndex {index_desc} ->
+        Format.sprintf "accessing at index %s" (MF.monospaced_to_string index_desc)
+    | ArrayLengthAccess ->
+        "accessing its length"
+  in
+  Format.sprintf "%s is nullable and is not locally checked for null when %s. %s"
+    nullable_object_descr action_descr origin_descr

infer/src/nullsafe/DereferenceRule.mli

@@ -0,0 +1,29 @@
+(*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *)
+open! IStd
+
+(** Dereference rule should be checked every type an object is dereferenced.
+    The rule checks if the reference is nullable.
+ *)
+
+type violation [@@deriving compare]
+
+val check : Nullability.t -> (unit, violation) result
+
+type dereference_type =
+  | MethodCall of Typ.Procname.t
+  | AccessToField of Typ.Fieldname.t
+  | AccessByIndex of {index_desc: string}
+  | ArrayLengthAccess
+[@@deriving compare]
+
+val violation_description :
+     violation
+  -> dereference_type
+  -> nullable_object_descr:string option
+  -> origin_descr:string
+  -> string

infer/src/nullsafe/InheritanceRule.ml

@@ -0,0 +1,59 @@
+(*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *)
+open! IStd
+
+type violation = {base: Nullability.t; overridden: Nullability.t} [@@deriving compare]
+
+type type_role = Param | Ret
+
+let check type_role ~base ~overridden =
+  let subtype, supertype =
+    match type_role with
+    | Ret ->
+        (* covariance for ret *)
+        (overridden, base)
+    | Param ->
+        (* contravariance for param *)
+        (base, overridden)
+  in
+  Result.ok_if_true (Nullability.is_subtype ~subtype ~supertype) ~error:{base; overridden}
+
+
+type violation_type =
+  | InconsistentParam of {param_description: string; param_position: int}
+  | InconsistentReturn
+[@@deriving compare]
+
+let violation_description _ violation_type ~base_proc_name ~overridden_proc_name =
+  let module MF = MarkupFormatter in
+  let nullable_annotation = "@Nullable" in
+  let base_method_descr = Typ.Procname.to_simplified_string ~withclass:true base_proc_name in
+  let overridden_method_descr =
+    Typ.Procname.to_simplified_string ~withclass:true overridden_proc_name
+  in
+  match violation_type with
+  | InconsistentReturn ->
+      Format.asprintf "Method %a is annotated with %a but overrides unannotated method %a."
+        MF.pp_monospaced overridden_method_descr MF.pp_monospaced nullable_annotation
+        MF.pp_monospaced base_method_descr
+  | InconsistentParam {param_description; param_position} ->
+      let translate_position = function
+        | 1 ->
+            "First"
+        | 2 ->
+            "Second"
+        | 3 ->
+            "Third"
+        | n ->
+            string_of_int n ^ "th"
+      in
+      Format.asprintf
+        "%s parameter %a of method %a is not %a but is declared %ain the parent class method %a."
+        (translate_position param_position)
+        MF.pp_monospaced param_description MF.pp_monospaced overridden_method_descr
+        MF.pp_monospaced nullable_annotation MF.pp_monospaced nullable_annotation MF.pp_monospaced
+        base_method_descr

infer/src/nullsafe/InheritanceRule.mli

@@ -0,0 +1,35 @@
+(*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *)
+open! IStd
+
+(** Inheritance rule:
+  a) Return type for an overridden method is covariant:
+       overridden method is allowed to narrow down the return value to a subtype of the one from the
+       base method; this means it is OK to make the return value non-null when it was nullable in the base)
+  b) Parameter type for an overridden method is contravariant.
+       It is OK for a derived method to accept nullable in the params even if the base does not accept nullable.
+  NOTE: Rule a) is based on Java covariance rule for the return type.
+        In contrast, rule b) is nullsafe specific as Java does not support type contravariance for method params.
+ *)
+
+type violation [@@deriving compare]
+
+type violation_type =
+  | InconsistentParam of {param_description: string; param_position: int}
+  | InconsistentReturn
+[@@deriving compare]
+
+type type_role = Param | Ret
+
+val check : type_role -> base:Nullability.t -> overridden:Nullability.t -> (unit, violation) result
+
+val violation_description :
+     violation
+  -> violation_type
+  -> base_proc_name:Typ.Procname.t
+  -> overridden_proc_name:Typ.Procname.t
+  -> string

infer/src/nullsafe/NullsafeRules.ml

@@ -1,35 +0,0 @@
-(*
- * Copyright (c) Facebook, Inc. and its affiliates.
- *
- * This source code is licensed under the MIT license found in the
- * LICENSE file in the root directory of this source tree.
- *)
-
-open! IStd
-
-let passes_assignment_rule ~lhs ~rhs = Nullability.is_subtype ~subtype:rhs ~supertype:lhs
-
-let passes_dereference_rule = function
-  | Nullability.Nullable ->
-      false
-  | Nullability.Nonnull ->
-      true
-
-
-type type_role = Param | Ret
-
-let passes_inheritance_rule type_role ~base ~overridden =
-  let subtype, supertype =
-    match type_role with
-    | Ret ->
-        (* covariance for ret *)
-        (overridden, base)
-    | Param ->
-        (* contravariance for param *)
-        (base, overridden)
-  in
-  Nullability.is_subtype ~subtype ~supertype
-
-
-let is_overannotated ~lhs ~rhs_upper_bound =
-  Nullability.is_strict_subtype ~subtype:rhs_upper_bound ~supertype:lhs

infer/src/nullsafe/NullsafeRules.mli

@@ -1,57 +0,0 @@
-(*
- * Copyright (c) Facebook, Inc. and its affiliates.
- *
- * This source code is licensed under the MIT license found in the
- * LICENSE file in the root directory of this source tree.
- *)
-
-open! IStd
-
-(** This is a single place consolidating core rules driving Nullsafe type checking.
-  Nullsafe enforces similar rules in different places (e.g. places dealing with fields,
-  function calls, assignments, local variables etc.).
-  Those places might have additional specifics, but core checks should be done through this class.
-  If you are writing a new or modifying an existing check, ask yourself if you can directly
-  use already existng rules from this module.
-  If you feel you need a rule of a completely new nature, add it to this module.
-  As a rule of thumb, every different "check" that is responsible for detecting issues, should query
-  this module instead of doing things on their own.
-  *)
-
-val passes_assignment_rule : lhs:Nullability.t -> rhs:Nullability.t -> bool
-(** Assignment rule: No expression of nullable type is ever assigned to a location
-    of non-nullable type.
- *)
-
-val passes_dereference_rule : Nullability.t -> bool
-(** Dereference rule: an object can be dereferenced only when it is not nullable (or believed to be so).
- *)
-
-type type_role = Param | Ret
-
-val passes_inheritance_rule : type_role -> base:Nullability.t -> overridden:Nullability.t -> bool
-(** Inheritance rule:
-  a) Return type for an overridden method is covariant:
-       overridden method is allowed to narrow down the return value to a subtype of the one from the
-       base method; this means it is OK to make the return value non-null when it was nullable in the base)
-  b) Parameter type for an overridden method is contravariant.
-       It is OK for a derived method to accept nullable in the params even if the base does not accept nullable.
-  NOTE: Rule a) is based on Java covariance rule for the return type.
-        In contrast, rule b) is nullsafe specific as Java does not support type contravariance for method params.
- *)
-
-val is_overannotated : lhs:Nullability.t -> rhs_upper_bound:Nullability.t -> bool
-(** Check if a type in signature (e.g. return value) can be made more specific.
-   If an upper bound of `rhs_i` over ALL assignents `lhs = rhs_i` that exist in the program
-   is a _strict_ subtype of lhs, `lhs`'s type can be narrowed to be that upper bound.
-   NOTE: This rule is complementatary to assignment rule.
-         While assignment rule checks a single assignment `lhs = rhs`, this rule
-         checks checks ALL assignments to `lhs` in the program.
-   NOTE: Violation of this rule is not a type violation, hence it should never be surfaced as error:
-         `lhs`'s type can be intentionally made broad by code author
-         (e.g. to anticipate future changes in the implementation).
-         Additional heuristits are required to correctly surface overannotated rule to the user.
-         This rule is useful for some scenarios, especially for nullability code conversions
-         when it is expected that some signatures were annotated with @Nullable defensively, so
-         surfacing such cases can improve API and make migration smooth.
- *)

infer/src/nullsafe/OverAnnotatedRule.ml

@@ -0,0 +1,34 @@
+(*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *)
+open! IStd
+
+type violation = {lhs: Nullability.t; rhs_upper_bound: Nullability.t} [@@deriving compare]
+
+let check ~lhs ~rhs_upper_bound =
+  if Nullability.is_strict_subtype ~subtype:rhs_upper_bound ~supertype:lhs then
+    Error {lhs; rhs_upper_bound}
+  else Ok ()
+
+
+type violation_type =
+  | FieldOverAnnoted of Typ.Fieldname.t
+  | ReturnOverAnnotated of Typ.Procname.t  (** Return value of a method can be made non-nullable *)
+[@@deriving compare]
+
+let violation_description _ violation_type =
+  let module MF = MarkupFormatter in
+  let nullable_annotation = "@Nullable" in
+  match violation_type with
+  | FieldOverAnnoted field_name ->
+      Format.asprintf "Field %a is always initialized in the constructor but is declared %a"
+        MF.pp_monospaced
+        (Typ.Fieldname.to_simplified_string field_name)
+        MF.pp_monospaced nullable_annotation
+  | ReturnOverAnnotated proc_name ->
+      Format.asprintf "Method %a is annotated with %a but never returns null." MF.pp_monospaced
+        (Typ.Procname.to_simplified_string proc_name)
+        MF.pp_monospaced nullable_annotation

infer/src/nullsafe/OverAnnotatedRule.mli

@@ -0,0 +1,34 @@
+(*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *)
+open! IStd
+
+(** Checks if a type in signature (e.g. return value) can be made more specific.
+   NOTE: This rule is complementatary to assignment rule.
+         While assignment rule checks a single assignment `lhs = rhs`, this rule
+         checks checks ALL assignments to `lhs` in the program.
+   NOTE: Violation of this rule is not a type violation, hence it should never be surfaced as error:
+         `lhs`'s type can be intentionally made broad by code author
+         (e.g. to anticipate future changes in the implementation).
+         Heuristits are required to correctly surface overannotated rule to the user.
+         This rule is useful for some scenarios, especially for nullability code conversions
+         when it is expected that some signatures were annotated with @Nullable defensively, so
+         surfacing such cases can improve API and make migration smooth.
+ *)
+
+type violation [@@deriving compare]
+
+val check : lhs:Nullability.t -> rhs_upper_bound:Nullability.t -> (unit, violation) result
+(** If an upper bound of `rhs_i` over ALL assignents `lhs = rhs_i` that exist in the program
+   is a _strict_ subtype of lhs, `lhs`'s type can be narrowed to be that upper bound.
+*)
+
+type violation_type =
+  | FieldOverAnnoted of Typ.Fieldname.t
+  | ReturnOverAnnotated of Typ.Procname.t  (** Return value of a method can be made non-nullable *)
+[@@deriving compare]
+
+val violation_description : violation -> violation_type -> string

infer/src/nullsafe/eradicateChecks.ml

@@ -28,17 +28,16 @@ let is_virtual = function
 
 let check_object_dereference tenv find_canonical_duplicate curr_pname node instr_ref object_exp
     dereference_type inferred_nullability loc =
-  if
-    not
-      (NullsafeRules.passes_dereference_rule
-         (InferredNullability.get_nullability inferred_nullability))
-  then
-    let origin_descr = InferredNullability.descr_origin inferred_nullability in
-    let nullable_object_descr = explain_expr tenv node object_exp in
-    let type_error =
-      TypeErr.Nullable_dereference {nullable_object_descr; dereference_type; origin_descr}
-    in
-    report_error tenv find_canonical_duplicate type_error (Some instr_ref) loc curr_pname
+  Result.iter_error
+    (DereferenceRule.check (InferredNullability.get_nullability inferred_nullability))
+    ~f:(fun dereference_violation ->
+      let origin_descr = InferredNullability.descr_origin inferred_nullability in
+      let nullable_object_descr = explain_expr tenv node object_exp in
+      let type_error =
+        TypeErr.Nullable_dereference
+          {dereference_violation; nullable_object_descr; dereference_type; origin_descr}
+      in
+      report_error tenv find_canonical_duplicate type_error (Some instr_ref) loc curr_pname )
 
 
 (** Where the condition is coming from *)
@@ -144,22 +143,27 @@ let check_field_assignment tenv find_canonical_duplicate curr_pdesc node instr_r
     in
     Annotations.ia_is_cleanup ret_annotation_deprecated
   in
-  let should_report_nullable =
-    (not
-       (NullsafeRules.passes_assignment_rule
-          ~lhs:(InferredNullability.get_nullability inferred_nullability_lhs)
-          ~rhs:(InferredNullability.get_nullability inferred_nullability_rhs)))
-    && (not (AndroidFramework.is_destroy_method curr_pname))
-    && PatternMatch.type_is_class t_lhs
-    && (not (Typ.Fieldname.Java.is_outer_instance fname))
-    && (not (field_is_injector_readwrite ()))
-    && not (field_is_in_cleanup_context ())
+  let assignment_check_result =
+    AssignmentRule.check
+      ~lhs:(InferredNullability.get_nullability inferred_nullability_lhs)
+      ~rhs:(InferredNullability.get_nullability inferred_nullability_rhs)
   in
-  if should_report_nullable then
-    let rhs_origin_descr = InferredNullability.descr_origin inferred_nullability_rhs in
-    report_error tenv find_canonical_duplicate
-      (TypeErr.Bad_assignment {rhs_origin_descr; assignment_type= TypeErr.AssigningToAField fname})
-      (Some instr_ref) loc curr_pdesc
+  Result.iter_error assignment_check_result ~f:(fun assignment_violation ->
+      let should_report =
+        (not (AndroidFramework.is_destroy_method curr_pname))
+        && PatternMatch.type_is_class t_lhs
+        && (not (Typ.Fieldname.Java.is_outer_instance fname))
+        && (not (field_is_injector_readwrite ()))
+        && not (field_is_in_cleanup_context ())
+      in
+      if should_report then
+        let rhs_origin_descr = InferredNullability.descr_origin inferred_nullability_rhs in
+        report_error tenv find_canonical_duplicate
+          (TypeErr.Bad_assignment
+             { assignment_violation
+             ; rhs_origin_descr
+             ; assignment_type= AssignmentRule.AssigningToField fname })
+          (Some instr_ref) loc curr_pdesc )
 
 
 let is_nonnull AnnotatedField.{annotated_type} =
@@ -289,17 +293,19 @@ let check_constructor_initialization tenv find_canonical_duplicate curr_construc
               | None ->
                   ()
               | Some annotated_field ->
-                  if
-                    Config.eradicate_field_over_annotated
-                    && NullsafeRules.is_overannotated
-                         ~lhs:
-                           (AnnotatedNullability.get_nullability
-                              annotated_field.annotated_type.nullability)
-                         ~rhs_upper_bound:(field_nullability_upper_bound_over_all_typestates ())
-                  then
-                    report_error tenv find_canonical_duplicate
-                      (TypeErr.Over_annotation (TypeErr.FieldOverAnnotedAsNullable field_name))
-                      None loc curr_constructor_pdesc )
+                  if Config.eradicate_field_over_annotated then
+                    let lhs =
+                      AnnotatedNullability.get_nullability
+                        annotated_field.annotated_type.nullability
+                    in
+                    let rhs_upper_bound = field_nullability_upper_bound_over_all_typestates () in
+                    Result.iter_error (OverAnnotatedRule.check ~lhs ~rhs_upper_bound)
+                      ~f:(fun over_annotated_violation ->
+                        report_error tenv find_canonical_duplicate
+                          (TypeErr.Over_annotation
+                             { over_annotated_violation
+                             ; violation_type= OverAnnotatedRule.FieldOverAnnoted field_name })
+                          None loc curr_constructor_pdesc ) )
           in
           List.iter ~f:do_field fields
       | None ->
@@ -313,12 +319,14 @@ let check_return_not_nullable tenv find_canonical_duplicate loc curr_pname curr_
   (* Returning from a function is essentially an assignment the actual return value to the formal `return` *)
   let lhs = AnnotatedNullability.get_nullability ret_signature.ret_annotated_type.nullability in
   let rhs = InferredNullability.get_nullability ret_inferred_nullability in
-  if not (NullsafeRules.passes_assignment_rule ~lhs ~rhs) then
-    let rhs_origin_descr = InferredNullability.descr_origin ret_inferred_nullability in
-    report_error tenv find_canonical_duplicate
-      (TypeErr.Bad_assignment
-         {rhs_origin_descr; assignment_type= TypeErr.ReturningFromAFunction curr_pname})
-      None loc curr_pdesc
+  Result.iter_error (AssignmentRule.check ~lhs ~rhs) ~f:(fun assignment_violation ->
+      let rhs_origin_descr = InferredNullability.descr_origin ret_inferred_nullability in
+      report_error tenv find_canonical_duplicate
+        (TypeErr.Bad_assignment
+           { assignment_violation
+           ; rhs_origin_descr
+           ; assignment_type= AssignmentRule.ReturningFromFunction curr_pname })
+        None loc curr_pdesc )
 
 
 let check_return_overrannotated tenv find_canonical_duplicate loc curr_pname curr_pdesc
@@ -330,10 +338,13 @@ let check_return_overrannotated tenv find_canonical_duplicate loc curr_pname cur
      correct upper bound.
     *)
   let rhs_upper_bound = InferredNullability.get_nullability ret_inferred_nullability in
-  if NullsafeRules.is_overannotated ~lhs ~rhs_upper_bound then
-    report_error tenv find_canonical_duplicate
-      (TypeErr.Over_annotation (TypeErr.ReturnOverAnnotatedAsNullable curr_pname)) None loc
-      curr_pdesc
+  Result.iter_error (OverAnnotatedRule.check ~lhs ~rhs_upper_bound)
+    ~f:(fun over_annotated_violation ->
+      report_error tenv find_canonical_duplicate
+        (TypeErr.Over_annotation
+           { over_annotated_violation
+           ; violation_type= OverAnnotatedRule.ReturnOverAnnotated curr_pname })
+        None loc curr_pdesc )
 
 
 (** Check the annotations when returning from a method. *)
@@ -373,7 +384,7 @@ let check_call_receiver tenv find_canonical_duplicate curr_pdesc node typestate
           loc
       in
       check_object_dereference tenv find_canonical_duplicate curr_pdesc node instr_ref
-        original_this_e (TypeErr.MethodCall callee_pname) this_inferred_nullability loc
+        original_this_e (DereferenceRule.MethodCall callee_pname) this_inferred_nullability loc
   | [] ->
       ()
 
@@ -389,7 +400,7 @@ let check_call_parameters tenv find_canonical_duplicate curr_pdesc node callee_a
     resolved_params loc instr_ref : unit =
   let callee_pname = callee_attributes.ProcAttributes.proc_name in
   let check {num= param_position; formal; actual= orig_e2, nullability_actual} =
-    let report () =
+    let report assignment_violation =
       let param_description =
         match explain_expr tenv node orig_e2 with
         | Some descr ->
@@ -400,9 +411,10 @@ let check_call_parameters tenv find_canonical_duplicate curr_pdesc node callee_a
       let rhs_origin_descr = InferredNullability.descr_origin nullability_actual in
       report_error tenv find_canonical_duplicate
         (TypeErr.Bad_assignment
-           { rhs_origin_descr
+           { assignment_violation
+           ; rhs_origin_descr
            ; assignment_type=
-               TypeErr.PassingParamToAFunction
+               AssignmentRule.PassingParamToFunction
                  {param_description; param_position; function_procname= callee_pname} })
         (Some instr_ref) loc curr_pdesc
     in
@@ -411,7 +423,7 @@ let check_call_parameters tenv find_canonical_duplicate curr_pdesc node callee_a
       to the formal param *)
       let lhs = AnnotatedNullability.get_nullability formal.param_annotated_type.nullability in
       let rhs = InferredNullability.get_nullability nullability_actual in
-      if not (NullsafeRules.passes_assignment_rule ~lhs ~rhs) then report ()
+      Result.iter_error (AssignmentRule.check ~lhs ~rhs) ~f:report
   in
   let should_check_parameters =
     match callee_pname with
@@ -430,35 +442,33 @@ let check_call_parameters tenv find_canonical_duplicate curr_pdesc node callee_a
 
 let check_inheritance_rule_for_return find_canonical_duplicate tenv loc ~base_proc_name
     ~overridden_proc_name ~overridden_proc_desc ~base_nullability ~overridden_nullability =
-  if
-    not
-      (NullsafeRules.passes_inheritance_rule NullsafeRules.Ret ~base:base_nullability
-         ~overridden:overridden_nullability)
-  then
-    report_error tenv find_canonical_duplicate
-      (TypeErr.Inconsistent_subclass
-         { overridden_proc_name
-         ; base_proc_name
-         ; inconsistent_subclass_type= TypeErr.InconsistentReturn })
-      None loc overridden_proc_desc
+  Result.iter_error
+    (InheritanceRule.check InheritanceRule.Ret ~base:base_nullability
+       ~overridden:overridden_nullability) ~f:(fun inheritance_violation ->
+      report_error tenv find_canonical_duplicate
+        (TypeErr.Inconsistent_subclass
+           { inheritance_violation
+           ; violation_type= InheritanceRule.InconsistentReturn
+           ; overridden_proc_name
+           ; base_proc_name })
+        None loc overridden_proc_desc )
 
 
 let check_inheritance_rule_for_param find_canonical_duplicate tenv loc ~overridden_param_name
     ~base_proc_name ~overridden_proc_name ~overridden_proc_desc ~param_position ~base_nullability
     ~overridden_nullability =
-  if
-    not
-      (NullsafeRules.passes_inheritance_rule NullsafeRules.Param ~base:base_nullability
-         ~overridden:overridden_nullability)
-  then
-    report_error tenv find_canonical_duplicate
-      (TypeErr.Inconsistent_subclass
-         { base_proc_name
-         ; overridden_proc_name
-         ; inconsistent_subclass_type=
-             TypeErr.InconsistentParam
-               {param_position; param_description= Mangled.to_string overridden_param_name} })
-      None loc overridden_proc_desc
+  Result.iter_error
+    (InheritanceRule.check InheritanceRule.Param ~base:base_nullability
+       ~overridden:overridden_nullability) ~f:(fun inheritance_violation ->
+      report_error tenv find_canonical_duplicate
+        (TypeErr.Inconsistent_subclass
+           { inheritance_violation
+           ; violation_type=
+               InheritanceRule.InconsistentParam
+                 {param_position; param_description= Mangled.to_string overridden_param_name}
+           ; base_proc_name
+           ; overridden_proc_name })
+        None loc overridden_proc_desc )
 
 
 let check_inheritance_rule_for_params find_canonical_duplicate tenv loc ~base_proc_name

infer/src/nullsafe/typeCheck.ml

@@ -148,7 +148,7 @@ let rec typecheck_expr find_canonical_duplicate visited checks tenv node instr_r
       in
       if checks.eradicate then
         EradicateChecks.check_object_dereference tenv find_canonical_duplicate curr_pdesc node
-          instr_ref exp (TypeErr.AccessToField field_name) inferred_nullability loc ;
+          instr_ref exp (DereferenceRule.AccessToField field_name) inferred_nullability loc ;
       tr_new
   | Exp.Lindex (array_exp, index_exp) ->
       let _, inferred_nullability =
@@ -161,7 +161,7 @@ let rec typecheck_expr find_canonical_duplicate visited checks tenv node instr_r
       if checks.eradicate then
         EradicateChecks.check_object_dereference tenv find_canonical_duplicate curr_pdesc node
           instr_ref array_exp
-          (TypeErr.AccessByIndex {index_desc})
+          (DereferenceRule.AccessByIndex {index_desc})
           inferred_nullability loc ;
       tr_default
   | _ ->
@@ -472,7 +472,7 @@ let typecheck_instr tenv calls_this checks (node : Procdesc.Node.t) idenv curr_p
       in
       if checks.eradicate then
         EradicateChecks.check_object_dereference tenv find_canonical_duplicate curr_pdesc node
-          instr_ref array_exp TypeErr.ArrayLengthAccess ta loc ;
+          instr_ref array_exp DereferenceRule.ArrayLengthAccess ta loc ;
       TypeState.add_id id
         (Typ.mk (Tint Typ.IInt), InferredNullability.create_nonnull TypeOrigin.New)
         typestate

infer/src/nullsafe/typeErr.ml

@@ -66,41 +66,25 @@ let compare_origin_descr _ _ = 0
 type err_instance =
   | Condition_redundant of (bool * string option)
   | Inconsistent_subclass of
-      { base_proc_name: Typ.Procname.t
-      ; overridden_proc_name: Typ.Procname.t
-      ; inconsistent_subclass_type: inconsistent_subclass_type }
+      { inheritance_violation: InheritanceRule.violation
+      ; violation_type: InheritanceRule.violation_type
+      ; base_proc_name: Typ.Procname.t
+      ; overridden_proc_name: Typ.Procname.t }
   | Field_not_initialized of Typ.Fieldname.t * Typ.Procname.t
-  | Over_annotation of over_annotation_type
+  | Over_annotation of
+      { over_annotated_violation: OverAnnotatedRule.violation
+      ; violation_type: OverAnnotatedRule.violation_type }
   | Nullable_dereference of
-      { nullable_object_descr: string option
-      ; dereference_type: dereference_type
+      { dereference_violation: DereferenceRule.violation
+      ; dereference_type: DereferenceRule.dereference_type
+      ; nullable_object_descr: string option
       ; origin_descr: origin_descr }
-  | Bad_assignment of {rhs_origin_descr: origin_descr; assignment_type: assignment_type}
+  | Bad_assignment of
+      { assignment_violation: AssignmentRule.violation
+      ; assignment_type: AssignmentRule.assignment_type
+      ; rhs_origin_descr: origin_descr }
 [@@deriving compare]
 
-and inconsistent_subclass_type =
-  | InconsistentParam of {param_description: string; param_position: int}
-  | InconsistentReturn
-
-and over_annotation_type =
-  | FieldOverAnnotedAsNullable of Typ.Fieldname.t
-  | ReturnOverAnnotatedAsNullable of Typ.Procname.t
-      (** Return value of a method can be made non-nullable *)
-
-and assignment_type =
-  | PassingParamToAFunction of
-      { param_description: string
-      ; param_position: int
-      ; function_procname: Typ.Procname.t }
-  | AssigningToAField of Typ.Fieldname.t
-  | ReturningFromAFunction of Typ.Procname.t
-
-and dereference_type =
-  | MethodCall of Typ.Procname.t
-  | AccessToField of Typ.Fieldname.t
-  | AccessByIndex of {index_desc: string}
-  | ArrayLengthAccess
-
 module H = Hashtbl.Make (struct
   type t = err_instance * InstrRef.t option [@@deriving compare]
 
@@ -221,35 +205,35 @@ type st_report_error =
 let get_infer_issue_type = function
   | Condition_redundant _ ->
       IssueType.eradicate_condition_redundant
-  | Over_annotation (FieldOverAnnotedAsNullable _) ->
+  | Over_annotation {violation_type= OverAnnotatedRule.FieldOverAnnoted _} ->
       IssueType.eradicate_field_over_annotated
-  | Over_annotation (ReturnOverAnnotatedAsNullable _) ->
+  | Over_annotation {violation_type= OverAnnotatedRule.ReturnOverAnnotated _} ->
       IssueType.eradicate_return_over_annotated
   | Field_not_initialized _ ->
       IssueType.eradicate_field_not_initialized
-  | Bad_assignment {assignment_type= PassingParamToAFunction _} ->
+  | Bad_assignment {assignment_type= PassingParamToFunction _} ->
       IssueType.eradicate_parameter_not_nullable
-  | Bad_assignment {assignment_type= AssigningToAField _} ->
+  | Bad_assignment {assignment_type= AssigningToField _} ->
       IssueType.eradicate_field_not_nullable
-  | Bad_assignment {assignment_type= ReturningFromAFunction _} ->
+  | Bad_assignment {assignment_type= ReturningFromFunction _} ->
       IssueType.eradicate_return_not_nullable
   | Nullable_dereference _ ->
       IssueType.eradicate_nullable_dereference
-  | Inconsistent_subclass {inconsistent_subclass_type= InconsistentReturn} ->
+  | Inconsistent_subclass {violation_type= InconsistentReturn} ->
       IssueType.eradicate_inconsistent_subclass_return_annotation
-  | Inconsistent_subclass {inconsistent_subclass_type= InconsistentParam _} ->
+  | Inconsistent_subclass {violation_type= InconsistentParam _} ->
       IssueType.eradicate_inconsistent_subclass_parameter_annotation
 
 
 (* If an error is related to a particular field, we support suppressing the
    error via a supress annotation placed near the field declaration *)
 let get_field_name_for_error_suppressing = function
-  | Over_annotation (FieldOverAnnotedAsNullable field_name) ->
+  | Over_annotation {violation_type= OverAnnotatedRule.FieldOverAnnoted field_name} ->
       Some field_name
   | Field_not_initialized (field_name, _) ->
       Some field_name
   | Condition_redundant _
-  | Over_annotation (ReturnOverAnnotatedAsNullable _)
+  | Over_annotation {violation_type= OverAnnotatedRule.ReturnOverAnnotated _}
   (* In case of assignment to a field, it should be fixed case by case for each assignment *)
   | Bad_assignment _
   | Nullable_dereference _
@@ -263,15 +247,8 @@ let get_error_description err_instance =
   | Condition_redundant (is_always_true, s_opt) ->
       P.sprintf "The condition %s is always %b according to the existing annotations."
         (Option.value s_opt ~default:"") is_always_true
-  | Over_annotation (FieldOverAnnotedAsNullable field_name) ->
-      Format.asprintf "Field %a is always initialized in the constructor but is declared %a"
-        MF.pp_monospaced
-        (Typ.Fieldname.to_simplified_string field_name)
-        MF.pp_monospaced nullable_annotation
-  | Over_annotation (ReturnOverAnnotatedAsNullable proc_name) ->
-      Format.asprintf "Method %a is annotated with %a but never returns null." MF.pp_monospaced
-        (Typ.Procname.to_simplified_string proc_name)
-        MF.pp_monospaced nullable_annotation
+  | Over_annotation {over_annotated_violation; violation_type} ->
+      OverAnnotatedRule.violation_description over_annotated_violation violation_type
   | Field_not_initialized (field_name, proc_name) ->
       let constructor_name =
         if Typ.Procname.is_constructor proc_name then "the constructor"
@@ -285,84 +262,20 @@ let get_error_description err_instance =
       Format.asprintf "Field %a is not initialized in %s and is not declared %a" MF.pp_monospaced
         (Typ.Fieldname.to_simplified_string field_name)
         constructor_name MF.pp_monospaced nullable_annotation
-  | Bad_assignment {rhs_origin_descr= origin_descr_string, _, _; assignment_type} -> (
-    match assignment_type with
-    | PassingParamToAFunction {param_description; param_position; function_procname} ->
-        Format.asprintf "%a needs a non-null value in parameter %d but argument %a can be null. %s"
-          MF.pp_monospaced
-          (Typ.Procname.to_simplified_string ~withclass:true function_procname)
-          param_position MF.pp_monospaced param_description origin_descr_string
-    | AssigningToAField field_name ->
-        Format.asprintf "Field %a can be null but is not declared %a. %s" MF.pp_monospaced
-          (Typ.Fieldname.to_simplified_string field_name)
-          MF.pp_monospaced nullable_annotation origin_descr_string
-    | ReturningFromAFunction function_proc_name ->
-        Format.asprintf "Method %a may return null but it is not annotated with %a. %s"
-          MF.pp_monospaced
-          (Typ.Procname.to_simplified_string function_proc_name)
-          MF.pp_monospaced nullable_annotation origin_descr_string )
-  | Nullable_dereference {nullable_object_descr; dereference_type; origin_descr= origin_str, _, _}
+  | Bad_assignment {rhs_origin_descr= rhs_origin_descr, _, _; assignment_type; assignment_violation}
     ->
-      let nullable_object_descr =
-        match dereference_type with
-        | MethodCall _ | AccessToField _ -> (
-          match nullable_object_descr with
-          | None ->
-              "Object"
-          (* Just describe an object itself *)
-          | Some descr ->
-              MF.monospaced_to_string descr )
-        | ArrayLengthAccess | AccessByIndex _ -> (
-          (* In Java, those operations can be applied only to arrays *)
-          match nullable_object_descr with
-          | None ->
-              "Array"
-          | Some descr ->
-              Format.sprintf "Array %s" (MF.monospaced_to_string descr) )
-      in
-      let action_descr =
-        match dereference_type with
-        | MethodCall method_name ->
-            Format.sprintf "calling %s"
-              (MF.monospaced_to_string (Typ.Procname.to_simplified_string method_name))
-        | AccessToField field_name ->
-            Format.sprintf "accessing field %s"
-              (MF.monospaced_to_string (Typ.Fieldname.to_simplified_string field_name))
-        | AccessByIndex {index_desc} ->
-            Format.sprintf "accessing at index %s" (MF.monospaced_to_string index_desc)
-        | ArrayLengthAccess ->
-            "accessing its length"
-      in
-      Format.sprintf "%s is nullable and is not locally checked for null when %s. %s"
-        nullable_object_descr action_descr origin_str
-  | Inconsistent_subclass {base_proc_name; overridden_proc_name; inconsistent_subclass_type} -> (
-      let base_method_descr = Typ.Procname.to_simplified_string ~withclass:true base_proc_name in
-      let overridden_method_descr =
-        Typ.Procname.to_simplified_string ~withclass:true overridden_proc_name
-      in
-      match inconsistent_subclass_type with
-      | InconsistentReturn ->
-          Format.asprintf "Method %a is annotated with %a but overrides unannotated method %a."
-            MF.pp_monospaced overridden_method_descr MF.pp_monospaced nullable_annotation
-            MF.pp_monospaced base_method_descr
-      | InconsistentParam {param_description; param_position} ->
-          let translate_position = function
-            | 1 ->
-                "First"
-            | 2 ->
-                "Second"
-            | 3 ->
-                "Third"
-            | n ->
-                string_of_int n ^ "th"
-          in
-          Format.asprintf
-            "%s parameter %a of method %a is not %a but is declared %ain the parent class method \
-             %a."
-            (translate_position param_position)
-            MF.pp_monospaced param_description MF.pp_monospaced overridden_method_descr
-            MF.pp_monospaced nullable_annotation MF.pp_monospaced nullable_annotation
-            MF.pp_monospaced base_method_descr )
+      AssignmentRule.violation_description assignment_violation assignment_type ~rhs_origin_descr
+  | Nullable_dereference
+      { dereference_violation
+      ; nullable_object_descr
+      ; dereference_type
+      ; origin_descr= origin_descr, _, _ } ->
+      DereferenceRule.violation_description dereference_violation dereference_type
+        ~nullable_object_descr ~origin_descr
+  | Inconsistent_subclass
+      {inheritance_violation; violation_type; base_proc_name; overridden_proc_name} ->
+      InheritanceRule.violation_description inheritance_violation violation_type ~base_proc_name
+        ~overridden_proc_name
 
 
 (** Report an error right now. *)

infer/src/nullsafe/typeErr.mli

@@ -38,41 +38,25 @@ type origin_descr = string * Location.t option * AnnotatedSignature.t option
 type err_instance =
   | Condition_redundant of (bool * string option)
   | Inconsistent_subclass of
-      { base_proc_name: Typ.Procname.t
-      ; overridden_proc_name: Typ.Procname.t
-      ; inconsistent_subclass_type: inconsistent_subclass_type }
+      { inheritance_violation: InheritanceRule.violation
+      ; violation_type: InheritanceRule.violation_type
+      ; base_proc_name: Typ.Procname.t
+      ; overridden_proc_name: Typ.Procname.t }
   | Field_not_initialized of Typ.Fieldname.t * Typ.Procname.t
-  | Over_annotation of over_annotation_type
+  | Over_annotation of
+      { over_annotated_violation: OverAnnotatedRule.violation
+      ; violation_type: OverAnnotatedRule.violation_type }
   | Nullable_dereference of
-      { nullable_object_descr: string option
-      ; dereference_type: dereference_type
+      { dereference_violation: DereferenceRule.violation
+      ; dereference_type: DereferenceRule.dereference_type
+      ; nullable_object_descr: string option
       ; origin_descr: origin_descr }
-  | Bad_assignment of {rhs_origin_descr: origin_descr; assignment_type: assignment_type}
+  | Bad_assignment of
+      { assignment_violation: AssignmentRule.violation
+      ; assignment_type: AssignmentRule.assignment_type
+      ; rhs_origin_descr: origin_descr }
 [@@deriving compare]
 
-and inconsistent_subclass_type =
-  | InconsistentParam of {param_description: string; param_position: int}
-  | InconsistentReturn
-
-and over_annotation_type =
-  | FieldOverAnnotedAsNullable of Typ.Fieldname.t
-  | ReturnOverAnnotatedAsNullable of Typ.Procname.t
-      (** Return value of a method can be made non-nullable *)
-
-and assignment_type =
-  | PassingParamToAFunction of
-      { param_description: string
-      ; param_position: int
-      ; function_procname: Typ.Procname.t }
-  | AssigningToAField of Typ.Fieldname.t
-  | ReturningFromAFunction of Typ.Procname.t
-
-and dereference_type =
-  | MethodCall of Typ.Procname.t  (** nullable_object.some_method() *)
-  | AccessToField of Typ.Fieldname.t  (** nullable_object.some_field *)
-  | AccessByIndex of {index_desc: string}  (** nullable_array[some_index] *)
-  | ArrayLengthAccess  (** nullable_array.length *)
-
 val node_reset_forall : Procdesc.Node.t -> unit
 
 type st_report_error =