Do not use infer_variance with covariant and contravariant flags

Summary:
We should not use infer_variance when we've already defined covariance or contravariance flags.

We could not catch this before because the variable definitions are not expressive enough.

In this diff, we fix this issue by extending variable declarations to include the infer_variance flag, as existing variable declarations erased that information. Then when we reach typecheck, we can check the flag, along with the variance information we parsed and raise the right error message.

This diff includes adding the new error message defintion and a unit test.

We can now see the conformance improvement.

Reviewed By: stroxler

Differential Revision: D65041792

fbshipit-source-id: 4b5a1e391b348f8fb786140fd3882aa1289a7a8c

source/analysis/analysisError.ml

@@ -788,6 +788,7 @@ and kind =
       parameter: type_parameter_name_and_variance;
       origin: type_variance_origin;
     }
+  | InvalidVarianceDefinition
   | InvalidInheritance of invalid_inheritance
   | InvalidOverride of {
       parent: Identifier.t;
@@ -997,6 +998,7 @@ let code_of_kind = function
   | NamedTupleMissingDefault -> 74
   | InvalidTypeVariableConstraint _ -> 75
   | AwaitOutsideAsyncDef -> 76
+  | InvalidVarianceDefinition -> 77
   | ParserFailure _ -> 404
   (* Additional errors. *)
   | UnawaitedAwaitable _ -> 1001
@@ -1041,6 +1043,7 @@ let name_of_kind = function
   | InvalidTypeParameters _ -> "Invalid type parameters"
   | InvalidTypeVariable _ -> "Invalid type variable"
   | InvalidTypeVariance _ -> "Invalid type variance"
+  | InvalidVarianceDefinition -> "Invalid variance definition"
   | InvalidInheritance _ -> "Invalid inheritance"
   | InvalidOverride _ -> "Invalid override"
   | InvalidPositionalOnlyParameter -> "Invalid positional-only parameter"
@@ -2165,6 +2168,8 @@ let rec messages ~concise ~signature location kind =
               base_parameter
       in
       [formatted; "See `https://pyre-check.org/docs/errors#35-invalid-type-variance` for details."]
+  | InvalidVarianceDefinition ->
+      [Format.asprintf "Cannot use infer_variance with predefined variance."]
   | InvalidInheritance invalid_inheritance -> (
       match invalid_inheritance with
       | ProtocolBaseClass ->
@@ -3383,6 +3388,7 @@ let due_to_analysis_limitations { kind; _ } =
   | InvalidTypeParameters _
   | InvalidTypeVariable _
   | InvalidTypeVariance _
+  | InvalidVarianceDefinition
   | InvalidInheritance _
   | InvalidOverride _
   | InvalidPositionalOnlyParameter
@@ -3929,6 +3935,7 @@ let join ~resolution left right =
     | InvalidTypeParameters _, _
     | InvalidTypeVariable _, _
     | InvalidTypeVariance _, _
+    | InvalidVarianceDefinition, _
     | InvalidInheritance _, _
     | InvalidOverride _, _
     | InvalidPositionalOnlyParameter, _
@@ -4466,6 +4473,7 @@ let dequalify
             origin = dequalify_type_variance_origin origin;
           }
     | InvalidInheritance name -> InvalidInheritance (dequalify_invalid_inheritance name)
+    | InvalidVarianceDefinition -> InvalidVarianceDefinition
     | InvalidOverride { parent; decorator } ->
         InvalidOverride { parent = dequalify_identifier parent; decorator }
     | InvalidPositionalOnlyParameter -> InvalidPositionalOnlyParameter

source/analysis/analysisError.mli

@@ -442,6 +442,7 @@ and kind =
       parameter: type_parameter_name_and_variance;
       origin: type_variance_origin;
     }
+  | InvalidVarianceDefinition
   | InvalidInheritance of invalid_inheritance
   | InvalidOverride of {
       parent: Identifier.t;

source/analysis/test/integration/typeVariableTest.ml

@@ -396,6 +396,20 @@ let test_type_variable_scoping =
               `ShouldBeInvariant1[int]` but is used as type `ShouldBeInvariant1[float]`.";
            ];
       labeled_test_case __FUNCTION__ __LINE__
+      @@ assert_type_errors
+           {|
+            from typing import *
+
+            S1 = TypeVar("S1", covariant=True, infer_variance=True)  # E: cannot use covariant with infer_variance
+            S2 = TypeVar("S2", contravariant=True, infer_variance=True)  # E: cannot use contravariant with infer_variance
+
+
+            |}
+           [
+             "Invalid variance definition [77]: Cannot use infer_variance with predefined variance.";
+             "Invalid variance definition [77]: Cannot use infer_variance with predefined variance.";
+           ];
+      labeled_test_case __FUNCTION__ __LINE__
       @@ assert_type_errors
            {|
             from typing import Sequence

source/analysis/test/typeTest.ml

@@ -20,7 +20,8 @@ let type_var_declaration_and_variable
     ?(variance = Type.Record.PreInferenceVariance.P_Invariant)
     name
   =
-  ( Type.Variable.Declaration.DTypeVar { name; constraints = declaration_constraints; variance },
+  ( Type.Variable.Declaration.DTypeVar
+      { name; constraints = declaration_constraints; variance; infer_variance = false },
     Type.Variable.TypeVar.create name ~constraints:type_constraints )
 
 
@@ -2697,6 +2698,7 @@ let test_parse_type_variable_declarations _ =
          name = "target";
          constraints = Unconstrained;
          variance = Type.Record.PreInferenceVariance.P_Invariant;
+         infer_variance = false;
        });
 
   assert_parses_declaration
@@ -2706,6 +2708,7 @@ let test_parse_type_variable_declarations _ =
          name = "target";
          constraints = Unconstrained;
          variance = Type.Record.PreInferenceVariance.P_Covariant;
+         infer_variance = false;
        });
 
   assert_parses_declaration
@@ -2715,6 +2718,7 @@ let test_parse_type_variable_declarations _ =
          name = "target";
          constraints = Unconstrained;
          variance = Type.Record.PreInferenceVariance.P_Invariant;
+         infer_variance = false;
        });
 
   assert_parses_declaration
@@ -2724,6 +2728,7 @@ let test_parse_type_variable_declarations _ =
          name = "target";
          constraints = Unconstrained;
          variance = Type.Record.PreInferenceVariance.P_Contravariant;
+         infer_variance = false;
        });
 
   assert_parses_declaration
@@ -2733,6 +2738,7 @@ let test_parse_type_variable_declarations _ =
          name = "target";
          constraints = Unconstrained;
          variance = Type.Record.PreInferenceVariance.P_Invariant;
+         infer_variance = false;
        });
   assert_parses_declaration_with_bounds
     "typing.TypeVar('_T', int)"
@@ -2741,6 +2747,7 @@ let test_parse_type_variable_declarations _ =
          name = "target";
          constraints = Type.Record.TypeVarConstraints.Explicit [Type.expression Type.integer];
          variance = Type.Record.PreInferenceVariance.P_Invariant;
+         infer_variance = false;
        });
 
   assert_parses_declaration_with_bounds
@@ -2751,6 +2758,7 @@ let test_parse_type_variable_declarations _ =
          constraints =
            Type.Record.TypeVarConstraints.Bound (Type.expression (Type.Primitive "\"C\""));
          variance = Type.Record.PreInferenceVariance.P_Invariant;
+         infer_variance = false;
        });
 
   assert_parses_declaration_with_bounds
@@ -2762,6 +2770,7 @@ let test_parse_type_variable_declarations _ =
            Type.Record.TypeVarConstraints.Explicit
              [Type.expression (Type.Primitive "\"C\""); Type.expression (Type.Primitive "X")];
          variance = Type.Record.PreInferenceVariance.P_Invariant;
+         infer_variance = false;
        });
 
   assert_parses_declaration_with_bounds
@@ -2771,6 +2780,7 @@ let test_parse_type_variable_declarations _ =
          name = "target";
          constraints = Type.Record.TypeVarConstraints.Explicit [Type.expression Type.integer];
          variance = Type.Record.PreInferenceVariance.P_Invariant;
+         infer_variance = false;
        });
 
   assert_parses_declaration_with_bounds
@@ -2782,6 +2792,7 @@ let test_parse_type_variable_declarations _ =
            Type.Record.TypeVarConstraints.Bound
              (Type.expression (Type.Primitive "\"typing.Callable\""));
          variance = Type.Record.PreInferenceVariance.P_Invariant;
+         infer_variance = false;
        });
 
   assert_declaration_does_not_parse "typing.TypeVarTuple('Ts', covariant=True)";

source/analysis/type.ml

@@ -3102,6 +3102,7 @@ module Variable = struct
           name: Identifier.t;
           constraints: Expression.t Record.TypeVarConstraints.t;
           variance: Record.PreInferenceVariance.t;
+          infer_variance: bool;
         }
       | DTypeVarTuple of { name: Identifier.t }
       | DParamSpec of { name: Identifier.t }
@@ -3160,8 +3161,20 @@ module Variable = struct
             List.find_map arguments ~f:variance_definition
             |> Option.value ~default:Record.PreInferenceVariance.P_Invariant
           in
+          let infer_variance =
+            let variance_definition = function
+              | {
+                  Call.Argument.name = Some { Node.value = name; _ };
+                  value = { Node.value = Constant Constant.True; _ };
+                }
+                when String.equal (Identifier.sanitized name) "infer_variance" ->
+                  true
+              | _ -> false
+            in
+            List.exists arguments ~f:variance_definition
+          in
 
-          Some (DTypeVar { name = Reference.show target; constraints; variance })
+          Some (DTypeVar { name = Reference.show target; constraints; variance; infer_variance })
       | {
        Node.value =
          Expression.Call
@@ -3179,6 +3192,7 @@ module Variable = struct
                  name = Reference.show target;
                  constraints = LiteralIntegers;
                  variance = Record.PreInferenceVariance.P_Invariant;
+                 infer_variance = false;
                })
       | {
           Node.value =
@@ -3604,7 +3618,7 @@ module GenericParameter = struct
 
   let of_declaration declaration ~create_type =
     match declaration with
-    | Variable.Declaration.DTypeVar { name; constraints; variance } ->
+    | Variable.Declaration.DTypeVar { name; constraints; variance; _ } ->
         let constraints =
           match constraints with
           | Bound expression -> Record.TypeVarConstraints.Bound (create_type expression)

source/analysis/type.mli

@@ -841,6 +841,7 @@ module Variable : sig
           name: Identifier.t;
           constraints: Expression.t Record.TypeVarConstraints.t;
           variance: Record.PreInferenceVariance.t;
+          infer_variance: bool;
         }
       | DTypeVarTuple of { name: Identifier.t }
       | DParamSpec of { name: Identifier.t }

source/analysis/typeCheck.ml

@@ -4643,13 +4643,22 @@ module State (Context : Context) = struct
 
   and forward_variable_alias_definition ~resolution ~location ~errors ~target ~value ~reference =
     let global_resolution = Resolution.global_resolution resolution in
-
     (* try to parse as a variable declaration and raise the appropriate errors for variables if we
        are successful *)
     let parse_as_declaration = Type.Variable.Declaration.parse value ~target:reference in
-
     match parse_as_declaration with
     | Some parsed ->
+        (* if infer_variance is true but variance is not undefined, we raise an error *)
+        let errors_from_variance_declarations =
+          match parsed with
+          | Type.Variable.Declaration.DTypeVar { variance; infer_variance = true; _ }
+            when not
+                   (Type.Record.PreInferenceVariance.equal
+                      variance
+                      Type.Record.PreInferenceVariance.P_Undefined) ->
+              emit_error ~errors ~location ~kind:Error.InvalidVarianceDefinition
+          | _ -> []
+        in
         let create_type =
           GlobalResolution.parse_annotation ~validation:NoValidation global_resolution
         in
@@ -4679,6 +4688,7 @@ module State (Context : Context) = struct
               errors
           | _ -> errors
         in
+        let errors = errors_from_variance_declarations @ errors in
         Value resolution, errors
     | _ -> Value resolution, errors