Let the typechecker recognize type variables used within type aliases

Summary: As shown in the unittests, we would like to collect type variables within type aliases and add them to the resolution, so that the typechecker recognizes them as type annotations.

Reviewed By: stroxler

Differential Revision: D62763697

fbshipit-source-id: e6b368fc2d139003e5face0272896a3acc3857bb

source/analysis/test/integration/typeVariableTest.ml

@@ -2263,7 +2263,6 @@ let test_generic_aliases =
 
             |}
            [
-             "Undefined or invalid type [11]: Annotation `T` is not defined as a type.";
              "Parsing failure [404]: PEP 695 type params are unsupported";
              "Revealed type [-1]: Revealed type for `test.func(x)` is \
               `typing.Union[typing.List[int], typing.Set[int]]`.";
@@ -2302,8 +2301,6 @@ let test_generic_aliases =
             reveal_type(apply_callback)
             |}
            [
-             "Undefined or invalid type [11]: Annotation `S1` is not defined as a type.";
-             "Undefined or invalid type [11]: Annotation `S2` is not defined as a type.";
              "Parsing failure [404]: PEP 695 type params are unsupported";
              "Revealed type [-1]: Revealed type for `test.apply_callback` is \
               `typing.Callable(apply_callback)[[Named(callback, typing.Callable[[int], \

source/analysis/typeCheck.ml

@@ -458,6 +458,18 @@ module State (Context : Context) = struct
     List.fold mismatches ~f:emit_error ~init:errors
 
 
+  let get_type_params_as_variables type_params =
+    List.map type_params ~f:(fun { Node.value; _ } ->
+        match value with
+        | Ast.Expression.TypeParam.TypeVar { name; _ } ->
+            Type.Variable.TypeVarVariable
+              (Type.Variable.TypeVar.create ~constraints:Unconstrained name)
+        | Ast.Expression.TypeParam.TypeVarTuple name ->
+            Type.Variable.TypeVarTupleVariable (Type.Variable.TypeVarTuple.create name)
+        | Ast.Expression.TypeParam.ParamSpec name ->
+            Type.Variable.ParamSpecVariable (Type.Variable.ParamSpec.create name))
+
+
   let add_invalid_type_parameters_errors ~resolution ~location ~errors annotation =
     let mismatches, annotation =
       GlobalResolution.validate_and_sanitize_type_arguments resolution annotation
@@ -5758,6 +5770,11 @@ module State (Context : Context) = struct
         forward_assignment ~resolution ~location ~target ~annotation:None ~value:(Some call)
     (* TODO(T196994965): handle type alias *)
     | TypeAlias { TypeAlias.name; type_params; value } ->
+        let resolution =
+          get_type_params_as_variables type_params
+          |> List.fold ~init:resolution ~f:(fun resolution variable ->
+                 Resolution.add_type_variable resolution ~variable)
+        in
         (* TODO: remove after PEP 695 is supported *)
         let type_params_errors =
           match type_params with
@@ -6352,20 +6369,10 @@ module State (Context : Context) = struct
       Context.define
     in
     (* collect type parameters for functions *)
-    let type_param_names =
-      List.map type_params ~f:(fun { Node.value; _ } ->
-          match value with
-          | Ast.Expression.TypeParam.TypeVar { name; _ } ->
-              Type.Variable.TypeVarVariable
-                (Type.Variable.TypeVar.create ~constraints:Unconstrained name)
-          | Ast.Expression.TypeParam.TypeVarTuple name ->
-              Type.Variable.TypeVarTupleVariable (Type.Variable.TypeVarTuple.create name)
-          | Ast.Expression.TypeParam.ParamSpec name ->
-              Type.Variable.ParamSpecVariable (Type.Variable.ParamSpec.create name))
-    in
+    let type_params = get_type_params_as_variables type_params in
     (* Add them to the resolution *)
     let resolution =
-      type_param_names
+      type_params
       |> List.fold ~init:resolution ~f:(fun resolution variable ->
              Resolution.add_type_variable resolution ~variable)
     in