Make closure and soft type specifiers a parse error

Summary:
These hints may never be used with `is`-expressions because:
- We have no information on a function's inputs/output at runtime.
- Soft typehints would be meaningless when testing types.

Reviewed By: periodic1236, oulgen

Differential Revision: D7076934

fbshipit-source-id: 42639d367cfa6a73b384098d6abf3796ad87b935

hphp/hack/src/parser/full_fidelity_parser_errors.ml

@@ -1746,6 +1746,18 @@ let expression_errors node parents is_hack is_hack_file hhvm_compat_mode errors
       && leading_width lambda_signature = 0
       -> failwith "syntax error, unexpected T_LAMBDA_ARROW";
     (* End of bug-port *)
+  | IsExpression
+    { is_right_operand = hint
+    ; _ } ->
+    begin match syntax hint with
+      | ClosureTypeSpecifier _ ->
+        make_error_from_node hint
+          (SyntaxError.invalid_is_expression_hint "Callable") :: errors
+      | SoftTypeSpecifier _ ->
+        make_error_from_node hint
+          (SyntaxError.invalid_is_expression_hint "Soft") :: errors
+      | _ -> errors
+    end
   | _ -> errors (* Other kinds of expressions currently produce no expr errors. *)
 
 let require_errors node parents hhvm_compat_mode trait_use_clauses errors =

hphp/hack/src/parser/full_fidelity_syntax_error.ml

@@ -392,6 +392,6 @@ let variadic_param_with_type_in_php name type_ =
   ^ type_ ^ "); variadic params with type constraints are not "
   ^ "supported in non-Hack files"
 let final_property = "Properties cannot be declared final"
-
 let property_has_multiple_visibilities name =
   "Multiple access type modifiers are not allowed: properties of " ^ name
+let invalid_is_expression_hint hint = hint ^ " typehints cannot be used with `is` expressions"

hphp/hack/src/parser/full_fidelity_syntax_error.mli

@@ -237,3 +237,4 @@ val self_or_parent_colon_colon_class_outside_of_class : string -> string
 val variadic_param_with_type_in_php : string -> string -> string
 val final_property : string
 val property_has_multiple_visibilities : string -> string 
+val invalid_is_expression_hint : string -> string

hphp/hack/test/full_fidelity/cases/is_expression/test_callable_hint.exp

@@ -0,0 +1 @@
+(13,16)-(13,32) Callable typehints cannot be used with `is` expressions

hphp/hack/test/full_fidelity/cases/is_expression/test_callable_hint.php

@@ -0,0 +1,14 @@
+<?hh
+/**
+ * Copyright (c) 2014, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the "hack" directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ */
+
+function test(mixed $e): bool {
+  return $e is (function(): int);
+}

hphp/hack/test/full_fidelity/cases/is_expression/test_soft_hint.exp

@@ -0,0 +1 @@
+(13,16)-(13,19) Soft typehints cannot be used with `is` expressions

hphp/hack/test/full_fidelity/cases/is_expression/test_soft_hint.php

@@ -0,0 +1,14 @@
+<?hh
+/**
+ * Copyright (c) 2014, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the "hack" directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ */
+
+function test(mixed $e): bool {
+  return $e is @int;
+}

hphp/hack/test/full_fidelity/full_fidelity_unit_test.ml

@@ -191,6 +191,8 @@ let error_tests =
     make_test_case_from_files testname test_errors in
   List.map
   [
+    "is_expression/test_callable_hint";
+    "is_expression/test_soft_hint";
     "test_default_param_errors";
     "test_alias_errors";
     "test_method_modifier_errors";