Ban aliases in catch blocks

Summary:
An alias is completely ignored by HHVM in catch blocks, leading to users thinking that their code will catch exceptions that it ignores.

This might be something we can support in the future when decls-in-compilation enables aliases in more positions, but today it's safer to update hh to reflect the runtime.

Differential Revision: D36915826

fbshipit-source-id: e60d5ed19314878f57fed8479faf11f31f5f520d

Author: Wilfred

hphp/hack/src/typing/nast_check/unbound_name_check.ml

@@ -336,7 +336,7 @@ let handler ctx =
       let () =
         check_type_name
           env
-          ~allow_typedef:true
+          ~allow_typedef:false
           ~allow_generics:false
           ~kind:Name_context.ClassContext
           id

hphp/hack/test/typecheck/catch_alias.php

@@ -0,0 +1,12 @@
+<?hh
+
+type ExceptionAlias = Exception;
+
+<<__EntryPoint>>
+function my_main(): void {
+  try {
+    throw new Exception();
+  } catch (ExceptionAlias $a) {
+    echo "never executed";
+  }
+}

hphp/hack/test/typecheck/catch_alias.php.exp

@@ -0,0 +1,4 @@
+File "catch_alias.php", line 9, characters 12-25:
+Expected a `class` but got a type alias. (Naming[2052])
+  File "catch_alias.php", line 3, characters 6-19:
+  Alias definition is here.

hphp/hack/test/typecheck/catch_newtype.php

@@ -0,0 +1,12 @@
+<?hh
+
+newtype ExceptionAlias = Exception;
+
+<<__EntryPoint>>
+function my_main(): void {
+  try {
+    throw new Exception();
+  } catch (ExceptionAlias $a) {
+    echo "never executed";
+  }
+}

hphp/hack/test/typecheck/catch_newtype.php.exp

@@ -0,0 +1,4 @@
+File "catch_newtype.php", line 9, characters 12-25:
+Expected a `class` but got a type alias. (Naming[2052])
+  File "catch_newtype.php", line 3, characters 9-22:
+  Alias definition is here.

hphp/hack/test/typecheck/unbound_name/catch.php.exp

@@ -1,3 +1,7 @@
+File "catch.php", line 15, characters 10-14:
+Expected a `class` but got a type alias. (Naming[2052])
+  File "catch.php", line 5, characters 6-10:
+  Alias definition is here.
 File "catch.php", line 21, characters 10-26:
 Unbound name: `NotFoundException` (an object type) (Naming[2049])
 File "catch.php", line 27, characters 10-10: