Build POISON_MARKER and TANY_MARKER

Summary:
We introduce two new type aliases to the `HH\FIXME` namespace such that

| Alias | Current Value | Sound Dynamic Value |
| -- | -- | -- |
| POISON_MARKER<T> | T | ~T |
| TANY_MARKER<T> | Tany | T |

> NOTE: in the examples below, commented out method declarations represent the code before migration.

`POISON_MARKER` will be used for hierarchy poisoning when an unenforceable type overrides an enforced one e.g. a closure

```
class C {
  // public function f(): nonnull {}
  public function f(): HH\FIXME\POISON_MARKER<nonnull> {}
}
class D extends C {
  public function f(): (function (): void) {
    /* HH_FIXME[4110] */
    return null;
  }
}

/**
 * POISON_MARKER will retain current behavior -- expression has type nonnull
 * but will become ~nonnull under sound dynamic
 */
function get_nonnull(C $c): nonnull {
  return $c->f(); // type hint violation, returning null
}
function test(): void {
  get_nonnull(new D());
}
```

`TANY_MARKER` will be used for migrating existing uses of Tany to desired types under sound dynamic without affecting current inference. This is why it points to `T` and not `~T` -- we want full manual control here. In some cases we may want a combination of TANY_MARKER and POISON_MARKER.
```
class C {
  // public function f(): int {
  public function f(): HH\FIXME\POISON_MARKER<arraykey> { // slightly weaken enforcement
    return 1;
  }
}
class D extends C {
  // public function f(): DECL_TANY {
  public function f(): HH\FIXME\TANY_MARKER<string> {
    return "hello";
  }
}
class E extends D {
  public function f(): string {
    return "hello";
  }
}
```

## Implementation
There is some sleight of hand here - despite outward appearance, the implementation of these aliases diverges.
- For `POISON_MARKER`, I've stripped off the alias for both type constraints and type structures, now matches like types in hint positions and almost matches for type structures (see test cases). The upshot is the runtime doesn't know about POISON_MARKER's existence.
- For `TANY_MARKER`, I strip off the type arguments to simulate how we do decl Tanys, but HHVM still needs to have the symbol name in scope to create the OF_GENERIC type structure, so it's declared in systemlib. See the `tany.php` example from D40516837 (9e8c173) for an analogue.

Reviewed By: andrewjkennedy

Differential Revision: D40371013

fbshipit-source-id: d2d9e4f4d57f6f88d1c31201d60d9c9e19656173

hphp/hack/hhi/soundness.hhi

@@ -46,3 +46,8 @@ function UNSAFE_CAST<<<__Explicit>> Tin, <<__Explicit>> Tout>(Tin $t, ?\HH\Forma
  * ```
  */
 function UNSAFE_NONNULL_CAST<T as nonnull>(?T $t, ?\HH\FormatString<nothing> $msg = null)[]: T;
+
+/* Acts as Tany under current semantics, and T under sound dynamic */
+type TANY_MARKER<T> = T;
+/* Acts as T under current semantics, and ~T under sound dynamic */
+type POISON_MARKER<T> = T;

hphp/hack/src/hackc/emitter/emit_type_constant.rs

@@ -12,6 +12,7 @@ use hhbc::TypedValue;
 use hhbc_string_utils as string_utils;
 use hhvm_types_ffi::ffi::TypeStructureKind;
 use naming_special_names_rust::classes;
+use naming_special_names_rust::typehints;
 use options::Options;
 use oxidized::aast;
 use oxidized::aast_defs;
@@ -287,6 +288,20 @@ fn hint_to_type_constant_list<'arena>(
                     ]);
                 }
             }
+            let hints = match &hints[..] {
+                [h] if name == typehints::POISON_MARKER => {
+                    return hint_to_type_constant_list(
+                        alloc,
+                        opts,
+                        tparams,
+                        targ_map,
+                        type_refinement_in_hint,
+                        h,
+                    );
+                }
+                [_h] if name == typehints::TANY_MARKER => <&[Hint]>::default(),
+                _ => hints,
+            };
             let (classname, s_res) = resolve_classname(alloc, tparams, name.to_owned());
             let mut r = bumpalo::vec![in alloc];
             if s_res.eq_ignore_ascii_case("tuple") || s_res.eq_ignore_ascii_case("shape") {

hphp/hack/src/hackc/emitter/emit_type_hint.rs

@@ -285,6 +285,12 @@ fn hint_to_type_constraint<'arena>(
                         _ => hint_to_type_constraint(alloc, kind, tparams, false, &hs[0]),
                     };
                 }
+                [h] if s == typehints::POISON_MARKER => {
+                    return hint_to_type_constraint(alloc, kind, tparams, false, h);
+                }
+                [_h] if s == typehints::TANY_MARKER => {
+                    return Ok(Constraint::default());
+                }
                 _ => {}
             };
             type_application_helper(alloc, tparams, kind, s)?

hphp/hack/src/naming/naming_special_names.ml

@@ -1090,6 +1090,12 @@ module HH = struct
   let contains = "\\HH\\Lib\\C\\contains"
 
   let contains_key = "\\HH\\Lib\\C\\contains_key"
+
+  module FIXME = struct
+    let tTanyMarker = "\\HH\\FIXME\\TANY_MARKER"
+
+    let tPoisonMarker = "\\HH\\FIXME\\POISON_MARKER"
+  end
 end
 
 module Shapes = struct

hphp/hack/src/naming/naming_special_names.rs

@@ -661,6 +661,9 @@ pub mod typehints {
 
     pub const HH_SUPPORTDYN: &str = "\\HH\\supportdyn";
 
+    pub const TANY_MARKER: &str = "\\HH\\FIXME\\TANY_MARKER";
+    pub const POISON_MARKER: &str = "\\HH\\FIXME\\POISON_MARKER";
+
     pub const WILDCARD: &str = "_";
 
     lazy_static! {

hphp/hack/src/typing/typing_phase.ml

@@ -227,6 +227,21 @@ let rec localize ~(ety_env : expand_env) env (dty : decl_ty) =
     when String.equal x Naming_special_names.FB.cIncorrectType
          && Env.is_typedef env x ->
     localize ~ety_env env (mk (get_reason dty, Tlike arg))
+  | Tapply ((_, x), [arg])
+    when String.equal x Naming_special_names.HH.FIXME.tTanyMarker ->
+    if TypecheckerOptions.enable_sound_dynamic (Env.get_tcopt env) then
+      localize ~ety_env env arg
+    else
+      ((env, None), mk (r, Typing_utils.tany env))
+  | Tapply ((_, x), [arg])
+    when String.equal x Naming_special_names.HH.FIXME.tPoisonMarker ->
+    let decl_ty =
+      if TypecheckerOptions.enable_sound_dynamic (Env.get_tcopt env) then
+        mk (get_reason dty, Tlike arg)
+      else
+        arg
+    in
+    localize ~ety_env env decl_ty
   | Tapply (((_p, cid) as cls), argl) ->
     begin
       match Env.get_class_or_typedef env cid with

hphp/hack/test/sound_dynamic/typing/marker_types.good.php

@@ -0,0 +1,13 @@
+<?hh
+
+function f(
+  HH\FIXME\TANY_MARKER<int> $tany,
+  HH\FIXME\POISON_MARKER<string> $poison,
+  vec<HH\FIXME\TANY_MARKER<float>> $vec_float,
+  vec<HH\FIXME\TANY_MARKER<HH\FIXME\POISON_MARKER<float>>> $vec_like_float,
+): void {
+  hh_show($tany);
+  hh_show($poison);
+  hh_show($vec_float);
+  hh_show($vec_like_float);
+}

hphp/hack/test/sound_dynamic/typing/marker_types.good.php.exp

@@ -0,0 +1,9 @@
+File "marker_types.good.php", line 9, characters 3-16:
+  int
+File "marker_types.good.php", line 10, characters 3-18:
+  ~string
+File "marker_types.good.php", line 11, characters 3-21:
+  vec<float>
+File "marker_types.good.php", line 12, characters 3-26:
+  vec<~float>
+No errors

hphp/hack/test/typecheck/sound_dynamic_marker_types.php

@@ -0,0 +1,13 @@
+<?hh
+
+function f(
+  HH\FIXME\TANY_MARKER<int> $tany,
+  HH\FIXME\POISON_MARKER<string> $poison,
+  vec<HH\FIXME\TANY_MARKER<float>> $vec_tany,
+  vec<HH\FIXME\TANY_MARKER<HH\FIXME\POISON_MARKER<float>>> $vec_tany2,
+): void {
+  hh_show($tany);
+  hh_show($poison);
+  hh_show($vec_tany);
+  hh_show($vec_tany2);
+}

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

@@ -0,0 +1,9 @@
+File "sound_dynamic_marker_types.php", line 9, characters 3-16:
+  _
+File "sound_dynamic_marker_types.php", line 10, characters 3-18:
+  string
+File "sound_dynamic_marker_types.php", line 11, characters 3-20:
+  vec<_>
+File "sound_dynamic_marker_types.php", line 12, characters 3-21:
+  vec<_>
+No errors

hphp/hack/test/typecheck/sound_dynamic_marker_types_is_as.php

@@ -0,0 +1,6 @@
+<?hh
+
+function f(): void {
+  3 as HH\FIXME\TANY_MARKER<int>;
+  4 as HH\FIXME\POISON_MARKER<string>;
+}

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

@@ -0,0 +1,8 @@
+File "sound_dynamic_marker_types_is_as.php", line 4, characters 8-32:
+Invalid `as` expression hint (Typing[4195])
+  File "sound_dynamic_marker_types_is_as.php", line 4, characters 8-32:
+  The `as` operator cannot be used with a type with generics, because generics are erased at runtime
+File "sound_dynamic_marker_types_is_as.php", line 5, characters 8-37:
+Invalid `as` expression hint (Typing[4195])
+  File "sound_dynamic_marker_types_is_as.php", line 5, characters 8-37:
+  The `as` operator cannot be used with a type with generics, because generics are erased at runtime

hphp/runtime/ext/hh/ext_hh.php

@@ -571,3 +571,7 @@ function reflection_class_is_interface(
 
 
 }
+
+namespace HH\FIXME {
+  type TANY_MARKER<T> = T;
+}

hphp/test/slow/sound_dynamic/poison_int.php

@@ -0,0 +1,29 @@
+<?hh
+
+function f<reify T>(<<__Soft>> T $t): void {
+  echo "\$t: $t [reified]\n";
+}
+function f_poison(<<__Soft>> HH\FIXME\POISON_MARKER<int> $poison): void {
+  echo "\$poison: $poison\n";
+}
+
+class Typeconsts {
+  const type Tpoison = HH\FIXME\POISON_MARKER<int>;
+}
+
+<<__EntryPoint>>
+function main(): void {
+  printf("\n===== HH\FIXME\POISON_MARKER<int> =====\n");
+  f_poison(4);
+  f_poison("not poison int");
+  f<HH\FIXME\POISON_MARKER<int>>(4);
+  f<HH\FIXME\POISON_MARKER<int>>("not poison int");
+
+  printf("\n===== Typeconsts::Tpoison =====\n");
+  f<Typeconsts::Tpoison>(4);
+  f<Typeconsts::Tpoison>("not poison int [typeconst]");
+
+  $rt = new ReflectionClass(Typeconsts::class)->getTypeConstant("Tpoison");
+  printf("Type structure kind: %d\n", $rt->getTypeStructure()["kind"]);
+  printf("Assigned type text: %s\n", $rt->getAssignedTypeText() ?? "<missing>");
+}

hphp/test/slow/sound_dynamic/poison_int.php.expectf

@@ -0,0 +1,17 @@
+===== HH\FIXME\POISON_MARKER<int> =====
+$poison: 4
+
+Warning: Argument 1 to f_poison() must be of type @int, string given in %s/test/slow/sound_dynamic/poison_int.php on line 18
+$poison: not poison int
+$t: 4 [reified]
+
+Warning: Argument 1 passed to f() must be an instance of @int, string given in %s/test/slow/sound_dynamic/poison_int.php on line 5
+$t: not poison int [reified]
+
+===== Typeconsts::Tpoison =====
+$t: 4 [reified]
+
+Warning: Argument 1 passed to f() must be an instance of @int, string given in %s/test/slow/sound_dynamic/poison_int.php on line 5
+$t: not poison int [typeconst] [reified]
+Type structure kind: 1
+Assigned type text: HH\int

hphp/test/slow/sound_dynamic/tany_int.php

@@ -0,0 +1,29 @@
+<?hh
+
+function f<reify T>(<<__Soft>> T $t): void {
+  echo "\$t: $t [reified]\n";
+}
+function f_tany_int(<<__Soft>> HH\FIXME\TANY_MARKER<int> $tany_int): void {
+  echo "\$tany_int: $tany_int\n";
+}
+
+class Typeconsts {
+  const type Tany_int = HH\FIXME\TANY_MARKER<int>;
+}
+
+<<__EntryPoint>>
+function main(): void {
+  printf("\n===== HH\FIXME\TANY_MARKER<int> =====\n");
+  f_tany_int(4);
+  f_tany_int("not Tany int");
+  f<HH\FIXME\TANY_MARKER<int>>(4);
+  f<HH\FIXME\TANY_MARKER<int>>("not Tany int");
+
+  printf("\n===== Typeconsts::Tany_int =====\n");
+  f<Typeconsts::Tany_int>(4);
+  f<Typeconsts::Tany_int>("not Tany int [typeconst]");
+
+  $rt = new ReflectionClass(Typeconsts::class)->getTypeConstant("Tany_int");
+  printf("Type structure kind: %d\n", $rt->getTypeStructure()["kind"]);
+  printf("Assigned type text: %s\n", $rt->getAssignedTypeText() ?? "<missing>");
+}

hphp/test/slow/sound_dynamic/tany_int.php.expect

@@ -0,0 +1,11 @@
+===== HH\FIXME\TANY_MARKER<int> =====
+$tany_int: 4
+$tany_int: not Tany int
+$t: 4 [reified]
+$t: not Tany int [reified]
+
+===== Typeconsts::Tany_int =====
+$t: 4 [reified]
+$t: not Tany int [typeconst] [reified]
+Type structure kind: 13
+Assigned type text: HH\FIXME\TANY_MARKER