Add projection reason for rewriting class<T> to classname<T>

Summary: Closes the TODOs in typing_subtype around rewriting -- this allows us to trace exposure of `class<C>` types to `classname` and other string-coercing points.

Reviewed By: enetsee

Differential Revision: D66132800

fbshipit-source-id: cb09bb31616bf89f18de86dda286d1bf0d647913

hphp/hack/src/oxidized/gen/typing_reason.rs

@@ -3,7 +3,7 @@
 // This source code is licensed under the MIT license found in the
 // LICENSE file in the "hack" directory of this source tree.
 //
-// @generated SignedSource<<2337a3a78f206543dedb8ac5ada2a89d>>
+// @generated SignedSource<<d4d3ae5e8bc4721b490313db730102fd>>
 //
 // To regenerate this file, run:
 //   hphp/hack/src/oxidized_regen.sh
@@ -310,6 +310,8 @@ pub enum PrjAsymm {
     PrjAsymmArraykey,
     #[rust_to_ocaml(name = "Prj_asymm_num")]
     PrjAsymmNum,
+    #[rust_to_ocaml(name = "Prj_rewrite_classname")]
+    PrjRewriteClassname,
 }
 impl TrivialDrop for PrjAsymm {}
 arena_deserializer::impl_deserialize_in_arena!(PrjAsymm);

hphp/hack/src/oxidized_by_ref/decl_visitor/node_impl_gen.rs

@@ -3,7 +3,7 @@
 // This source code is licensed under the MIT license found in the
 // LICENSE file in the "hack" directory of this source tree.
 //
-// @generated SignedSource<<697117f438c1d0dc72305e8d9a2862ca>>
+// @generated SignedSource<<32e6ae4375299e5a185a8ebc19c7a465>>
 //
 // To regenerate this file, run:
 //   hphp/hack/src/oxidized_regen.sh
@@ -1630,6 +1630,7 @@ impl<'a> Node<'a> for PrjAsymm {
             PrjAsymm::PrjAsymmNullable => {}
             PrjAsymm::PrjAsymmArraykey => {}
             PrjAsymm::PrjAsymmNum => {}
+            PrjAsymm::PrjRewriteClassname => {}
         }
     }
 }

hphp/hack/src/typing/typing_reason.ml

@@ -255,6 +255,7 @@ type prj_asymm =
   | Prj_asymm_nullable
   | Prj_asymm_arraykey
   | Prj_asymm_num
+  | Prj_rewrite_classname
 [@@deriving hash]
 
 let prj_asymm_to_json = function
@@ -264,6 +265,7 @@ let prj_asymm_to_json = function
   | Prj_asymm_nullable -> Hh_json.JSON_String "Prj_asymm_nullable"
   | Prj_asymm_arraykey -> Hh_json.JSON_String "Prj_asymm_arraykey"
   | Prj_asymm_num -> Hh_json.JSON_String "Prj_asymm_num"
+  | Prj_rewrite_classname -> Hh_json.JSON_String "Prj_rewrite_classname"
 
 (* ~~ Flow kinds ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ *)
 
@@ -2745,6 +2747,9 @@ module Constructors = struct
   let prj_arraykey_super ~super ~super_prj =
     prj_asymm_super ~super ~super_prj Prj_asymm_arraykey
 
+  let prj_rewrite_classname ~sub ~sub_prj =
+    prj_asymm_sub ~sub ~sub_prj Prj_rewrite_classname
+
   let missing_field = Missing_field
 
   let pessimised_this p = from_witness_decl @@ Pessimised_this p
@@ -3262,6 +3267,8 @@ module Derivation = struct
         "The subtype is an arraykey type so next I checked the subtype constraint is satisfied for both the int and string parts."
       | Prj_asymm_neg ->
         "The subtype is a negated type so next I checked the inner type."
+      | Prj_rewrite_classname ->
+        "The subtype is a class<T> type and the supertype might be classname<T> or one of its supertypes, so next I checked the constraint with the subtype rewritten to classname<T>."
 
     let explain_prj_asymm_super prj =
       match prj with
@@ -3277,6 +3284,8 @@ module Derivation = struct
         "The supertype is an arraykey type so next I checked the subtype constraint is satisfied for either the int or string part."
       | Prj_asymm_neg ->
         "The supertype is a negated type so I checked the inner type."
+      | Prj_rewrite_classname ->
+        failwith "The rewrites only happen for the subtype"
 
     let explain = function
       | Using_prj prj -> explain_prj prj

hphp/hack/src/typing/typing_reason.mli

@@ -573,6 +573,12 @@ val prj_arraykey_sub :
 val prj_arraykey_super :
   super:locl_phase t_ -> super_prj:locl_phase t_ -> locl_phase t_
 
+(** Record the rewrite of a subtype constraint between a class<T> type in the
+    subtype position and a string-ish type in the supertype position to
+    classname<T> <: Tsuper *)
+val prj_rewrite_classname :
+  sub:locl_phase t_ -> sub_prj:locl_phase t_ -> locl_phase t_
+
 val missing_field : t
 
 val pessimised_this : Pos_or_decl.t -> 'phase t_

hphp/hack/src/typing/typing_subtype.ml

@@ -3171,32 +3171,32 @@ end = struct
            && is_nonexact exact_super
            && (String.equal class_nm_super SN.Classes.cXHPChild
               || String.equal class_nm_super SN.Classes.cStringish) ->
-      (* TODO(T199610905) replace reason with upcoming rewrite reasons *)
+      let ty_classname = MakeType.classname r_sub [ty_sub] in
+      let t =
+        Typing_env.update_reason env ty_classname ~f:(fun r_sub_prj ->
+            Typing_reason.prj_rewrite_classname ~sub:r_sub ~sub_prj:r_sub_prj)
+      in
       simplify
         ~subtype_env
         ~this_ty
-        ~lhs:{ sub_supportdyn; ty_sub = MakeType.classname r_sub [ty_sub] }
+        ~lhs:{ sub_supportdyn; ty_sub = t }
         ~rhs:{ super_like; super_supportdyn; ty_super }
         env
     (* -- Rewrite: class<T> <: N ---> classname<T> <: N
           instead of e.g. considering class<T> as an element in a case type *)
     | ((r_sub, Tclass_ptr ty_sub), (_r_super, Tnewtype _))
-      when TypecheckerOptions.class_sub_classname env.genv.tcopt ->
-      (* TODO(T199610905) replace reason with upcoming rewrite reasons *)
-      simplify
-        ~subtype_env
-        ~this_ty
-        ~lhs:{ sub_supportdyn; ty_sub = MakeType.classname r_sub [ty_sub] }
-        ~rhs:{ super_like; super_supportdyn; ty_super }
-        env
     (* -- Rewrite: class<T> <: prim ---> classname<T> <: prim *)
     | ((r_sub, Tclass_ptr ty_sub), (_r_super, Tprim _))
       when TypecheckerOptions.class_sub_classname env.genv.tcopt ->
-      (* TODO(T199610905) replace reason with upcoming rewrite reasons *)
+      let ty_classname = MakeType.classname r_sub [ty_sub] in
+      let t =
+        Typing_env.update_reason env ty_classname ~f:(fun r_sub_prj ->
+            Typing_reason.prj_rewrite_classname ~sub:r_sub ~sub_prj:r_sub_prj)
+      in
       simplify
         ~subtype_env
         ~this_ty
-        ~lhs:{ sub_supportdyn; ty_sub = MakeType.classname r_sub [ty_sub] }
+        ~lhs:{ sub_supportdyn; ty_sub = t }
         ~rhs:{ super_like; super_supportdyn; ty_super }
         env
     (* -- C-Var-R ----------------------------------------------------------- *)

hphp/hack/test/extended_reasons/class_pointers/class_expr_classname.php.exp

@@ -44,7 +44,7 @@ File class_expr_classname.php, line 6, character 58 - line 6, character 58:
 Here's why:
 
 
-  Step 1 of 4                                                                   
+  Step 1 of 5                                                                   
 
 I started by checking this subtype relationship.
 
@@ -122,7 +122,7 @@ File class_expr_classname.php, line 8, character 29 - line 8, character 31:
 11 | }
 
 
-  Step 2 of 4                                                                   
+  Step 2 of 5                                                                   
 
 The subtype is a union type so next I checked the subtype constraint is satisfied for all its elements.
 
@@ -184,7 +184,69 @@ File class_expr_classname.php, line 8, character 29 - line 8, character 31:
 11 | }
 
 
-  Step 3 of 4                                                                   
+  Step 3 of 5                                                                   
+
+The subtype is a class<T> type and the supertype might be classname<T> or one of its supertypes, so next I checked the constraint with the subtype rewritten to classname<T>.
+
+The subtype comes from this generic parameter T of generic_classname
+
+File class_expr_classname.php, line 9, character 9 - line 9, character 25:
+
+ 6 | function generic_classname<T as classname<mixed>>(T $t): T { return $t; }
+ 7 | 
+ 8 | function test(class<C> $c): int {
+ 9 |   $gc = »generic_classname«($c);
+10 |   return $gc;
+11 | }
+
+and flows into this hint
+
+File class_expr_classname.php, line 6, character 58 - line 6, character 58:
+
+ 5 | class C {}
+ 6 | function generic_classname<T as classname<mixed>>(T $t): »T« { return $t; }
+ 7 | 
+ 8 | function test(class<C> $c): int {
+ 9 |   $gc = generic_classname($c);
+
+as the instantiation of the generic T
+
+which I solved to this generic parameter T of generic_classname
+
+File class_expr_classname.php, line 9, character 9 - line 9, character 25:
+
+ 6 | function generic_classname<T as classname<mixed>>(T $t): T { return $t; }
+ 7 | 
+ 8 | function test(class<C> $c): int {
+ 9 |   $gc = »generic_classname«($c);
+10 |   return $gc;
+11 | }
+
+and flows into this hint
+
+File class_expr_classname.php, line 6, character 51 - line 6, character 51:
+
+ 5 | class C {}
+ 6 | function generic_classname<T as classname<mixed>>(»T« $t): T { return $t; }
+ 7 | 
+ 8 | function test(class<C> $c): int {
+ 9 |   $gc = generic_classname($c);
+
+as the instantiation of the generic T
+
+The supertype is the same as before.
+
+File class_expr_classname.php, line 8, character 29 - line 8, character 31:
+
+ 6 | function generic_classname<T as classname<mixed>>(T $t): T { return $t; }
+ 7 | 
+ 8 | function test(class<C> $c): »int« {
+ 9 |   $gc = generic_classname($c);
+10 |   return $gc;
+11 | }
+
+
+  Step 4 of 5                                                                   
 
 The subtype declares an upper bound so next I checked that was a subtype of the supertype.
 
@@ -246,7 +308,7 @@ File class_expr_classname.php, line 8, character 29 - line 8, character 31:
 11 | }
 
 
-  Step 4 of 4                                 (here is where the error occurred) 
+  Step 5 of 5                                 (here is where the error occurred) 
 
 The subtype declares an upper bound so next I checked that was a subtype of the supertype.
 

hphp/hack/test/extended_reasons/class_pointers/class_expr_string.php.exp

@@ -47,7 +47,7 @@ File class_expr_string.php, line 6, character 45 - line 6, character 45:
 Here's why:
 
 
-  Step 1 of 4                                                                   
+  Step 1 of 5                                                                   
 
 I started by checking this subtype relationship.
 
@@ -127,7 +127,7 @@ File class_expr_string.php, line 8, character 18 - line 8, character 20:
 11 | }
 
 
-  Step 2 of 4                                                                   
+  Step 2 of 5                                                                   
 
 The subtype is a union type so next I checked the subtype constraint is satisfied for all its elements.
 
@@ -193,7 +193,73 @@ File class_expr_string.php, line 8, character 18 - line 8, character 20:
 11 | }
 
 
-  Step 3 of 4                                                                   
+  Step 3 of 5                                                                   
+
+The subtype is a class<T> type and the supertype might be classname<T> or one of its supertypes, so next I checked the constraint with the subtype rewritten to classname<T>.
+
+The subtype comes from this generic parameter T of generic_string
+
+File class_expr_string.php, line 9, character 9 - line 9, character 22:
+
+ 6 | function generic_string<T as string>(T $t): T { return $t; }
+ 7 | 
+ 8 | function test(): int {
+ 9 |   $gc = »generic_string«(C::class);
+10 |   return $gc;
+11 | }
+
+and flows into this hint
+
+File class_expr_string.php, line 6, character 45 - line 6, character 45:
+
+ 3 | <<file:__EnableUnstableFeatures('class_type')>>
+ 4 | 
+ 5 | class C {}
+ 6 | function generic_string<T as string>(T $t): »T« { return $t; }
+ 7 | 
+ 8 | function test(): int {
+ 9 |   $gc = generic_string(C::class);
+
+as the instantiation of the generic T
+
+which I solved to this generic parameter T of generic_string
+
+File class_expr_string.php, line 9, character 9 - line 9, character 22:
+
+ 6 | function generic_string<T as string>(T $t): T { return $t; }
+ 7 | 
+ 8 | function test(): int {
+ 9 |   $gc = »generic_string«(C::class);
+10 |   return $gc;
+11 | }
+
+and flows into this hint
+
+File class_expr_string.php, line 6, character 38 - line 6, character 38:
+
+ 3 | <<file:__EnableUnstableFeatures('class_type')>>
+ 4 | 
+ 5 | class C {}
+ 6 | function generic_string<T as string>(»T« $t): T { return $t; }
+ 7 | 
+ 8 | function test(): int {
+ 9 |   $gc = generic_string(C::class);
+
+as the instantiation of the generic T
+
+The supertype is the same as before.
+
+File class_expr_string.php, line 8, character 18 - line 8, character 20:
+
+ 6 | function generic_string<T as string>(T $t): T { return $t; }
+ 7 | 
+ 8 | function test(): »int« {
+ 9 |   $gc = generic_string(C::class);
+10 |   return $gc;
+11 | }
+
+
+  Step 4 of 5                                                                   
 
 The subtype declares an upper bound so next I checked that was a subtype of the supertype.
 
@@ -259,7 +325,7 @@ File class_expr_string.php, line 8, character 18 - line 8, character 20:
 11 | }
 
 
-  Step 4 of 4                                 (here is where the error occurred) 
+  Step 5 of 5                                 (here is where the error occurred) 
 
 The subtype declares an upper bound so next I checked that was a subtype of the supertype.