Special case typing of top-level function- and static method pointers

Summary:
The treatment of function pointers to top-level function and static methods is baked into the lowering of expression trees. The new typing as first-class polymorphic functions introduces two issues:

1) Inference behavior is changed meaning we need hints in many places we didn't before

2) Type checking performance degrades for very complex expression tree blocks

This diff adds a flag to the funciton pointer AST nodes and modifies typing so that we instantiate polymorphic function types when they were generated during lowering.

Reviewed By: andrewjkennedy

Differential Revision: D85429843

fbshipit-source-id: 9772b6fb3c31a6b5f25dc8cb72df7db5deeecfde

Author: Michael Thomas

hphp/hack/src/annotated_ast/aast_defs.ml

@@ -528,7 +528,8 @@ and ('ex, 'en) expr_ =
        *     async { return 1; }
        *     // lowered to:
        *     (async () ==> { return 1; })() *)
-  | FunctionPointer of ('ex, 'en) function_ptr_id * 'ex targ list
+  | FunctionPointer of
+      ('ex, 'en) function_ptr_id * 'ex targ list * function_pointer_source
       (** A reference to a function or method.
        *
        *     foo_fun<>
@@ -791,6 +792,10 @@ and hole_source =
   | UnsafeNonnullCast
   | EnforcedCast of hint list
 
+and function_pointer_source =
+  | Code
+  | Lowered
+
 and ('ex, 'en) binop = {
   bop: Ast_defs.bop; [@transform.opaque]
   lhs: ('ex, 'en) expr; [@transform.explicit]

hphp/hack/src/client_and_server/identifySymbolService.ml

@@ -379,9 +379,9 @@ let visitor =
           let class_id = process_class_id cid in
           let xhp_attributes = process_xml_attrs (snd cid) attrs in
           self#plus class_id xhp_attributes
-        | Aast.FunctionPointer (Aast.FP_id id, _targs) -> process_fun_id id
-        | Aast.FunctionPointer (Aast.FP_class_const ((ty, _, _cid), mid), _targs)
-          ->
+        | Aast.FunctionPointer (Aast.FP_id id, _targs, _) -> process_fun_id id
+        | Aast.FunctionPointer
+            (Aast.FP_class_const ((ty, _, _cid), mid), _targs, _) ->
           typed_method env ty mid
         | Aast.Method_caller (((_, cid) as pcid), mid) ->
           process_fun_id (pos, SN.AutoimportedFunctions.meth_caller)

hphp/hack/src/client_and_server/serverFunDepsBatch.ml

@@ -92,8 +92,9 @@ let collect_in_decl =
         | T.Method_caller ((p, cid), mid) ->
           process_function (p, SN.AutoimportedFunctions.meth_caller)
           + process_method_cid mid cid
-        | T.FunctionPointer (T.FP_id id, _targs) -> process_function id
-        | T.FunctionPointer (T.FP_class_const ((ty, _, _cid), mid), _targs) ->
+        | T.FunctionPointer (T.FP_id id, _targs, _) -> process_function id
+        | T.FunctionPointer (T.FP_class_const ((ty, _, _cid), mid), _targs, _)
+          ->
           process_method env ty mid
         | _ -> self#zero
       in

hphp/hack/src/elab/pass.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<<9f71ac8f6616bafee402c8b82064b9d5>>
+// @generated SignedSource<<6eac454cb9cb6efbd8d67a1e59cad6fb>>
 //
 // To regenerate this file, run:
 //   buck run @fbcode//mode/dev-nosan-lg fbcode//hphp/hack/src:oxidized_regen
@@ -288,6 +288,22 @@ pub trait Pass: PassClone {
         Continue(())
     }
     #[inline(always)]
+    fn on_ty_function_pointer_source_top_down(
+        &mut self,
+        env: &Env,
+        elem: &mut FunctionPointerSource,
+    ) -> ControlFlow<()> {
+        Continue(())
+    }
+    #[inline(always)]
+    fn on_ty_function_pointer_source_bottom_up(
+        &mut self,
+        env: &Env,
+        elem: &mut FunctionPointerSource,
+    ) -> ControlFlow<()> {
+        Continue(())
+    }
+    #[inline(always)]
     fn on_ty_binop_top_down(&mut self, env: &Env, elem: &mut Binop<Ex, En>) -> ControlFlow<()> {
         Continue(())
     }
@@ -1780,6 +1796,28 @@ impl Pass for Passes {
         Continue(())
     }
     #[inline(always)]
+    fn on_ty_function_pointer_source_top_down(
+        &mut self,
+        env: &Env,
+        elem: &mut FunctionPointerSource,
+    ) -> ControlFlow<()> {
+        for pass in &mut self.passes {
+            pass.on_ty_function_pointer_source_top_down(env, elem)?;
+        }
+        Continue(())
+    }
+    #[inline(always)]
+    fn on_ty_function_pointer_source_bottom_up(
+        &mut self,
+        env: &Env,
+        elem: &mut FunctionPointerSource,
+    ) -> ControlFlow<()> {
+        for pass in &mut self.passes {
+            pass.on_ty_function_pointer_source_bottom_up(env, elem)?;
+        }
+        Continue(())
+    }
+    #[inline(always)]
     fn on_ty_binop_top_down(&mut self, env: &Env, elem: &mut Binop<Ex, En>) -> ControlFlow<()> {
         for pass in &mut self.passes {
             pass.on_ty_binop_top_down(env, elem)?;

hphp/hack/src/elab/transform.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<<7a60ba5cdc7ba5e7590c4c75178f01a5>>
+// @generated SignedSource<<3af89af5cb694a41535c3f5734aec361>>
 //
 // To regenerate this file, run:
 //   buck run @fbcode//mode/dev-nosan-lg fbcode//hphp/hack/src:oxidized_regen
@@ -762,6 +762,22 @@ impl Transform for HoleSource {
         }
     }
 }
+impl Transform for FunctionPointerSource {
+    fn transform(&mut self, env: &Env, pass: &mut (impl Pass + Clone)) {
+        let mut in_pass = pass.clone();
+        if let Break(..) = pass.on_ty_function_pointer_source_top_down(env, self) {
+            return;
+        }
+        stack_limit::maybe_grow(|| self.traverse(env, pass));
+        let _ = in_pass.on_ty_function_pointer_source_bottom_up(env, self);
+    }
+    fn traverse(&mut self, env: &Env, pass: &mut (impl Pass + Clone)) {
+        match self {
+            FunctionPointerSource::Code => {}
+            FunctionPointerSource::Lowered => {}
+        }
+    }
+}
 impl Transform for Binop {
     fn transform(&mut self, env: &Env, pass: &mut (impl Pass + Clone)) {
         let mut in_pass = pass.clone();

hphp/hack/src/hackc/print_expr/print.rs

@@ -635,7 +635,7 @@ fn print_expr(
         }
         Expr_::Efun(f) => print_efun(ctx, w, env, f),
         Expr_::FunctionPointer(fp) => {
-            let (fp_id, targs) = &**fp;
+            let (fp_id, targs, _) = &**fp;
             match fp_id {
                 ast::FunctionPtrId::FPId(ast::Id(_, sid)) => {
                     w.write_all(lstrip(adjust_id(env, sid).as_ref(), "\\").as_bytes())?

hphp/hack/src/naming/elaborate_namespaces_visitor.rs

@@ -400,7 +400,7 @@ impl<'ast> VisitorMut<'ast> for ElaborateNamespacesVisitor {
                     func.accept(env, self.object())?;
                 }
             }
-            Expr_::FunctionPointer(box (fpid, targs)) => {
+            Expr_::FunctionPointer(box (fpid, targs, _)) => {
                 if let Some(sid) = fpid.as_fpid_mut() {
                     namespaces::elaborate_id(&env.namespace, namespaces::ElaborateKind::Fun, sid);
                 } else if let Some(cc) = fpid.as_fpclass_const_mut() {

hphp/hack/src/naming/naming_elab_dynamic_class_name.ml

@@ -59,7 +59,7 @@ let on_expr on_error ((ex, pos, expr_) as expr) ~ctx =
         Err.naming @@ Naming_error.Dynamic_class_name_in_strict_mode cg_pos
       in
       Error [err]
-    | Aast.(FunctionPointer (FP_class_const ((_, _, ci), _), _))
+    | Aast.(FunctionPointer (FP_class_const ((_, _, ci), _), _, _))
       when is_dynamic ci ->
       (* TODO[mjt] report error in strict mode *)
       Error []

hphp/hack/src/naming/naming_elaborate_namespaces_endo.ml

@@ -320,17 +320,20 @@ class ['a, 'b, 'c, 'd] generic_elaborator =
             }
         in
         handle_meth_caller env renamed_call
-      | FunctionPointer (FP_id fn, targs) ->
+      | FunctionPointer (FP_id fn, targs, source) ->
         let fn = NS.elaborate_id env.namespace NS.ElaborateFun fn in
         let targs = List.map targs ~f:(self#on_targ env) in
-        FunctionPointer (FP_id fn, targs)
+        FunctionPointer (FP_id fn, targs, source)
       | FunctionPointer
-          (FP_class_const (((), p1, CIexpr ((), p2, Id x1)), meth_name), targs)
-        ->
+          ( FP_class_const (((), p1, CIexpr ((), p2, Id x1)), meth_name),
+            targs,
+            source ) ->
         let name = elaborate_type_name env x1 in
         let targs = List.map targs ~f:(self#on_targ env) in
         FunctionPointer
-          (FP_class_const (((), p1, CIexpr ((), p2, Id name)), meth_name), targs)
+          ( FP_class_const (((), p1, CIexpr ((), p2, Id name)), meth_name),
+            targs,
+            source )
       | Obj_get (e1, (ty, p, Id x), null_safe, in_parens) ->
         Obj_get (self#on_expr env e1, (ty, p, Id x), null_safe, in_parens)
       | Id ((_, name) as sid) ->

hphp/hack/src/naming/nast.ml

@@ -835,7 +835,7 @@ module Visitor_DEPRECATED = struct
         | Class_const (cid, id) -> this#on_class_const acc cid id
         | Call { func = e; args = el; unpacked_arg; _ } ->
           this#on_call acc e el unpacked_arg
-        | FunctionPointer (fpid, targs) ->
+        | FunctionPointer (fpid, targs, _) ->
           this#on_function_pointer acc fpid targs
         | String2 el -> this#on_string2 acc el
         | PrefixedString (_, e) -> this#on_expr acc e