feat: uncurry 0

Changes.md

@@ -139,6 +139,12 @@ Unreleased
   ([#1017](https://github.com/melange-re/melange/pull/1017))
 - BREAKING(core): only allow strings in `{j| ... |j}` interpolation
   ([#1024](https://github.com/melange-re/melange/pull/1024))
+- BREAKING(ppx): use `[@u0]` for 0-arity uncurried application instead of `()`
+  ([#949](https://github.com/melange-re/melange/pull/949))
+    - Melange wouldn't previously allow to invoke a 1-argument uncurried
+      function with `()` (`unit`). After this change, 0-arity functions must be
+      applied with `[@u0]`. Melange will issue an alert if old 0-arity
+      functions are applied with `[@u]` to help upgrade codebases.
 
 2.2.0 2023-12-05
 ---------------

jscomp/others/node_fs.ml

@@ -67,7 +67,7 @@ module Watch = struct
     f:
       ([ `change of
          (string (*eventType*) -> Node.string_buffer (* filename *) -> unit[@u])
-       | `error of (unit -> unit[@u]) ]
+       | `error of (unit -> unit[@u0]) ]
       [@mel.string]) ->
     t = "on"
   [@@mel.send]

jscomp/runtime/caml_external_polyfill.ml

@@ -28,7 +28,7 @@ open struct
   module Js = Js_internal
 end
 
-let getGlobalThis : (unit -> global[@u]) =
+let getGlobalThis : (unit -> global[@u0]) =
   [%raw
     {| function(){
   if (typeof globalThis !== 'undefined') return globalThis;

jscomp/stdlib/camlinternalLazy.ml

@@ -36,8 +36,8 @@ type 'a concrete = {
 
 exception Undefined
 
-external fnToVal : (unit -> 'a [@u]) -> 'a = "%identity"
-external valToFn :  'a -> (unit -> 'a [@u])  = "%identity"
+external fnToVal : (unit -> 'a [@u0]) -> 'a = "%identity"
+external valToFn :  'a -> (unit -> 'a [@u0])  = "%identity"
 external castToConcrete : 'a lazy_t -> 'a concrete   = "%identity"
 external of_concrete : 'a concrete -> 'a lazy_t   = "%identity"
 
@@ -46,15 +46,15 @@ let is_val (type a ) (l : a lazy_t) : bool =
 
 
 
-let forward_with_closure (type a ) (blk : a concrete) (closure : unit -> a [@u]) : a =
-  let result = closure () [@u] in
+let forward_with_closure (type a ) (blk : a concrete) (closure : unit -> a [@u0]) : a =
+  let result = closure () [@u0] in
   (* do set_field BEFORE set_tag *)
   blk.value <- result;
   blk.tag<- true;
   result
 
 
-let raise_undefined =  (fun [@u] () -> raise Undefined)
+let raise_undefined =  (fun [@u0] () -> raise Undefined)
 
 (* Assume [blk] is a block with tag lazy *)
 let force_lazy_block (type a ) (blk : a t) : a  =
@@ -64,7 +64,7 @@ let force_lazy_block (type a ) (blk : a t) : a  =
   try
     forward_with_closure blk closure
   with e ->
-    blk.value <- fnToVal (fun [@u] () -> raise e);
+    blk.value <- fnToVal (fun [@u0] () -> raise e);
     raise e
 
 

jscomp/test/demo.ml

@@ -94,7 +94,7 @@ let ui_layout
       with  e -> ()
     end;
     let fmt v = toFixed v 2 in
-    set_interval (fun [@u] () ->
+    set_interval (fun [@u0] () ->
 
       grid##dataSource #=
         ( array_map data (fun [@u] {ticker; price } ->

jscomp/test/demo_binding.ml

@@ -102,7 +102,7 @@ class type textArea =
   end[@u]
 
 
-external set_interval : (unit -> unit [@u]) -> float -> unit  =  "setInterval"
+external set_interval : (unit -> unit [@u0]) -> float -> unit  =  "setInterval"
      [@@mel.module "@runtime", "Runtime"]
 
 external toFixed : float -> int -> string = "toFixed" [@@mel.send]