Remove printing of arrow functions with "multiple" dots (#668)

* Remove printing of arrow functions with "multiple" dots

Arrow functions with multiple dots `(. a, . b) => a + b` are considered an anti-pattern.
This syntax *will be removed* in the future. As a first step, the printer will know print this as multiple arrow functions. (Like in JavaScript)

**Before**
```rescript
let f = (. a, . b) => a + b
type f = (. int, . int) => int
```

**After**
```rescript
let f = (. a) => (. b) => a + b
type f = (. int) => (. int) => int
```

* Remove processing of "res.async" in `arrowType`.

Type expressions can't use the "async" keyword.

* Add Changelog entry for consecutive arrow function printing

Co-authored-by: Maxim <mvalcke@hubspot.com>

Author: IwanKaramazow

CHANGELOG.md

@@ -35,6 +35,10 @@
 - Fix issue where formatter erases tail comments inside JSX tag https://github.com/rescript-lang/syntax/issues/663
 - Fix issue where the JSX prop has type annotation of the first class module https://github.com/rescript-lang/syntax/pull/666
 
+#### :eyeglasses: Spec Compliance
+
+- Functions with consecutive dots now print as multiple arrow functions like in JavaScript.
+
 ## ReScript 10.0
 
 - Fix printing for inline nullary functor types [#477](https://github.com/rescript-lang/syntax/pull/477)

src/res_parsetree_viewer.ml

@@ -10,11 +10,12 @@ let arrowType ct =
       let arg = ([], lbl, typ1) in
       process attrsBefore (arg :: acc) typ2
     | {
-     ptyp_desc = Ptyp_arrow ((Nolabel as lbl), typ1, typ2);
-     ptyp_attributes = [({txt = "bs" | "res.async"}, _)] as attrs;
+     ptyp_desc = Ptyp_arrow (Nolabel, _typ1, _typ2);
+     ptyp_attributes = [({txt = "bs"}, _)];
     } ->
-      let arg = (attrs, lbl, typ1) in
-      process attrsBefore (arg :: acc) typ2
+      (* stop here, the uncurried attribute always indicates the beginning of an arrow function
+         * e.g. `(. int) => (. int)` instead of `(. int, . int)` *)
+      (attrsBefore, List.rev acc, typ)
     | {ptyp_desc = Ptyp_arrow (Nolabel, _typ1, _typ2); ptyp_attributes = _attrs}
       as returnType ->
       let args = List.rev acc in
@@ -156,12 +157,10 @@ let funExpr expr =
       let stringLocs, returnExpr = collectNewTypes [stringLoc] rest in
       let param = NewTypes {attrs; locs = stringLocs} in
       collect attrsBefore (param :: acc) returnExpr
-    | {
-     pexp_desc = Pexp_fun (lbl, defaultExpr, pattern, returnExpr);
-     pexp_attributes = [({txt = "bs"}, _)] as attrs;
-    } ->
-      let parameter = Parameter {attrs; lbl; defaultExpr; pat = pattern} in
-      collect attrsBefore (parameter :: acc) returnExpr
+    | {pexp_desc = Pexp_fun _; pexp_attributes = [({txt = "bs"}, _)]} ->
+      (* stop here, the uncurried attribute always indicates the beginning of an arrow function
+       * e.g. `(. a) => (. b)` instead of `(. a, . b)` *)
+      (attrsBefore, List.rev acc, expr)
     | {
      pexp_desc =
        Pexp_fun

tests/conversion/reason/expected/uncurrried.res.txt

@@ -44,7 +44,7 @@ let () = switch something(. x, y) {
 
 let () = {
   // ok
-  let dontDoThisAhome = (. a, b, . c, d, . e, f) => a + b + c + d + e + f
+  let dontDoThisAhome = (. a, b) => (. c, d) => (. e, f) => a + b + c + d + e + f
   // ok
   dontDoThisAhome(. a, b)(. c, d)(. e, f)
 }

tests/printer/expr/expected/fun.res.txt

@@ -352,3 +352,7 @@ let query = (~url, ()): ((unit, unit) => unit) => {
 let query = (~url, ()): ((unit, unit, unit) => unit) => {
   ((), (), ()) => Js.log("Queried " ++ url)
 }
+
+let f = (. a) => (. b) => a + b
+let f = (. a, b) => (. b, c) => a + b + c + d
+let f = (. a, b) => (. b, c) => (. e, f, g) => a + b + c + d + e + f + g

tests/printer/expr/fun.res

@@ -293,3 +293,7 @@ let query = (~url, ()): (unit => unit => unit) => {
 let query = (~url, ()): (unit => unit => unit => unit) => {
   () => () => () => Js.log("Queried " ++ url)
 }
+
+let f = (. a) => (. b) => a + b
+let f = (. a, b) => (. b, c) => a + b + c + d
+let f = (. a, b) => (. b , c) => (. e , f, g) => a + b + c + d  + e + f + g

tests/printer/typexpr/expected/arrow.res.txt

@@ -205,12 +205,12 @@ float
 // uncurried
 type t = (. int) => int
 type t = (. int, int) => int
-type t = (. int, . int) => int
-type t = (. int, int, . int, int) => int
+type t = (. int) => (. int) => int
+type t = (. int, int) => (. int, int) => int
 
 type t = (. @attr int) => unit
-type t = (. @attr int, . @attr2 int) => unit
-type t = (. @attrOnInt int, @attrOnInt int, . @attrOnInt int, @attrOnInt int) => int
+type t = (. @attr int) => (. @attr2 int) => unit
+type t = (. @attrOnInt int, @attrOnInt int) => (. @attrOnInt int, @attrOnInt int) => int
 type t = (. @attr ~x: int, ~y: int, . @attr ~z: int, @attr ~omega: int) => unit
 
 @val external requestAnimationFrame: (float => unit) => unit = "requestAnimationFrame"