Interpret arity of uncurried explicitly.

CHANGELOG.md

@@ -20,6 +20,7 @@
 - Remove obsolete built-in project templates and the "rescript init" functionality. This will be replaced by the create-rescript-app project that is maintained separately.
 - Parse the attributes of labelled argument to the pattern attributes of argument instead of function.
 - Made pinned dependencies transitive: if *a* is a pinned dependency of *b* and *b* is a pinned dependency of *c*, then *a* is implicitly a pinned dependency of *c*. This change is only breaking if your build process assumes non-transitivity.
+- Curried after uncurried is not fused anymore: `(. x) => y => 3` is not equivalent to `(. x, y) => 3` anymore. It's instead equivalent to `(. x) => { y => 3 }`.
 
 #### :nail_care: Polish
 

lib/4.06.1/unstable/js_compiler.ml

@@ -56050,7 +56050,8 @@ and printExpression ~customLayout (e : Parsetree.expression) cmtTbl =
         (ParsetreeViewer.rewriteUnderscoreApply e)
         cmtTbl
     | Pexp_fun _ | Pexp_newtype _ -> printArrow ~isUncurried:false e
-    | Pexp_record ([({txt = Ldot (Ldot (Lident "Js", "Fn"), name)}, funExpr)], None)
+    | Pexp_record
+        ([({txt = Ldot (Ldot (Lident "Js", "Fn"), name)}, funExpr)], None)
       when String.length name >= 1 && name.[0] = 'I' ->
       printArrow ~isUncurried:true funExpr
     | Pexp_record (rows, spreadExpr) ->

lib/4.06.1/unstable/js_playground_compiler.ml

@@ -56050,7 +56050,8 @@ and printExpression ~customLayout (e : Parsetree.expression) cmtTbl =
         (ParsetreeViewer.rewriteUnderscoreApply e)
         cmtTbl
     | Pexp_fun _ | Pexp_newtype _ -> printArrow ~isUncurried:false e
-    | Pexp_record ([({txt = Ldot (Ldot (Lident "Js", "Fn"), name)}, funExpr)], None)
+    | Pexp_record
+        ([({txt = Ldot (Ldot (Lident "Js", "Fn"), name)}, funExpr)], None)
       when String.length name >= 1 && name.[0] = 'I' ->
       printArrow ~isUncurried:true funExpr
     | Pexp_record (rows, spreadExpr) ->

lib/4.06.1/whole_compiler.ml

@@ -231912,7 +231912,8 @@ and printExpression ~customLayout (e : Parsetree.expression) cmtTbl =
         (ParsetreeViewer.rewriteUnderscoreApply e)
         cmtTbl
     | Pexp_fun _ | Pexp_newtype _ -> printArrow ~isUncurried:false e
-    | Pexp_record ([({txt = Ldot (Ldot (Lident "Js", "Fn"), name)}, funExpr)], None)
+    | Pexp_record
+        ([({txt = Ldot (Ldot (Lident "Js", "Fn"), name)}, funExpr)], None)
       when String.length name >= 1 && name.[0] = 'I' ->
       printArrow ~isUncurried:true funExpr
     | Pexp_record (rows, spreadExpr) ->

res_syntax/src/res_core.ml

@@ -1515,6 +1515,18 @@ and parseEs6ArrowExpression ?(arrowAttrs = []) ?(arrowStartPos = None) ?context
   in
   Parser.eatBreadcrumb p;
   let endPos = p.prevEndPos in
+  let body =
+    match parameters with
+    | TermParameter {uncurried = true} :: _
+      when match body.pexp_desc with
+           | Pexp_fun _ -> true
+           | _ -> false ->
+      {
+        body with
+        pexp_attributes = makeBracesAttr body.pexp_loc :: body.pexp_attributes;
+      }
+    | _ -> body
+  in
   let arrowExpr, _arity =
     List.fold_right
       (fun parameter (expr, arity) ->

res_syntax/tests/parsing/grammar/expressions/expected/uncurried.res.txt

@@ -9,9 +9,13 @@ let f =
   (({
       Js.Fn.I1 =
         (fun a ->
-           ((fun b -> (({ Js.Fn.I1 = (fun c -> ((fun d -> ())[@attr4 ])) })
+           ((fun b ->
+               (({
+                   Js.Fn.I1 =
+                     (fun c -> ((fun d -> ())[@ns.braces ][@attr4 ]))
+                 })
                [@attr3 ]))
-           [@attr2 ]))
+           [@ns.braces ][@attr2 ]))
     })
   [@attr ])
 let f =

res_syntax/tests/printer/expr/asyncAwait.res

@@ -115,9 +115,5 @@ let b3 = await (foo->bar(~arg))
 let b4 = await (foo.bar.baz)
 
 let c1 = @foo x => @bar y => x + y
-
-// This is not idempotent:
-// let c2 = (. x) => y => x+y
-
-let c2 = (. x, y) => x+y
+let c2 = (. x) => y => x+y
 let c3 = (. x) => @foo y => x+y

res_syntax/tests/printer/expr/expected/asyncAwait.res.txt

@@ -137,9 +137,5 @@ let b3 = await foo->bar(~arg)
 let b4 = await foo.bar.baz
 
 let c1 = @foo x => @bar y => x + y
-
-// This is not idempotent:
-// let c2 = (. x) => y => x+y
-
-let c2 = (. x, y) => x + y
-let c3 = (. x) => @foo y => x + y
+let c2 = (. x) => {y => x + y}
+let c3 = (. x) => {@foo y => x + y}