Example of broken formatting for foo(a,_) in uncurried mode. (#6148)

* Example of broken formatting for foo(a,_) in uncurried mode.

See #6146

* Fix pretty printing.

Fixes #6148

* Fix second case.

* Update CHANGELOG.md

* Somehow roundtrip tests are not happy.

Author: cristianoc

CHANGELOG.md

@@ -12,6 +12,10 @@
 
 # 11.0.0-alpha.4 (Unreleased)
 
+#### :bug: Bug Fix
+
+- Fix broken formatting in uncurried mode for functions with _ placeholder args. https://github.com/rescript-lang/rescript-compiler/pull/6148
+
 # 11.0.0-alpha.3
 
 #### :rocket: Main New Feature

res_syntax/src/res_parsetree_viewer.ml

@@ -154,13 +154,27 @@ let funExpr expr =
   let rec collect ~uncurried ~nFun attrsBefore acc expr =
     match expr with
     | {
-     pexp_desc =
-       Pexp_fun
-         ( Nolabel,
-           None,
-           {ppat_desc = Ppat_var {txt = "__x"}},
-           {pexp_desc = Pexp_apply _} );
-    } ->
+        pexp_desc =
+          Pexp_fun
+            ( Nolabel,
+              None,
+              {ppat_desc = Ppat_var {txt = "__x"}},
+              {pexp_desc = Pexp_apply _} );
+      }
+    | {
+        pexp_desc =
+          Pexp_construct
+            ( {txt = Lident "Function$"},
+              Some
+                {
+                  pexp_desc =
+                    Pexp_fun
+                      ( Nolabel,
+                        None,
+                        {ppat_desc = Ppat_var {txt = "__x"}},
+                        {pexp_desc = Pexp_apply _} );
+                } );
+      } ->
       (uncurried, attrsBefore, List.rev acc, rewriteUnderscoreApply expr)
     | {pexp_desc = Pexp_newtype (stringLoc, rest); pexp_attributes = attrs} ->
       let stringLocs, returnExpr = collectNewTypes [stringLoc] rest in

res_syntax/src/res_printer.ml

@@ -2671,18 +2671,32 @@ and printExpression ~state (e : Parsetree.expression) cmtTbl =
       (Doc.concat
          [attrs; parametersDoc; typConstraintDoc; Doc.text " =>"; returnExprDoc])
   in
+  let uncurried = Ast_uncurried.exprIsUncurriedFun e in
+  let e_fun =
+    if uncurried then Ast_uncurried.exprExtractUncurriedFun e else e
+  in
   let printedExpression =
-    match e.pexp_desc with
+    match e_fun.pexp_desc with
     | Pexp_fun
         ( Nolabel,
           None,
           {ppat_desc = Ppat_var {txt = "__x"}},
-          {pexp_desc = Pexp_apply _} ) ->
+          {pexp_desc = Pexp_apply _} )
+    | Pexp_construct
+        ( {txt = Lident "Function$"},
+          Some
+            {
+              pexp_desc =
+                Pexp_fun
+                  ( Nolabel,
+                    None,
+                    {ppat_desc = Ppat_var {txt = "__x"}},
+                    {pexp_desc = Pexp_apply _} );
+            } ) ->
       (* (__x) => f(a, __x, c) -----> f(a, _, c)  *)
       printExpressionWithComments ~state
-        (ParsetreeViewer.rewriteUnderscoreApply e)
+        (ParsetreeViewer.rewriteUnderscoreApply e_fun)
         cmtTbl
-    | _ when Ast_uncurried.exprIsUncurriedFun e -> printArrow e
     | Pexp_fun _ | Pexp_newtype _ -> printArrow e
     | Parsetree.Pexp_constant c ->
       printConstant ~templateLiteral:(ParsetreeViewer.isTemplateLiteral e) c