Fix printing of underscore Pexp_fun sugar in context of Array.get (rescript-lang#414)

Fixes GH413

`Array.get(_, 0)` shouldn't be printed as `_[0]`

Author: IwanKaramazow

syntax/src/res_parsetree_viewer.ml

@@ -569,3 +569,8 @@ let isUnderscoreApplySugar expr =
       {pexp_desc = Pexp_apply _}
     ) -> true
   | _ -> false
+
+let isRewrittenUnderscoreApplySugar expr =
+  match expr.pexp_desc with
+  | Pexp_ident {txt = Longident.Lident "_"} -> true
+  | _ -> false

syntax/src/res_parsetree_viewer.mli

@@ -128,3 +128,5 @@ val rewriteUnderscoreApply: Parsetree.expression -> Parsetree.expression
 val isUnderscoreApplySugar: Parsetree.expression -> bool
 
 val hasIfLetAttribute: Parsetree.attributes -> bool
+
+val isRewrittenUnderscoreApplySugar: Parsetree.expression -> bool

syntax/src/res_printer.ml

@@ -3670,7 +3670,8 @@ and printPexpApply expr cmtTbl =
   | Pexp_apply (
       {pexp_desc = Pexp_ident {txt = Longident.Ldot (Lident "Array", "get")}},
       [Nolabel, parentExpr; Nolabel, memberExpr]
-    ) ->
+    ) when not (ParsetreeViewer.isRewrittenUnderscoreApplySugar parentExpr) ->
+      (* Don't print the Array.get(_, 0) sugar a.k.a. (__x) => Array.get(__x, 0) as _[0] *)
       let member =
         let memberDoc =
           let doc = printExpressionWithComments memberExpr cmtTbl in

syntax/tests/conversion/reason/expected/underscoreSugar.re.txt

@@ -0,0 +1 @@
+let photo = pricedRoom["room"]["photos"] |> filterNone |> Array.get(_, 0)

syntax/tests/conversion/reason/underscoreSugar.re

@@ -0,0 +1 @@
+let photo = pricedRoom#room#photos |> filterNone |> Array.get(_, 0);

syntax/tests/printer/expr/expected/underscoreApply.res.txt

@@ -52,3 +52,12 @@ f(a, b, _)[ix]
 f(a, b, _)[ix] = 2
 
 getDirector(a, b, _).name = "Steve"
+
+filterNone |> Array.get(_, 0)
+filterNone->Array.get(_, 0)
+Array.get(_, 0)
+1 + Array.get(_, 0)
+Array.get(_, 1) + Array.get(_, 0)
+let f = Array.get(_, 0)
+
+let photo = pricedRoom["room"]["photos"] |> filterNone |> Array.get(_, 0)

syntax/tests/printer/expr/underscoreApply.res

@@ -54,3 +54,12 @@ f(a, b, _)[ix]
 f(a, b, _)[ix] = 2
 
 getDirector(a, b, _).name = "Steve"
+
+filterNone |> Array.get(_, 0)
+filterNone->Array.get(_, 0)
+Array.get(_, 0)
+1 + Array.get(_, 0)
+Array.get(_, 1) + Array.get(_, 0)
+let f = Array.get(_, 0)
+
+let photo = pricedRoom["room"]["photos"] |> filterNone |> Array.get(_, 0)