Fix issue where nested pipe discards await

Fixes #687

Certain nested patterns for binary operators are printed "manually" so the special printing for await is not used.

Author: cristianoc

src/res_printer.ml

@@ -3604,17 +3604,23 @@ and printBinaryExpression ~customLayout (expr : Parsetree.expression) cmtTbl =
               | [] -> doc
               | _ -> addParens doc
             in
+            let isAwait =
+              ParsetreeViewer.hasAwaitAttribute expr.pexp_attributes
+            in
             let doc =
               Doc.concat
                 [
+                  (if isAwait then Doc.text "await " else Doc.nil);
                   leftPrinted;
                   printBinaryOperator ~inlineRhs:false operator;
                   rightPrinted;
                 ]
             in
             let doc =
-              if (not isLhs) && Parens.rhsBinaryExprOperand operator expr then
-                Doc.concat [Doc.lparen; doc; Doc.rparen]
+              if
+                isAwait
+                || ((not isLhs) && Parens.rhsBinaryExprOperand operator expr)
+              then Doc.concat [Doc.lparen; doc; Doc.rparen]
               else doc
             in
             printComments doc cmtTbl expr.pexp_loc

tests/printer/expr/asyncAwait.res

@@ -96,3 +96,6 @@ let f11 = (. ~x) => (. ~y) => 3
 
 let f12 = @a (@b x) => 3
 let f13 = @a @b (~x) => 3
+
+let aw = (await (server->start))->foo
+let aw = (@foo (server->start))->foo

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

@@ -118,3 +118,6 @@ let f11 = (. ~x) => (. ~y) => 3
 
 let f12 = @a x => 3
 let f13 = (@a @b ~x) => 3
+
+let aw = (await server->start)->foo
+let aw = @foo (server->start)->foo