Fix several printing issues with async including an infinite loop.

CHANGELOG.md

@@ -40,6 +40,7 @@
 - Fix issue where the JSX prop has type annotation of the first class module https://github.com/rescript-lang/syntax/pull/666
 - Fix issue where a spread `...x` in non-last position would not be reported as syntax error https://github.com/rescript-lang/syntax/pull/673/
 - Fix issue where the formatter would delete `async` in a function with labelled arguments.
+- Fix several printing issues with `async` including an infinite loop https://github.com/rescript-lang/syntax/pull/680
 
 #### :eyeglasses: Spec Compliance
 

src/res_parsetree_viewer.ml

@@ -136,7 +136,7 @@ let funExpr expr =
       collectNewTypes (stringLoc :: acc) returnExpr
     | returnExpr -> (List.rev acc, returnExpr)
   in
-  let rec collect attrsBefore acc expr =
+  let rec collect n attrsBefore acc expr =
     match expr with
     | {
      pexp_desc =
@@ -152,13 +152,17 @@ let funExpr expr =
      pexp_attributes = [];
     } ->
       let parameter = Parameter {attrs = []; lbl; defaultExpr; pat = pattern} in
-      collect attrsBefore (parameter :: acc) returnExpr
+      collect (n + 1) attrsBefore (parameter :: acc) returnExpr
     | {pexp_desc = Pexp_newtype (stringLoc, rest); pexp_attributes = attrs} ->
       let stringLocs, returnExpr = collectNewTypes [stringLoc] rest in
       let param = NewTypes {attrs; locs = stringLocs} in
-      collect attrsBefore (param :: acc) returnExpr
-    | {pexp_desc = Pexp_fun _; pexp_attributes = [({txt = "bs"}, _)]} ->
-      (* stop here, the uncurried attribute always indicates the beginning of an arrow function
+      collect (n + 1) attrsBefore (param :: acc) returnExpr
+    | {pexp_desc = Pexp_fun _; pexp_attributes}
+      when pexp_attributes
+           |> List.exists (fun ({Location.txt}, _) ->
+                  txt = "bs" || txt = "res.async")
+           && n > 0 ->
+      (* stop here, the uncurried or async attribute always indicates the beginning of an arrow function
        * e.g. `(. a) => (. b)` instead of `(. a, . b)` *)
       (attrsBefore, List.rev acc, expr)
     | {
@@ -175,16 +179,16 @@ let funExpr expr =
       let parameter =
         Parameter {attrs = attrs_other; lbl; defaultExpr; pat = pattern}
       in
-      collect (attrs_async @ attrsBefore) (parameter :: acc) returnExpr
+      collect (n + 1) (attrs_async @ attrsBefore) (parameter :: acc) returnExpr
     | expr -> (attrsBefore, List.rev acc, expr)
   in
   match expr with
   | {
       pexp_desc = Pexp_fun (Nolabel, _defaultExpr, _pattern, _returnExpr);
       pexp_attributes = attrs;
     } as expr ->
-    collect attrs [] {expr with pexp_attributes = []}
-  | expr -> collect [] [] expr
+    collect 0 attrs [] {expr with pexp_attributes = []}
+  | expr -> collect 0 [] [] expr
 
 let processBracesAttr expr =
   match expr.pexp_attributes with

src/res_printer.ml

@@ -4698,7 +4698,7 @@ and printExprFunParameters ~customLayout ~inCallback ~async ~uncurried
     let txtDoc =
       let var = printIdentLike stringLoc.txt in
       let var = if hasConstraint then addParens var else var in
-      if async then addAsync (Doc.concat [Doc.lparen; var; Doc.rparen]) else var
+      if async then addAsync var else var
     in
     printComments txtDoc cmtTbl stringLoc.loc
   (* let f = () => () *)

tests/printer/expr/asyncAwait.res

@@ -82,6 +82,17 @@ let _ = await {
     Js.Promise.resolve(x)
 }
 
-let f = async (~x, ~y) => x + y
-let f = async (@foo ~x, @bar ~y) => x + y
-let f = @foo async ( @bar ~x as @zz z, ~y) => x + y
+let f1 = async (~x, ~y) => x + y
+let f2 = async (@foo ~x, @bar ~y) => x + y
+let f3 = @foo async (@bar ~x as @zz z, ~y) => x + y
+let f4 = async x => x
+let f5 = async x => async y => 3
+let f6 = async (~x1, ~x2) => async y => 3
+let f7 = async x => async (~y) => 3
+let f8 = async (~x1, ~x2) => async (~y) => 3
+let f9 = x => async (~y) => 3
+let f10 = x => async y => 3
+let f11 = (. ~x) => (. ~y) => 3
+
+let f12 = @a (@b x) => 3
+let f13 = @a @b (~x) => 3

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

@@ -8,7 +8,7 @@ let sequentialAwait = async () => {
 
 let f = async () => ()
 let f = async (. ()) => ()
-let f = async (f) => f()
+let f = async f => f()
 let f = async (a, b) => a + b
 let f = async (. a, b) => a + b
 
@@ -104,6 +104,17 @@ let _ = await {
   Js.Promise.resolve(x)
 }
 
-let f = async (~x, ~y) => x + y
-let f = async (@foo ~x, @bar ~y) => x + y
-let f = async (@bar @foo ~x as @zz z, ~y) => x + y
+let f1 = async (~x, ~y) => x + y
+let f2 = async (@foo ~x, @bar ~y) => x + y
+let f3 = async (@bar @foo ~x as @zz z, ~y) => x + y
+let f4 = async x => x
+let f5 = async x => async y => 3
+let f6 = async (~x1, ~x2) => async y => 3
+let f7 = async x => async (~y) => 3
+let f8 = async (~x1, ~x2) => async (~y) => 3
+let f9 = x => async (~y) => 3
+let f10 = x => async y => 3
+let f11 = (. ~x) => (. ~y) => 3
+
+let f12 = @a x => 3
+let f13 = (@a @b ~x) => 3

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

@@ -73,7 +73,7 @@ let f = @attr (@attrOnA a, @attrOnB b) => @attr2 (@attrOnC c, @attrOnD d) => ()
 let f = @attr (. a, b) => @attr2 (. c, d) => ()
 
 let f = (@attr ~a, @attr ~b) => ()
-let f = (. @attr ~a, . @attr ~b) => ()
+let f = (. @attr ~a) => (. @attr ~b) => ()
 
 let f = (
   thisIsAVeryLongNaaaaaaaaaaaaaaaaaaameeeeeeeeeeeee,