Fix printing of externals that happen to have newlines/quotes in them.

Summary:Before this diff, we would print these as "" strings with \n inside of them.

Test Plan:Added test cases

Reviewers:

CC:

formatTest/unit_tests/expected_output/externals.re

@@ -4,4 +4,31 @@
 external foo: type_ = "%caml_something_or_other";
 
 external multilineStringExtern: int => int =
-  "\n Did you know you can put whatver you want inside\n of an extern? Good luck with the linker though!\n";
+  {|
+ Did you know you can put whatver you want inside
+ of an extern? Good luck with the linker though!
+|};
+
+module Nested = {
+  external multilineStringExtern: int => int =
+    {|
+   Did you know you can put whatver you want inside
+   of an extern? Good luck with the linker though!
+  |};
+  external multilineStringExternWithTag:
+    int => int =
+    {|
+   Did you know you can put whatver you want inside
+   of an extern? Good luck with the linker though!
+  |};
+  external multilineStringExtern: int => int =
+    {|
+   And this has a newline in it, so will be formatted with { | | } style string|};
+  external containsQuote: int => int =
+    {|This has a quote in it " so will be formatted as { | | } style string|};
+  external noIndentation: int => int =
+    {|
+Did you know you can put whatver you want inside
+of an extern? Good luck with the linker though!
+|};
+};

formatTest/unit_tests/input/externals.re

@@ -7,3 +7,21 @@ external multilineStringExtern : int => int = {|
  Did you know you can put whatver you want inside
  of an extern? Good luck with the linker though!
 |};
+
+module Nested = {
+  external multilineStringExtern : int => int = {|
+   Did you know you can put whatver you want inside
+   of an extern? Good luck with the linker though!
+  |};
+  external multilineStringExternWithTag : int => int = {js|
+   Did you know you can put whatver you want inside
+   of an extern? Good luck with the linker though!
+  |js};
+  external multilineStringExtern : int => int = "
+   And this has a newline in it, so will be formatted with { | | } style string";
+  external containsQuote : int => int = "This has a quote in it \" so will be formatted as { | | } style string";
+  external noIndentation : int => int = {|
+Did you know you can put whatver you want inside
+of an extern? Good luck with the linker though!
+|};
+};

src/reason-parser/reason_pprint_ast.ml

@@ -1991,8 +1991,12 @@ let paren b fu ppf x =
   then Format.fprintf ppf "(%a)" fu x
   else fu ppf x
 
-let constant_string ppf s =
-  Format.fprintf ppf "%S" s
+let constant_string_for_primitive ppf s =
+  let hasQuote = try String.index s '"' with Not_found -> -1 in
+  let hasNewline = try String.index s '\n' with Not_found -> -1 in
+  if hasQuote > -1 || hasNewline > -1 then
+    Format.fprintf ppf "{|%s|}" s
+  else Format.fprintf ppf "%S" s
 
 let tyvar ppf str =
   Format.fprintf ppf "'%s" str
@@ -2430,7 +2434,7 @@ let printer = object(self:'self)
   method constant ?raw_literal ?(parens=true) =
     wrap (constant ?raw_literal ~parens)
 
-  method constant_string = wrap constant_string
+  method constant_string_for_primitive = wrap constant_string_for_primitive
   method tyvar = wrap tyvar
 
   (* c ['a,'b] *)
@@ -6684,7 +6688,8 @@ let printer = object(self:'self)
       | [""] -> lblBefore
       | _ ->
         let frstHalf = makeList ~postSpace:true [lblBefore; atom "="] in
-        let sndHalf = makeSpacedBreakableInlineList (List.map self#constant_string vd.pval_prim) in
+        let sndHalf =
+          makeSpacedBreakableInlineList (List.map self#constant_string_for_primitive vd.pval_prim) in
         label ~space:true frstHalf sndHalf
     in
     match vd.pval_attributes with