Wrap arrays using an hov box only if they contain only simple elements.

CHANGES.md

@@ -8,7 +8,8 @@
 
 ### Fixed
 
-- Fix pretty-printing behavior for lists/objects inside lists (#141, @c-cube)
+- Fix pretty-printing behavior for lists/objects inside lists (@c-cube
+  #141, @mjambon #142)
 
 ## 2.0.0
 

lib/pretty.ml

@@ -1,8 +1,59 @@
+(*
+   Pretty-print JSON data in an attempt to maximize readability.
+
+   1. What fits on one line stays on one line.
+   2. What doesn't fit on one line gets printed more vertically so as to not
+      exceed a reasonable page width, if possible.
+
+   Arrays containing only simple elements ("atoms") are pretty-printed with
+   end-of-line wrapping like ordinary text:
+
+     [
+        "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello",
+        "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello"
+     ]
+
+   Other arrays are printed either horizontally or vertically depending
+   on whether they fit on a single line:
+
+     [ { "hello": "world" }, { "hello": "world" }, { "hello": "world" } ]
+
+   or
+
+     [
+       { "hello": "world" },
+       { "hello": "world" },
+       { "hello": "world" },
+       { "hello": "world" }
+     ]
+*)
 
 let pp_list sep ppx out l =
   let pp_sep out () = Format.fprintf out "%s@ " sep in
   Format.pp_print_list ~pp_sep ppx out l
 
+let is_atom (x: [> t]) =
+  match x with
+  | `Null
+  | `Bool _
+  | `Int _
+  | `Float _
+  | `String _
+  | `Intlit _
+  | `Floatlit _
+  | `Stringlit _
+  | `List []
+  | `Assoc []
+  | `Tuple []
+  | `Variant (_, None) -> true
+  | `List _
+  | `Assoc _
+  | `Tuple _
+  | `Variant (_, Some _) -> false
+
+let is_atom_list l =
+  List.for_all is_atom l
+
 let rec format ~inside_box std (out:Format.formatter) (x:t) : unit =
   match x with
     | `Null -> Format.pp_print_string out "null"
@@ -33,7 +84,15 @@ let rec format ~inside_box std (out:Format.formatter) (x:t) : unit =
     | `List [] -> Format.pp_print_string out "[]"
     | `List l ->
       if not inside_box then Format.fprintf out "@[<hov2>";
-      Format.fprintf out "[@;<1 0>@[<hov>%a@]@;<1 -2>]" (pp_list "," (format ~inside_box:false std)) l;
+      if is_atom_list l then
+        (* use line wrapping like we would do for a paragraph of text *)
+        Format.fprintf out "[@;<1 0>@[<hov>%a@]@;<1 -2>]"
+          (pp_list "," (format ~inside_box:false std)) l
+      else
+        (* print the elements horizontally if they fit on the line,
+           otherwise print them in a column *)
+        Format.fprintf out "[@;<1 0>@[<hv>%a@]@;<1 -2>]"
+          (pp_list "," (format ~inside_box:false std)) l;
       if not inside_box then Format.fprintf out "@]";
     | `Assoc [] -> Format.pp_print_string out "{}"
     | `Assoc l ->

test/pretty/atd.expected.json

@@ -1,12 +1,35 @@
 [
-  { "r1": "testing" }, { "r2": [ "Some", 2 ] }, { "r2": "None" },
-  { "r3": [ "Some", 3 ] }, {}, { "r4": true }, { "r5": [ "Some", 5 ] }, {},
-  { "r6": 6 }, {}, { "r7": -1000 }, { "r8": [ 1, 2, 3 ] }, [ "foo", "bar" ],
-  [], null, [ 1, 2, 3 ], 99, { "foo": 7, "bar": 8, "baz": 43 },
-  { "foo2": 5, "bar2": 6, "baz2": 41, "42": 42 }, [ 100, "foo" ],
-  [ 100, 200, 42 ], [ 100, 200, -1 ],
+  { "r1": "testing" },
+  { "r2": [ "Some", 2 ] },
+  { "r2": "None" },
+  { "r3": [ "Some", 3 ] },
+  {},
+  { "r4": true },
+  { "r5": [ "Some", 5 ] },
+  {},
+  { "r6": 6 },
+  {},
+  { "r7": -1000 },
+  { "r8": [ 1, 2, 3 ] },
+  [ "foo", "bar" ],
+  [],
+  null,
+  [ 1, 2, 3 ],
+  99,
+  { "foo": 7, "bar": 8, "baz": 43 },
+  { "foo2": 5, "bar2": 6, "baz2": 41, "42": 42 },
+  [ 100, "foo" ],
+  [ 100, 200, 42 ],
+  [ 100, 200, -1 ],
   [
-    "V1", "v22", [ "V3", "testing" ], [ "V44", 255 ], [ "V5", "None" ],
-    [ "V5", [ "Some", true ] ] ], { "v2": "A" }, { "v2": [ "B", 100 ] },
-  [ "C1", [ "C2", true ], [ "C2", false ] ], [ 50, 30, -1, 400 ]
+    "V1",
+    "v22",
+    [ "V3", "testing" ],
+    [ "V44", 255 ],
+    [ "V5", "None" ],
+    [ "V5", [ "Some", true ] ] ],
+  { "v2": "A" },
+  { "v2": [ "B", 100 ] },
+  [ "C1", [ "C2", true ], [ "C2", false ] ],
+  [ 50, 30, -1, 400 ]
 ]