Fix whitespace processing bug

.gitignore

@@ -2,7 +2,3 @@
 .vscode
 _opam/
 _build/
-**/.merlin
-*.xml
-*.xlsx
-!test/files

src/xml.ml

@@ -88,17 +88,7 @@ module SAX = struct
     true
   | _ -> false
 
-  let squish_into raw final acc =
-    String.fold raw ~init:acc ~f:(fun acc c ->
-      match acc with
-      | after_first, _ when is_ws c -> after_first, true
-      | true, true ->
-        Buffer.add_char final ' ';
-        Buffer.add_char final c;
-        true, false
-      | _ ->
-        Buffer.add_char final c;
-        true, false )
+  let find_not_ws (_ : int) c = not (is_ws c)
 
   let render attrs text =
     match Queue.length text with
@@ -114,7 +104,16 @@ module SAX = struct
             if after_first && not prev_ws then Buffer.add_char final ' ';
             Buffer.add_string final raw;
             true, is_ws raw.[String.length raw - 1]
-          | { raw; _ } -> squish_into raw final (if after_first then true, true else acc) )
+          | { raw; _ } -> (
+            match String.lfindi raw ~f:find_not_ws with
+            | None -> acc
+            | Some start -> (
+              match String.rfindi raw ~f:find_not_ws with
+              | None -> raise (Sys_error "Impossible case in Xml.render. Please report this bug.")
+              | Some stop ->
+                if after_first && not prev_ws then Buffer.add_char final ' ';
+                Buffer.add_substring final raw ~pos:start ~len:(stop - start + 1);
+                true, false ) ) )
       in
       Buffer.contents final
 

test/files/spaces.json

@@ -0,0 +1,16 @@
+{
+  "data": [
+    [
+      null,
+      null
+    ],
+    [
+      "Shen  LI",
+      null,
+      null,
+      null,
+      null,
+      null
+    ]
+  ]
+}

test/xlsx.ml

@@ -195,6 +195,7 @@ let () =
              "zip64.xlsx", `Quick, xlsx "zip64";
              "formatting.xlsx", `Quick, xlsx "formatting";
              "inline.xlsx", `Quick, xlsx "inline";
+             "spaces.xlsx", `Quick, xlsx "spaces";
              "Readme example 1", `Quick, readme_example1 "financial";
              "Readme example 2", `Quick, readme_example2 "financial";
              "Unbuffed stream", `Quick, stream_rows "financial";

test/xml.ml

@@ -105,7 +105,7 @@ comment -->
       {
         "tag": "t",
         "attrs": [],
-        "text": "hello world y",
+        "text": "hello  world y",
         "children": [
           { "tag": "x", "attrs": [], "text": "", "children": [] }
         ]
@@ -344,7 +344,7 @@ module Test4 = struct
       {
         "tag": "head",
         "attrs": [],
-        "text": "clear head text X some lost text back to the top",
+        "text": "clear head   text X some lost text back to the top",
         "children": [
           {
             "tag": "meta",