Reimplement string escape in oprint

typing/oprint.ml

@@ -74,21 +74,50 @@ let parenthesize_if_neg ppf fmt v isneg =
   fprintf ppf fmt v;
   if isneg then pp_print_char ppf ')'
 
+let escape s =
+  (* Escape only C0 control characters (bytes <= 0x1F), DEL(0x7F) and '"' *)
+   let n = ref 0 in
+  for i = 0 to String.length s - 1 do
+    n := !n +
+      (match String.unsafe_get s i with
+       | '\"' | '\\' | '\n' | '\t' | '\r' | '\b' -> 2
+       | '\x00' .. '\x1F'
+       | '\x7F' -> 4
+       | _ -> 1)
+  done;
+  if !n = String.length s then s else begin
+    let s' = Bytes.create !n in
+    n := 0;
+    for i = 0 to String.length s - 1 do
+      begin match String.unsafe_get s i with
+      | ('\"' | '\\') as c ->
+          Bytes.unsafe_set s' !n '\\'; incr n; Bytes.unsafe_set s' !n c
+      | '\n' ->
+          Bytes.unsafe_set s' !n '\\'; incr n; Bytes.unsafe_set s' !n 'n'
+      | '\t' ->
+          Bytes.unsafe_set s' !n '\\'; incr n; Bytes.unsafe_set s' !n 't'
+      | '\r' ->
+          Bytes.unsafe_set s' !n '\\'; incr n; Bytes.unsafe_set s' !n 'r'
+      | '\b' ->
+          Bytes.unsafe_set s' !n '\\'; incr n; Bytes.unsafe_set s' !n 'b'
+      | '\x00' .. '\x1F' | '\x7F' as c ->
+          let a = Char.code c in
+          Bytes.unsafe_set s' !n '\\';
+          incr n;
+          Bytes.unsafe_set s' !n (Char.chr (48 + a / 100));
+          incr n;
+          Bytes.unsafe_set s' !n (Char.chr (48 + (a / 10) mod 10));
+          incr n;
+          Bytes.unsafe_set s' !n (Char.chr (48 + a mod 10));
+      | c -> Bytes.unsafe_set s' !n c
+      end;
+      incr n
+    done;
+    Bytes.to_string s'
+  end
+
+
 let print_out_string ppf s =
-  let rec segm left right ppf s =
-    (* Escape only C0 control characters (bytes <= 0x1F), DEL(0x7F) and '"' *)
-    if right >= String.length s then
-      pp_print_string ppf (String.sub s left (right - left))
-    else
-      let c = s.[right] in
-      if Char.code c <= 0x1F || c = '\x7F' || c = '"' || c ='\\' then
-        begin
-          pp_print_string ppf (String.sub s left (right - left));
-          pp_print_string ppf (if c ='"' then {|\"|} else Char.escaped c);
-          segm (right+1) (right+1) ppf s
-        end
-      else
-        segm left (right+1) ppf s in
   let not_escaped =
     (* let the user dynamically choose if strings should be escaped: *)
     match Sys.getenv_opt "OCAMLTOP_UTF_8" with
@@ -98,7 +127,7 @@ let print_out_string ppf s =
         | None -> true
         | Some f -> f in
   if not_escaped then
-    fprintf ppf "\"%a\"" (segm 0 0) s
+    fprintf ppf "\"%s\"" (escape s)
   else
     fprintf ppf "%S" s