fix fd leak and optimize Eol_detect.get_eol_for_file

src/refmt/eol_detect.ml

@@ -7,17 +7,11 @@ let default_eol = match Sys.win32 with true -> CRLF | _ -> LF
 
 let get_eol_for_file filename =
   let ic = open_in_bin filename in
-  let line = ref "" in
-  let c = ref ' ' in
-  let prev = ref None in
-  try
-    while !c <> '\n' do
-      prev := Some !c;
-      c := input_char ic;
-      line := !line ^ String.make 1 !c
-    done;
-    match !prev with None -> default_eol | Some '\r' -> CRLF | Some _ -> LF
-  with
-  | End_of_file ->
-    close_in ic;
-    default_eol
+  let rec loop prev =
+    match input_char ic with
+    | '\n' -> if prev = Some '\r' then CRLF else LF
+    | c -> loop (Some c)
+  in
+  let eol = try loop None with End_of_file -> default_eol in
+  close_in ic;
+  eol