Preserve trailing newline characters at the end of template files when present (#123)

* Add new Spin_std.Sys test

This test verifies that newline char at end of file are preserved
during templating.

This test is currently broken and is fixed by the next commit.

* Fix Spin_std.Sys.read_file

Make it preserve newline characters at the end of the template files.

Files without trailing newline make dune @fmt and git produce
warnings.

Author: mbarbin

CHANGES.md

@@ -1,3 +1,10 @@
+# Unreleased
+
+## Fixed
+
+- Preserve trailing newline characters at the end of template files
+  when present
+
 # 0.8.3
 
 ## Fixed

lib/spin_std/sys.ml

@@ -88,20 +88,14 @@ let with_chdir dir f =
 
 let write_file file content =
   let oc = open_out file in
-  Printf.fprintf oc "%s" content;
-  close_out oc
+  Fun.protect
+    (fun () -> output_string oc content)
+    ~finally:(fun () -> close_out oc)
 
-let read_lines file : string list =
-  let ic = open_in file in
-  let try_read () = try Some (input_line ic) with End_of_file -> None in
-  let rec loop acc =
-    match try_read () with
-    | Some s ->
-      loop (s :: acc)
-    | None ->
-      close_in ic;
-      List.rev acc
-  in
-  loop []
-
-let read_file file = String.concat "\n" (read_lines file)
+let read_file file =
+  let ic = open_in_bin file in
+  Fun.protect
+    (fun () ->
+      let length = in_channel_length ic in
+      really_input_string ic length)
+    ~finally:(fun () -> close_in ic)

test/spin_std/sys_test.ml

@@ -9,4 +9,17 @@ let test_ls_dir () =
   let f_list = Spin_std.Sys.ls_dir (Filename.dirname temp_file) in
   check (list string) "equals" f_list [ temp_file ]
 
-let suite = [ "ls_dir returns the files in the directory", `Quick, test_ls_dir ]
+let test_read_write_file () =
+  let temp_dir = Spin_std.Sys.mk_temp_dir "spin-test" in
+  let temp_file = Filename.concat temp_dir "file" in
+  let contents = "Hello world!\n" in
+  Spin_std.Sys.write_file temp_file contents;
+  let read_contents = Spin_std.Sys.read_file temp_file in
+  check string "equals" contents read_contents
+
+let suite =
+  [ "ls_dir returns the files in the directory", `Quick, test_ls_dir
+  ; ( "write_file/read_file preserves newlines at end of file"
+    , `Quick
+    , test_read_write_file )
+  ]