unikernel/duniverse/ppxlib/print-diff/ppxlib_print_diff.ml

@@ -0,0 +1,49 @@
+open StdLabels
+
+let patdiff_cmd ~use_color ~extra_patdiff_args =
+  let args =
+    List.concat
+      [
+        [ "-keep-whitespace" ];
+        [ "-location-style omake" ];
+        (if use_color then [] else [ "-ascii" ]);
+        extra_patdiff_args;
+      ]
+  in
+  String.concat ~sep:" " ("patdiff" :: args)
+
+let print ?diff_command ?(extra_patdiff_args = []) ?(use_color = false) ~file1
+    ~file2 () =
+  let exec cmd =
+    let cmd =
+      Printf.sprintf "%s %s %s 1>&2" cmd (Filename.quote file1)
+        (Filename.quote file2)
+    in
+    match Sys.command cmd with
+    | 0 -> `Same
+    | 1 -> `Different
+    | n -> `Error (n, cmd)
+  in
+  match diff_command with
+  | Some s -> ignore (exec s : [> `Same | `Different | `Error of int * string ])
+  | None -> (
+      match exec (patdiff_cmd ~use_color ~extra_patdiff_args) with
+      | `Same ->
+          (* patdiff produced no output, fallback to diff -u *)
+          Printf.eprintf "File \"%s\", line 1, characters 0-0:\n%!" file1;
+          ignore
+            (exec "diff -u" : [> `Same | `Different | `Error of int * string ])
+      | `Different ->
+          (* patdiff successfully found a difference *)
+          ()
+      | `Error (err_code, cmd) ->
+          (* patdiff threw an error... perhaps it wasn't installed? fallback to diff -u *)
+          Printf.eprintf
+            "Error:\n\
+             > %S exited with code %d\n\
+             > Perhaps patdiff is not installed? Hint, try: opam install patdiff\n\
+             > Falling back to diff -u\n\n"
+            cmd err_code;
+          Printf.eprintf "File \"%s\", line 1, characters 0-0:\n%!" file1;
+          ignore
+            (exec "diff -u" : [> `Same | `Different | `Error of int * string ]))