fix(cli): diagnose an INI overlay passed to --overlay

The INI overlay form is a SOURCE format that 'colitur convert' turns into
the S-expression one. Handing the INI to --overlay instead failed deep in
the sexp reader with 'more than one S-expression in file', which names
neither the cause nor the cure -- and the shipped examples under
data/ef/examples/ are exactly the files someone would try that with.

The detector reads past the comment header to the first real line and
looks for a [section]. Its first version capped that scan at 40 lines and
poland.ini's own header is 43, so it silently never fired on the very
file it was written for; the cap now bounds only how much of a binary
gets read, and is not a guess at header length.

1 files changed, 34 insertions, 0 deletions

diff --git a/bin/main.ml b/bin/main.ml
index 51c4989..c915255 100644
--- a/bin/main.ml
+++ b/bin/main.ml
@@ -169,8 +169,42 @@ let load_ef_layer ?(user_overlays = []) () =
   let dir = data_dir () in
   let sanctoral_path = Filename.concat dir "sanctoral.sexp" in
   let adjustments_path = Filename.concat dir "adjustments.sexp" in
+  (* An overlay handed to --overlay must be the S-expression form. The INI
+     form is real but is a SOURCE format: `colitur convert` turns it into one.
+     Feeding the INI here otherwise fails deep inside the sexp reader with
+     "more than one S-expression in file", which names neither the cause nor
+     the cure. Detect it and say both. *)
+  let looks_like_ini path =
+    match open_in path with
+    | exception _ -> false
+    | ic ->
+        (* Skip the comment header and stop at the first real line. The cap
+           only bounds how much of a binary file gets read; it is NOT a guess
+           at how long a header may be. The first version capped at 40 and
+           poland.ini's own header is 43 lines, so the detection silently
+           never fired on the very file it was written for. *)
+        let rec scan n =
+          if n > 2000 then false
+          else
+            match input_line ic with
+            | exception End_of_file -> false
+            | line ->
+                let l = String.trim line in
+                if l = "" || l.[0] = ';' || l.[0] = '#' then scan (n + 1)
+                else String.length l > 1 && l.[0] = '[' && l.[String.length l - 1] = ']'
+        in
+        let r = scan 0 in
+        close_in_noerr ic;
+        r
+  in
   let load_overlay path =
     match Colitur_kernel.Overlay.load Rite_ef.Vocab_ef.rank_of_sexp path with
+    | Error _ when looks_like_ini path ->
+        Error
+          (Printf.sprintf
+             "%s looks like an INI overlay, not an S-expression one.\n\
+              colitur: convert it first:  colitur convert %s > overlay.sexp"
+             path path)
     | Error e -> Error (Printf.sprintf "failed to load %s: %s" path e)
     | Ok o -> Ok o
   in