kernel: loaders never escape as an exception, date-spec validates on load

Layer.load narrowed its catch to Sexplib0.Sexp_conv_error.Of_sexp_error,
but rank_of_sexp is caller-supplied and may raise anything -- e.g. a
hand-written rank parser that calls invalid_arg. Overlay.load already
catches every exception from the equivalent call; mirror that here so
layer.mli's "never as an exception" promise actually holds.

Date_spec.t derived its sexp converters with plain ppx_sexp_conv, unlike
Slug and Lang, which hand-write validating parsers specifically so
malformed data is rejected at load. (Fixed (month 13) (day 40)) used to
deserialise cleanly into a spec that simply never resolves -- a saint
quietly vanishing with no diagnostic. t_of_sexp now re-runs the value
through the existing fixed validator, the same shape Slug and Lang
already use.

Covering tests: a Layer.load case where rank_of_sexp raises
Invalid_argument instead of Of_sexp_error (would have escaped
uncaught before this fix); two Date_spec.t_of_sexp cases (month 13,
31 April) that must raise Of_sexp_error rather than silently
constructing an unresolvable spec.

1 files changed, 19 insertions, 0 deletions

diff --git a/test/test_overlay.ml b/test/test_overlay.ml
index 6131f65..b5edd5a 100644
--- a/test/test_overlay.ml
+++ b/test/test_overlay.ml
@@ -111,6 +111,23 @@ let test_layer_load_invalid_slug () =
       | Ok _ -> Alcotest.fail "expected Error for an invalid slug"
       | Error _ -> ())
 
+let test_layer_load_rank_of_sexp_raises_other_exception () =
+  (* Register finding 7: [rank_of_sexp] is caller-supplied and may raise
+     anything, not only [Of_sexp_error] -- [layer.mli] promises "never as an
+     exception". Before the fix this call did not reach the [Ok]/[Error]
+     match at all: [Invalid_argument] escaped [L.load] uncaught, and this
+     test would have errored rather than exercised the [Error _ -> ()]
+     branch. *)
+  let l = base () in
+  with_temp_file (fun path ->
+      let oc = open_out path in
+      output_string oc (Sexplib.Sexp.to_string (L.sexp_of_t sexp_of_rank l));
+      close_out oc;
+      let exploding_rank_of_sexp _sexp = invalid_arg "boom" in
+      match L.load exploding_rank_of_sexp path with
+      | Ok _ -> Alcotest.fail "expected Error, not a successful load"
+      | Error _ -> ())
+
 module O = Colitur_kernel.Overlay
 module N = Colitur_kernel.Names
 module Lang = Colitur_kernel.Lang
@@ -298,6 +315,8 @@ let suite =
       Alcotest.test_case "layer load missing file" `Quick test_layer_load_missing_file;
       Alcotest.test_case "layer load malformed sexp" `Quick test_layer_load_malformed;
       Alcotest.test_case "layer load invalid slug" `Quick test_layer_load_invalid_slug;
+      Alcotest.test_case "layer load: rank_of_sexp raises a non-Of_sexp_error exception" `Quick
+        test_layer_load_rank_of_sexp_raises_other_exception;
       Alcotest.test_case "empty is identity" `Quick test_empty_is_identity;
       Alcotest.test_case "add and suppress" `Quick test_add_and_suppress;
       Alcotest.test_case "order matters" `Quick test_order_matters;