fix(naming): config fix round 1 -- unknown sections, O(n) accumulate

F1: test_unknown_key_is_reported_not_fatal never asserted unknown_keys
itself, only that parsing survives -- a no-op accumulator passed it.
Now asserts the key is actually collected.

F2: a misspelled section name, e.g. [deafults], was silently discarded --
Ok empty, lang and everything else gone, nothing reported. That is the
highest-value typo this feature exists to catch. Any section other than
[defaults] is now collected into a new Config.unknown_sections, kept
separate from unknown_keys so the CLI can word the two warnings
differently. Still non-fatal: a newer colitur's added section must not
break an older binary.

F3: overlays and unknown_keys accumulated with '@ [v]' per line, O(n^2)
over the field count. Cons during the fold, List.rev once at the end.

F4: documented that lang/template/format are last-wins on a repeated
key, the opposite direction from Overlay_ini.get's first-wins over the
same section type.

1 files changed, 19 insertions, 3 deletions

diff --git a/test/test_config.ml b/test/test_config.ml
index 9100380..067b255 100644
--- a/test/test_config.ml
+++ b/test/test_config.ml
@@ -46,11 +46,25 @@ let test_malformed_is_error_not_crash () =
 
 (* An unknown key is a WARNING case, not a hard error: a config written for a
    newer colitur must still work on an older one. But it must be reportable, so
-   it is not silently dropped either. *)
+   it is not silently dropped either -- assert it is actually COLLECTED, not
+   only that parsing survives it: a no-op accumulator would also pass a test
+   that checked survival alone. *)
 let test_unknown_key_is_reported_not_fatal () =
   match C.of_string "[defaults]\nlang = la\nnonsense = 1\n" with
   | Error _ -> Alcotest.fail "an unknown key must not be fatal"
-  | Ok c -> Alcotest.(check (option string)) "known key still read" (Some "la") (C.lang c)
+  | Ok c ->
+      Alcotest.(check (option string)) "known key still read" (Some "la") (C.lang c);
+      Alcotest.(check (list string)) "unknown key reported" [ "nonsense" ] (C.unknown_keys c)
+
+(* The highest-value case: a misspelled SECTION name (not merely a misspelled
+   key inside a recognised one). Before this fix the whole section, lang
+   included, vanished with nothing reported -- exactly the typo this feature
+   exists to surface, in its worst form: a user whose config silently does
+   nothing has no way to discover why. *)
+let test_misspelled_section_is_reported_not_silently_dropped () =
+  let c = ok (C.of_string "[deafults]\nlang = pl\n") in
+  Alcotest.(check (option string)) "lang not read from the wrong section" None (C.lang c);
+  Alcotest.(check (list string)) "section reported" [ "deafults" ] (C.unknown_sections c)
 
 let suite =
   ( "Config",
@@ -59,4 +73,6 @@ let suite =
       Alcotest.test_case "empty is all none" `Quick test_empty_config_is_all_none;
       Alcotest.test_case "precedence and provenance" `Quick test_precedence_and_provenance;
       Alcotest.test_case "malformed is error" `Quick test_malformed_is_error_not_crash;
-      Alcotest.test_case "unknown key not fatal" `Quick test_unknown_key_is_reported_not_fatal ] )
+      Alcotest.test_case "unknown key not fatal" `Quick test_unknown_key_is_reported_not_fatal;
+      Alcotest.test_case "misspelled section reported"
+        `Quick test_misspelled_section_is_reported_not_silently_dropped ] )