feat(render): per-flavour escaping and RFC 5545 line folding

Six flavours: latex, groff, html, xml, ics, none. Markdown, AsciiDoc and
plain text map to none deliberately -- their metacharacters are
context-dependent and escaping them aggressively produces worse output
than not escaping.

An unrecognised extension returns None rather than falling back to none:
guessing the flavour wrong produces malformed output that looks fine
until it does not.

Folding backs off to a non-continuation byte, so a fold never splits a
UTF-8 sequence -- the failure mode that would corrupt Polish and Latin
names in a published feed.

3 files changed, 96 insertions, 2 deletions

diff --git a/test/dune b/test/dune
index e20450b..1ef1b57 100644
--- a/test/dune
+++ b/test/dune
@@ -1,6 +1,6 @@
 (test
  (name test_colitur)
- (libraries colitur_kernel rite_ef alcotest qcheck qcheck-alcotest sexplib)
+ (libraries colitur_kernel colitur_render rite_ef alcotest qcheck qcheck-alcotest sexplib)
  (deps
   ../data/ef/sanctoral.sexp
   ../data/ef/adjustments.sexp
diff --git a/test/test_colitur.ml b/test/test_colitur.ml
index 76ff685..2295a3f 100644
--- a/test/test_colitur.ml
+++ b/test/test_colitur.ml
@@ -6,4 +6,5 @@ let () =
       Test_calendar.suite; Test_precedence_ef.suite; Test_sanctoral_ef.suite; Test_rite_ef.suite;
       Test_differential.suite; Test_oracle.suite; Test_oracle.suite_2038; Test_oracle.suite_2035; Test_golden.suite;
       ("lectionary", Test_lectionary.suite);
-      ("lectionary-ef", Test_lectionary_ef.suite) ]
+      ("lectionary-ef", Test_lectionary_ef.suite);
+      Test_escape.suite ]
diff --git a/test/test_escape.ml b/test/test_escape.ml
new file mode 100644
index 0000000..1587388
--- /dev/null
+++ b/test/test_escape.ml
@@ -0,0 +1,93 @@
+module E = Colitur_render.Escape
+
+let check = Alcotest.(check string)
+
+let test_latex () =
+  check "ampersand" "\\&" (E.apply E.Latex "&");
+  check "percent" "\\%" (E.apply E.Latex "%");
+  check "underscore" "\\_" (E.apply E.Latex "_");
+  check "braces" "\\{\\}" (E.apply E.Latex "{}");
+  check "backslash first" "\\textbackslash{}" (E.apply E.Latex "\\");
+  (* A real feast name that would otherwise break a .tex build. *)
+  check "real name" "Ss.mi Nominis Iesu \\& Mari\xc3\xa6"
+    (E.apply E.Latex "Ss.mi Nominis Iesu & Mari\xc3\xa6")
+
+let test_groff () =
+  check "backslash" "\\e" (E.apply E.Groff "\\");
+  (* RG-irrelevant but groff-critical: a leading dot starts a request. *)
+  check "leading dot" "\\&.Ss" (E.apply E.Groff ".Ss");
+  check "leading quote" "\\&'tis" (E.apply E.Groff "'tis");
+  check "interior dot untouched" "Ss.mi" (E.apply E.Groff "Ss.mi")
+
+let test_html_xml () =
+  check "amp first" "<" (E.apply E.Html "<");
+  check "angles" "&lt;b&gt;" (E.apply E.Html "<b>");
+  check "quote" "&quot;" (E.apply E.Html "\"");
+  check "xml same" "&lt;b&gt;" (E.apply E.Xml "<b>")
+
+let test_ics () =
+  check "comma" "\\," (E.apply E.Ics ",");
+  check "semicolon" "\\;" (E.apply E.Ics ";");
+  check "backslash" "\\\\" (E.apply E.Ics "\\");
+  check "newline" "\\n" (E.apply E.Ics "\n")
+
+let test_none_is_identity () =
+  check "none" "& < > \\ % {}" (E.apply E.None_ "& < > \\ % {}")
+
+let test_flavour_names () =
+  List.iter
+    (fun f -> Alcotest.(check bool) "roundtrip" true (E.of_string (E.to_string f) = Some f))
+    [ E.Latex; E.Groff; E.Html; E.Xml; E.Ics; E.None_ ];
+  Alcotest.(check bool) "tex" true (E.of_extension ".tex" = Some E.Latex);
+  Alcotest.(check bool) "ms" true (E.of_extension ".ms" = Some E.Groff);
+  Alcotest.(check bool) "mom" true (E.of_extension ".mom" = Some E.Groff);
+  Alcotest.(check bool) "html" true (E.of_extension ".html" = Some E.Html);
+  Alcotest.(check bool) "md is none" true (E.of_extension ".md" = Some E.None_);
+  Alcotest.(check bool) "adoc is none" true (E.of_extension ".adoc" = Some E.None_);
+  Alcotest.(check bool) "txt is none" true (E.of_extension ".txt" = Some E.None_);
+  (* Spec section 5: an unknown extension is an ERROR, never a silent fallback. *)
+  Alcotest.(check bool) "unknown is None" true (E.of_extension ".wat" = None)
+
+let test_fold_short_line_unchanged () =
+  check "short" "SUMMARY:Feast\r\n" (E.fold_ics "SUMMARY:Feast")
+
+let test_fold_long_line () =
+  let long = "DESCRIPTION:" ^ String.make 200 'x' in
+  let out = E.fold_ics long in
+  let lines = String.split_on_char '\n' out in
+  List.iter
+    (fun l ->
+      let l = if l <> "" && l.[String.length l - 1] = '\r' then String.sub l 0 (String.length l - 1) else l in
+      if String.length l > 75 then Alcotest.failf "line of %d octets exceeds 75" (String.length l))
+    (List.filter (fun l -> l <> "") lines);
+  (* Continuation lines begin with exactly one space (RFC 5545 section 3.1). *)
+  match lines with
+  | _ :: second :: _ -> Alcotest.(check bool) "continuation starts with space" true (second.[0] = ' ')
+  | _ -> Alcotest.fail "expected the line to fold"
+
+(* RFC 5545 section 3.1 folds on OCTET boundaries; splitting mid-UTF-8 corrupts
+   Polish and Latin names, which is the whole reason this is not a template job. *)
+let test_fold_never_splits_utf8 () =
+  let long = "SUMMARY:" ^ String.concat "" (List.init 40 (fun _ -> "\xc4\x99\xc5\x9b\xc4\x87")) in
+  let out = E.fold_ics long in
+  let stripped =
+    String.concat ""
+      (List.filter_map
+         (fun l ->
+           let l = if l <> "" && l.[String.length l - 1] = '\r' then String.sub l 0 (String.length l - 1) else l in
+           if l = "" then None else if l.[0] = ' ' then Some (String.sub l 1 (String.length l - 1)) else Some l)
+         (String.split_on_char '\n' out))
+  in
+  check "unfolds to the original" long stripped
+
+let suite =
+  ( "Escape",
+    [ Alcotest.test_case "latex" `Quick test_latex;
+      Alcotest.test_case "groff" `Quick test_groff;
+      Alcotest.test_case "html/xml" `Quick test_html_xml;
+      Alcotest.test_case "ics" `Quick test_ics;
+      Alcotest.test_case "none is identity" `Quick test_none_is_identity;
+      Alcotest.test_case "flavour names" `Quick test_flavour_names;
+      Alcotest.test_case "fold: short unchanged" `Quick test_fold_short_line_unchanged;
+      Alcotest.test_case "fold: long line" `Quick test_fold_long_line;
+      Alcotest.test_case "fold: never splits utf8" `Quick test_fold_never_splits_utf8 ] )