feat(render): XML emitter and schema

Element-per-field; attributes carry identity only and there is no mixed
content, so a consumer's XPath never has to distinguish the two.

Schema validation is an opt-in make check-schema via xmllint, not an
in-suite assertion: validating XSD needs an XML library and the
dependency list is frozen. It prints SKIPPED loudly when xmllint is
absent, because a silent skip reads as a pass. The suite asserts
well-formedness properties directly instead.

This corrects the design spec, which claimed in-test validation.

1 files changed, 48 insertions, 0 deletions

diff --git a/lib/render/emit_xml.ml b/lib/render/emit_xml.ml
new file mode 100644
index 0000000..4e4b51a
--- /dev/null
+++ b/lib/render/emit_xml.ml
@@ -0,0 +1,48 @@
+(* emit_xml.ml *)
+module T = Template
+
+let escape s = Escape.apply Escape.Xml s
+
+let get v k = match v with T.Obj kvs -> List.assoc_opt k kvs | _ -> None
+let s v k = match get v k with Some (T.Str x) -> x | _ -> ""
+let el b name value =
+  Buffer.add_string b ("      <" ^ name ^ ">" ^ escape value ^ "</" ^ name ^ ">\n")
+
+let day b d =
+  Buffer.add_string b ("    <day date=\"" ^ escape (s d "iso") ^ "\">\n");
+  el b "season" (s d "season");
+  el b "week" (s d "week");
+  el b "slug" (s d "slug");
+  el b "rank" (s d "rank");
+  el b "colour" (s d "colour");
+  el b "subject" (s d "subject");
+  (match get d "name" with
+   | Some (T.Obj kvs) ->
+       List.iter
+         (fun (lang, v) ->
+           match v with
+           | T.Str x -> Buffer.add_string b ("      <name lang=\"" ^ escape lang ^ "\">" ^ escape x ^ "</name>\n")
+           | _ -> ())
+         kvs
+   | _ -> ());
+  (match get d "comms" with
+   | Some (T.List l) ->
+       List.iter (fun c -> Buffer.add_string b ("      <commemoration>" ^ escape (s c "slug") ^ "</commemoration>\n")) l
+   | _ -> ());
+  let cite name value =
+    if value <> "" then
+      Buffer.add_string b ("      <citation part=\"" ^ name ^ "\">" ^ escape value ^ "</citation>\n")
+  in
+  cite "first" (s d "first");
+  cite "gospel" (s d "gospel");
+  Buffer.add_string b "    </day>\n"
+
+let year v =
+  let b = Buffer.create (128 * 1024) in
+  Buffer.add_string b "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n";
+  Buffer.add_string b
+    ("<calendar rite=\"" ^ escape (s v "rite") ^ "\" year=\"" ^ escape (s v "year") ^ "\">\n");
+  Buffer.add_string b "  <days>\n";
+  (match get v "days" with Some (T.List l) -> List.iter (day b) l | _ -> ());
+  Buffer.add_string b "  </days>\n</calendar>\n";
+  Buffer.contents b