feat(html): warn on the element types the renderer drops, instead of dropping them silently

CHANGELOG.md

@@ -16,6 +16,10 @@ The release run heads these entries with the version and opens a fresh
 
 ## Unreleased
 
+- The HTML renderer warns, rather than silently dropping, when it reaches an
+  element type it has no `translate_*` for. Across the test corpus that is
+  `page_break` and nothing else. Towards #150.
+
 - An ODF `draw:object` chart is drawn from the chart part's own markup, not
   from the replacement image beside it: bar, line, area, scatter, pie and ring,
   with their titles, legends, axes and series colours. An object holding no

src/odr/internal/html/document_element.cpp

@@ -3,6 +3,7 @@
 #include <odr/document_element.hpp>
 #include <odr/document_path.hpp>
 #include <odr/html.hpp>
+#include <odr/logger.hpp>
 #include <odr/style.hpp>
 
 #include <odr/internal/common/path.hpp>
@@ -19,6 +20,72 @@
 
 namespace odr::internal {
 
+namespace {
+
+/// Names every enumerator, with no `default`, so a type added to
+/// @ref ElementType has to be named here too.
+const char *element_type_name(const ElementType type) {
+  switch (type) {
+  case ElementType::none:
+    return "none";
+  case ElementType::root:
+    return "root";
+  case ElementType::slide:
+    return "slide";
+  case ElementType::sheet:
+    return "sheet";
+  case ElementType::page:
+    return "page";
+  case ElementType::master_page:
+    return "master_page";
+  case ElementType::sheet_cell:
+    return "sheet_cell";
+  case ElementType::text:
+    return "text";
+  case ElementType::line_break:
+    return "line_break";
+  case ElementType::page_break:
+    return "page_break";
+  case ElementType::paragraph:
+    return "paragraph";
+  case ElementType::span:
+    return "span";
+  case ElementType::link:
+    return "link";
+  case ElementType::bookmark:
+    return "bookmark";
+  case ElementType::list:
+    return "list";
+  case ElementType::list_item:
+    return "list_item";
+  case ElementType::table:
+    return "table";
+  case ElementType::table_column:
+    return "table_column";
+  case ElementType::table_row:
+    return "table_row";
+  case ElementType::table_cell:
+    return "table_cell";
+  case ElementType::frame:
+    return "frame";
+  case ElementType::image:
+    return "image";
+  case ElementType::rect:
+    return "rect";
+  case ElementType::line:
+    return "line";
+  case ElementType::circle:
+    return "circle";
+  case ElementType::custom_shape:
+    return "custom_shape";
+  case ElementType::group:
+    return "group";
+  }
+  return "?";
+}
+
+} // namespace
+
 void html::translate_children(const ElementRange &range,
                               const WritingState &state) {
   for (const Element child : range) {
@@ -78,7 +145,11 @@ void html::translate_element(const Element &element,
     translate_children(element.children(), state);
     break;
   default:
-    // TODO log
+    // The element and its whole subtree are dropped. Logged rather than
+    // thrown: a renderer shows what it can, and the corpus run is what ranks
+    // the gaps by how often they actually occur.
+    ODR_WARNING(state.logger(), "html: dropped unhandled element "
+                                    << element_type_name(element.type()));
     break;
   }
 }

test/src/html_output_test.cpp

@@ -194,7 +194,13 @@ TEST_P(HtmlOutputTests, html_meta) {
 
   const std::string output_path_tmp = output_path + "/tmp";
   fs::create_directories(output_path_tmp);
-  HtmlService service = html::translate(file, output_path_tmp, config);
+  // The renderer used to get the null logger, so nothing it reported was ever
+  // read. Warnings only: its debug output is per pdf operator and per svm
+  // action, and would bury the corpus log.
+  const Logger render_logger =
+      Logger::create_stdio("odr-test", LogLevel::warning);
+  HtmlService service =
+      html::translate(file, output_path_tmp, config, render_logger);
   Html html = service.bring_offline(output_path);
   fs::remove_all(output_path_tmp);