add type and n.elems info to hover page

src/rntuple.cpp

@@ -99,11 +99,18 @@ void gather_ntuple_metadata(Arena *arena, RMicroFileReader &reader, const RNTupl
 
   Cluster_Info *clusters = arena_push_array<Cluster_Info>(arena, descriptor.GetNActiveClusters());
 
+  // @ForeignAlloc: currently using directly the RColumnElementBase API which forces foreign allocations.
+  // If we don't want to have this we could create our own function to retrieve a column type name.
+  std::string elem_type_name;
+  
   // gather clusters and pages metadata
   for (const RClusterDescriptor &cluster_desc : descriptor.GetClusterIterable()) {
     ++n_clusters;
 
     for (const RClusterDescriptor::RColumnRange &col_range : cluster_desc.GetColumnRangeIterable()) {
+      const auto &col_descriptor = descriptor.GetColumnDescriptor(col_range.fPhysicalColumnId);
+      elem_type_name = RColumnElementBase::GetTypeName(col_descriptor.GetType()); // @ForeignAlloc
+
       // insert page infos sorted by byte range
       const auto &page_range = cluster_desc.GetPageRange(col_range.fPhysicalColumnId);
       for (const auto &page_info : page_range.fPageInfos) {
@@ -116,6 +123,7 @@ void gather_ntuple_metadata(Arena *arena, RMicroFileReader &reader, const RNTupl
         // If in the future we get RNTuples with more than 4B clusters we can just change the type to u64.
         assert(cluster_desc.GetId() <= UINT_MAX);
         pinfo->cluster_id = cluster_desc.GetId();
+        pinfo->elem_type_name = push_str8f(arena, "%s", elem_type_name.c_str());
 
         Cluster_Info &cluster = clusters[pinfo->cluster_id];
         if (!cluster.first_page || pinfo->range.start < cluster.first_page->range.start) {
@@ -474,6 +482,7 @@ Section find_section(App_State &app, u64 off, i64 hilite_cluster = -1)
       sec.pre_size = pre_size;
       sec.post_size = app.last_pinfo->checksum_size();
       sec.highlighted = hilite_cluster >= 0 && app.last_pinfo->cluster_id == (u64)hilite_cluster;
+      sec.info = app.last_pinfo;
       return sec;
     }
 
@@ -488,6 +497,7 @@ Section find_section(App_State &app, u64 off, i64 hilite_cluster = -1)
         sec.pre_size = pre_size;
         sec.post_size = app.last_pinfo->checksum_size();
         sec.highlighted = hilite_cluster >= 0 && app.last_pinfo->cluster_id == (u64)hilite_cluster;
+        sec.info = app.last_pinfo;
         return sec;
       }
     }
@@ -561,6 +571,7 @@ Section find_section(App_State &app, u64 off, i64 hilite_cluster = -1)
             sec.pre_size = pre_size;
             sec.post_size = pinfo->checksum_size();
             sec.highlighted = hilite_cluster >= 0 && pinfo->cluster_id == (u64)hilite_cluster;
+            sec.info = pinfo;
             return sec;
           }
         }
@@ -788,7 +799,14 @@ Sec_Hover_Info get_section_hover_info(Arena *arena, Section section, u64 off, co
   // printf("off: 0x%lX, sec start - pre_size: (0x%lX - %lu) = 0x%lX\n", off, section.range.start, section.pre_size, section.range.start - section.pre_size);
   assert(off >= section.range.start - section.pre_size);
   
-  info.desc = push_str8_node(arena, nullptr, section_names[section.id].c());
+  // Hover info header
+  String8 sec_name = section_names[section.id];
+  if (section.id == Sec_Page && section.info) {
+    Page_Info_Node *pinfo = (Page_Info_Node *)section.info;
+    info.desc = push_str8_node(arena, nullptr, "%s [%s, n.elems: %d]", sec_name.c(), pinfo->elem_type_name.c(), abs(pinfo->n_elems));
+  } else {
+    info.desc = push_str8_node(arena, nullptr, "%s", sec_name.c());
+  }
 
   u64 start = section.range.start - section.pre_size;
   u64 roff = off - start; // offset relative to `section`

src/rntuple.h

@@ -18,6 +18,8 @@ struct Page_Info_Node {
   u32 cluster_id;
   b8 is_first_in_cluster;
 
+  String8 elem_type_name;
+
   inline u64 checksum_size() const {
     return (n_elems < 0) * 8;
   }
@@ -120,6 +122,10 @@ struct Section {
   u64 pre_size;  // usually the TKey header, excluded from `range`
   u64 post_size; // usually the checksum, included in `range`
   b8 highlighted;
+
+  // Optional pointer to the specific information for the section.
+  // e.g. if the section is a Page this points to the relative Page_Info_Node
+  const void *info;
 };
 
 internal const String8 section_names[Sec_COUNT] = {

src/root/root_inc.h

@@ -1,3 +1,4 @@
 #include <ROOT/RNTupleSerialize.hxx>
 #include <ROOT/RNTupleDescriptor.hxx>
 #include <ROOT/RNTupleZip.hxx>
+#include <ROOT/RColumnElement.hxx>