reorganize some hover info in Sec_Page

src/rntuple.cpp

@@ -62,6 +62,34 @@ ROOT::Experimental::RNTupleDescriptor create_descriptor(Arena *arena, RMicroFile
   return descriptor;
 }
 
+internal
+String8 build_fully_qualified_field_name(Arena *arena, const ROOT::Experimental::RNTupleDescriptor &desc,
+                                         const ROOT::Experimental::RFieldDescriptor *field_desc)
+{
+  String8_Node *sn = push_str8_node(arena, nullptr, "%s", field_desc->GetFieldName().c_str());
+  ROOT::Experimental::DescriptorId_t field_id = field_desc->GetParentId();
+  u64 size = sn->str.size;
+  while (field_id != ROOT::Experimental::kInvalidDescriptorId) {
+    field_desc = &desc.GetFieldDescriptor(field_id);
+    if (field_desc->GetFieldName().empty())
+      break;
+    sn = push_str8_node(arena, sn, "%s", field_desc->GetFieldName().c_str());
+    field_id = field_desc->GetParentId();
+    size += sn->str.size + 1;
+  }
+  String8 str;
+  str.str = arena_push_array_nozero<u8>(arena, size + 1);
+  str.str[size] = 0;
+  str.size = 0;
+  for (String8_Node *snode = sn; snode; snode = snode->prev) {
+    memcpy(str.str + str.size, snode->str.str, snode->str.size);
+    str.size += snode->str.size;
+    if (str.size < size)
+      str.str[str.size++] = '.';
+  }
+  return str;
+}
+  
 internal
 void gather_ntuple_metadata(Arena *arena, RMicroFileReader &reader, const RNTuple_File_Info &info, RNTuple_Data &rndata)
 {
@@ -112,6 +140,8 @@ void gather_ntuple_metadata(Arena *arena, RMicroFileReader &reader, const RNTupl
     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
+      const auto &field_desc = descriptor.GetFieldDescriptor(col_descriptor.GetFieldId());
+      const String8 owner_field_name = build_fully_qualified_field_name(arena, descriptor, &field_desc);
 
       // insert page infos sorted by byte range
       const auto &page_range = cluster_desc.GetPageRange(col_range.fPhysicalColumnId);
@@ -126,6 +156,7 @@ void gather_ntuple_metadata(Arena *arena, RMicroFileReader &reader, const RNTupl
         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());
+        pinfo->owner_field_name = owner_field_name;
         pinfo->bits_per_elem = col_descriptor.GetBitsOnStorage();
 
         Cluster_Info &cluster = clusters[pinfo->cluster_id];
@@ -686,6 +717,9 @@ struct Try_Sec_Hover_Fn {
   template <typename T>
   b8 field(const char *desc_fmt, Display_Fn<T> display_val = hover_display_val_be<T>) const
   {
+    if constexpr (std::is_same_v<T, String8>) {
+      return field_str8(desc_fmt, display_val);
+    } else {
       u64 field_len = sizeof(T);
       if (roff < cur_field_off + field_len) {
         info.rng = { start + cur_field_off, field_len };
@@ -697,9 +731,9 @@ struct Try_Sec_Hover_Fn {
       cur_field_off += field_len;
       return false;
     }
+  }
 
-  template <>
-  b8 field<String8>(const char *desc_fmt, Display_Fn<String8> display_val) const
+  b8 field_str8(const char *desc_fmt, Display_Fn<String8> display_val) const
   {
     u8 str_size = data[start + cur_field_off];
     if (roff < cur_field_off + 1 + str_size) {
@@ -748,7 +782,11 @@ struct Try_Sec_Hover_Fn {
         return true;
       }
       // discard the description (it's fine since it's allocated in the scratch arena)
-      info.desc->first_child = nullptr;
+      if (info.desc->first_child == info.desc->last_child) {
+        info.desc->first_child = info.desc->last_child = nullptr;
+      } else {
+        info.desc->last_child = info.desc->last_child->prev;
+      }
       cur_field_off += range_len;
     }
     return false;
@@ -811,8 +849,12 @@ Sec_Hover_Info get_section_hover_info(Arena *arena, Section section, u64 off, co
   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 (%u b)]", 
-                               sec_name.c(), pinfo->elem_type_name.c(), abs(pinfo->n_elems), pinfo->bits_per_elem);
+    info.desc = push_str8_node(arena, nullptr, "%s [%s]", 
+                               sec_name.c(), pinfo->elem_type_name.c());
+    push_str8_node_child(arena, info.desc, "Field: %s", pinfo->owner_field_name.c());
+    push_str8_node_child(arena, info.desc, "N. Elems: %d", abs(pinfo->n_elems));
+    push_str8_node_child(arena, info.desc, "Bits per elem: %u", pinfo->bits_per_elem);
+    push_str8_node_child(arena, info.desc, "-----------");
   } else {
     info.desc = push_str8_node(arena, nullptr, "%s", sec_name.c());
   }

src/rntuple.h

@@ -20,6 +20,7 @@ struct Page_Info_Node {
 
   u8 bits_per_elem;
   String8 elem_type_name;
+  String8 owner_field_name;
 
   inline u64 checksum_size() const {
     return (n_elems < 0) * 8;

src/str.cpp

@@ -48,8 +48,13 @@ String8_Node *push_str8_node(Arena *arena, String8_Node *prev, const char *fmt,
   snode->str = push_str8fv(arena, fmt, args);
   va_end(args);
 
-  if (prev)
+  if (prev) {
     prev->next = snode;
+    snode->head = prev->head;
+  } else {
+    snode->head = snode;
+  }
+  snode->prev = prev;
 
   return snode;
 }
@@ -66,6 +71,7 @@ String8_Node *push_str8_node_child(Arena *arena, String8_Node *parent, const cha
   snode->str = push_str8fv(arena, fmt, args);
   va_end(args);
 
+  snode->prev = parent->last_child;
   if (parent->first_child) {
     parent->last_child->next = snode;
     parent->last_child = snode;

src/str.h

@@ -12,7 +12,7 @@ struct String8 {
 #define str8(s) String8 { (u8*)(s), sizeof(s) - 1 }
 
 struct String8_Node {
-  String8_Node *next;
+  String8_Node *next, *prev, *head;
   String8_Node *first_child, *last_child;
   String8 str;
 };