[TTreeReader] No diagnostics printed before crash when reading a type with no dictionaries

[eguiraud]

Given a tree with a branch of type map<string, bool>, like the one in this forum post, reading it with TTreeReader just yields a crash, while reading it with TTree first prints an error about the missing dictionary, then crashes.

TTreeReader

void repro_treereader() {
  TFile f("flatntuple_MC_.root");
  auto *t = f.Get<TTree>("ntuplizer/tree");
  R__ASSERT(t != nullptr);
  TTreeReader r(t);
  TTreeReaderValue<std::map<std::string, bool>> rv(r, "HLT_BPH_isFired");
  r.Next();
  *rv;
}

$ root -l repro_treereader.C
root [0]
Processing repro_treereader.C...

 *** Break *** segmentation violation
Root > .qqqqq
Info in <TRint::ProcessLine>: Bye... (try '.qqqqqqq' if still running)

 *** Break *** segmentation violation
Root > .qqqqqqq

TTree

void repro_tree() {
  TFile f("flatntuple_MC_.root");
  auto *t = f.Get<TTree>("ntuplizer/tree");
  R__ASSERT(t != nullptr);
  std::map<std::string, bool> *m = nullptr;
  t->SetBranchAddress("HLT_BPH_isFired", &m);
  t->GetEntry(0);
}

$ root -l -b -q repro_tree.C

Processing repro_tree.C...
Error in <TTree::SetBranchAddress>: The class requested (map<string,bool>) for the branch "HLT_BPH_isFired" is an instance of an stl collection and does not have a compiled CollectionProxy. Please generate the dictionary for this collection (map<string,bool>) to avoid to write corrupted data.

 *** Break *** segmentation violation
Root >
 *** Break *** segmentation violation

The TTreeReader version should also print the error, so users don't get confused.

[pcanal]

The second case fails because the I/O representation of the map is different from the compiler and the user is requested the former to loaded in the later.
The first case is failing to warn because TTreeReader is

• asking the TTree to manage the memory (in which case, for example, TTreeFormula can still read/use the data)
• unconditionally casting the address to the compile form
  The solution is to add code to TTreeReader to check if the type is properly loaded (see code in TTree::SetBranchAddress[Impl])