Can't parse streams containing empty documents in 0.9.0

[wthrowe]

The following program prints 2 (correctly, I believe) with version 0.8.0, but prints 0 with version 0.9.0:

#include <iostream>
#include <yaml.h>

int main() {
  const char* const docs = R"(                                                  
---                                                                             
---                                                                             
A                                                                               
)";

  const auto parsed = YAML::LoadAll(docs);
  std::cout << parsed.size() << "\n";
  return 0;
}

This appears to have been caused by #1319.

[SGSSGene]

I can confirm that commit #254d72d53698236ba50b0203e730e4adc83fa6c4 introduces this bug.

So my understanding is, yaml-cpp accepted bad input like , PR #1318 fixes this.
Without PR #1318 yaml-cpp would get stuck into a infinite loop because it wouldn't parse any tokens?
Now #1319 fixes potential (currently unknown) loopholes like #1318 and avoids that YAML::LoadAll() gets stuck in an infinite loop.
But now we have the issue that if there are empty YAML documents YAML::LoadAll() accidentally detects as being stuck in an infinite loop an exits.

So what we need to do is replace the check on || builder.Root().IsNull()
with something like || !parser.IsArchivingProgress(). (This function currently does not exists)

[SGSSGene]

Hi @wthrowe ,
I wrote a potential fix in PR #1403 .

[wthrowe]

I have confirmed that our real code that hit this problem works again with yaml-cpp master. Thanks!