Handling of std::conditional by Cling in ROOT 6.32.02.

[ktf]

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Description

When running with 6.32.02 the ALICE reconstruction we were plagued by errors like the following:

./itstpcMatch.log[16548:itstpc-track-writer]: Error in : o2::dataformats::AbstractRef<25,5,2>, unknown type: typename std::conditional<(32> mRef

which were not there when using 6.30.0. We have since been able to workaround this by doing:

https://github.com/AliceO2Group/AliceO2/pull/13310/files

however I was wondering if this is not some more serious issue. In particular I am puzzled by the "(32" template argument, which seems to indicate some weird memory overwrite / macro expansion of NBIT.

Reproducer

I do not have a simple reproducer.

ROOT version

6.32.02

Installation method

aliBuild

Operating system

Linux

Additional context

No response

[dpiparo]

I quickly tried to see whether the name normalisation had a bug, and that is not obvious

template<int NBIT>
struct S {
  using type = typename std::conditional<(NBIT > 32), uint64_t, typename std::conditional<(NBIT > 16), uint32_t, typename std::conditional<(NBIT > 8), uint16_t, uint8_t>::type>::type>;
};

void a(){
  using T = typename S<32>::type;
  auto c = TClass::GetClass(typeid(T));
  cout << c->GetName() << endl;
  // gives conditional<false,ULong64_t,unsigned int>
}

[ktf]

Indeed, that I tried as well and I can confirm it works also for us ... It looks like you need the whole parent class.

[ktf]

Ok, I have a very trivial reproducer. In our environment, when running the following on the root prompt:

root [19] TClassEdit::GetNormalizedName(foo, "std::conditional<(NBIT > 32), uint64_t, typename std::conditional<(NBIT > 16), uint32_t, typename std::conditional<(NBIT > 8), uint16_t, uint8_t>::type>::type>::type")

I get:

root [20] foo
(std::string &) "conditional<(NBIT>"

[ktf]

actually, even easier:

root [23] TClassEdit::GetNormalizedName(foo, "std::conditional<1 > 32, int, float>")
root [24] foo
(std::string &) "conditional<1>"

[ktf]

For the record, I confirm also that your example works for me a well. However I also have:

root [4] TClassEdit::GetNormalizedName(foo, "std::conditional<(1 > 32), int, float>")
root [5] foo
(std::string &) "conditional<(1>"

which is exactly the wrong behaviour I originally reported...

[ktf]

BTW, TClassEdit::GetNormalizedName is also broken in 6.30.01, so I suspect the issue we had is due to the way it is being used by TStreamerInfo::Build.

[ktf]

Any news on this issue? Do you need anything else on my side? Apparently my workaround prevents reading old data, so we might have to go back to the version which breaks.