Cross component prediction tool in VTM but not described in spec

[jonathang]

In VTM 5.0 within CABACReader::transform_unit, the following code may result in the decoding of a CCP flag, and then a CCP alpha value

        if( TU::hasCrossCompPredInfo( tu, compID ) )
        {
          cross_comp_pred( tu, compID );
        }


void CABACReader::cross_comp_pred( TransformUnit& tu, ComponentID compID )
{
  signed char alpha   = 0;
  unsigned    ctxBase = ( compID == COMPONENT_Cr ? 5 : 0 );
  unsigned    symbol  = m_BinDecoder.decodeBin( Ctx::CrossCompPred(ctxBase) );
  if( symbol )
  {
    // Cross-component prediction alpha is non-zero.
    symbol = m_BinDecoder.decodeBin( Ctx::CrossCompPred(ctxBase+1) );
    if( symbol )
    {
      // alpha is 2 (symbol=1), 4(symbol=2) or 8(symbol=3).
      // Read up to two more bits
      symbol += unary_max_symbol( Ctx::CrossCompPred(ctxBase+2), Ctx::CrossCompPred(ctxBase+3), 2 );
    }
    alpha = ( 1 << symbol );
    if( m_BinDecoder.decodeBin( Ctx::CrossCompPred(ctxBase+4) ) )
    {
      alpha = -alpha;
    }
  }
  tu.compAlpha[compID] = alpha;
}

In the current spec there are no syntax elements for CCP. Given the CCLM intra prediction mode and the joint chroma residual coding, is CCP to be removed?

[jonathang]

Seems resolved by ​https://vcgit.hhi.fraunhofer.de/jvet/VVCSoftware_VTM/-/merge_requests/1821