Conditionals must be updated to match schema

[kdk]

Addresses #1283 by updating assemble_circuits to replace QASM-style conditionals with a bfunc+Qobj-conditional. Also, updates qobj json schema to allow bfuncs with single integer register and memory attributes.

[kdk]

Should be on hold until #861 supports qobj-conditionals for basic aer.

[diego-plan9]

Also, updates qobj json schema to allow bfuncs with single integer register and memory attributes.

Can you add the type: specs label, if indeed the PR contains changes to the schema? It would help in collecting the list of schema changes and book-keeping in general.

[kdk]

Can be taken off on-hold after #1955 merges.

[ajavadia]

can you please rebase this? circuits_to_qobj is now deprecated in favor of qiskit.compiler.assembler (#1856) and there are a couple changes to qobj (#1909)

[ajavadia]

The 'conditional' field in a qobj should be an integer right (conditioned on a single register bit)? I wonder why the schema has it as follows:

                "conditional": {
                    "oneOf": [
                        {
                            "minimum": 0,
                            "type": "integer"
                        },
                        {
                            "type": "object"
                        }
                    ]

                },

It should definitely NOT be an array. But the example given in #1283 seems to expect an array. @chriseclectic can you double check that in Aer you don't expect an array?

With this patch, that example correctly outputs integers for the conditionals:

[QasmQobjInstruction(mask='0x3', name='bfunc', register=2, relation='==', val='0x0'),
 QasmQobjInstruction(conditional=2, name='x', qubits=[0]),
 QasmQobjInstruction(mask='0x3', name='bfunc', register=3, relation='==', val='0x1'),
 QasmQobjInstruction(conditional=3, name='y', qubits=[0]),
 QasmQobjInstruction(mask='0x3', name='bfunc', register=4, relation='==', val='0x2'),
 QasmQobjInstruction(conditional=4, name='z', qubits=[0]),
 QasmQobjInstruction(mask='0x3', name='bfunc', register=5, relation='==', val='0x3'),
 QasmQobjInstruction(conditional=5, name='h', qubits=[0])]

[kdk]

@ajavadia Updated, thanks for the comments.

Agree that conditonals in the schema can be either integers (qobj-style) for objects (deprecated qasm-style). I don't know of a case where they would be an array.

aer checks for an integer, and falls back to assuming an object:
https://github.com/Qiskit/qiskit-aer/blob/e002af4f02cb956d8a9d73881d9e63e6a9e5c162/src/framework/operations.hpp#L511
basic-aer does the same:
https://github.com/Qiskit/qiskit-terra/blob/b123277669445bf1e8b1e2533c6db9d4a4ed0e84/qiskit/providers/basicaer/qasm_simulator.py#L496