Add custom_deserialisation argument to BasePass.from_dict

[sjdilkes]

Description

Replaces the use of nlohmann::json implicit construction of c++ objects from json using json and from_json with a new method deserialise that directly produces the PassPtr object. This allows a new argument custom_deserialisation to be supplied, which is a map between std::string corrresponding to CustomPass label and a Circuit->Circuit function that can be used to generate a customPass.

Related issues

Please mention any github issues addressed by this PR.

Checklist

• I have performed a self-review of my code.
• I have commented hard-to-understand parts of my code.
• I have made corresponding changes to the public API documentation.
• I have added tests that prove my fix is effective or that my feature works.
• I have updated the changelog with any user-facing changes.

[cqc-alec]

This argument should be optional, then we don't break the API.

[sjdilkes]

done

[cqc-alec]

Why can't this still return a dict?

[sjdilkes]

This is auto generated based on the serialise method now returning json in the c++

[cqc-alec]

If we called these to_json and from_json as before, can we avoid some of the changes in CompilerPass.cpp (not sure how the magic in nlohmann::json works).

[cqc-alec]

(And also change the signature to match the signatures in JSON_DECL but with the addition of the one optional argument.)

[sjdilkes]

My look through the nlohmann docs/code suggested that this wasn't possible, with the nlohmann magic relying one using well defined to_json/from_json with two arguments - the json and the object. So I don't think this is possible

[cqc-alec]

Need to add new tests for cusom-pass round serialization.

[sjdilkes]

done

[yao-cqc]

What about typing custom_deserialisation std::map<std::string, std::function<PassPtr(const ConfigType &)>>?
Here ConfigType can be something like nlohmann::json (I don't know what is the best), and it's used for parametrise the pass.

Then we can do something like this:

config ={
            "optimisation_level":optimisation_level,
            "seed":seed
        }
def get_routing_pass(config:Dict) -> CustomPass:
    def transformation(circ: Circuit) -> Circuit:
        # code for transforming the circuit
        # that uses the config
        return Circuit()
    return CustomPass(
        transformation,
        label="MyPass",
        config=config
        )

# serialisation
serialised_pass = get_routing_pass(config).to_dict()
# deserialisation
deserialised_pass = BasePass.from_dict(
    serialised_pass,
    custom_deserialisation={
        "MyPass": get_routing_pass
    }
)   

This does require adding a config field to CustomPass.

[sjdilkes]

What about typing custom_deserialisation std::map<std::string, std::function<PassPtr(const ConfigType &)>>? Here ConfigType can be something like nlohmann::json (I don't know what is the best), and it's used for parametrise the pass.

Then we can do something like this:

config ={
            "optimisation_level":optimisation_level,
            "seed":seed
        }
def get_routing_pass(config:Dict) -> CustomPass:
    def transformation(circ: Circuit) -> Circuit:
        # code for transforming the circuit
        # that uses the config
        return Circuit()
    return CustomPass(
        transformation,
        label="MyPass",
        config=config
        )

# serialisation
serialised_pass = get_routing_pass(config).to_dict()
# deserialisation
deserialised_pass = BasePass.from_dict(
    serialised_pass,
    custom_deserialisation={
        "MyPass": get_routing_pass
    }
)   

This does require adding a config field to CustomPass.

I think we would have to force the config to be std::map<std::string, int>to make thetypework at the c++ level. Personally I don't think not being able to pass parameters is a problem, as the user has fine control over what they pass tocustom_deserialisation`

[cqc-alec]

Thanks, just a couple of small comments.

Please also update changelog.

[cqc-alec]

This needs more documentation of the custom_deserialization parameter.

[sjdilkes]

added