Serializing/Deserializing type Any: bugfix and simplification

[kmalik22]

Summary:
Current serialization and de-serialization of type Any in PyText has a bug. This diff:

• Fixes the bug, by just simplifying handling of Any.
• Adds a unit-test that exposes the bug.

====================

PyText Config Serialization for Any

PyText config serializes type Any by prefixing the real type of the object before the actual object.
This type prepending is important for PyText specific types (like Model). However, for a generic type like Any, this is unnecessary, and instead causes a bug.

Eg: if a config looks like this:
class AConfig(ConfigBase):
a_param: Any

a_config: AConfig

And at run-time, the input is:

a_config: {
    a_param: [1, 2, 3]
}

Pytext will serialize this config by converting a_param into a dict, and pre-pending the type of the input:
a_config: {
a_param: {'list': [1,2,3]}
}

====================

Bug

When de-serializing a config, we handle this type prepending for Any something like this:
def _any_from_json(json_obj):
if(_is_dict(json_obj)):
# aha, this must be type pre-pending!
assert(len(json_obj) == 1
# return the first value
return list(json_obj.values())[0]

This creates a bug if something of type Any is actually a Dict. E.g.:

class AConfig(ConfigBase):
    param_2: Dict[str, Any]
a_config: AConfig

Assume at run-time, the input is:
a_config: {
"param_2" : {
"nested_param1": 10,
"nested_param2": 2,
}
}

Parsing this config generates an error:

{F235368935}

====================

Fix and simplification

This bug is fixed by simpler serialization of Any: type doesn't need to prepended at all

====================

Unit Test

Added a unit test that exposes the bug above by taking a json input, and checks that deserialized(serialized(input)) == input

====================

Who does this affect

AFAIK, only Federated Learning trainers use type Any (for information hiding). This doesn't affect anyone other than people working on Federated Learning.

Reviewed By: jessemin, psuzhanhy

Differential Revision: D21244134

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D21244134

[facebook-github-bot]

This pull request has been merged in 51de260.