Unexpected behavior when setting field to itself

[1matthewli]

Describe the bug
Under certain conditions, setting an entry of config to itself ends up clearing the entry entirely.

To Reproduce

cfg1 = OmegaConf.create({'a': 10})
cfg2 = OmegaConf.create({'b': 20})
cfg1["c"] = cfg2
print(cfg1["c"])
cfg1["c"] = cfg1["c"]
print(cfg1["c"])

The first print will be as expected, and the second print will be empty dictionary.
One workaround I have figured out is to set cfg2.__dict__['_metadata'].ref_type = typing.Any right after creating it, and it works as expected.

Expected behavior
It is expected for both prints to be the same, potentially with some interpolation resolution happening on access.

Additional context

• OmegaConf version: 2.0.4
• Python version: 3.7.9
• Operating system : Ubuntu 16.04.7 LTS
• Please provide a minimal repro

[omry]

Thanks for reporting.