feat: Support union schemas

[edgarrmondragon]

Related:

• Advanced config validation requirements for SDK-based taps and targets #1519
• feat: Break out host, user, port, etc. into individual config values MeltanoLabs/tap-postgres#121
• bug: ConfigValidationError when ssh_tunnel disabled MeltanoLabs/tap-postgres#135

Docs: https://meltano-sdk--1525.org.readthedocs.build/en/1525/classes/typing/singer_sdk.typing.DiscriminatedUnion.html

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📚 Documentation preview 📚: https://meltano-sdk--1525.org.readthedocs.build/en/1525/

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Codecov Report

Merging #1525 (650c18c) into main (c6a8933) will decrease coverage by 0.14%.
The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##             main    #1525      +/-   ##
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- Coverage   86.12%   85.98%   -0.14%     
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- Misses        485      492       +7     
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Impacted Files	Coverage Δ
singer_sdk/typing.py	97.00% <100.00%> (+0.23%)	⬆️

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[edgarrmondragon]

@ReubenFrankel I'd love to get your thoughts on this? Is it helpful, intuitive?

[ReubenFrankel]

@edgarrmondragon I think this looks great - really like the syntax! I've spent a while thinking about what this might not cover with more complex cases, but I think its better to tackle those as and when they come up, since the only scenarios I can think of at the moment are pretty unrealistic. My only question is what does a validation error for this look like? Is it helpful to the user?

This would be great to get into tap-github once it's merged (see Accepted Config Options) - OneOf is perfect for the mode options (i.e. repositories, organizations, searches, etc).

[edgarrmondragon]

My only question is what does a validation error for this look like? Is it helpful to the user?

@ReubenFrankel The default jsonschema exception message is not the most readable:

jsonschema.exceptions.ValidationError: {'flow': 'oauth', 'client_id': '123', 'username': '456', 'password': '789'} is not valid under any of the given schemas

Failed validating 'oneOf' in schema:
    {'oneOf': [{'additionalProperties': False,
                'properties': {'client_id': {'secret': True,
                                             'type': ['string'],
                                             'writeOnly': True},
                               'client_secret': {'secret': True,
                                                 'type': ['string'],
                                                 'writeOnly': True},
                               'flow': {'const': 'oauth',
                                        'description': 'Discriminator for '
                                                       'object of type '
                                                       "'oauth'."}},
                'required': ['flow', 'client_id', 'client_secret'],
                'type': 'object'},
               {'additionalProperties': False,
                'properties': {'flow': {'const': 'password',
                                        'description': 'Discriminator for '
                                                       'object of type '
                                                       "'password'."},
                               'password': {'secret': True,
                                            'type': ['string'],
                                            'writeOnly': True},
                               'username': {'type': ['string']}},
                'required': ['flow', 'username', 'password'],
                'type': 'object'}]}

On instance:
    {'client_id': '123',
     'flow': 'oauth',
     'password': '789',
     'username': '456'}

But we could of course grab the context and print something that better explains the error and expectation. I have a PR where it might make sense to add that: #768.

[edgarrmondragon]

@kgpayne can you give this PR a look when get a chance?