Pass current_state in when calling custom and built-in sources.

[mnbbrown]

This will allow sources to dynamically decided if to provide a value for the attribute. For example, a higher priority source can decided to leave the low-priority source "as is" if it's not None.

Note: I think this is considered a breaking change as the signature of __call__ on the source abstract type is changing.

See https://github.com/pydantic/pydantic-settings/issues/223#issuecomment-1913196648 for context Interested in the maintainers thoughts here :)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (40230ab) 97.69% compared to head (e024247) 97.71%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #224      +/-   ##
==========================================
+ Coverage   97.69%   97.71%   +0.01%     
==========================================
  Files           5        5              
  Lines         347      350       +3     
  Branches       76       76              
==========================================
+ Hits          339      342       +3     
  Misses          6        6              
  Partials        2        2              

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[hramezani]

Thanks @mnbbrown for this PR.

we need some tests for this and have to wait to merge it before V3 because it is a breaking change.

[hramezani]

Superseded by https://github.com/pydantic/pydantic-settings/pull/326