[GH-3519] Deprecate passing the same class with different discriminator values.

[beberlei]

Prepares the deprecation for the later removal of this mapping inconsistency.

Related: #3519

[derrabus]

LGTM, once @greg0ire's suggestion is applied.

[mpdude]

@beberlei This might be an easy thing to bring to an end, and it would add one more mapping consistency check to the codebase.

[github-actions]

There hasn't been any activity on this pull request in the past 90 days, so it has been marked as stale and it will be closed automatically if no further activity occurs in the next 7 days.
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[stof]

shouldn't this target the 3.4.x branch instead, as this is about a deprecation for a removal in 4.0 ?

[stof]

And maybe the schema validator should already report an error for such case

[greg0ire]

@stof you're probably right about the target branch, this was created in 2022, and 3.0 did not exist back then. Regarding the schema validator, maybe the initial intent was to contribute the validation in the next major?

[stof]

AFAICT, the intent seems to be to turn the deprecation into a MappingException in the next major (which is stricter than something reported only by the SchemaValidator). But maybe the deprecation is indeed enough in that case, instead of turning it into an error reported only to people validating their schema.

[SenseException]

And maybe the schema validator should already report an error for such case

But maybe the deprecation is indeed enough in that case, instead of turning it into an error reported only to people validating their schema.

I assume the schema validator error report is off the table. (sql-pun intended)