evalengine: implement AggregateEvalTypes

[vmg]

Description

As requested by @systay in #15069 (review), this PR implements a helper in the evalengine that performs type aggregation on the engine's native Type struct, as opposed to sqltypes.Type which is what we were previously using.

cc @dbussink

Related Issue(s)

• Copy expression types to avoid weight_strings and derived tables #15069 (review)

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• "Backport to:" labels have been added if this change should be back-ported to release branches
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• Tests were added or are not required
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[vitess-bot]

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[dbussink]

I think we should have some tests for this as well?

[vmg]

Tests added, and whattdoyaknow they even caught a missing TODO that I've just implemented. :)

[systay]

🕺 License yo

[codecov]

Codecov Report

Attention: 14 lines in your changes are missing coverage. Please review.

Comparison is base (c156ca2) 47.70% compared to head (792f231) 47.70%.
Report is 5 commits behind head on main.

Files	Patch %	Lines
go/vt/vtgate/evalengine/api_type_aggregation.go	67.44%	11 Missing and 3 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #15085   +/-   ##
=======================================
  Coverage   47.70%   47.70%           
=======================================
  Files        1155     1155           
  Lines      240231   240264   +33     
=======================================
+ Hits       114610   114629   +19     
- Misses     117018   117032   +14     
  Partials     8603     8603           

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[dbussink]

Anything where this happens in practice? Wouldn’t instead MySQL fail with an overflow error if this happens?

[vmg]

No, this is not an overflow, this is explicitly listed in the refman:

If there is a combination of signed and unsigned integer types, the result is signed and the precision may be higher. For example, if the types are signed INT and unsigned INT, the result is signed BIGINT.

The exception is unsigned BIGINT combined with any signed integer type. The result is DECIMAL with sufficient precision and scale 0.

[dbussink]

One question I had but doesn’t have to be blocking.