fix: $if inside with is { [x: string]: any }[].

[igalklebanov]

closes #785.

This is voodoo, but works. Nothing else I tried did - the result of the inner $if was always { [x: string]: any }[].

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Name	Status	Preview	Comments	Updated (UTC)
kysely	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Dec 29, 2023 10:51am

[koskimas]

I haven't told you this yet, but I spent a couple of days trying to understand the type performance issues in Kysely by profiling the typescript compiler. I found very serious issues like just checking if a SelectQueryBuilder A extends SelectQueryBuilder B takes about 100ms per check! It doesn't even matter how simple the DB interface is. It takes over 200ms to compare two ExpressionBuilder types. The comparisons are cached and each subsequent comparison of the exact same types takes no time. But each new variant takes 200ms, which is horrifying.

These type comparisons only get done if the user writes functions that take a specific type as an argument, or if the user uses explicit types. Most common Kysely code is not affected.

Each method in SelectQueryBuilder and ExpressionBuilder that return a new variant of SelectQueryBuilder or ExpressionBuilder make this much worse each time. For example removing the selectNoFrom method from ExpressionBuilder takes the comparison time from 200ms to 100ms. I think we need to remove selectNoFrom from ExpressionBuilder.

I need to setup a performance test suite so that we can keep track of this each time we add/change something. Including this PR.

I think we need to start seriously thinking what we can add to Kysely or it'll become unusable very soon.

[igalklebanov]

Wow, great stuff. We sure need these benchmarks in place!

Was thinking about testing against multiple typescript versions too, at least the typings tests, so we're aware of what breaks for what version in latest 5 or so.

[koskimas]

Awesome! Checked this and it didn't slow things down.