more type safe dual signature, closes #2967

[kristiannotari]

Type

• Refactor
• Feature
• Bug Fix
• Optimization
• Documentation Update

Description

Ad discussed in #2967, the dual type signature could be improved to avoid inferring an (...args: any[]) => any function type, which is assignable to every function signature you define for your dual api, and instead be precise over the implementation signature used. Of course the rest of the type signature would still be unsafe, but that's unavoidable.

This should help prevent errors when the type signature of the implementation used for the dual api is different to the one used as the final signature of such dual api.

NOTICE:

There are a couple of tests failing, regarding the schema package, which should not be related to this change. In fact, if you run the tests on the main this pr is based on, those tests keep failing.

This PR should be type level only. I added dtslint tests for the dual signature type checks I did in the first place that brought this change to exist. This should help to assert those cases are preserved in the future.

Related

• Closes More precise dual signature (prevent type errors/issues) #2967

[changeset-bot]

🦋 Changeset detected

Latest commit: fb2b42f

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 30 packages

Name	Type
@effect/typeclass	Major
@effect/platform	Major
effect	Minor
@effect/schema	Major
@effect/printer-ansi	Major
@effect/printer	Major
@effect/cli	Major
@effect/cluster-browser	Major
@effect/cluster-node	Major
@effect/cluster	Major
@effect/experimental	Major
@effect/platform-browser	Major
@effect/platform-bun	Major
@effect/platform-node-shared	Major
@effect/platform-node	Major
@effect/rpc-http	Major
@effect/rpc	Major
@effect/sql-d1	Major
@effect/sql-mssql	Major
@effect/sql-mysql2	Major
@effect/sql-pg	Major
@effect/sql-sqlite-bun	Major
@effect/sql-sqlite-node	Major
@effect/sql	Major
@effect/cluster-workflow	Major
@effect/opentelemetry	Major
@effect/sql-drizzle	Major
@effect/sql-sqlite-react-native	Major
@effect/sql-sqlite-wasm	Major
@effect/vitest	Major

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[kristiannotari]

Not sure why this is needed, but I had to put it here to make it work. Remember the dual application before was inferred as (...args: any[]) => any so this stuff is expected on complex cases, still, should be doable without casting. Probably the user facing error case is giving some problems in using such types within the implementation code. Not sure how you all want to deal with this, so I left it here.

[mikearnaldi]

Imho seems to be over complexifying usage, also it would be a breaking change that potentially breaks user code, not sure about it

[kristiannotari]

Imho seems to be over complexifying usage, also it would be a breaking change that potentially breaks user code, not sure about it

Usage should be the same in the "common case" scenario. There are a couple of instances where it can't infer automatically the whole type you'd like your dual signature to be, and require you to type the Other and Impl parts of it as generic types. This, btw, remove the need to type the implementation internally though, so it's more like moving and typing more directly than just inferring.

It's true some user code could be breaking due to this change, at least at the type level, since this PR is all about types, even if it's just about reordering types so to put generics in place. But it should help spot places where inference would put you in a possibly bad situation runtime wise, due to (...args: any[]) => any being inferred, which if you want to, could be considered a "fixed bug", in the sense the original user code could be potentially broken already, and this pr help spotting and let user fix those cases.

[tim-smart]

This would be a major change, the changeset will need adjusting.

dual was also made quite "relaxed" on purpose, so I'm on fence about this change.