Fix Context.Tag unification

[KhraksMamtsov]

Type

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

Description

Related

• Related Issue #
• Closes #

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🦋 Changeset detected

Latest commit: aa64445

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

This PR includes changesets to release 35 packages

Name	Type
effect	Patch
@effect/cli	Patch
@effect/cluster-browser	Patch
@effect/cluster-node	Patch
@effect/cluster-workflow	Patch
@effect/cluster	Patch
@effect/experimental	Patch
@effect/opentelemetry	Patch
@effect/platform-browser	Patch
@effect/platform-bun	Patch
@effect/platform-node-shared	Patch
@effect/platform-node	Patch
@effect/platform	Patch
@effect/printer-ansi	Patch
@effect/printer	Patch
@effect/rpc-http	Patch
@effect/rpc	Patch
@effect/sql-clickhouse	Patch
@effect/sql-d1	Patch
@effect/sql-drizzle	Patch
@effect/sql-kysely	Patch
@effect/sql-libsql	Patch
@effect/sql-mssql	Patch
@effect/sql-mysql2	Patch
@effect/sql-pg	Patch
@effect/sql-sqlite-bun	Patch
@effect/sql-sqlite-do	Patch
@effect/sql-sqlite-node	Patch
@effect/sql-sqlite-react-native	Patch
@effect/sql-sqlite-wasm	Patch
@effect/sql	Patch
@effect/typeclass	Patch
@effect/vitest	Patch
@effect/ai	Patch
@effect/ai-openai	Patch

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[KhraksMamtsov]

@mikearnaldi
I investigated the issue and concluded that TypeScript fails to infer types, for example, in the case of Layer.succeed used with this in class body(It looks like a shortcoming on Typescript's side because it works if the function is used outside the class body).

The issue can be resolved by using type parameters directly instead of inferring them from the provided tag — this approach is used in Micro(https://github.com/Effect-TS/effect/blob/main/packages/effect/src/Micro.ts#L1835) and other modules.

// before
export const succeed: {
  <T extends Context.Tag<any, any>>(tag: T): (resource: Context.Tag.Service<T>) => Layer<Context.Tag.Identifier<T>>
  <T extends Context.Tag<any, any>>(
    tag: T,
    resource: Context.Tag.Service<T>
  ): Layer<Context.Tag.Identifier<T>>
} = internal.succeed
// after 
export const succeed: {
  <I, S>(tag: Context.Tag<I, S>): (resource: S) => Layer<I>
  <I, S>(tag: Context.Tag<I, S>, resource: S): Layer<I>
} = internal.succeed

This approach seems more correct since type parameters are invariant, and union tags cannot be unified into a tag of unions.

However, this would be a breaking change, though it might be reasonable to treat it as a bug fix.
What do you think? I'm not sure whether the use case for unification is common enough to justify fixing it at the cost of a breaking change. On the other hand, I believe this change is theoretically correct.