reducer .ifLet seems to be causing unable to type-check this expression in reasonable time

[tisohjung]

Description

Hello, I'd love to get any suggestions, thank you 🙏

I get type-check error in swift-composable-architecture version > 1.4.0
if I downgrade to 1.3.0 the error is gone.
if I comment out .ifLet chaining, the error is gone. It works up to 7 subFeatures

Here is the sample project where you can see main branch doesn't build, but feature/downgrade-tca branch works
I'd love to get any suggestions, thanks

https://github.com/tisohjung/ifletstore/blob/ad815a88a1969e7a7365e05b808ccfcbc295e294/IfLetStore/Feature1/Feature1.swift#L54

    .ifLet(\.subFeature1, action: /Action.subFeature1) { SubFeature1() }
    .ifLet(\.subFeature2, action: /Action.subFeature2) { SubFeature2() }
    .ifLet(\.subFeature3, action: /Action.subFeature3) { SubFeature3() }
    .ifLet(\.subFeature4, action: /Action.subFeature4) { SubFeature4() }
    .ifLet(\.subFeature5, action: /Action.subFeature5) { SubFeature5() }
    .ifLet(\.subFeature6, action: /Action.subFeature6) { SubFeature6() }
    .ifLet(\.subFeature7, action: /Action.subFeature7) { SubFeature7() }
    .ifLet(\.subFeature8, action: /Action.subFeature8) { SubFeature8() }
    .ifLet(\.subFeature9, action: /Action.subFeature9) { SubFeature9() }

Checklist

• I have determined whether this bug is also reproducible in a vanilla SwiftUI project.
• If possible, I've reproduced the issue using the main branch of this package.
• This issue hasn't been addressed in an existing GitHub issue or discussion.

Expected behavior

App should build on the latest version or main branch of swift-composable-architecture

Actual behavior

App build under version 1.3.0, and can't build above 1.4.0

error shows:
Feature1.swift:7:48 The compiler is unable to type-check this expression in reasonable time; try breaking up the expression into distinct sub-expressions

Steps to reproduce

if I comment out .ifLet chaining, the error is gone. it works up to 7 subFeatures

The Composable Architecture version information

1.6.0

Destination operating system

iOS 17.2

Xcode version information

Version 15.2 (15C500b)

Swift Compiler version information

swift-driver version: 1.87.3 Apple Swift version 5.9.2 (swiftlang-5.9.2.2.56 clang-1500.1.0.2.5)
Target: arm64-apple-macosx14.0

[stephencelis]

Hi @tisohjung! Version 1.4 introduced "case key path" overloads for ifLet, which unfortunately expands the type checking space enough to cause regressions like this. While we will be able to remove these overloads in 2.0, we cannot make breaking changes till then.

In the meantime, you can extract these helpers to a dedicated place to improve compile times:

extension Reducer where State == Feature1.State, Action == Feature1.Action {
  func subFeatures() -> some ReducerOf<Self> {
    self
      .ifLet(\.subFeature1, action: /Action.subFeature1) { SubFeature1() }
      .ifLet(\.subFeature2, action: /Action.subFeature2) { SubFeature2() }
      .ifLet(\.subFeature3, action: /Action.subFeature3) { SubFeature3() }
      .ifLet(\.subFeature4, action: /Action.subFeature4) { SubFeature4() }
      .ifLet(\.subFeature5, action: /Action.subFeature5) { SubFeature5() }
      .ifLet(\.subFeature6, action: /Action.subFeature6) { SubFeature6() }
      .ifLet(\.subFeature7, action: /Action.subFeature7) { SubFeature7() }
      .ifLet(\.subFeature8, action: /Action.subFeature8) { SubFeature8() }
      .ifLet(\.subFeature9, action: /Action.subFeature9) { SubFeature9() }
  }
}

And you can break these methods down into subFeatures1, subFeatures2, etc., if need be.

Since this is more of a compiler issue than a bug in the library, I'm going to convert to a discussion.

[tisohjung]

awesome thanks 👍

fix of the sample project is in feature/fix branch for those interested.
https://github.com/tisohjung/ifletstore/tree/feature/fix

extension Reducer where State == Feature1.State, Action == Feature1.Action {
  func subFeatures1to5() -> some ReducerOf<Self> {
    self
      .ifLet(\.subFeature1, action: /Action.subFeature1) { SubFeature1() }
      .ifLet(\.subFeature2, action: /Action.subFeature2) { SubFeature2() }
      .ifLet(\.subFeature3, action: /Action.subFeature3) { SubFeature3() }
      .ifLet(\.subFeature4, action: /Action.subFeature4) { SubFeature4() }
      .ifLet(\.subFeature5, action: /Action.subFeature5) { SubFeature5() }
  }

  func subFeatures6to9() -> some ReducerOf<Self> {
    self
      .ifLet(\.subFeature6, action: /Action.subFeature6) { SubFeature6() }
      .ifLet(\.subFeature7, action: /Action.subFeature7) { SubFeature7() }
      .ifLet(\.subFeature8, action: /Action.subFeature8) { SubFeature8() }
      .ifLet(\.subFeature9, action: /Action.subFeature9) { SubFeature9() }
  }
}