The poor man's feature flag

[oscbyspro]

I don't know where to put this, but I invented a poor man's feature flag while working on (#55):

print("Hello")
/*/TAG*/print("Old")
//*TAG*/print("New")
print("World")

By replacing the regex /([*/])([*/])(TAG)\*/ with /$2$1$3*/ you can toggle lines on and off:

print("Hello")
//*TAG*/print("Old")
/*/TAG*/print("New")
print("World")

---

TL;DR: Here's the best one yet:

// The poor man's feature flag:
//
// FIND...: \/([*/-])([*/-])(FLAG)([*/-])\/
// REPLACE: \/$2$1$3$4\/
//
// LINE...: //*FLAG*/ or /*/FLAG*/
// HEAD...: //*FLAG-/ or /*/FLAG-/
// TAIL...: //-FLAG*/ or /-/FLAG*/

[oscbyspro]

It's even possible the stack them:

//*TAG0*///*TAG1*/print("1st")
//*TAG0*//*/TAG1*/print("2nd")
/*/TAG0*///*TAG1*/print("3rd")
/*/TAG0*//*/TAG1*/print("4th")

The above maps to something like:

let TAG0 = true 
let TAG1 = true

switch (TAG0, TAG1) {
case (false, false): print("1st")
case (false, true ): print("2nd")
case (true,  false): print("3rd")
case (true,  true ): print("4th") }

[oscbyspro]

Caveat: it does not work on // swift-tools-version: 5.8 because that one requires a specific format :(

[oscbyspro]

With some modifications to the original regex, you can write feature blocks too:

FIND...: (?:(\/\/|\*)(\/\/|\*))?/([*/])([*/])(TAG)\*/(?:(/)([*/])([*/]))?
REPLACE: $2$1/$4$3$5*/$6$8$7

Edit: this one cannot be stacked ☹️

print("Hello")

/*/TAG*//*/
print("Bave")
*///*/TAG*/

//*TAG*/print("New")
/*/TAG*/print("Old")

print("World")

print("Hello")

//*TAG*///*
print("Bave")
//*//*TAG*/

/*/TAG*/print("New")
//*TAG*/print("Old")

print("World")

[oscbyspro]

This regex is a bit tidier but the pattern has one more character:

FIND...: /([*/])([*/])(TAG\*)/(?:(/)([*/])([*/])(\*))?
REPLACE: /$2$1$3/$4$6$5$7

Edit: this one can be stacked in-line 🥳
Edit: this one cannot be stacked in-row ☹️

print("Hello")

/*/TAG*//*/*
print("Bave")
//**/*/TAG*/

//*TAG*/print("New")
/*/TAG*/print("Old")

print("World")

print("Hello")

//*TAG*///**
print("Bave")
//**//*TAG*/

/*/TAG*/print("New")
//*TAG*/print("Old")

print("World")

[oscbyspro]

Oh, I like this regex and pattern:

FIND...: ([*/][*/])?/([*/])([*/])(TAG\*)/([*/][*/])?
REPLACE: $5/$3$2$4/$1

Edit: this one cannot be stacked ☹️

print("Hello")

/*/*/TAG*/
print("Bave")
*//*/TAG*/

//*TAG*//*
print("Cowardly")
//*TAG*/*/

//*TAG*/print("New")
/*/TAG*/print("Old")

print("World")

print("Hello")

//*TAG*//*
print("Bave")
//*TAG*/*/

/*/*/TAG*/
print("Cowardly")
*//*/TAG*/

/*/TAG*/print("New")
//*TAG*/print("Old")

print("World")

[oscbyspro]

Here's a cool one that forms both stackable lines and feature blocks:

// FIND...: (?:(\/\*)(?:(\*)(\/)|(\/)(\*)))?\/(?:(\*)(\/)|(\/)(\*))(TAG0\*)\/(?:(?:(\*)(\/)|(\/)(\*))(\*\/))?
// REPLACE: $01$03$02$05$04\/$7$06$09$08$10\/$12$11$14$13$15

print("Hello")

//*TAG0*///*TAG1*/ print("1th")
/*/TAG0*//*/TAG1*/ print("2nd")
//*TAG0*///*TAG1*/ print("3rd")
//*TAG0*//*/TAG1*/ print("4th")

/**//*/TAG0*/
/*/*//*TAG1*/
print("Cruel")
//*TAG1*/*/*/
/**//*/TAG1*/
print("Clown")
/*/TAG1*//**/
/*/TAG0*//**/
/*/*//*TAG0*/
/*/*//*TAG1*/
print("Sweet")
//*TAG1*/*/*/
/**//*/TAG1*/
print("Brave")
/*/TAG1*//**/
//*TAG0*/*/*/

print("World")

print("Hello")

//*TAG0*///*TAG1*/ print("1th")
//*TAG0*//*/TAG1*/ print("2nd")
/*/TAG0*///*TAG1*/ print("3rd")
/*/TAG0*//*/TAG1*/ print("4th")

/*/*//*TAG0*/
/*/*//*TAG1*/
print("Cruel")
//*TAG1*/*/*/
/**//*/TAG1*/
print("Clown")
/*/TAG1*//**/
//*TAG0*/*/*/
/**//*/TAG0*/
/*/*//*TAG1*/
print("Sweet")
//*TAG1*/*/*/
/**//*/TAG1*/
print("Brave")
/*/TAG1*//**/
/*/TAG0*//**/

print("World")

[oscbyspro]

OK, this one's genius:

// FIND...: \/([/*!])([/*!])(FLAG)([*!])\/
// REPLACE: \/$2$1$3$4\/
//
// LINE...: //*FLAG*/ or /*/FLAG*/
// HEAD...: //*FLAG!/ or /*/FLAG!/
// TAIL...: //!FLAG*/ or /!/FLAG*/

Edit: I suppose - is easier to read than !.

/*/TAG0*///*TAG1*/ print("1th")
/*/TAG0*//*/TAG1*/ print("2nd")
//*TAG0*///*TAG1*/ print("3rd")
//*TAG0*//*/TAG1*/ print("4th")

//*TAG0!/
/*/TAG1!/
print("1st")
/!/TAG1*/
//*TAG1!/
print("2nd")
//!TAG1*/
//!TAG0*/
/*/TAG0!/
/*/TAG1!/
print("3rd")
/!/TAG1*/
//*TAG1!/
print("4th")
//!TAG1*/
/!/TAG0*/

//*TAG0*///*TAG1*/ print("1th")
//*TAG0*//*/TAG1*/ print("2nd")
/*/TAG0*///*TAG1*/ print("3rd")
/*/TAG0*//*/TAG1*/ print("4th")

/*/TAG0!/
/*/TAG1!/
print("1st")
/!/TAG1*/
//*TAG1!/
print("2nd")
//!TAG1*/
/!/TAG0*/
//*TAG0!/
/*/TAG1!/
print("3rd")
/!/TAG1*/
//*TAG1!/
print("4th")
//!TAG1*/
//!TAG0*/

[oscbyspro]

Look at me. I am the compiler now 👀

[ypopovych]

you can do it simpler inside the Swift parts.

Add compiler definitions to SPM target like swiftSettings: [.define("SBI")] end in code check it as #if SBI ... #else ... #endif. The same can be done in CocoaPods through xcode target configuration - add the -DSBI compiler flag.

In the case of CocoaPods you can even set it up as an environment variable while calling the pod command and get it from there (Podfile is a Ruby file). So you can add/remove variables based on ENV settings. It will work because it will send serialized JSON to their trunk, not a file with custom code

[oscbyspro]

I see, thanks for the advice. I thought flags were banned in Swift packages for some reason, but perhaps that's just .unsafeFlags(_:_:)? Or maybe I was completely mistaken.

[ypopovych]

.unsafeFlags(_:_:) is banned, yes. Other is good.

[ypopovych]

// swift-tools-version: 5.8 can be simply set to 5.7, I haven't found where you need 5.8 SPM features. Inside code simply use #if swift(>=5.8) ... #else ... #endif for features that require 5.8+

[oscbyspro]

I see. I'll change it to 5.7. I think I wanted the pointer methods from SE-0370 at some point, but then it turned out I didn't need them as I ended up doing things differently (#21).

[oscbyspro]

...and obviously I wanted to use StaticBigInt.

[ypopovych]

We had a discussion on Swift forums before about the #if available(...) macro method, but it was never implemented. Only #available and @available. If we had this method SBI could be implemented simply by macro definitions and automatically enabled when built for the new OS.

[oscbyspro]

That's what I wanted to do but it wasn't an option, then I got a bit too creative 😅

[ypopovych]

so for the SBI feature in the code, it can be like

#if swift(>=5.8) && SBI
extension NBKDoubleWidth { 
 // StaticBigInt code
}
#else 
extension NBKDoubleWidth { 
 // Int64 code
}
#endif

and in Package.swift

// swift-tools-version: 5.7
//=----------------------------------------------------------------------------=
// This source file is part of the Numberick open source project.
//
// Copyright (c) 2023 Oscar Byström Ericsson
// Licensed under Apache License, Version 2.0
//
// See http://www.apache.org/licenses/LICENSE-2.0 for license information.
//=----------------------------------------------------------------------------=

import PackageDescription

//*============================================================================*
// MARK: * Numberick
//*============================================================================*

// CHANGE THIS VARIABLE BY REGEX TO true
let featureStaticBigInt = false

// it's a var, not a let, because we will modify it
var package = Package(
    name: "Numberick",
    platforms: [
        .iOS(.v14),
        .macCatalyst(.v14),
        .macOS(.v11),
        .tvOS(.v14),
        .watchOS(.v7),
    ],
    products: [
        //=--------------------------------------=
        // NBK
        //=--------------------------------------=
        .library(
        name: "Numberick",
        targets: ["Numberick"]),
        //=--------------------------------------=
        // NBK x Core Kit
        //=--------------------------------------=
        .library(
        name: "NBKCoreKit",
        targets: ["NBKCoreKit"]),
        //=--------------------------------------=
        // NBK x Double Width Kit
        //=--------------------------------------=
        .library(
        name: "NBKDoubleWidthKit",
        targets: ["NBKDoubleWidthKit"]),
    ],
    targets: [
        //=--------------------------------------=
        // NBK
        //=--------------------------------------=
        .target(
        name: "Numberick",
        dependencies: ["NBKCoreKit", "NBKDoubleWidthKit"]),
        //=--------------------------------------=
        // NBK x Core Kit
        //=--------------------------------------=
        .target(
        name: "NBKCoreKit",
        dependencies: []),
        
        .testTarget(
        name: "NBKCoreKitBenchmarks",
        dependencies: ["NBKCoreKit"]),
        
        .testTarget(
        name: "NBKCoreKitTests",
        dependencies: ["NBKCoreKit"]),
        //=--------------------------------------=
        // NBK x Double Width Kit
        //=--------------------------------------=
        .target(
        name: "NBKDoubleWidthKit",
        dependencies: ["NBKCoreKit"]),
        
        .testTarget(
        name: "NBKDoubleWidthKitBenchmarks",
        dependencies: ["NBKDoubleWidthKit"]),
        
        .testTarget(
        name: "NBKDoubleWidthKitTests",
        dependencies: ["NBKDoubleWidthKit"]),
    ]
)

if featureStaticBigInt {
    package.platforms = [.iOS("16.4"),  .macCatalyst("16.4"), .macOS("13.3"), .tvOS("16.4"), .watchOS("9.4")]
    package.targets.first{ $0.name == "NBKDoubleWidthKit" }!.swiftSettings = [.define("SBI")]
}

[ypopovych]

I have one idea. You can try it (I don't have right now access to a machine with swift 5.8)

// swift-tools-version: 5.7
//=----------------------------------------------------------------------------=
// This source file is part of the Numberick open source project.
//
// Copyright (c) 2023 Oscar Byström Ericsson
// Licensed under Apache License, Version 2.0
//
// See http://www.apache.org/licenses/LICENSE-2.0 for license information.
//=----------------------------------------------------------------------------=

import PackageDescription

//*============================================================================*
// MARK: * Numberick
//*============================================================================*

var package = Package(
    name: "Numberick",
    platforms: [
        .iOS(.v14),
        .macCatalyst(.v14),
        .macOS(.v11),
        .tvOS(.v14),
        .watchOS(.v7),
    ],
    products: [
        //=--------------------------------------=
        // NBK
        //=--------------------------------------=
        .library(
        name: "Numberick",
        targets: ["Numberick"]),
        //=--------------------------------------=
        // NBK x Core Kit
        //=--------------------------------------=
        .library(
        name: "NBKCoreKit",
        targets: ["NBKCoreKit"]),
        //=--------------------------------------=
        // NBK x Double Width Kit
        //=--------------------------------------=
        .library(
        name: "NBKDoubleWidthKit",
        targets: ["NBKDoubleWidthKit"]),
    ],
    targets: [
        //=--------------------------------------=
        // NBK
        //=--------------------------------------=
        .target(
        name: "Numberick",
        dependencies: ["NBKCoreKit", "NBKDoubleWidthKit"]),
        //=--------------------------------------=
        // NBK x Core Kit
        //=--------------------------------------=
        .target(
        name: "NBKCoreKit",
        dependencies: []),
        
        .testTarget(
        name: "NBKCoreKitBenchmarks",
        dependencies: ["NBKCoreKit"]),
        
        .testTarget(
        name: "NBKCoreKitTests",
        dependencies: ["NBKCoreKit"]),
        //=--------------------------------------=
        // NBK x Double Width Kit
        //=--------------------------------------=
        .target(
        name: "NBKDoubleWidthKit",
        dependencies: ["NBKCoreKit"]),
        
        .testTarget(
        name: "NBKDoubleWidthKitBenchmarks",
        dependencies: ["NBKDoubleWidthKit"]),
        
        .testTarget(
        name: "NBKDoubleWidthKitTests",
        dependencies: ["NBKDoubleWidthKit"]),
    ]
)

if #available(iOS 16.4, macCatalyst 16.4, macOS 13.3,
              tvOS 16.4, watchOS 9.4, *)
{
    package.targets.first{$0.name == "NBKDoubleWidthKit"}!.swiftSettings = [.define("SBI")]
}

[oscbyspro]

Hm. I could not get this method to work on iOS 15.0. Instead, I got:

🛑 Compiling for iOS 15.0, but module 'Numberick' has a minimum deployment target of iOS 16.4: [...]

[oscbyspro]

Oh, never-mind, I misread what you wanted to try.

[oscbyspro]

This time Numberick refuses to build 😞

🛑 'StaticBigInt' is only available in iOS 16.4 or newer // at init(integerLiteral:)

Also, it does not seem like the app deployment target affects the #available check.

[oscbyspro]

I checked on iOS 15, #available succeeds in the package manifest but fails inside the package. So, does #available inside the package manifest query the machine that builds it? It probably does given that it fails when I set the macOS version to 999.

[ypopovych]

I tested it on GitHub Actions too and it doesn't work. It uses a machine/SDK version for Package.swift, not a target version :(

[ypopovych]

updated CI scripts in the https://github.com/ypopovych/Numberick/tree/pods-swift57 branch.

How it works:

1. Testing
   In this mode, it enforces features from the CI config. It runs on different Xcode versions with different features enabled. The script expects variables in the Package.swift file to be written as let with${feature} = true|false. For CocoaPods, it sets the environment variable NDK_FEATURE_${feature}. Podspec file then checks the environment for this variable value and updates settings if it's 'true'. You can check how it works here: https://github.com/ypopovych/Numberick/actions/runs/5860477729
2. Deployment
   In this mode, it works in a different way. It sets variables based on variables in Package.swift. It parses them by regex and renaming all let with${feature} = true|false lines to NDK_FEATURE_${feature}=true|false environment variables. I did it this way so you can setup sources of the release in a proper way in Package.swift and it will be mirrored in CocoaPods releases.

[oscbyspro]

That sounds awesome. I'll have to set aside some time to audit the code.

[ypopovych]

I updated my branch from upstream main, right not it's simply 5 files - 2 GA workflows + 3 Podspecs

[oscbyspro]

Well, yes, I suppose so. I just want to make sure I understand the setup well enough to merge/maintain.

[ypopovych]

Sure. Ask if something is unclear.