Constant doesn't take effect if declared at the end of `Package.swift`

[MahdiBM]

Description

A constant of type [SwiftSettings] doesn't take effect at all if declared at the end of the Package.swift. There are no warnings or errors either. It's just a silent fail.
It still does take effect if declared at the beginning.

I would assume the scope of the issue is larger than just array of SwiftSettings. This is just what I caught in Penny.

This is a preview of the reproducible example:

// swift-tools-version: 5.8
// The swift-tools-version declares the minimum version of Swift required to build this package.

import PackageDescription

/// Uncomment this, and the `ExistentialAny` settings **will** take effect.
/// Comment the one below instead.
//let swiftSettings: [SwiftSetting] = [
//    .unsafeFlags(["-enable-upcoming-feature", "ExistentialAny"])
//]

let package = Package(
    name: "SPMPackageConstantsBug",
    products: [
        // Products define the executables and libraries a package produces, making them visible to other packages.
        .library(
            name: "SPMPackageConstantsBug",
            targets: ["SPMPackageConstantsBug"]),
    ],
    targets: [
        // Targets are the basic building blocks of a package, defining a module or a test suite.
        // Targets can depend on other targets in this package and products from dependencies.
        .target(
            name: "SPMPackageConstantsBug",
            swiftSettings: swiftSettings
        )
    ]
)


/// Uncomment this, and the `ExistentialAny` settings **won't** take effect.
/// Comment the one above instead.
let swiftSettings: [SwiftSetting] = [
    .unsafeFlags(["-enable-upcoming-feature", "ExistentialAny"])
]

Expected behavior

The declared constant should just work.

Actual behavior

The declared constant fails silently if at the end of a file.

Steps to reproduce

• Clone https://github.com/MahdiBM/SPMPackageConstantsBug
• Go to Package.swift.
• Comment and uncomment the two swiftSettings constants. Rebuild (Clean build possibly needed).
• Observe the inconsistent behavior.

Swift Package Manager version/commit hash

swift package --version: Swift Package Manager - Swift 5.8.0

Swift & OS version (output of swift --version ; uname -a)

% swift --version ; uname -a
swift-driver version: 1.75.2 Apple Swift version 5.8 (swiftlang-5.8.0.124.2 clang-1403.0.22.11.100)
Target: arm64-apple-macosx13.0
Darwin MahdiBM-Macbook.local 22.4.0 Darwin Kernel Version 22.4.0: Mon Mar  6 20:59:28 PST 2023; root:xnu-8796.101.5~3/RELEASE_ARM64_T6000 arm64

[neonichu]

Feels like a compiler issue?

I would expect this to not compile, e.g. can be reproduced with

print(lunch)

let lunch: [String] = ["foo"]

as well, but that crashes at runtime. The same code inside a function yields a more expected

bar.swift:2:8: error: use of local variable 'lunch' before its declaration
        print(lunch)
              ^
bar.swift:4:6: note: 'lunch' declared here
        let lunch: [String] = [

Maybe a quirk specific to top-level code.

[neonichu]

@shahmishal would you mind transferring over to the Swift repo?

[hamishknight]

Yeah this is a known issue with top-level variables