Compiler Crash When Building With Swift 6.2.x Release Toolchain (swift.org)

[briancoyner]

Summary

Building swift-configuration 1.0.0 with the Swift Static Linux SDK appears to cause the Swift 6.2.x compiler to crash. This was discovered after upgrading a project to Swift 6.2 and Hummingbird 2.18.x (which introduced a dependency on swift-configuration). Not sure if anyone else has witnessed and/ or reported this (did not find any reports).

Environment

Component	Version
swift-configuration	1.0.0
Swiftly	1.0.0
Swift	6.2.2 (swift-6.2.2-RELEASE)
Static Linux SDK	swift-6.2.2-release_static-linux-0.0.1
macOS	Tahoe 26.2
Selected Xcode	26.2.0

Note: Static Linux SDK 6.2.0 and 6.2.1 experience the same crash.

Build Command

The command below can be executed against a package that depends on swift-configuration or building swift-configuration directly.

swiftly run swift build -c release --swift-sdk aarch64-swift-linux-musl                                                                                 
                                                                                                                                                                                                     
[1/1] Planning build
Building for production...
error: compile command failed due to signal 6 (use -v to see invocation)                                                                                                                                                                                  
SIL verification failed: inconsistent stack heights entering basic block: state.Stack == foundState.Stack || isUnreachable()                                                                         

...
                                                                                                                                       
In function:                                                                                                                                                                                         
// FileProvider.init<A>(snapshotType:parsingOptions:filePath:allowMissing:fileSystem:)                                                                                                               
// Isolation: caller_isolation_inheriting                                                                                                                                                            

...

Other notes

• The build succeeds when targeting the Xcode 26.2 Swift toolchain.
• The crash occurs in both debug (-c debug) and release (-c release) configurations.
• The crash occurs on both target architectures: aarch64-swift-linux-musl and x86_64-swift-linux-musl

[czechboy0]

Hi @briancoyner,

this is unexpected - our CI against the Musl SDK is passing here: https://github.com/apple/swift-configuration/actions/runs/20391474388/job/58601245702#step:4:1

What does "swift -version" say? Curious if you're using a toolchain with assertions enabled, where we've seen this happen (fixed in 6.3).

[briancoyner]

Hi @czechboy0,

Here's what swift -version says. Also, I tried Swift 6.2.3 (same issue). I have not yet tried Swift 6.3 (snapshot).

$ swift -version
Apple Swift version 6.2.2 (swift-6.2.2-RELEASE)
Target: arm64-apple-macosx26.0
Build config: +assertions

Here's a bit more context in case it's helpful:

$ swift package --version
Swift Package Manager - Swift 6.2.2

$ swiftly use
Swift 6.2.2 (default)

$ swiftly list
Installed release toolchains
----------------------------
Swift 6.2.3
Swift 6.2.2 (in use) (default)
Swift 6.2.1
Swift 6.2.0
Swift 6.1.2
Swift 6.1.0
Swift 6.0.3
Swift 6.0.2
Swift 6.0.1

$ swiftly use --print-location
/Users/<redacted>/Library/Developer/Toolchains/swift-6.2.2-RELEASE.xctoolchain

Thank you for taking a look.

[czechboy0]

Yeah, so it appears the toolchain you downloaded using swiftly from swift.org has assertions enabled, so this is being tripped up.

If you use the same Swift 6.2.x toolchain from Xcode instead, that won't cause the crash.

I'm slightly surprised that release toolchains from swift.org have assertions enabled, I thought it was only for development toolchains? @FranzBusch @shahmishal

[briancoyner]

Couple of notes/ updates

• The issue's title is updated to reflect the issue is independent of building with the Static Linux SDK.
• Discovered this seemingly related thread:
  • https://forums.swift.org/t/can-we-get-consistent-assertion-behavior-in-the-latest-release-swift-compiler-across-host-platforms/80545

[aoberoi]

This issue is blocking the adoption of swift-configuration. The assertion crashes the compiler on Swift 6.2.3 from Swiftly (the current OSS latest). Aside from the policy for assertions for various builds, is there an issue for the compiler that is tracking the underlying bug?

Apple Swift version 6.2.3 (swift-6.2.3-RELEASE)
Target: arm64-apple-macosx26.0
Build config: +assertions

[czechboy0]

Yes, this is a bug in the compiler. There isn't anything that we can do in Swift Configuration to work around it, as far as I know. If you do have a workaround, please share.

[shahmishal]

Yeah, so it appears the toolchain you downloaded using swiftly from swift.org has assertions enabled, so this is being tripped up.

If you use the same Swift 6.2.x toolchain from Xcode instead, that won't cause the crash.

I'm slightly surprised that release toolchains from swift.org have assertions enabled, I thought it was only for development toolchains? @FranzBusch @shahmishal

This is expected, I am looking into switching over to no-assert build for macOS release starting 6.3.