Swift 6 / Xcode 16: Segmentation fault during Analyzing… (v3.3.0) and build failure in JobPool.swift from v3.4.0+

[matheuspcunha]

Hi 👋

I'm experiencing two separate but related issues when using Periphery with Xcode 16 (Swift 6) in a real-world iOS workspace (CocoaPods-based project).

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1️⃣ Segmentation fault during Analyzing… (v3.3.0)

Version

Periphery 3.3.0
Xcode 16.0
Swift 6 toolchain
macOS (Apple Silicon)

Symptom

make periphery fails with:

Segmentation fault: 11 (exit 139)

The crash happens during the:

* Inspecting project...
* Building Rewards...
* Indexing...
* Analyzing...

Build and indexing complete successfully. The crash occurs specifically during the analysis phase.

Observations

• Project builds successfully via xcodebuild.
• Index store is generated.
• Crash occurs inside the Periphery binary during analysis (reading the index store and performing reference / unused code analysis via SwiftParser / IndexStore).
• Not caused by incorrect paths or failed build.
• Workspace contains CocoaPods + SPM tooling.

This appears to be an internal crash during analysis rather than a configuration issue.

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2️⃣ Swift 6 compilation failure from v3.4.0+

Starting from Periphery 3.4.0, the package fails to compile under Swift 6 (Xcode 16).

Error

/Tools/.build/checkouts/periphery/Sources/Shared/JobPool.swift:33:13:
error: 'results' used after consume

Relevant code snippet (JobPool.swift)

public func flatMap<Result>(_ block: @escaping (Job) throws -> [Result]) throws -> [Result] {
    var error: Error?
    let results = Mutex<[Result]>([])

    DispatchQueue.concurrentPerform(iterations: jobs.count) { idx in
        guard error == nil else { return }

        do {
            let jobResults = try block(jobs[idx])
            results.withLock { $0.append(contentsOf: jobResults) }
        } catch {
            error = error
        }
    }

    if let error {
        throw error
    }

    return results.withLock { $0 }
}

Root cause hypothesis

Swift 6 introduces stricter ownership and concurrency rules.
The compiler now reports:

'results' used after consumption

This appears to be due to Mutex usage combined with concurrentPerform and Swift 6's stricter move/consume checking.

Versions ≤ 3.3.0 compile because they were built under Swift 5 rules (pre–Swift 6 enforcement).

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Expected behavior

• Periphery should compile under Swift 6 / Xcode 16.
• Periphery should not crash during the Analyzing… stage for a valid indexed workspace.

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What we tested

• Running via SPM (swift run -c release periphery)
• Running isolated via Tools/Package.swift
• Using .xcworkspace
• Using --skip-build
• Using existing DerivedData index

Results:

• v3.3.0 compiles but crashes during analysis (SIGSEGV).
• v3.4.0+ fails to compile under Swift 6 due to JobPool.swift.

---

Request

Could you confirm:

1. Is there known Swift 6 compatibility work ongoing?
2. Is the segmentation fault during analysis a known issue with larger CocoaPods-based workspaces?
3. Is there a recommended version for Xcode 16 compatibility?

Happy to provide:

• Full crash logs
• Sample project reproduction
• Toolchain / macOS details

Thank you 🙏

---

Se você quiser, posso também preparar uma versão ainda mais técnica (com stack trace formatting e sugestão de patch no JobPool.swift).

[ileitch]

Please try again with the latest version 3.6.0, and use at least Swift 6.1.2 (Xcode 16.4+) when trying to build from source.