Heads-up: release-mode crash when co-linked with swift-transformers (Tokenizers); upstream tracker swiftlang/swift#88794

[aurascoper]

Heads-up: release-mode crash when co-linked with huggingface/swift-transformers (Tokenizers)

Filing as a courtesy / FYI — this looks like a Swift release-mode codegen issue, not a defect in postgres-nio. Upstream tracker: swiftlang/swift#88794.

Symptom

A Swift release build that links both postgres-nio (1.33.0) and huggingface/swift-transformers (Tokenizers product, 1.3.0) into the same executable crashes with freed pointer was not the last allocation on the second consecutive PostgresClient.query(...) call. The first query succeeds; the second aborts the process.

Either dependency on its own works fine in release. A swift build -c debug build with both deps also works fine.

The trigger is import Tokenizers itself — no Tokenizers API has to be called for the crash to fire.

Environment

• Swift 6.3.1 (swiftlang-6.3.1.1.2) / Xcode 26.4.1 / macOS 26.4.1, Apple M4
• postgres-nio 1.33.0
• swift-transformers 1.3.0
• swift-nio 2.99.0

Minimal repro

The full minimal Package.swift + main.swift (≈30 lines) is in swiftlang/swift#88794. Two SELECT N queries are enough to reproduce.

Why I'm posting here

Pure FYI in case:

1. There's a known interaction between NIO's allocator paths and Tokenizers' module-load code that the postgres-nio side has ideas about, or
2. you want this on your radar in case other users hit it.

I'm not asking postgres-nio to fix this; the diagnosis points at the Swift toolchain. Feel free to close after triage. If a workaround on the postgres-nio side is feasible, that'd be a nice-to-have, but a Swift compiler patch is the right durable fix.

Workarounds for users hitting this today

• Build the executable with swift build -c debug when both libraries are linked.
• Avoid linking Tokenizers and PostgresNIO into the same executable target (split into two executables that talk over IPC, or keep tokenization in a separate process).