The Swift test job pulls in grpc-swift-2 -> grpc-swift-nio-transport ->
swift-nio-ssl -> swift-crypto, and this package ships no Package.resolved,
so that whole graph is resolved afresh on every run. On 2026-10-15 it
resolved swift-crypto 5.0.1 (released three days earlier) and "Test Swift
Linux (6.2)" turned red before a single line of FlatBuffers' Swift code was
compiled:
Sources/Crypto/HPKE/Ciphersuite/HPKE-AEAD.swift:27:6: error: unknown
attribute 'nonexhaustive'
5.x declares swift-tools-version 6.2, which is why only the 6.2 job selects
it; the 6.0 and 6.1 jobs prune it and keep building. The 6.2.x toolchains
then reject the `@nonexhaustive` that 5.x uses, a combination swift-crypto
does not exercise because it builds on nightly.
Restrict the test-only graph to 4.0.0 ..< 4.4.0, which resolves to 4.3.0:
the last 4.x release that declares swift-tools-version 6.0 and so builds
with every toolchain in the matrix. 4.4+ asks for 6.1 and would break the 6.0
job, and the whole 4.x line is free of `@nonexhaustive`.
Co-authored-by: Derek Bailey <derekbailey@google.com>
