Fresh `swift build --build-tests` fails for HuggingFace-trait-off consumers (regression in 0.46.0)

[roryford]

Summary

A downstream package that enables a non-default subset of ManifoldKit traits excluding HuggingFace can no longer resolve its test graph against MK 0.46.0. A fresh swift build --build-tests (and swift test) fails during package-graph planning with:

error: 'manifoldkit': product 'HuggingFace' required by package 'manifoldkit' target 'ManifoldHuggingFace' not found in package 'swift-huggingface'.

This is a regression: the identical consumer trait set resolved fine against 0.45.0.

Affected consumer

Fireside's Packages/FiresideEval enables:

.package(
    url: "https://github.com/roryford/ManifoldKit.git",
    exact: "0.46.0",
    traits: ["CloudSaaS", "Ollama", "MLX", "Llama"]   // note: no "HuggingFace"
),

It imports ManifoldBackends, ManifoldRuntime, ManifoldPersistenceSwiftData, ManifoldInference — none of which should pull ManifoldHuggingFace with the trait off.

Key diagnostic: it's the test graph, not the build graph

Against 0.46.0 with HuggingFace off:

Command	Result
swift build --package-path Packages/FiresideEval	✅ Build complete!
swift build --package-path Packages/FiresideEval --build-tests	❌ product 'HuggingFace' … not found
--build-tests with "HuggingFace" added to the trait list	✅ Build complete!

So the normal product/library graph is correctly trait-gated; only the --build-tests graph derivation drags ManifoldHuggingFace (and thus the swift-huggingface HuggingFace product) into the plan when the HuggingFace trait is disabled.

What looks correct in the manifest

In v0.46.0:Package.swift, every edge to ManifoldHuggingFace is gated, e.g.:

• ManifoldUIModelManagement → .target(name: "ManifoldHuggingFace", condition: .when(traits: ["HuggingFace"])) (~L605)
• ManifoldHuggingFaceTests → .target(name: "ManifoldHuggingFace", condition: .when(traits: ["HuggingFace"])) (~L934)
• ManifoldServerTests → same, gated (~L1014)
• ManifoldHuggingFace target's own .product(name: "HuggingFace", package: "swift-huggingface", condition: .when(traits: ["HuggingFace"])) (~L618)

ManifoldBackends (target ~L557) does not depend on ManifoldHuggingFace (HuggingFace is only a .define there). So statically nothing unconditional pulls it.

Hypotheses (for maintainer to confirm)

1. SwiftPM --build-tests includes dependency-package test targets (ManifoldHuggingFaceTests, ManifoldServerTests) in graph planning in a way that doesn't honor the .when(traits:) condition on their ManifoldHuggingFace/product edges — i.e. the known SwiftPM trait+test-graph derivation issue already noted in Fireside's CI workaround comment.
2. Something in the 0.46.0 ManifoldBackends umbrella rework (the conditional ManifoldLlama/ManifoldCloud edges were restructured between 0.45.0 and 0.46.0) shifted which test targets land in a consumer's --build-tests plan.

Since plain swift build is clean and only --build-tests breaks, (1) is the more likely root cause.

Impact

Breaks the documented lean trait combos (e.g. FoundationOnly, or any consumer that omits HuggingFace) for anyone running swift test / --build-tests on a fresh resolve. It's masked by warm Package.resolved caches, so it only bites fresh CI checkouts.

Current workaround (downstream)

Add "HuggingFace" to the consumer's trait list (done in Fireside PR #781). This pulls swift-huggingface into the eval build unnecessarily, so a proper fix in MK / SwiftPM trait handling is preferred.

Reproduction

# In a consumer that enables MK traits WITHOUT "HuggingFace":
rm -f Package.resolved
swift build --build-tests        # fails on 0.46.0; passes on 0.45.0

Versions

• Broken: ManifoldKit 0.46.0
• Last good: ManifoldKit 0.45.0

[roryford]

Diagnosis (2026-06-12) — root cause is upstream SwiftPM, resolved structurally in v0.48

This is not a 0.46.0 regression. The trait-gating bytes are identical across 0.45→0.46, the same error hit Fireside CI on 2026-05-07, and five faithful clean-state repros all reproduce it independent of version.

Root cause: .when(traits:) conditions on product-dependency edges are evaluated inconsistently between dependency resolution and --build-tests / --filter graph derivation upstream (swiftlang/swift-package-manager#8350, #8398, #9286). Every trait-gated .product edge (MLX, LlamaSwift, Hummingbird, the HuggingFace edge, …) carries the same latent hazard — it's a structural property of trait-conditional product edges, not a single bad gate.

Resolution: v0.48 (#1771 + the trait-retirement train) eliminates the bug class structurally — traits are replaced by library products and companion packages, so there are no trait-conditional product edges left to evaluate inconsistently. The defensive 2-line ungate was deliberately not shipped (whack-a-mole on one of N identical edges).

Consumer-side note: the failure also depends on stale Package.resolved state — clean-state CI (e.g. Fireside's force-clean step) should also rm -f Package.resolved before resolving.

Closing recommendation: upstream-SwiftPM + consumer-CI-state, fixed by the v0.48 packaging rebuild.