Issues

Minimal Swift packages reproducing toolchain and compiler bugs encountered while developing the Swift Institute ecosystem — the institute's own defect records: each entry carries the reduced reproducer, evidence captures, duplicate differentiation against upstream reports, and the verified workaround the ecosystem ships.

Overview

Each swift-issue-*/ subdirectory holds one minimum reproducer of a single Swift toolchain or compiler bug. Reproducers are reduced to the minimum trigger: no package-internal types, no transitive dependencies, no special swiftSettings beyond what the bug requires.

When a bug catalog entry says "this code miscompiles on Linux release," the issue reproducer proves it — runnable from swift test (or directly via the standalone executable) and verified by CI on every supported platform.

The companion research repository is at swift-institute/Research. The companion experiments repository is at swift-institute/Experiments.

Per-Issue Convention

Every swift-issue-*/ subdirectory follows this steady-state layout. The convention was established by swift-issue-pointer-arithmetic-linux-miscompile/ and applies to every subsequent issue.

swift-issue-<topic>/
├── README.md                  — bug summary, trigger characterization, workaround
├── INVESTIGATION-ARC.md       — (optional) multi-round convergence record
├── ISSUE-<NNNN>-COMMENT.md    — (optional, historical) extended characterization notes from earlier entries
├── Tests/
│   └── Reproducer.swift       — Swift Testing harness, withKnownIssue flip semantics
├── Sources/
│   └── Reproducer/
│       └── main.swift         — standalone exit-code reproducer
└── evidence/                  — (optional) bisection artifacts from investigation
    ├── README.md
    └── …

Each issue declares exactly two SwiftPM targets in the root Package.swift:

.testTarget(
    name: "swift-issue-<topic>-Tests",
    path: "swift-issue-<topic>/Tests"
),
.executableTarget(
    name: "swift-issue-<topic>-Repro",
    path: "swift-issue-<topic>/Sources/Reproducer"
),

Target names match the issue directory so swift test --filter <issue-dir-underscored> selects exactly this issue's tests via substring match on the module-name prefix (SwiftPM converts hyphenated target names to underscored module identifiers).

Two harnesses per issue

• Tests/Reproducer.swift — Swift Testing. Wraps the bug's minimum trigger in withKnownIssue("swiftlang/swift#NNNN", when: { <platform-precondition> }). Green while the bug fires on the configured platforms (current toolchain state); flips red the moment the upstream fix lands and the bug stops firing. The red flip IS the fix-detection signal — captured by the weekly nightly CI cron.
• Sources/Reproducer/main.swift — standalone executable. exit(0) on no-bug-fired, exit(1) on bug-fired. Covers codegen surfaces that the SwiftPM test runner may mask on some toolchains. Useful for ad-hoc probing against a specific toolchain image (e.g., docker run --rm swift:6.3 swift run swift-issue-<topic>-Repro).

Why withKnownIssue and not .disabled(if: …)

.disabled(if: …) is silent when upstream lands a fix — no signal, no PR-trigger, no detection. withKnownIssue flips red the moment the bug stops firing on the configured platform, which IS the upstream-fix detection mechanism. Skipping via .disabled alone is a regression of detection capability and is forbidden per the per-issue convention.

Adding a new issue

1. Create swift-issue-<topic>/ at the repo root.
2. Write the bug README.md + (optional) INVESTIGATION-ARC.md.
3. Author Tests/Reproducer.swift and Sources/Reproducer/main.swift.
4. Add the two targets to the root Package.swift.
5. Push. CI auto-includes the new issue via enumerate-issues's ls -d swift-issue-*/ — zero CI maintenance.

Building

Each issue is a target in this repo's root Package.swift. Clone and test from the repo root:

git clone https://github.com/swift-institute/Issues.git
cd Issues
swift test                                                             # all issues
swift test --filter swift_issue_<topic>                                # one issue
swift run swift-issue-<topic>-Repro                                    # standalone executable

Requires Swift 6.3 or newer.

CI

Continuous integration is per-issue × per-platform.

• A single enumerate-issues job emits the swift-issue-*/ directory list as a JSON array.
• A per-issue matrix job consumes that list and calls the centralized swift-institute/.github reusable workflow once per issue with test-filter: <issue-dir> — one full reusable invocation (macOS / Linux release / Linux nightly / Windows + format + lint + advisory linters) per issue. Each (issue × reusable-job) leg is its own status check.
• fail-fast: false — one issue's red leg never cancels sibling issues' legs.
• Weekly cron at Monday 06:00 UTC re-runs the matrix. The reusable's linux-nightly leg (swiftlang/swift:nightly-main-jammy) is where withKnownIssue flips red on upstream-fix-landing.
• No ci-ok aggregator-gating. The Issues repo's branch protection doesn't reference ci-ok; per-issue test legs are the actionable signals; one red issue does not block merges.

For an issue reproducer, a permanently-red Linux release leg is the bug's running evidence. When the upstream fix lands and the withKnownIssue block stops firing on nightly-main-jammy, that's the signal to close the issue and either remove the reproducer or relocate it as a regression fixture.

Index

Each issue subdirectory documents its bug in README.md. Current issues:

• swift-issue-conditional-extension-typealias-name-capture/ — conditional-extension member typealias named after an enclosing type's generic parameter captures declaring-context references; bogus rejects-valid does not conform diagnostic at -typecheck (swiftlang/swift#89684); present 6.3.2 → 6.5-dev, unfixed.
• swift-issue-borrowing-actor-closure/ — MoveOnlyTypeEliminator crashes when an actor method captures a borrowing class parameter in a non-escaping closure (swift-institute/Issues#3); verified on Swift 6.2.3.
• swift-issue-emit-module-noncopyable-sequence/ — module emission rejects a valid ~Copyable Sequence conformance (Issues#4); source evidence retained.
• swift-issue-embedded-typed-throws-crash/ — Embedded Swift typed-throws protocol conformances crash compilation (Issues#5); source evidence retained.
• swift-issue-copypropagation-nonescapable-mark-dependence/ — CopyPropagation ~Escapable coroutine-yield crash (Issues#6); fixed in Swift 6.3 (Xcode 26.4).
• swift-issue-inlinearray-deinit-value-generic/ — a value-generic InlineArray skips cross-module ~Copyable deinitialization (Issues#7); source evidence retained.
• swift-issue-irgen-async-typed-throws-noncopyable/ — async typed throws with a nested generic error crashes IRGen (Issues#8); source evidence retained.
• swift-issue-irgen-typed-throws-nested-error-generic/ — a typed-throws closure using a nested generic error crashes IRGen (Issues#9); source evidence retained.
• swift-issue-nested-generic-subscript-performance/ — nested value-generic subscript access has debug-build overhead (Issues#10); benchmark and SIL evidence retained.
• swift-issue-nested-copyable-extension-bug/ — same-file extension of a deeply nested ~Copyable type corrupts name lookup (Issues#11); forensic evidence retained.
• swift-issue-noncopyable-sequence-conformance/ — an associated-type conformance leaks Copyable into a nested ~Copyable type (Issues#12); source evidence retained.
• swift-issue-embedded-wasm-mandatory-perf-crash/ — Wasm Embedded MandatoryPerformanceOptimizations SIL crash on cross-module use of the Tagged<Tag, Ordinal> + Tagged<Tag, Cardinal> operator; verified on Swift 6.3.2 Wasm SDK Embedded. Terminal record — not filed. (investigation-arc + standalone repro only; no withKnownIssue test harness yet)
• swift-issue-extension-table-uint16-datalength-overflow/ — the serialized extension-lookup-table dataLength is written and read as uint16_t, so it overflows once one type's extensions exceed 65535 bytes of table data (EmitKeyDataLength, Serialization.cpp:239): crash (signal 6) on +assertions toolchains, silent module truncation on release (valid member references then fail as has no member 'Artikel N'). Present 6.3.3 (silent) → 6.5-dev (asserts), unfixed. Natural trigger: a statute-book namespace with ~700 per-article extensions (the real package overflows at 736). FILED — swiftlang/swift#90319 (2026-07-01). Upstream fix: widen the on-disk width to uint32/VBR, or at minimum diagnose instead of silently truncating on release.
• swift-issue-functionsignatureopts-generic-typed-throws-error/ — FunctionSignatureOpts !type.hasTypeParameter() assertion (SILArgument.cpp:40) at -O on a generic function whose typed-throws error type carries its own generic parameter (swiftlang/swift#89617); present 6.2 → 6.5-dev, unfixed.
• swift-issue-noncopyable-extension-member-mangling-collision/ — a member of a where Element: Copyable extension and the same-signature member in the primary body of a type nested in extension P where Element: ~Copyable mangle to one symbol (the defaulted requirement is never mangled; ASTMangler then treats the extension as unconstrained) — Sema-valid constraint-split twins die at IRGen with multiple definitions of symbol; generalizes to ~Escapable, any member kind, depth-2 nesting; present 6.2 → 6.5-dev, unfixed. Terminal record — STAGED, not filed (standing policy). Workarounds: member-level where clause (SE-0267) or both twins extension-homed.
• swift-issue-noncopyable-rawlayout-trailing-field-miscompile/ — ~Copyable value-witness IRGen SSA dominance violation (LLVM "Instruction does not dominate all uses", signal 6 at -O) when a generic @_rawLayout(likeArrayOf:count:) buffer precedes a trailing scalar field in a type with a deinit. Swift 6.3.1 → 6.5-dev, macOS arm64 + Linux aarch64. Workaround: field reorder. Related to swiftlang/swift#86652. Terminal record — not filed.
• swift-issue-noncopyable-sametype-conditional-conformance/ — the runtime cannot verify a conditional conformance whose same-type requirement RHS is a ~Copyable type: null-metadata SIGSEGV at -Onone AND silent wrong is results at any optimization level (catalog §A15; traced to ProtocolConformance.cpp:1843); broken on every compiler × runtime combination tested, 6.2 → 6.5-dev, unfixed. Terminal record — STAGED, not filed (standing policy). Verified workaround recorded in-dossier; the shipped mitigation is the Memory.Pooling capability seam.
• swift-issue-parameterized-typealias-opaque-return-ice/ — parameterized-typealias × parameterized-protocol opaque-return ICE ("failed to produce diagnostic"); fixed upstream on Swift 6.4-dev nightly-main.
• swift-issue-pointer-arithmetic-linux-miscompile/ — pointer-arithmetic release-mode miscompile (swiftlang/swift#77558); fixed on 6.4-dev nightly-main.
• swift-issue-rawlayout-noncopyable-deinit/ — @_rawLayout element-destruction LLVM IR domination crash (swiftlang/swift#86652).
• swift-issue-rawlayout-noncopyable-extension-rejection/ — unconditional protocol-conformance extension leaks Copyable back to the primary declaration of a ~Copyable-generic nested type; workaround where Element: ~Copyable. Terminal record — not filed.
• swift-issue-spm-identity-conflict-path-enumeration-hang/ — SwiftPM graph-load hang: one package identity reachable under two canonical locations (e.g. .git vs bare spelling across an exact-string mirror table) enters createResolvedPackages' conflicting-identity branch, whose findAllTransitiveDependencies (PR #8390) enumerates ALL paths with no visited set — exponential on dense DAGs, effectively non-terminating at institute scale. Present Swift 6.2 → 6.3.2 → main, unfixed. Workaround: dual-spelling mirror coverage + uniform .git manifest spellings; verify with swift build, never show-dependencies (its tree dumper is independently exponential). Terminal record — not filed. (topology reproducer via evidence/gen-synthetic.sh; no withKnownIssue harness — same deferral as the spm-planning-build-stall entry)
• swift-issue-spm-planning-build-stall/ — SwiftPM planning-build stall at heavy consumers. Terminal record — not filed.
• swift-issue-tagged-noncopyable-atomic-metadata-crash/ — Atomic<Tagged<Tag, Ordinal>>.advance(within:) runtime metadata SIGSEGV on Apple Swift 6.3.x (demangle-time lookup of a cross-module conditional AtomicRepresentable conformance with ~Copyable Tag suppression); fixed on Swift 6.4-dev nightly 2026-03-16-a and later. Terminal record — not filed.
• swift-issue-property-view-tag-constraint-cross-module/ — cross-module constrained Property.View extensions are incorrectly diagnosed as redeclarations (Issues#13); exact multi-module evidence retained.
• swift-issue-rawlayout-deinit-cross-package/ — @_rawLayout element deinitialization is skipped across package boundaries (Issues#14); exact package evidence retained.
• swift-issue-sil-verifier-read-escapable-lifetime/ — _read yielding a ~Escapable lifetime-dependent value fails SIL ownership verification (Issues#15).
• swift-issue-silgen-pack-expansion-cross-module/ — a cross-module parameter-pack expansion call crashes SILGen (Issues#16).
• swift-issue-silgen-property-wrapper-noncopyable/ — cross-module property-wrapper access on a ~Copyable type crashes SILGen (Issues#17).
• swift-issue-testing-suite-discovery-generic-specialization/ — Swift Testing omits suites declared in generic-specialization extensions (Issues#18).
• swift-issue-testing-xcode-nested-suite-filter/ — Xcode gutter actions report zero tests for deeply nested Swift Testing suites (Issues#19).
• swift-issue-typed-throws-autoclosure-inference/ — @autoclosure prevents Never inference for typed throws (Issues#20).
• swift-issue-windows-existential-crash/ — Windows debug-info mangling crashes for a cross-package existential type (Issues#21); both source identities are retained in one dossier.
• swift-issue-spm-repository-url-identity/ — parent record for SwiftPM repository-URL identity and redirect behavior (Issues#22); the three remote fixtures remain active test infrastructure.

License

Apache 2.0.