Surface dlerror/GetLastError reason on Loader load failure#843
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johnfairh merged 1 commit intoJun 29, 2026
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Thanks for the PR - looks good. I think it's OK to not go any further to decode the windows error given the state of support there. |
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I do want to take this, just mired in thinking about currency updates, WWDC ... |
Capture each candidate path that was tried and the OS-reported reason (dlerror() on POSIX, GetLastError() on Windows), and include the full list in the fatalError message.
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Summary
Today, when
Loader.load(path:)cannot dlopensourcekitdInProcit traps with the bare messageLoading <path> failed. That message discards the actual OS error and forces downstream users (SwiftLint, jazzy, sourcekitten itself) to guess at the root cause. Users hitting this — e.g. realm/SwiftLint#6475 — end up chasing red herrings (sandboxing, Xcode versions, mise pinning) before the actual cause is found.This PR collects
dlerror()(POSIX) /GetLastError()(Windows) for every candidate path attempted, and includes them in the fatalError message. Successful-load paths are unchanged.Why it matters
The motivating case is Xcode 26 shipping
sourcekitdInProc.frameworkas arm64-only. When SwiftLint is invoked from an x86_64-rooted process tree (e.g. an x86_64 Ruby running fastlane on an Apple Silicon machine), the universal SwiftLint binary launches x86_64 to match its parent, and dlopen fails with:Before this PR users see
Loading sourcekitdInProc.framework/Versions/A/sourcekitdInProc failedand have no idea what to do. After this PR they see the actual reason and can immediately rebuild Ruby as arm64 (or run througharch -arm64) instead.Changes
Loader.loadcollects per-attempt errors and feeds them into a newLoader.failureMessage(path:attemptFailures:)helper.staticso it can be tested without triggeringfatalError.LoaderTestscovers both the populated-attempts path and the empty-attempts edge case.CHANGELOG.mdentry under a new## Mainsection.Test plan
swift build— cleanswift test --filter LoaderTests— 2/2 passswift test— no new failures (6 pre-existingSourceKitTestsfailures are Swift-toolchain-version drift on Xcode 26.4, unrelated to this change)Refs realm/SwiftLint#6475