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Honor fallbackAfterTimeout: false when inferring a file's target - #2791
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setouchi-h wants to merge 2 commits into
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setouchi-h wants to merge 2 commits into
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setouchi-h
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October 8, 2026 07:21
`buildSettingsInferredFromMainFile` infers the document's target before it asks the build server for the build settings in that target. Since swiftlang#2322 the target inference is wrapped in `withTimeoutResult` and returns fallback build settings when `buildTarget/sources` takes longer than `buildSettingsTimeout`, even if the caller passed `fallbackAfterTimeout: false`. Only the second step honored the flag. This showed up in swiftlang/swift-syntax#3460, where `SwiftSourceKitPluginTests.testCompletionImportDepth` failed on Windows CI because `buildTarget/sources` took 5s and the test ended up with `-sdk`-only fallback arguments. The same applies to `workspace/_sourceKitOptions` with `allowFallbackSettings: false`, `OnDiskDocumentManager` and the `compileCommand(for:fallbackAfterTimeout: false)` calls in `SwiftLanguageService`. Await `canonicalTarget(for:)` directly when `fallbackAfterTimeout` is false, which is what we did before swiftlang#2322. The `fallbackAfterTimeout: true` path and the handling of files the build server doesn't know about are unchanged.
The second sentence of the `allowFallbackSettings` docs described the `false` case but said `true`.
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buildSettingsInferredFromMainFilefirst infers the document's target and then asks the build server for the buildsettings in that target. The second step honors
fallbackAfterTimeout, but since #2322 the first step always runswith a
buildSettingsTimeoutand returns fallback settings when it fires, even if the caller passedfallbackAfterTimeout: false.This bit me in swiftlang/swift-syntax#3460:
SwiftSourceKitPluginTests.testCompletionImportDepthfailed on Windows CI (https://ci-external.swift.org/job/swift-syntax-PR-windows/4967/) becausebuildTarget/sourcestook 5s instead of afew milliseconds, so code completion ran with
-sdk-only fallback arguments.workspace/_sourceKitOptionswithallowFallbackSettings: falseand the other callers that passfallbackAfterTimeout: falsehave the same problem.Await
canonicalTarget(for:)directly iffallbackAfterTimeoutisfalse, which is what we did before #2322. ThefallbackAfterTimeout: truepath and the handling of files the build server doesn't know about are unchanged. The new test fails without the fix and passes with it.The second commit fixes a typo in the
allowFallbackSettingsdocs, which described thefalsecase but saidtrue.