Adopt Swift 6 language mode with strict concurrency checking by thuyetngocluong · Pull Request #832 · malcommac/SwiftDate

thuyetngocluong · 2026-07-20T18:36:21Z

Summary

This PR migrates SwiftDate to Swift 6 language mode with strict concurrency (data-race safety) enabled, while keeping the public API source-compatible and the runtime behavior unchanged. The library now builds with 0 errors and 0 warnings in Swift 6 mode, and the full test suite passes — including under ThreadSanitizer.

What changed

Package manifest

swift-tools-version: 6.0 + swiftLanguageModes: [.v6] (platforms stay at macOS 10.15 / iOS 13 / watchOS 6 / tvOS 13).
Removed the two resources: entries pointing at Formatters/RelativeFormatter/langs and Resources — those directories were deleted together with the RelativeFormatter removal, and under tools 6.0 the missing paths are a hard build error (they were silently warned about under 5.5).
SwiftDate.podspec: swift_versions bumped to 6.0.

Concurrency-safe shared state

SwiftDate.defaultRegion and DateFormats.autoFormats were stored mutable globals — a hard error under Swift 6. They are now computed properties backed by an internal OSUnfairLocked<Value: Sendable> box:

Uses OSAllocatedUnfairLock on iOS 16 / macOS 13 and later, and falls back to the C os_unfair_lock API (heap-allocated, so the lock has a stable address) on older systems.
The public synchronous get/set API is unchanged, so every existing call site — including the many region: Region = SwiftDate.defaultRegion default arguments — keeps compiling as-is.

Sendable conformances

Region (its only stored property is a Calendar), ISOFormatter.Options, ISOParser.Options, DateToStringStyles, StringToDateStyles. The ISOFormatter.Options conformance is what resolves the 13 "static property is not concurrency-safe" errors on its option-set constants.

Newer SDK enum cases

Recent SDKs added Calendar.Component.dayOfYear (iOS 18/macOS 15) and .isLeapMonth/.isRepeatedDay (iOS 26/macOS 26), plus 11 new Calendar.Identifier cases — all of which made existing exhaustive switches warn (@unknown default does not cover cases that are known to the SDK you compile against):

Calendar.Component.nsCalendarUnit maps the three new cases to their NSCalendar.Unit counterparts behind availability guards (empty set on older OSes, where those values cannot even be constructed).
Date.difference(in:) / differences(in:from:) now return a real value for .dayOfYear on iOS 18/macOS 15+; .isLeapMonth/.isRepeatedDay return nil (they are Boolean metadata — no integer difference exists).
Calendar.Identifier.description covers the 11 new identifiers, and the conformance is marked @retroactive.

Dead code removal

The unused @Atomic property wrapper and Bundle.appModule/BundleFinder (orphaned since the RelativeFormatter removal, and itself a Swift 6 violation as a stored mutable static).

Tests

New TestConcurrencySafety stress tests hammer defaultRegion/autoFormats with DispatchQueue.concurrentPerform while other threads parse and format through them.
Two pre-existing test failures on current toolchains were fixed (both reproduce on master): newer Foundation zero-fills and attaches calendar/timeZone to dateComponents(from:to:) results, breaking whole-value DateComponents equality against 1.hours; and JSONEncoder key order is randomized per process, breaking the raw-JSON string comparison (now uses .sortedKeys).

Verification

swift build in Swift 6 mode: 0 errors, 0 warnings (Swift 6.3.3 toolchain)
swift test: 71/71 passing, repeatedly
swift test --sanitize=thread: clean, including the new concurrency stress tests

Notes for reviewers

Consuming the package via SwiftPM now requires a Swift 6.0+ toolchain (Xcode 16+). CocoaPods consumers need Xcode 16+ as well (for @retroactive).
OSUnfairLocked makes each get/set individually atomic; compound read-modify-write patterns like SwiftDate.autoFormats.append(...) are not atomic as a whole (this is documented on the property, and matches the previous unsynchronized behavior).

🤖 Generated with Claude Code

@atomic

Migrate the package to swift-tools-version 6.0 with swiftLanguageModes [.v6] so it builds cleanly (0 errors, 0 warnings) under Swift 6 strict data-race safety, preserving the public API and runtime behavior. - Replace the stored mutable globals SwiftDate.defaultRegion and DateFormats.autoFormats with computed properties backed by an internal OSUnfairLocked box (OSAllocatedUnfairLock on iOS 16/macOS 13+, C os_unfair_lock on older systems), keeping the synchronous get/set API. - Add Sendable conformances: Region, ISOFormatter.Options, ISOParser.Options, DateToStringStyles, StringToDateStyles. - Remove dead code that violated strict concurrency: the unused @atomic property wrapper and Bundle.appModule/BundleFinder (orphaned since the RelativeFormatter removal), plus the Package.swift resource entries pointing at directories deleted in that same cleanup (hard error under tools 6.0). - Handle the Calendar.Component cases introduced by newer SDKs (.dayOfYear, .isLeapMonth, .isRepeatedDay) and the new Calendar.Identifier cases in exhaustive switches, with availability guards; difference(in:) now returns a real value for .dayOfYear on iOS 18/macOS 15+. Mark the Calendar.Identifier CustomStringConvertible conformance @retroactive. - Add TestConcurrencySafety stress tests (concurrent defaultRegion and autoFormats access); suite is clean under ThreadSanitizer. - Fix two tests broken by newer Foundation behavior (dateComponents zero-fills and attaches calendar/timeZone; JSONEncoder key order is randomized per process - use .sortedKeys). Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Copilot

Pull request overview

This PR updates SwiftDate to Swift 6 language mode with strict concurrency checking, replacing previously mutable global/shared state with synchronized access while keeping the public API surface largely source-compatible. It also updates several types for Sendable compliance, adjusts logic for newer Foundation/SDK enum cases, and updates tests to be deterministic and to validate concurrency safety.

Changes:

Adopt Swift 6 tools/language mode in SwiftPM and CocoaPods, and remove stale SwiftPM resource entries.
Make SwiftDate.defaultRegion and DateFormats.autoFormats concurrency-safe via an unfair-lock-backed storage wrapper.
Add/adjust Sendable conformances and update code/tests for newer Foundation behaviors and newer SDK enum cases.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
Tests/SwiftDateTests/TestRegion.swift	Makes JSON encoding deterministic by using `.sortedKeys` and updates expected JSON string order.
Tests/SwiftDateTests/TestDateInRegion+Components.swift	Updates a component comparison to avoid brittle whole-`DateComponents` equality with newer Foundation.
Tests/SwiftDateTests/TestConcurrencySafety.swift	Adds stress tests for concurrent reads/writes of `defaultRegion` and `autoFormats`.
SwiftDate.podspec	Bumps CocoaPods `swift_versions` to 6.0.
Sources/SwiftDate/SwiftDate.swift	Replaces stored mutable `defaultRegion` with synchronized computed access; keeps `autoFormats` passthrough.
Sources/SwiftDate/Supports/Commons.swift	Introduces `OSUnfairLocked` and uses it to synchronize `DateFormats.autoFormats`; updates Calendar component mapping for new cases.
Sources/SwiftDate/Supports/Calendars.swift	Adds `@retroactive` and expands `Calendar.Identifier.description` for new identifiers.
Sources/SwiftDate/Formatters/ISOParser.swift	Marks `ISOParser.Options` as `Sendable`.
Sources/SwiftDate/Formatters/ISOFormatter.swift	Marks `ISOFormatter.Options` as `Sendable`.
Sources/SwiftDate/Formatters/Formatter+Protocols.swift	Marks style enums as `Sendable`.
Sources/SwiftDate/DateInRegion/Region.swift	Marks `Region` as `Sendable`.
Sources/SwiftDate/Date/Date+Compare.swift	Handles newer `Calendar.Component` cases in component extraction.
Package.swift	Moves to swift-tools 6.0, removes deleted resources, and sets `swiftLanguageModes: [.v6]`.

Comments suppressed due to low confidence (1)

Sources/SwiftDate/Supports/Calendars.swift:79

New Calendar.Identifier cases were added to description, but init(_ rawValue:) doesn’t map these strings back to the corresponding identifiers. This breaks round-tripping/decoding for the newly supported identifiers (e.g. "bangla" will fall into default and silently become the default calendar).

		case .vikram:				return "vikram"
		@unknown default:
			fatalError("Unsupported calendar \(self)")
		}
	}

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Copilot

Pull request overview

Copilot reviewed 13 out of 13 changed files in this pull request and generated 1 comment.

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Copilot reviewed 13 out of 13 changed files in this pull request and generated 2 comments.

+		case .isLeapMonth:
+			if #available(macOS 26.0, iOS 26.0, tvOS 26.0, watchOS 26.0, visionOS 26.0, *) {
+				return NSCalendar.Unit.isLeapMonth
+			} else {
+				return []
+			}


+		case .isRepeatedDay:
+			if #available(macOS 26.0, iOS 26.0, tvOS 26.0, watchOS 26.0, visionOS 26.0, *) {
+				return NSCalendar.Unit.isRepeatedDay
+			} else {
+				return []
+			}


The Calendar.Identifier cases added by the iOS 26 SDK and the Calendar.Component/NSCalendar.Unit additions have different SDK floors: Calendar.Component.isLeapMonth ships since the iOS 17 SDK, .dayOfYear since iOS 18, while .isRepeatedDay, NSCalendar.Unit.isLeapMonth/ .isRepeatedDay and the 11 regional calendar identifiers exist only in the iOS 26 SDK. Wrap each usage in the matching #if compiler(...) so older toolchains neither fail to compile the missing symbols nor emit exhaustiveness warnings for cases their SDK does have. Minimum supported toolchain is Xcode 16 (Swift 6.0), imposed by swift-tools-version 6.0. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Copilot

Pull request overview

Copilot reviewed 13 out of 13 changed files in this pull request and generated 4 comments.

 import Foundation
+import os
+
+// MARK: - Lock Protected Value Support
+
+/// An unfair-lock protected mutable box used to expose the library-wide
+/// configuration (`SwiftDate.defaultRegion`, `DateFormats.autoFormats`) as
+/// concurrency-safe shared state under Swift 6 strict data-race safety.
+/// On iOS 16/macOS 13 and later it uses Apple's `OSAllocatedUnfairLock`;
+/// on older systems it falls back to the C `os_unfair_lock` API.
+internal final class OSUnfairLocked<Value: Sendable>: @unchecked Sendable {


 }

 // MARK: - DateFormatter


+				let region = SwiftDate.defaultRegion
+				XCTAssertFalse(region.timeZone.identifier.isEmpty)
+				_ = DateInRegion(Date(), region: region).toISO()
+				_ = Region() // fills every attribute from a single defaultRegion snapshot


+#endif
 		@unknown default:
-			fatalError("Unsupported calendar \(self)")
+			fatalError("Unsupported calendar identifier")
 		}
 	}


Copilot AI review requested due to automatic review settings July 20, 2026 18:36

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Adopt Swift 6 language mode with strict concurrency checking#832

Adopt Swift 6 language mode with strict concurrency checking#832
thuyetngocluong wants to merge 4 commits into
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thuyetngocluong:feature/swift6-strict-concurrency

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thuyetngocluong commented Jul 20, 2026

Summary

What changed

Package manifest

Concurrency-safe shared state

Sendable conformances

Newer SDK enum cases

Dead code removal

Tests

Verification

Notes for reviewers

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Pull request overview

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