Calling NSDecimalString function crashes the Swift compiler (also FB14697842)

[flockoffiles]

Description

The following code that calls NSDecimalString crashes the compiler with the message:

SILFunction type mismatch for 'NSDecimalString': '$@convention(c) (UnsafePointer, Optional) -> @autoreleased Optional' != '$@convention(c) (UnsafePointer, Optional) -> @autoreleased NSString'

Reproduction

import Foundation
var tmpDecimal: Decimal = 5.5
let decimalString = NSDecimalString(&tmpDecimal, Locale.current)

Stack dump

Stack dump:
0.	Program arguments: /Applications/Xcode-beta5.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift-frontend -frontend -c /Users/gl68pl/Developer/Temp/DecimalStringBug/DecimalStringBug/ViewController.swift -primary-file /Users/gl68pl/Developer/Temp/DecimalStringBug/DecimalStringBug/AppDelegate.swift /Users/gl68pl/Developer/Temp/DecimalStringBug/DecimalStringBug/SceneDelegate.swift /Users/gl68pl/Library/Developer/Xcode/DerivedData/DecimalStringBug-aauwvbqieqteiaeknfmiqmgohuwq/Build/Intermediates.noindex/DecimalStringBug.build/Debug-iphoneos/DecimalStringBug.build/DerivedSources/GeneratedAssetSymbols.swift -emit-dependencies-path /Users/gl68pl/Library/Developer/Xcode/DerivedData/DecimalStringBug-aauwvbqieqteiaeknfmiqmgohuwq/Build/Intermediates.noindex/DecimalStringBug.build/Debug-iphoneos/DecimalStringBug.build/Objects-normal/arm64/AppDelegate.d -emit-const-values-path /Users/gl68pl/Library/Developer/Xcode/DerivedData/DecimalStringBug-aauwvbqieqteiaeknfmiqmgohuwq/Build/Intermediates.noindex/DecimalStringBug.build/Debug-iphoneos/DecimalStringBug.build/Objects-normal/arm64/AppDelegate.swiftconstvalues -emit-reference-dependencies-path /Users/gl68pl/Library/Developer/Xcode/DerivedData/DecimalStringBug-aauwvbqieqteiaeknfmiqmgohuwq/Build/Intermediates.noindex/DecimalStringBug.build/Debug-iphoneos/DecimalStringBug.build/Objects-normal/arm64/AppDelegate.swiftdeps -serialize-diagnostics-path /Users/gl68pl/Library/Developer/Xcode/DerivedData/DecimalStringBug-aauwvbqieqteiaeknfmiqmgohuwq/Build/Intermediates.noindex/DecimalStringBug.build/Debug-iphoneos/DecimalStringBug.build/Objects-normal/arm64/AppDelegate.dia -emit-localized-strings -emit-localized-strings-path /Users/gl68pl/Library/Developer/Xcode/DerivedData/DecimalStringBug-aauwvbqieqteiaeknfmiqmgohuwq/Build/Intermediates.noindex/DecimalStringBug.build/Debug-iphoneos/DecimalStringBug.build/Objects-normal/arm64 -target arm64-apple-ios18.0 -Xllvm -aarch64-use-tbi -enable-objc-interop -stack-check -sdk /Applications/Xcode-beta5.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS18.0.sdk -I /Users/gl68pl/Library/Developer/Xcode/DerivedData/DecimalStringBug-aauwvbqieqteiaeknfmiqmgohuwq/Build/Products/Debug-iphoneos -F /Users/gl68pl/Library/Developer/Xcode/DerivedData/DecimalStringBug-aauwvbqieqteiaeknfmiqmgohuwq/Build/Products/Debug-iphoneos -no-color-diagnostics -enable-testing -g -debug-info-format=dwarf -dwarf-version=5 -module-cache-path /Users/gl68pl/Library/Developer/Xcode/DerivedData/ModuleCache.noindex -swift-version 5 -enforce-exclusivity=checked -Onone -D DEBUG -serialize-debugging-options -const-gather-protocols-file /Users/gl68pl/Library/Developer/Xcode/DerivedData/DecimalStringBug-aauwvbqieqteiaeknfmiqmgohuwq/Build/Intermediates.noindex/DecimalStringBug.build/Debug-iphoneos/DecimalStringBug.build/Objects-normal/arm64/DecimalStringBug_const_extract_protocols.json -enable-experimental-feature DebugDescriptionMacro -enable-experimental-feature OpaqueTypeErasure -enable-bare-slash-regex -empty-abi-descriptor -validate-clang-modules-once -clang-build-session-file /Users/gl68pl/Library/Developer/Xcode/DerivedData/ModuleCache.noindex/Session.modulevalidation -Xcc -working-directory -Xcc /Users/gl68pl/Developer/Temp/DecimalStringBug -resource-dir /Applications/Xcode-beta5.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift -enable-anonymous-context-mangled-names -file-compilation-dir /Users/gl68pl/Developer/Temp/DecimalStringBug -Xcc -D_LIBCPP_HARDENING_MODE=_LIBCPP_HARDENING_MODE_DEBUG -Xcc -ivfsstatcache -Xcc /Users/gl68pl/Library/Developer/Xcode/DerivedData/SDKStatCaches.noindex/iphoneos18.0-22A5326g-db8e1de5f26549a68b1cfeeb5c021498.sdkstatcache -Xcc -I/Users/gl68pl/Library/Developer/Xcode/DerivedData/DecimalStringBug-aauwvbqieqteiaeknfmiqmgohuwq/Build/Intermediates.noindex/DecimalStringBug.build/Debug-iphoneos/DecimalStringBug.build/swift-overrides.hmap -Xcc -iquote -Xcc /Users/gl68pl/Library/Developer/Xcode/DerivedData/DecimalStringBug-aauwvbqieqteiaeknfmiqmgohuwq/Build/Intermediates.noindex/DecimalStringBug.build/Debug-iphoneos/DecimalStringBug.build/DecimalStringBug-generated-files.hmap -Xcc -I/Users/gl68pl/Library/Developer/Xcode/DerivedData/DecimalStringBug-aauwvbqieqteiaeknfmiqmgohuwq/Build/Intermediates.noindex/DecimalStringBug.build/Debug-iphoneos/DecimalStringBug.build/DecimalStringBug-own-target-headers.hmap -Xcc -I/Users/gl68pl/Library/Developer/Xcode/DerivedData/DecimalStringBug-aauwvbqieqteiaeknfmiqmgohuwq/Build/Intermediates.noindex/DecimalStringBug.build/Debug-iphoneos/DecimalStringBug.build/DecimalStringBug-all-target-headers.hmap -Xcc -iquote -Xcc /Users/gl68pl/Library/Developer/Xcode/DerivedData/DecimalStringBug-aauwvbqieqteiaeknfmiqmgohuwq/Build/Intermediates.noindex/DecimalStringBug.build/Debug-iphoneos/DecimalStringBug.build/DecimalStringBug-project-headers.hmap -Xcc -I/Users/gl68pl/Library/Developer/Xcode/DerivedData/DecimalStringBug-aauwvbqieqteiaeknfmiqmgohuwq/Build/Products/Debug-iphoneos/include -Xcc -I/Users/gl68pl/Library/Developer/Xcode/DerivedData/DecimalStringBug-aauwvbqieqteiaeknfmiqmgohuwq/Build/Intermediates.noindex/DecimalStringBug.build/Debug-iphoneos/DecimalStringBug.build/DerivedSources-normal/arm64 -Xcc -I/Users/gl68pl/Library/Developer/Xcode/DerivedData/DecimalStringBug-aauwvbqieqteiaeknfmiqmgohuwq/Build/Intermediates.noindex/DecimalStringBug.build/Debug-iphoneos/DecimalStringBug.build/DerivedSources/arm64 -Xcc -I/Users/gl68pl/Library/Developer/Xcode/DerivedData/DecimalStringBug-aauwvbqieqteiaeknfmiqmgohuwq/Build/Intermediates.noindex/DecimalStringBug.build/Debug-iphoneos/DecimalStringBug.build/DerivedSources -Xcc -DDEBUG=1 -module-name DecimalStringBug -frontend-parseable-output -disable-clang-spi -target-sdk-version 18.0 -target-sdk-name iphoneos18.0 -external-plugin-path /Applications/Xcode-beta5.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/lib/swift/host/plugins#/Applications/Xcode-beta5.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/swift-plugin-server -external-plugin-path /Applications/Xcode-beta5.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/local/lib/swift/host/plugins#/Applications/Xcode-beta5.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/swift-plugin-server -plugin-path /Applications/Xcode-beta5.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/host/plugins -plugin-path /Applications/Xcode-beta5.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/local/lib/swift/host/plugins -o /Users/gl68pl/Library/Developer/Xcode/DerivedData/DecimalStringBug-aauwvbqieqteiaeknfmiqmgohuwq/Build/Intermediates.noindex/DecimalStringBug.build/Debug-iphoneos/DecimalStringBug.build/Objects-normal/arm64/AppDelegate.o -index-unit-output-path /DecimalStringBug.build/Debug-iphoneos/DecimalStringBug.build/Objects-normal/arm64/AppDelegate.o -index-store-path /Users/gl68pl/Library/Developer/Xcode/DerivedData/DecimalStringBug-aauwvbqieqteiaeknfmiqmgohuwq/Index.noindex/DataStore -index-system-modules
1.	Apple Swift version 6.0 (swiftlang-6.0.0.7.6 clang-1600.0.24.1)
2.	Compiling with effective version 5.10
3.	While evaluating request ExecuteSILPipelineRequest(Run pipelines { Mandatory Diagnostic Passes + Enabling Optimization Passes } on SIL for DecimalStringBug)
4.	While running pass #847 SILModuleTransform "MandatorySILLinker".
5.	While deserializing SIL function "NSDecimalString"
6.	*** DESERIALIZATION FAILURE ***
*** If any module named here was modified in the SDK, please delete the ***
*** new swiftmodule files from the SDK and keep only swiftinterfaces.   ***
module 'Foundation', builder version '6.0(5.10)/Apple Swift version 6.0 (swiftlang-6.0.0.7.6 clang-1600.0.24.1)', built from swiftinterface, resilient, loaded from '/Applications/Xcode-beta5.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/iphoneos/prebuilt-modules/18.0/Foundation.swiftmodule/arm64-apple-ios.swiftmodule'
SILFunction type mismatch for 'NSDecimalString': '$@convention(c) (UnsafePointer<Decimal>, Optional<AnyObject>) -> @autoreleased Optional<NSString>' != '$@convention(c) (UnsafePointer<Decimal>, Optional<AnyObject>) -> @autoreleased NSString'


Stack dump without symbol names (ensure you have llvm-symbolizer in your PATH or set the environment var `LLVM_SYMBOLIZER_PATH` to point to it):
0  swift-frontend           0x0000000105b6d194 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 56
1  swift-frontend           0x0000000105b6b3e8 llvm::sys::RunSignalHandlers() + 112
2  swift-frontend           0x0000000105b6d760 SignalHandler(int) + 292
3  libsystem_platform.dylib 0x000000018b612584 _sigtramp + 56
4  libsystem_pthread.dylib  0x000000018b5e1c20 pthread_kill + 288
5  libsystem_c.dylib        0x000000018b4eea30 abort + 180
6  swift-frontend           0x0000000100c9b658 swift::ModuleFileSharedCore::outputDiagnosticInfo(llvm::raw_ostream&) const + 0
7  swift-frontend           0x0000000100c2fab4 swift::ModuleFile::getSourceLoc() const + 0
8  swift-frontend           0x0000000100c77ce8 swift::SILDeserializer::readSILFunctionChecked(llvm::PointerEmbeddedInt<unsigned int, 31>, swift::SILFunction*, llvm::StringRef, bool, bool) + 1916
9  swift-frontend           0x0000000100c869d8 swift::SILDeserializer::lookupSILFunction(swift::SILFunction*, bool) + 452
10 swift-frontend           0x0000000100d48c24 swift::SILLinkerVisitor::maybeAddFunctionToWorklist(swift::SILFunction*, swift::SerializedKind_t) + 360
11 swift-frontend           0x0000000100d48e44 swift::SILLinkerVisitor::process() + 476
12 swift-frontend           0x0000000100dc3d0c swift::SILModule::linkFunction(swift::SILFunction*, swift::SILModule::LinkingMode) + 120
13 swift-frontend           0x000000010147f8f0 (anonymous namespace)::SILLinker::run() + 64
14 swift-frontend           0x0000000101357a4c swift::SILPassManager::executePassPipelinePlan(swift::SILPassPipelinePlan const&) + 13436
15 swift-frontend           0x00000001013909dc swift::SimpleRequest<swift::ExecuteSILPipelineRequest, std::__1::tuple<> (swift::SILPipelineExecutionDescriptor), (swift::RequestFlags)1>::evaluateRequest(swift::ExecuteSILPipelineRequest const&, swift::Evaluator&) + 56
16 swift-frontend           0x0000000101374340 swift::ExecuteSILPipelineRequest::OutputType swift::Evaluator::getResultUncached<swift::ExecuteSILPipelineRequest, swift::ExecuteSILPipelineRequest::OutputType swift::evaluateOrFatal<swift::ExecuteSILPipelineRequest>(swift::Evaluator&, swift::ExecuteSILPipelineRequest)::'lambda'()>(swift::ExecuteSILPipelineRequest const&, swift::ExecuteSILPipelineRequest::OutputType swift::evaluateOrFatal<swift::ExecuteSILPipelineRequest>(swift::Evaluator&, swift::ExecuteSILPipelineRequest)::'lambda'()) + 412
17 swift-frontend           0x0000000101376abc swift::runSILDiagnosticPasses(swift::SILModule&) + 612
18 swift-frontend           0x00000001008f42cc swift::CompilerInstance::performSILProcessing(swift::SILModule*) + 84
19 swift-frontend           0x0000000100520268 performCompileStepsPostSILGen(swift::CompilerInstance&, std::__1::unique_ptr<swift::SILModule, std::__1::default_delete<swift::SILModule>>, llvm::PointerUnion<swift::ModuleDecl*, swift::SourceFile*>, swift::PrimarySpecificPaths const&, int&, swift::FrontendObserver*) + 1376
20 swift-frontend           0x000000010051f474 swift::performCompileStepsPostSema(swift::CompilerInstance&, int&, swift::FrontendObserver*) + 984
21 swift-frontend           0x0000000100522728 performCompile(swift::CompilerInstance&, int&, swift::FrontendObserver*) + 1680
22 swift-frontend           0x0000000100521458 swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 3572
23 swift-frontend           0x00000001004a850c swift::mainEntry(int, char const**) + 3680
24 dyld                     0x000000018b257154 start + 2476
Command SwiftCompile failed with a nonzero exit code

Expected behavior

I expect it compile without a crash.

Environment

swift-driver version: 1.113 Apple Swift version 6.0 (swiftlang-6.0.0.7.6 clang-1600.0.24.1)
Target: arm64-apple-macosx14.0

Additional information

DecimalStringBug.zip

[aehlke]

Do you have a workaround?

[flockoffiles]

The only workaround I know is going back to Xcode 16 beta 4 (and praying that this issue gets fixed soon).

[Cedrick84]

Experiencing the same issue.

[flockoffiles]

ok. There seems to be a work-around. It's quite verbose, but it works:

    let decimalNumber = NSDecimalNumber(decimal: tmpDecimal)
    let numberFormatter = NumberFormatter()
    numberFormatter.numberStyle = .decimal
    numberFormatter.locale = locale
    let formattedString = numberFormatter.string(from: decimalNumber) ?? "\(tmpDecimal)"

[alvesmarcel]

EDIT: Please see @robertmryan's comment below before choosing to use the approach I suggested here. Decimal.FormatStyle behaves differently from NumberFormatter in some scenarios.

---

It seems this is a known issue on Xcode 16.

According to the release notes, the suggested workaround is to use Decimal.FormatStyle. If you're supporting iOS 15.0 and above, you can do something like this too:

let decimalNumber: Decimal = 12345.67
let formatStyle = Decimal.FormatStyle(locale: locale)
let formattedNumber = decimalNumber.formatted(formatStyle)
let formattedNumberStr = String(formattedNumber)

The main advantage of this approach is that you don't have to deal with optionals.

[robertmryan]

I agree that for now we can just avoid using NSDecimalString, but, FWIW, the error message tells us what the problem is: The Swift interface indicates that the result is not optional, as indicated in the docs, but clearly elsewhere behind the scenes, it is being inferred as optional.

[robertmryan]

@alvesmarcel

It seems this is a known issue on Xcode 16.

According to the release notes, the suggested workaround is to use Decimal.FormatStyle. If you're supporting iOS 15.0 and above, you can do something like this too:

let decimalNumber: Decimal = 12345.67
let formatStyle = Decimal.FormatStyle(locale: locale)
let formattedNumber = decimalNumber.formatted(formatStyle)
let formattedNumberStr = String(formattedNumber)

The main advantage of this approach is that you don't have to deal with optionals.

I would be cautious with this: If the locale is your current locale, this will use the default numeric format for that locale, but it will ignore whatever custom number formatting you may have changed in settings. NumberFormatter will honor the device settings, but Decimal.FormatStyle will not. If you’re trying to generate some invariant style (a la en_US_POSIX), this doesn’t matter. But if trying to localize in a manner to honor the device settings, this is problematic.

[aehlke]

@robertmryan that solution has merged so you might want to copy your feedback to that PR or share an alternative