Compiler Hangs on Swift 5.10 and Crashes with Latest Swift 6.0 Snapshot When Using lazy var with try

[CrazyFanFan]

Description

I've encountered an issue where the compiler hangs when building the following code with Swift 5.10. When switching to the latest daily build of Swift 6.0,(swift-6.0-DEVELOPMENT-SNAPSHOT-2024-04-15-a) the compiler crashes instead.

1.	Apple Swift version 6.0-dev (LLVM c5ac128e678cf31, Swift 59748d9cf60064b)
2.	Compiling with effective version 5.10
3.	While evaluating request ASTLoweringRequest(Lowering AST to SIL for file "/Users/kkk/repo/lark/lazytry/Sources/main.swift")
4.	While silgen emitFunction SIL function "@$s7lazytry4foo2yyKF".
 for 'foo2()' (at /Users/kkk/repo/lark/lazytry/Sources/main.swift:6:1)
5.	While silgen emitFunction SIL function "@$s7lazytry4foo2yyKF1xL_Sivg".
 for getter for x (at /Users/kkk/repo/lark/lazytry/Sources/main.swift:7:14)
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           0x0000000107d96e08 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 56
1  swift-frontend           0x0000000107d955d4 llvm::sys::RunSignalHandlers() + 112
2  swift-frontend           0x0000000107d97450 SignalHandler(int) + 304
3  libsystem_platform.dylib 0x0000000180593584 _sigtramp + 56
4  libsystem_pthread.dylib  0x0000000180562c20 pthread_kill + 288
5  libsystem_c.dylib        0x000000018046fa30 abort + 180
6  libsystem_c.dylib        0x000000018046ed20 err + 0
7  swift-frontend           0x0000000107ed6230 swift::Lowering::SILGenFunction::emitThrow(swift::SILLocation, swift::Lowering::ManagedValue, bool) (.cold.2) + 0
8  swift-frontend           0x0000000103044cd4 swift::Lowering::SILGenFunction::emitThrow(swift::SILLocation, swift::Lowering::ManagedValue, bool) + 2228
9  swift-frontend           0x00000001030443d4 swift::Lowering::SILGenFunction::getTryApplyErrorDest(swift::SILLocation, swift::CanTypeWrapper<swift::SILFunctionType>, swift::Lowering::ExecutorBreadcrumb, swift::SILResultInfo, swift::SILValue, bool) + 548
10 swift-frontend           0x0000000102f61300 emitRawApply(swift::Lowering::SILGenFunction&, swift::SILLocation, swift::Lowering::ManagedValue, swift::SubstitutionMap, llvm::ArrayRef<swift::Lowering::ManagedValue>, swift::CanTypeWrapper<swift::SILFunctionType>, swift::optionset::OptionSet<swift::ApplyFlags, unsigned char>, llvm::ArrayRef<swift::SILValue>, swift::SILValue, llvm::SmallVectorImpl<swift::SILValue>&, swift::Lowering::ExecutorBreadcrumb) + 2760
11 swift-frontend           0x0000000102f61c80 swift::Lowering::SILGenFunction::emitApply(std::__1::unique_ptr<swift::Lowering::ResultPlan, std::__1::default_delete<swift::Lowering::ResultPlan>>&&, swift::Lowering::ArgumentScope&&, swift::SILLocation, swift::Lowering::ManagedValue, swift::SubstitutionMap, llvm::ArrayRef<swift::Lowering::ManagedValue>, swift::Lowering::CalleeTypeInfo const&, swift::optionset::OptionSet<swift::ApplyFlags, unsigned char>, swift::Lowering::SGFContext, std::__1::optional<swift::ActorIsolation>) + 1340
12 swift-frontend           0x0000000102f671b8 (anonymous namespace)::CallEmission::apply(swift::Lowering::SGFContext) + 2028
13 swift-frontend           0x0000000102f65768 swift::Lowering::SILGenFunction::emitApplyExpr(swift::ApplyExpr*, swift::Lowering::SGFContext) + 2028
14 swift-frontend           0x0000000102fbcaa0 swift::Lowering::SILGenFunction::emitExprInto(swift::Expr*, swift::Lowering::Initialization*, std::__1::optional<swift::SILLocation>) + 156
15 swift-frontend           0x0000000102faabf8 swift::Lowering::SILGenFunction::emitPatternBinding(swift::PatternBindingDecl*, unsigned int, bool) + 1308
16 swift-frontend           0x0000000102fb0ce0 swift::ASTVisitor<swift::Lowering::SILGenFunction, void, void, void, void, void, void>::visit(swift::Decl*) + 180
17 swift-frontend           0x000000010304188c swift::ASTVisitor<(anonymous namespace)::StmtEmitter, void, void, void, void, void, void>::visit(swift::Stmt*) + 4196
18 swift-frontend           0x000000010304081c swift::Lowering::SILGenFunction::emitStmt(swift::Stmt*) + 24
19 swift-frontend           0x0000000102fe1770 swift::Lowering::SILGenFunction::emitFunction(swift::FuncDecl*) + 432
20 swift-frontend           0x0000000102f53aec swift::Lowering::SILGenModule::emitFunctionDefinition(swift::SILDeclRef, swift::SILFunction*) + 6324
21 swift-frontend           0x0000000102f54920 swift::Lowering::SILGenModule::emitOrDelayFunction(swift::SILDeclRef) + 252
22 swift-frontend           0x0000000102f52200 swift::Lowering::SILGenModule::emitFunction(swift::FuncDecl*) + 196
23 swift-frontend           0x0000000103fe12e0 swift::AbstractStorageDecl::visitExpectedOpaqueAccessors(llvm::function_ref<void (swift::AccessorKind)>) const + 68
24 swift-frontend           0x0000000103fe1284 swift::AbstractStorageDecl::visitEmittedAccessors(llvm::function_ref<void (swift::AccessorDecl*)>) const + 160
25 swift-frontend           0x0000000102f569c0 swift::Lowering::SILGenModule::visitEmittedAccessors(swift::AbstractStorageDecl*, llvm::function_ref<void (swift::AccessorDecl*)>) + 48
26 swift-frontend           0x0000000102faaed0 swift::Lowering::SILGenFunction::visitVarDecl(swift::VarDecl*) + 148
27 swift-frontend           0x000000010304188c swift::ASTVisitor<(anonymous namespace)::StmtEmitter, void, void, void, void, void, void>::visit(swift::Stmt*) + 4196
28 swift-frontend           0x000000010304081c swift::Lowering::SILGenFunction::emitStmt(swift::Stmt*) + 24
29 swift-frontend           0x0000000102fe1770 swift::Lowering::SILGenFunction::emitFunction(swift::FuncDecl*) + 432
30 swift-frontend           0x0000000102f53aec swift::Lowering::SILGenModule::emitFunctionDefinition(swift::SILDeclRef, swift::SILFunction*) + 6324
31 swift-frontend           0x0000000102f54920 swift::Lowering::SILGenModule::emitOrDelayFunction(swift::SILDeclRef) + 252
32 swift-frontend           0x0000000102f52200 swift::Lowering::SILGenModule::emitFunction(swift::FuncDecl*) + 196
33 swift-frontend           0x0000000102f57260 swift::ASTLoweringRequest::evaluate(swift::Evaluator&, swift::ASTLoweringDescriptor) const + 880
34 swift-frontend           0x0000000103040274 swift::SimpleRequest<swift::ASTLoweringRequest, std::__1::unique_ptr<swift::SILModule, std::__1::default_delete<swift::SILModule>> (swift::ASTLoweringDescriptor), (swift::RequestFlags)9>::evaluateRequest(swift::ASTLoweringRequest const&, swift::Evaluator&) + 148
35 swift-frontend           0x0000000102f5cb54 swift::ASTLoweringRequest::OutputType swift::Evaluator::getResultUncached<swift::ASTLoweringRequest, swift::ASTLoweringRequest::OutputType swift::evaluateOrFatal<swift::ASTLoweringRequest>(swift::Evaluator&, swift::ASTLoweringRequest)::'lambda'()>(swift::ASTLoweringRequest const&, swift::ASTLoweringRequest::OutputType swift::evaluateOrFatal<swift::ASTLoweringRequest>(swift::Evaluator&, swift::ASTLoweringRequest)::'lambda'()) + 340
36 swift-frontend           0x0000000102f57b64 swift::performASTLowering(swift::FileUnit&, swift::Lowering::TypeConverter&, swift::SILOptions const&, swift::IRGenOptions const*) + 96
37 swift-frontend           0x0000000102945b94 swift::performCompileStepsPostSema(swift::CompilerInstance&, int&, swift::FrontendObserver*) + 568
38 swift-frontend           0x0000000102956db8 withSemanticAnalysis(swift::CompilerInstance&, swift::FrontendObserver*, llvm::function_ref<bool (swift::CompilerInstance&)>, bool) + 160
39 swift-frontend           0x00000001029481e0 performCompile(swift::CompilerInstance&, int&, swift::FrontendObserver*) + 708
40 swift-frontend           0x000000010294714c swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 2380
41 swift-frontend           0x0000000102761a78 swift::mainEntry(int, char const**) + 3096
42 dyld                     0x00000001801da0e0 start + 2360

Reproduction

func foo() throws -> Int { 0 }

func foo2() throws {
    lazy var x = try foo()
}

Expected behavior

The compiler should handle the lazy var initialization with a try without hanging or crashing, and either compile the code or produce a meaningful compilation error if the usage is incorrect.

Environment

swift

swift-driver version: 1.90.11.1 Apple Swift version 5.10 (swiftlang-5.10.0.13 clang-1500.3.9.4)
Target: arm64-apple-macosx14.0

MacOS

macOS Sonoma 14.4

Additional information

No response

[CrazyFanFan]

In Swift 6, this issue has been fixed, and now exceptions can be correctly thrown: Call can throw, but errors cannot be thrown out of a lazy variable initializer.

[hamishknight]

Yup this was fixed by #74591