compiler crash: optional chaining on ~Copyable type

[mayoff]

Description

I tried to use optional chaining on an Optional<NonCopyable>, where struct NonCopyable: ~Copyable. The compiler crashed.

Reproduction

Put this in nc.swift:

struct NonCopyable: ~Copyable {
    var shared: Self { .init() }
}

func f() {
    _ = (Optional<NonCopyable>.none)?.shared
}

Then compile it:

~/Library/Developer/Toolchains/swift-latest.xctoolchain/usr/bin/swiftc -c nc.swift

Stack dump

Assertion failed: (Ptr && "Cannot dereference a null Type!"), function operator->, file Type.h, line 229.
Please submit a bug report (https://swift.org/contributing/#reporting-bugs) and include the crash backtrace.
Stack dump:
0.	Program arguments: /Users/mayoff/Library/Developer/Toolchains/swift-latest.xctoolchain/usr/bin/swift-frontend -frontend -c -primary-file /Users/mayoff/t/nc.swift -target arm64-apple-macosx14.0 -Xllvm -aarch64-use-tbi -enable-objc-interop -empty-abi-descriptor -Xcc -working-directory -Xcc /Users/mayoff/t -resource-dir /Users/mayoff/Library/Developer/Toolchains/swift-latest.xctoolchain/usr/lib/swift -module-name nc -in-process-plugin-server-path /Users/mayoff/Library/Developer/Toolchains/swift-latest.xctoolchain/usr/lib/swift/host/libSwiftInProcPluginServer.dylib -plugin-path /Users/mayoff/Library/Developer/Toolchains/swift-latest.xctoolchain/usr/lib/swift/host/plugins -plugin-path /Users/mayoff/Library/Developer/Toolchains/swift-latest.xctoolchain/usr/local/lib/swift/host/plugins -o /Users/mayoff/t/nc.o
1.	Apple Swift version 6.0-dev (LLVM 6c1a2ac10cabb71, Swift 54908861448c8e8)
2.	Compiling with effective version 5.10
3.	While evaluating request TypeCheckSourceFileRequest(source_file "/Users/mayoff/t/nc.swift")
4.	While evaluating request TypeCheckFunctionBodyRequest(nc.(file).f()@/Users/mayoff/t/nc.swift:6:6)
5.	While type-checking statement at [/Users/mayoff/t/nc.swift:6:10 - line:8:1] RangeText="{
    _ = (Optional<NonCopyable>.none)?.shared
"
6.	While type-checking expression at [/Users/mayoff/t/nc.swift:7:5 - line:7:39] RangeText="_ = (Optional<NonCopyable>.none)?."
7.	While type-checking-target starting at /Users/mayoff/t/nc.swift:7:5
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           0x0000000106197b08 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 56
1  swift-frontend           0x00000001061962d4 llvm::sys::RunSignalHandlers() + 112
2  swift-frontend           0x0000000106198150 SignalHandler(int) + 304
3  libsystem_platform.dylib 0x0000000183e62584 _sigtramp + 56
4  libsystem_pthread.dylib  0x0000000183e31c20 pthread_kill + 288
5  libsystem_c.dylib        0x0000000183d3ea30 abort + 180
6  libsystem_c.dylib        0x0000000183d3dd20 err + 0
7  swift-frontend           0x000000010662cd04 swift::findSyntacticErrorForConsume(swift::ModuleDecl*, swift::SourceLoc, swift::Expr*) (.cold.4) + 0
8  swift-frontend           0x0000000101edf440 swift::findSyntacticErrorForConsume(swift::ModuleDecl*, swift::SourceLoc, swift::Expr*) + 1064
9  swift-frontend           0x0000000101fa28b0 swift::canAddExplicitConsume(swift::ModuleDecl*, swift::Expr*) + 92
10 swift-frontend           0x0000000101d6d788 (anonymous namespace)::ExprRewriter::diagnoseOptionalInjection(swift::InjectIntoOptionalExpr*, swift::constraints::ConstraintLocatorBuilder) + 196
11 swift-frontend           0x0000000101d4c2a8 (anonymous namespace)::ExprRewriter::coerceToType(swift::Expr*, swift::Type, swift::constraints::ConstraintLocatorBuilder) + 2836
12 swift-frontend           0x0000000101d526bc (anonymous namespace)::ExprWalker::walkToExprPost(swift::Expr*) + 14592
13 swift-frontend           0x000000010230ca14 (anonymous namespace)::Traversal::doIt(swift::Expr*) + 988
14 swift-frontend           0x000000010230ded0 (anonymous namespace)::Traversal::visitAssignExpr(swift::AssignExpr*) + 60
15 swift-frontend           0x000000010230c818 (anonymous namespace)::Traversal::doIt(swift::Expr*) + 480
16 swift-frontend           0x000000010230c62c swift::Expr::walk(swift::ASTWalker&) + 32
17 swift-frontend           0x0000000101d49cd8 (anonymous namespace)::ExprWalker::rewriteTarget(swift::constraints::SyntacticElementTarget) + 596
18 swift-frontend           0x0000000101d496fc swift::constraints::ConstraintSystem::applySolution(swift::constraints::Solution&, swift::constraints::SyntacticElementTarget) + 620
19 swift-frontend           0x0000000101f9bb44 swift::TypeChecker::typeCheckTarget(swift::constraints::SyntacticElementTarget&, swift::optionset::OptionSet<swift::TypeCheckExprFlags, unsigned int>) + 392
20 swift-frontend           0x0000000101f9b964 swift::TypeChecker::typeCheckExpression(swift::constraints::SyntacticElementTarget&, swift::optionset::OptionSet<swift::TypeCheckExprFlags, unsigned int>) + 184
21 swift-frontend           0x0000000101f9b838 swift::TypeChecker::typeCheckExpression(swift::Expr*&, swift::DeclContext*, swift::constraints::ContextualTypeInfo, swift::optionset::OptionSet<swift::TypeCheckExprFlags, unsigned int>) + 92
22 swift-frontend           0x0000000102074778 (anonymous namespace)::StmtChecker::typeCheckASTNode(swift::ASTNode&) + 264
23 swift-frontend           0x00000001020780b8 swift::ASTVisitor<(anonymous namespace)::StmtChecker, void, swift::Stmt*, void, void, void, void>::visit(swift::Stmt*) + 160
24 swift-frontend           0x00000001020765c0 bool (anonymous namespace)::StmtChecker::typeCheckStmt<swift::BraceStmt>(swift::BraceStmt*&) + 136
25 swift-frontend           0x0000000102075d14 (anonymous namespace)::StmtChecker::typeCheckBody(swift::BraceStmt*&) + 32
26 swift-frontend           0x0000000102075a9c swift::TypeCheckFunctionBodyRequest::evaluate(swift::Evaluator&, swift::AbstractFunctionDecl*) const + 1360
27 swift-frontend           0x000000010241ca1c swift::TypeCheckFunctionBodyRequest::OutputType swift::Evaluator::getResultUncached<swift::TypeCheckFunctionBodyRequest, swift::TypeCheckFunctionBodyRequest::OutputType swift::evaluateOrDefault<swift::TypeCheckFunctionBodyRequest>(swift::Evaluator&, swift::TypeCheckFunctionBodyRequest, swift::TypeCheckFunctionBodyRequest::OutputType)::'lambda'()>(swift::TypeCheckFunctionBodyRequest const&, swift::TypeCheckFunctionBodyRequest::OutputType swift::evaluateOrDefault<swift::TypeCheckFunctionBodyRequest>(swift::Evaluator&, swift::TypeCheckFunctionBodyRequest, swift::TypeCheckFunctionBodyRequest::OutputType)::'lambda'()) + 240
28 swift-frontend           0x0000000102386510 swift::AbstractFunctionDecl::getTypecheckedBody() const + 120
29 swift-frontend           0x00000001024ca8a4 swift::SourceFile::typeCheckDelayedFunctions() + 104
30 swift-frontend           0x00000001020b6210 swift::TypeCheckSourceFileRequest::evaluate(swift::Evaluator&, swift::SourceFile*) const + 256
31 swift-frontend           0x00000001020b7c74 swift::TypeCheckSourceFileRequest::OutputType swift::Evaluator::getResultUncached<swift::TypeCheckSourceFileRequest, swift::TypeCheckSourceFileRequest::OutputType swift::evaluateOrDefault<swift::TypeCheckSourceFileRequest>(swift::Evaluator&, swift::TypeCheckSourceFileRequest, swift::TypeCheckSourceFileRequest::OutputType)::'lambda'()>(swift::TypeCheckSourceFileRequest const&, swift::TypeCheckSourceFileRequest::OutputType swift::evaluateOrDefault<swift::TypeCheckSourceFileRequest>(swift::Evaluator&, swift::TypeCheckSourceFileRequest, swift::TypeCheckSourceFileRequest::OutputType)::'lambda'()) + 232
32 swift-frontend           0x00000001020b60e8 swift::performTypeChecking(swift::SourceFile&) + 84
33 swift-frontend           0x0000000100f28e90 bool llvm::function_ref<bool (swift::SourceFile&)>::callback_fn<swift::CompilerInstance::performSema()::$_8>(long, swift::SourceFile&) + 16
34 swift-frontend           0x0000000100f22058 swift::CompilerInstance::forEachFileToTypeCheck(llvm::function_ref<bool (swift::SourceFile&)>) + 76
35 swift-frontend           0x0000000100f21fec swift::CompilerInstance::performSema() + 76
36 swift-frontend           0x0000000100ce80a4 withSemanticAnalysis(swift::CompilerInstance&, swift::FrontendObserver*, llvm::function_ref<bool (swift::CompilerInstance&)>, bool) + 60
37 swift-frontend           0x0000000100cddca4 performCompile(swift::CompilerInstance&, int&, swift::FrontendObserver*) + 716
38 swift-frontend           0x0000000100cdd370 swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 2304
39 swift-frontend           0x0000000100acad98 swift::mainEntry(int, char const**) + 3096
40 dyld                     0x0000000183aa7154 start + 2476

Expected behavior

I expected the compiler to not crash. Not sure what else there is to say…

Environment

Apple Swift version 6.0-dev (LLVM 6c1a2ac10cabb71, Swift 54908861448c8e8)
Target: arm64-apple-macosx14.0

I used the “main” Swift development snapshot of 2024-08-20: swift-DEVELOPMENT-SNAPSHOT-2024-08-19-a.xctoolchain

It also crashes with the toolchains of Xcode 16.0 beta 4 and Xcode 16.1 beta 1, but does not crash with the toolchain of Xcode-16.0 beta 3.

Additional information

Changing the ? to ! makes the compiler not crash.