Assertion failure when emitting Obj-C header for function that uses C++ type

[hamishknight]

For e.g:

// cmodule.h
struct Foo {
  void *foo;
};

// module.modulemap
module CModule [system] {
  header "cmodule.h"
  requires cplusplus
  export *
}

The following hits an assertion failure when using -emit-objc-header:

import CModule

public func bar(x: Foo, y: UnsafeMutablePointer<UnsafeMutableRawPointer?>) {}

Assertion failed: (!s.isUnsupported()), function operator(), file PrintClangFunction.cpp, line 921.
Please submit a bug report (https://swift.org/contributing/#reporting-bugs) and include the crash backtrace.
Stack dump:
0.      Program arguments: /Users/hamish/src/swift-dev/build/Release/swift-macosx-arm64/bin/swift-frontend -typecheck /Users/hamish/src/swift-test-arena/main.swift -sdk /Users/hamish/src/MacOSX.sdk -debug-diagnostic-names -diagnostic-style=llvm -emit-objc-header -emit-objc-header-path /tmp/foo.h -I /Users/hamish/src/swift-test-arena/CModule -cxx-interoperability-mode=default
1.      Swift version 6.2-dev (LLVM 52a70e588b5dd9e, Swift dfe1f9cc53a1678)
2.      Compiling with effective version 5.10
3.      While generating Clang header
4.      While printing forward declarations needed by function 'bar(x:y:)' (at /Users/hamish/src/swift-test-arena/main.swift:577:8)
5.      While printing 'bar(x:y:)' (at /Users/hamish/src/swift-test-arena/main.swift:577:8)
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           0x00000001069575d0 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 56
1  swift-frontend           0x00000001069558ec llvm::sys::RunSignalHandlers() + 112
2  swift-frontend           0x0000000106957c2c SignalHandler(int) + 292
3  libsystem_platform.dylib 0x00000001810b4184 _sigtramp + 56
4  libsystem_pthread.dylib  0x000000018107ef70 pthread_kill + 288
5  libsystem_c.dylib        0x0000000180f8b908 abort + 128
6  libsystem_c.dylib        0x0000000180f8ac1c err + 0
7  swift-frontend           0x00000001069e0a64 void llvm::function_ref<void (swift::LoweredFunctionSignature::GenericRequirementParameter const&)>::callback_fn<swift::DeclAndTypeClangFunctionPrinter::printFunctionSignature(swift::AbstractFunctionDecl const*, swift::LoweredFunctionSignature const&, llvm::StringRef, swift::Type, swift::DeclAndTypeClangFunctionPrinter::FunctionSignatureKind, swift::DeclAndTypeClangFunctionPrinter::FunctionSignatureModifiers)::$_8>(long, swift::LoweredFunctionSignature::GenericRequirementParameter const&) (.cold.1) + 0
8  swift-frontend           0x000000010113e9cc void llvm::function_ref<void (swift::LoweredFunctionSignature::IndirectParameter const&)>::callback_fn<swift::DeclAndTypeClangFunctionPrinter::printFunctionSignature(swift::AbstractFunctionDecl const*, swift::LoweredFunctionSignature const&, llvm::StringRef, swift::Type, swift::DeclAndTypeClangFunctionPrinter::FunctionSignatureKind, swift::DeclAndTypeClangFunctionPrinter::FunctionSignatureModifiers)::$_7>(long, swift::LoweredFunctionSignature::IndirectParameter const&) + 0
9  swift-frontend           0x000000010113daac void llvm::function_ref<void (swift::LoweredFunctionSignature::DirectParameter const&)>::callback_fn<swift::DeclAndTypeClangFunctionPrinter::printFunctionSignature(swift::AbstractFunctionDecl const*, swift::LoweredFunctionSignature const&, llvm::StringRef, swift::Type, swift::DeclAndTypeClangFunctionPrinter::FunctionSignatureKind, swift::DeclAndTypeClangFunctionPrinter::FunctionSignatureModifiers)::$_6>(long, swift::LoweredFunctionSignature::DirectParameter const&) + 820
10 swift-frontend           0x00000001013e37bc swift::LoweredFunctionSignature::visitParameterList(llvm::function_ref<void (swift::LoweredFunctionSignature::IndirectResultValue const&)>, llvm::function_ref<void (swift::LoweredFunctionSignature::DirectParameter const&)>, llvm::function_ref<void (swift::LoweredFunctionSignature::IndirectParameter const&)>, llvm::function_ref<void (swift::LoweredFunctionSignature::GenericRequirementParameter const&)>, llvm::function_ref<void (swift::LoweredFunctionSignature::MetadataSourceParameter const&)>, llvm::function_ref<void (swift::LoweredFunctionSignature::ContextParameter const&)>, llvm::function_ref<void (swift::LoweredFunctionSignature::ErrorResultValue const&)>) const + 504
11 swift-frontend           0x0000000101133bec swift::DeclAndTypeClangFunctionPrinter::printFunctionSignature(swift::AbstractFunctionDecl const*, swift::LoweredFunctionSignature const&, llvm::StringRef, swift::Type, swift::DeclAndTypeClangFunctionPrinter::FunctionSignatureKind, swift::DeclAndTypeClangFunctionPrinter::FunctionSignatureModifiers) + 4308
12 swift-frontend           0x0000000101119258 swift::DeclAndTypePrinter::Implementation::printCFunctionWithLoweredSignature(swift::AbstractFunctionDecl*, swift::DeclAndTypePrinter::Implementation::FunctionSwiftABIInformation const&, swift::Type, swift::AnyFunctionType*, llvm::StringRef, llvm::StringRef) + 216
13 swift-frontend           0x0000000101118698 swift::DeclAndTypePrinter::Implementation::printSwiftABIFunctionSignatureAsCxxFunction(swift::AbstractFunctionDecl*, std::__1::optional<swift::FunctionType*>, std::__1::optional<swift::NominalTypeDecl*>) + 540
14 swift-frontend           0x000000010110e960 swift::DeclAndTypePrinter::Implementation::visitFuncDecl(swift::FuncDecl*) + 256
15 swift-frontend           0x000000010110a59c swift::DeclAndTypePrinter::print(swift::Decl const*) + 96
16 swift-frontend           0x0000000101121f0c (anonymous namespace)::ModuleWriter::writeFunc(swift::FuncDecl const*) + 188
17 swift-frontend           0x000000010111f3d4 (anonymous namespace)::ModuleWriter::write() + 2060
18 swift-frontend           0x0000000101120e78 swift::printModuleContentsAsCxx(llvm::raw_ostream&, swift::ModuleDecl&, swift::SwiftToClangInteropContext&, bool, llvm::StringSet<llvm::MallocAllocator>&) + 1392
19 swift-frontend           0x0000000101130550 void llvm::function_ref<void ()>::callback_fn<swift::printAsClangHeader(llvm::raw_ostream&, swift::ModuleDecl*, llvm::StringRef, swift::FrontendOptions const&, swift::IRGenOptions const&, clang::HeaderSearch&)::$_2>(long) + 736
20 swift-frontend           0x000000010112bc8c emitCxxConditional(llvm::raw_ostream&, llvm::function_ref<void ()>, llvm::function_ref<void ()>) + 124
21 swift-frontend           0x000000010112ba24 swift::printAsClangHeader(llvm::raw_ostream&, swift::ModuleDecl*, llvm::StringRef, swift::FrontendOptions const&, swift::IRGenOptions const&, clang::HeaderSearch&) + 6392
22 swift-frontend           0x0000000100d78840 swift::withOutputPath(swift::DiagnosticEngine&, llvm::vfs::OutputBackend&, llvm::StringRef, llvm::function_ref<bool (llvm::raw_pwrite_stream&)>) + 152
23 swift-frontend           0x0000000100f60660 performEndOfPipelineActions(swift::CompilerInstance&) + 3732
24 swift-frontend           0x0000000100f5c95c performCompile(swift::CompilerInstance&, int&, swift::FrontendObserver*) + 732
25 swift-frontend           0x0000000100f5c190 swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 2204
26 swift-frontend           0x0000000100d53118 swift::mainEntry(int, char const**) + 3052
27 dyld                     0x0000000180cfc274 start + 2840
fish: Job 1, './swift -frontend -typecheck ~/…' terminated by signal SIGABRT (Abort)