Compiler crash: Unhandled coercion

[jasonbobier]

Description

Attempting to access a member of an existential crashes.

Steps to reproduce

Please run this code:

protocol U {}

protocol CU<VT>: U {
	associatedtype VT
}

protocol TN: Numeric {}

extension Double: TN { }

struct EU<VT: TN & Hashable>: CU {}

protocol MP {
	associatedtype VT: TN
	associatedtype UT: U

	var value: VT { get set }
	var unit: UT { get set }
}


struct M<VT: TN, UT: U>: MP {
	var value: VT
	var unit: UT
}

let m = M(value: 1.0, unit: EU<Double>())

var mp: any MP = m

let v = mp.value

This produces the following crash in a playground:

Thread 15 Crashed:: RPC packet thread for client tid 009e689b (10381467)
0   libsystem_kernel.dylib        	       0x187b28724 __pthread_kill + 8
1   libsystem_pthread.dylib       	       0x187b5fc28 pthread_kill + 288
2   libsystem_c.dylib             	       0x187a6dae8 abort + 180
3   LLDB                          	       0x11a07843c (anonymous namespace)::ExprRewriter::coerceToType(swift::Expr*, swift::Type, swift::constraints::ConstraintLocatorBuilder, llvm::Optional<swift::Pattern*>) (.cold.1) + 64
4   LLDB                          	       0x116b2abb0 (anonymous namespace)::ExprRewriter::coerceToType(swift::Expr*, swift::Type, swift::constraints::ConstraintLocatorBuilder, llvm::Optional<swift::Pattern*>) + 7580
5   LLDB                          	       0x116b2a374 (anonymous namespace)::ExprRewriter::coerceToType(swift::Expr*, swift::Type, swift::constraints::ConstraintLocatorBuilder, llvm::Optional<swift::Pattern*>) + 5472
6   LLDB                          	       0x116b40bb8 (anonymous namespace)::ExprRewriter::closeExistential(swift::Expr*&, swift::constraints::ConstraintLocatorBuilder, bool) + 328
7   LLDB                          	       0x116b3bef0 (anonymous namespace)::ExprRewriter::buildMemberRef(swift::Expr*, swift::SourceLoc, swift::constraints::SelectedOverload, swift::DeclNameLoc, swift::constraints::ConstraintLocatorBuilder, swift::constraints::ConstraintLocatorBuilder, bool, swift::AccessSemantics) + 6160
8   LLDB                          	       0x116b3228c (anonymous namespace)::ExprRewriter::walkToExprPost(swift::Expr*) + 15612
9   LLDB                          	       0x116b2c090 (anonymous namespace)::ExprWalker::walkToExprPost(swift::Expr*) + 24
10  LLDB                          	       0x116faf768 swift::Expr::walk(swift::ASTWalker&) + 116
11  LLDB                          	       0x116b27278 (anonymous namespace)::ExprWalker::rewriteTarget(swift::constraints::SolutionApplicationTarget) + 284
12  LLDB                          	       0x116b26d50 swift::constraints::ConstraintSystem::applySolution(swift::constraints::Solution&, swift::constraints::SolutionApplicationTarget) + 568
13  LLDB                          	       0x116cf66d0 swift::TypeChecker::typeCheckTarget(swift::constraints::SolutionApplicationTarget&, swift::OptionSet<swift::TypeCheckExprFlags, unsigned int>) + 512
14  LLDB                          	       0x116cf64a8 swift::TypeChecker::typeCheckExpression(swift::constraints::SolutionApplicationTarget&, swift::OptionSet<swift::TypeCheckExprFlags, unsigned int>) + 176
15  LLDB                          	       0x116cf7584 swift::TypeChecker::typeCheckBinding(swift::Pattern*&, swift::Expr*&, swift::DeclContext*, swift::Type, swift::PatternBindingDecl*, unsigned int, swift::OptionSet<swift::TypeCheckExprFlags, unsigned int>) + 192
16  LLDB                          	       0x116cf7778 swift::TypeChecker::typeCheckPatternBinding(swift::PatternBindingDecl*, unsigned int, swift::Type, swift::OptionSet<swift::TypeCheckExprFlags, unsigned int>) + 288
17  LLDB                          	       0x116db03c0 swift::PatternBindingEntryRequest::evaluate(swift::Evaluator&, swift::PatternBindingDecl*, unsigned int, bool) const + 2036
18  LLDB                          	       0x116d370ac llvm::Expected<swift::PatternBindingEntryRequest::OutputType> swift::Evaluator::getResultUncached<swift::PatternBindingEntryRequest>(swift::PatternBindingEntryRequest const&) + 268
19  LLDB                          	       0x116d36f40 swift::PatternBindingEntryRequest::OutputType swift::evaluateOrDefault<swift::PatternBindingEntryRequest>(swift::Evaluator&, swift::PatternBindingEntryRequest, swift::PatternBindingEntryRequest::OutputType) + 108
20  LLDB                          	       0x116d2a710 (anonymous namespace)::DeclChecker::visit(swift::Decl*) + 3256
21  LLDB                          	       0x116d29a40 swift::TypeChecker::typeCheckDecl(swift::Decl*, bool) + 120
22  LLDB                          	       0x116dabf1c swift::ASTVisitor<(anonymous namespace)::StmtChecker, void, swift::Stmt*, void, void, void, void>::visit(swift::Stmt*) + 292
23  LLDB                          	       0x116dab1b8 bool (anonymous namespace)::StmtChecker::typeCheckStmt<swift::BraceStmt>(swift::BraceStmt*&) + 136
24  LLDB                          	       0x116dab234 swift::TypeChecker::typeCheckTopLevelCodeDecl(swift::TopLevelCodeDecl*) + 52
25  LLDB                          	       0x116ddb7b4 swift::TypeCheckSourceFileRequest::evaluate(swift::Evaluator&, swift::SourceFile*) const + 204
26  LLDB                          	       0x116ddd14c llvm::Expected<swift::TypeCheckSourceFileRequest::OutputType> swift::Evaluator::getResultUncached<swift::TypeCheckSourceFileRequest>(swift::TypeCheckSourceFileRequest const&) + 268
27  LLDB                          	       0x116ddcfb0 llvm::Expected<swift::TypeCheckSourceFileRequest::OutputType> swift::Evaluator::getResultCached<swift::TypeCheckSourceFileRequest, (void*)0>(swift::TypeCheckSourceFileRequest const&) + 68
28  LLDB                          	       0x116ddb67c swift::performTypeChecking(swift::SourceFile&) + 48
29  LLDB                          	       0x1159f1060 lldb_private::SwiftExpressionParser::Parse(lldb_private::DiagnosticManager&, unsigned int, unsigned int) + 7548
30  LLDB                          	       0x115a0169c lldb_private::SwiftUserExpression::GetTextAndSetExpressionParser(lldb_private::DiagnosticManager&, std::__1::unique_ptr<lldb_private::SwiftExpressionSourceCode, std::__1::default_delete<lldb_private::SwiftExpressionSourceCode>>&, lldb_private::ExecutionContext&, lldb_private::ExecutionContextScope*) + 4640
31  LLDB                          	       0x115a02020 lldb_private::SwiftUserExpression::Parse(lldb_private::DiagnosticManager&, lldb_private::ExecutionContext&, lldb_private::ExecutionPolicy, bool, bool) + 1272
32  LLDB                          	       0x11583cb68 lldb_private::UserExpression::Evaluate(lldb_private::ExecutionContext&, lldb_private::EvaluateExpressionOptions const&, llvm::StringRef, llvm::StringRef, std::__1::shared_ptr<lldb_private::ValueObject>&, lldb_private::Status&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>*, lldb_private::ValueObject*) + 2048
33  LLDB                          	       0x11593c6bc lldb_private::Target::EvaluateExpression(llvm::StringRef, lldb_private::ExecutionContextScope*, std::__1::shared_ptr<lldb_private::ValueObject>&, lldb_private::EvaluateExpressionOptions const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>*, lldb_private::ValueObject*) + 832
34  LLDB                          	       0x115618a44 lldb::SBFrame::EvaluateExpression(char const*, lldb::SBExpressionOptions const&) + 444
35  lldb-rpc-server               	       0x1045451dc rpc_server::_ZN4lldb7SBFrame18EvaluateExpressionEPKcRKNS_19SBExpressionOptionsE::HandleRPCCall(rpc_common::Connection&, rpc_common::RPCStream&, rpc_common::RPCStream&) + 208
36  lldb-rpc-server               	       0x10455a7a4 rpc_common::Connection::PrivateHandleRPCPacket(rpc_common::RPCPacket&, rpc_common::RPCPacket&, bool&) + 628
37  lldb-rpc-server               	       0x10455b6e8 rpc_common::Connection::HandleRPCPacket(rpc_common::RPCPacket&) + 72
38  lldb-rpc-server               	       0x10455e58c Packets::ProcessPackets() + 660
39  lldb-rpc-server               	       0x10455e26c Packets::ReadThread() + 276
40  lldb-rpc-server               	       0x10455e14c Packets::RunReadThread(void*) + 12
41  libsystem_pthread.dylib       	       0x187b5ffa8 _pthread_start + 148
42  libsystem_pthread.dylib       	       0x187b5ada0 thread_start + 8

Environment
swift-driver version: 1.75.2 Apple Swift version 5.8 (swiftlang-5.8.0.124.2 clang-1403.0.22.11.100)
Xcode 14.3
Build version 14E222b

Also note, filed with more information here: FB12117149

[xedin]

@angela-laar Another instance of l-value existential type being opened.

[AnthonyLatsis]

Reduced:

protocol TN: Numeric {}
protocol MP {
  associatedtype VT: TN

  var value: VT { get set }
}

var mp: any MP

let v = mp.value

@jasonbobier FYI currently you are not supposed to be allowed to access a {get set} requirement on an existential if it has a type parameter in its type (only if any such type parameter is known to be concrete).

[AnthonyLatsis]

Duplicate of #62219

[jasonbobier]

OK, thanks. So I can do something like this? (seems to work)

func unbox(m: some MP) -> some MP {
	return m
}

let v = unbox(m: mp).value

[AnthonyLatsis]

Sure thing, these limitations are exclusive to values of any type.

A hand-written getter will do the job as well:

extension MP {
  func getValue() -> VT { value }
}

[jasonbobier]

With the solution being that simple, is there something missing about why it isn't implemented in the compiler itself?

[xedin]

It’s a just bug we need to fix.

[jasonbobier]

Awesome! Thanks for the help and explanation all!