func takesKP(_ kp: KeyPath<R, Int>) {}

struct S {
  subscript() -> Int { 0 }
}

@dynamicMemberLookup
struct R {
  subscript(dynamicMember kp: KeyPath<S, Int>) -> Int! { 0 }
}

takesKP(\R.[])

1.  Apple Swift version 5.6-dev (LLVM 70b82c8b83f6294, Swift a66435c61f9a895)
2.  Compiling with the current language version
3.  While evaluating request TypeCheckSourceFileRequest(source_file "/Users/hamish/projects/swift-test-arena/swift-test-arena/main.swift")
4.  While type-checking statement at [/Users/hamish/projects/swift-test-arena/swift-test-arena/main.swift:75:1 - line:75:14] RangeText="takesKP(\R.[]"
5.  While type-checking expression at [/Users/hamish/projects/swift-test-arena/swift-test-arena/main.swift:75:1 - line:75:14] RangeText="takesKP(\R.[]"
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           0x00000001148e72d7 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 39
1  swift-frontend           0x00000001148e64f5 llvm::sys::RunSignalHandlers() + 85
2  swift-frontend           0x00000001148e7b26 SignalHandler(int) + 278
3  libsystem_platform.dylib 0x00007fff20492d7d _sigtramp + 29
4  libsystem_platform.dylib 0x000000011e8cfd6b _sigtramp + 18446603344782020619
5  libsystem_c.dylib        0x00007fff203a2406 abort + 125
6  libsystem_c.dylib        0x00007fff203a17d8 err + 0
7  swift-frontend           0x0000000114cac9b3 swift::constraints::Solution::getDisjunctionChoice(swift::constraints::ConstraintLocator*) const (.cold.1) + 35
8  swift-frontend           0x0000000110b515e4 swift::constraints::Solution::getDisjunctionChoice(swift::constraints::ConstraintLocator*) const + 180
9  swift-frontend           0x0000000110b59bb7 (anonymous namespace)::ExprRewriter::buildKeyPathSubscriptComponent(swift::constraints::SelectedOverload const&, swift::SourceLoc, swift::ArgumentList*, swift::constraints::ConstraintLocator*, llvm::SmallVectorImpl<swift::KeyPathExpr::Component>&) + 2695
10 swift-frontend           0x0000000110b4753a swift::ASTVisitor<(anonymous namespace)::ExprRewriter, swift::Expr*, void, void, void, void, void>::visit(swift::Expr*) + 21386
11 swift-frontend           0x0000000110b40146 (anonymous namespace)::ExprWalker::walkToExprPost(swift::Expr*) + 22
12 swift-frontend           0x0000000110ffd1d2 (anonymous namespace)::Traversal::doIt(swift::ArgumentList*) + 210
13 swift-frontend           0x0000000110fff2ef swift::ASTVisitor<(anonymous namespace)::Traversal, swift::Expr*, swift::Stmt*, bool, swift::Pattern*, bool, void>::visit(swift::Expr*) + 8351
14 swift-frontend           0x0000000110ffcaa9 swift::Expr::walk(swift::ASTWalker&) + 73
15 swift-frontend           0x0000000110b388be (anonymous namespace)::ExprWalker::rewriteTarget(swift::constraints::SolutionApplicationTarget) + 302
16 swift-frontend           0x0000000110b385b3 swift::constraints::ConstraintSystem::applySolution(swift::constraints::Solution&, swift::constraints::SolutionApplicationTarget) + 563
17 swift-frontend           0x0000000110d0858d swift::TypeChecker::typeCheckExpression(swift::constraints::SolutionApplicationTarget&, swift::OptionSet<swift::TypeCheckExprFlags, unsigned int>) + 621
18 swift-frontend           0x0000000110d0829e swift::TypeChecker::typeCheckExpression(swift::Expr*&, swift::DeclContext*, swift::constraints::ContextualTypeInfo, swift::OptionSet<swift::TypeCheckExprFlags, unsigned int>) + 78
19 swift-frontend           0x0000000110dc94e9 (anonymous namespace)::StmtChecker::typeCheckASTNode(swift::ASTNode&) + 249
20 swift-frontend           0x0000000110dcb44c swift::ASTVisitor<(anonymous namespace)::StmtChecker, void, swift::Stmt*, void, void, void, void>::visit(swift::Stmt*) + 140
21 swift-frontend           0x0000000110dca730 bool (anonymous namespace)::StmtChecker::typeCheckStmt<swift::BraceStmt>(swift::BraceStmt*&) + 128
22 swift-frontend           0x0000000110dca7b2 swift::TypeChecker::typeCheckTopLevelCodeDecl(swift::TopLevelCodeDecl*) + 50
23 swift-frontend           0x0000000110dfc79f swift::TypeCheckSourceFileRequest::evaluate(swift::Evaluator&, swift::SourceFile*) const + 223
24 swift-frontend           0x0000000110dfe58e llvm::Expected<swift::TypeCheckSourceFileRequest::OutputType> swift::Evaluator::getResultUncached<swift::TypeCheckSourceFileRequest>(swift::TypeCheckSourceFileRequest const&) + 430
25 swift-frontend           0x0000000110dfe312 llvm::Expected<swift::TypeCheckSourceFileRequest::OutputType> swift::Evaluator::getResultCached<swift::TypeCheckSourceFileRequest, (void*)0>(swift::TypeCheckSourceFileRequest const&) + 114
26 swift-frontend           0x0000000110dfc5ad swift::TypeCheckSourceFileRequest::OutputType swift::evaluateOrDefault<swift::TypeCheckSourceFileRequest>(swift::Evaluator&, swift::TypeCheckSourceFileRequest, swift::TypeCheckSourceFileRequest::OutputType) + 45
27 swift-frontend           0x000000011006c33e swift::CompilerInstance::forEachFileToTypeCheck(llvm::function_ref<void (swift::SourceFile&)>) + 158
28 swift-frontend           0x000000011006c1ea swift::CompilerInstance::performSema() + 74
29 swift-frontend           0x000000010ff184c5 swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 4725
30 swift-frontend           0x000000010fee09d2 swift::mainEntry(int, char const**) + 546
31 libdyld.dylib            0x00007fff20468f3d start + 1
32 libdyld.dylib            0x0000000000000045 start + 18446603339974668553
error: Abort trap: 6 (in target 'swift-test-arena' from project 'swift-test-arena')