[SR-5013] Assertion failed: (isa<X>(Val) && "cast<Ty>() argument of incompatible type!")

[hartbit]

Previous ID	SR-5013
Radar	None
Original Reporter	@hartbit
Type	Bug
Status	Resolved
Resolution	Done

Environment

24-05-2107 master snapshot

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, CompilerCrash, TypeChecker
Assignee	@slavapestov
Priority	Medium

md5: eadb1113b7c82fbbd2d939bbcdda1c72

Issue Description:

The compiler crasher when trying to compile the following piece of code on the 24-05-2107 master toolchain:

protocol A {
    associatedtype B
}

extension A {
    func foo() {
        (B.self as! Sequence.Type).Element
    }
}

Assertion failed: (isa<X>(Val) && "cast<Ty>() argument of incompatible type!"), function cast, file /Users/buildnode/jenkins/workspace/oss-swift-package-osx/llvm/include/llvm/Support/Casting.h, line 236.
0  swift                    0x0000000109f12908 llvm::sys::PrintStackTrace(llvm::raw_ostream&) + 40
1  swift                    0x0000000109f118d6 llvm::sys::RunSignalHandlers() + 86
2  swift                    0x0000000109f12ec9 SignalHandler(int) + 361
3  libsystem_platform.dylib 0x00007fffdf351b3a _sigtramp + 26
4  libsystem_platform.dylib 0x010000010b8a0e00 _sigtramp + 743764704
5  libsystem_c.dylib        0x00007fffdf1d6420 abort + 129
6  libsystem_c.dylib        0x00007fffdf19d893 basename_r + 0
7  swift                    0x0000000107b1fc4b swift::constraints::ConstraintSystem::getTypeOfMemberReference(swift::Type, swift::ValueDecl*, swift::DeclContext*, bool, bool, swift::FunctionRefKind, swift::constraints::ConstraintLocatorBuilder, swift::DeclRefExpr const*, llvm::DenseMap<swift::GenericTypeParamType*, swift::TypeVariableType*, llvm::DenseMapInfo<swift::GenericTypeParamType*>, llvm::detail::DenseMapPair<swift::GenericTypeParamType*, swift::TypeVariableType*> >*) + 3227
8  swift                    0x0000000107b20397 swift::constraints::ConstraintSystem::resolveOverload(swift::constraints::ConstraintLocator*, swift::Type, swift::constraints::OverloadChoice, swift::DeclContext*) + 791
9  swift                    0x0000000107b1fef9 swift::constraints::ConstraintSystem::addOverloadSet(swift::Type, llvm::ArrayRef<swift::constraints::OverloadChoice>, swift::DeclContext*, swift::constraints::ConstraintLocator*, swift::constraints::OverloadChoice*) + 233
10 swift                    0x0000000107ae4df3 swift::constraints::ConstraintSystem::simplifyMemberConstraint(swift::constraints::ConstraintKind, swift::Type, swift::DeclName, swift::Type, swift::DeclContext*, swift::FunctionRefKind, swift::OptionSet<swift::constraints::ConstraintSystem::TypeMatchFlags, unsigned int>, swift::constraints::ConstraintLocatorBuilder) + 515
11 swift                    0x0000000107ad0543 swift::constraints::ConstraintSystem::addValueMemberConstraint(swift::Type, swift::DeclName, swift::Type, swift::DeclContext*, swift::FunctionRefKind, swift::constraints::ConstraintLocatorBuilder) + 179
12 swift                    0x0000000107ad0b9d (anonymous namespace)::ConstraintGenerator::addMemberRefConstraints(swift::Expr*, swift::Expr*, swift::DeclName, swift::FunctionRefKind) + 237
13 swift                    0x0000000107ac6610 swift::ASTVisitor<(anonymous namespace)::ConstraintGenerator, swift::Type, void, void, void, void, void>::visit(swift::Expr*) + 11584
14 swift                    0x0000000107acbbfa (anonymous namespace)::ConstraintWalker::walkToExprPost(swift::Expr*) + 58
15 swift                    0x0000000107c9ace6 swift::Expr::walk(swift::ASTWalker&) + 118
16 swift                    0x0000000107ac28c8 swift::constraints::ConstraintSystem::generateConstraints(swift::Expr*) + 264
17 swift                    0x0000000107af1a1f swift::constraints::ConstraintSystem::solve(swift::Expr*&, swift::Type, swift::ExprTypeCheckListener*, llvm::SmallVectorImpl<swift::constraints::Solution>&, swift::FreeTypeVariableBinding) + 415
18 swift                    0x0000000107b706e4 swift::TypeChecker::solveForExpression(swift::Expr*&, swift::DeclContext*, swift::Type, swift::FreeTypeVariableBinding, swift::ExprTypeCheckListener*, swift::constraints::ConstraintSystem&, llvm::SmallVectorImpl<swift::constraints::Solution>&, swift::OptionSet<swift::TypeCheckExprFlags, unsigned int>) + 340
19 swift                    0x0000000107b7375f swift::TypeChecker::typeCheckExpression(swift::Expr*&, swift::DeclContext*, swift::TypeLoc, swift::ContextualTypePurpose, swift::OptionSet<swift::TypeCheckExprFlags, unsigned int>, swift::ExprTypeCheckListener*, swift::constraints::ConstraintSystem*) + 655
20 swift                    0x0000000107bf1098 swift::ASTVisitor<(anonymous namespace)::StmtChecker, void, swift::Stmt*, void, void, void, void>::visit(swift::Stmt*) + 520
21 swift                    0x0000000107bf0389 (anonymous namespace)::StmtChecker::typeCheckBody(swift::BraceStmt*&) + 25
22 swift                    0x0000000107bef709 swift::TypeChecker::typeCheckFunctionBodyUntil(swift::FuncDecl*, swift::SourceLoc) + 345
23 swift                    0x0000000107bef54f swift::TypeChecker::typeCheckAbstractFunctionBodyUntil(swift::AbstractFunctionDecl*, swift::SourceLoc) + 111
24 swift                    0x0000000107bf00db swift::TypeChecker::typeCheckAbstractFunctionBody(swift::AbstractFunctionDecl*) + 251
25 swift                    0x0000000107c0c87a typeCheckFunctionsAndExternalDecls(swift::TypeChecker&) + 202
26 swift                    0x0000000107c0d7ee swift::performTypeChecking(swift::SourceFile&, swift::TopLevelContext&, swift::OptionSet<swift::TypeCheckingFlags, unsigned int>, unsigned int, unsigned int) + 1806
27 swift                    0x000000010775eaf9 swift::CompilerInstance::performSema() + 3881
28 swift                    0x0000000106d06c5b performCompile(swift::CompilerInstance&, swift::CompilerInvocation&, llvm::ArrayRef<char const*>, int&, swift::FrontendObserver*, swift::UnifiedStatsReporter*) + 2427
29 swift                    0x0000000106d0520a swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 2650
30 swift                    0x0000000106cc1860 main + 3312
31 libdyld.dylib            0x00007fffdf142235 start + 1
32 libdyld.dylib            0x000000000000003e start + 552328714
Stack dump:
0.  Program arguments: /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2017-05-21-a.xctoolchain/usr/bin/swift -frontend -c /Users/david/Desktop/Crasher/Crasher/ViewController.swift /Users/david/Desktop/Crasher/Crasher/AppDelegate.swift -primary-file /Users/david/Desktop/Crasher/Crasher/Crasher.swift -target x86_64-apple-ios10.3 -enable-objc-interop -sdk /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator10.3.sdk -I /Users/david/Library/Developer/Xcode/DerivedData/Crasher-dwlabxbfwpmpbqgzvhgmayanfazd/Build/Products/Debug-iphonesimulator -F /Users/david/Library/Developer/Xcode/DerivedData/Crasher-dwlabxbfwpmpbqgzvhgmayanfazd/Build/Products/Debug-iphonesimulator -enable-testing -g -module-cache-path /Users/david/Library/Developer/Xcode/DerivedData/ModuleCache -D DEBUG -serialize-debugging-options -Xcc -I/Users/david/Library/Developer/Xcode/DerivedData/Crasher-dwlabxbfwpmpbqgzvhgmayanfazd/Build/Intermediates/Crasher.build/Debug-iphonesimulator/Crasher.build/swift-overrides.hmap -Xcc -iquote -Xcc /Users/david/Library/Developer/Xcode/DerivedData/Crasher-dwlabxbfwpmpbqgzvhgmayanfazd/Build/Intermediates/Crasher.build/Debug-iphonesimulator/Crasher.build/Crasher-generated-files.hmap -Xcc -I/Users/david/Library/Developer/Xcode/DerivedData/Crasher-dwlabxbfwpmpbqgzvhgmayanfazd/Build/Intermediates/Crasher.build/Debug-iphonesimulator/Crasher.build/Crasher-own-target-headers.hmap -Xcc -I/Users/david/Library/Developer/Xcode/DerivedData/Crasher-dwlabxbfwpmpbqgzvhgmayanfazd/Build/Intermediates/Crasher.build/Debug-iphonesimulator/Crasher.build/Crasher-all-target-headers.hmap -Xcc -iquote -Xcc /Users/david/Library/Developer/Xcode/DerivedData/Crasher-dwlabxbfwpmpbqgzvhgmayanfazd/Build/Intermediates/Crasher.build/Debug-iphonesimulator/Crasher.build/Crasher-project-headers.hmap -Xcc -I/Users/david/Library/Developer/Xcode/DerivedData/Crasher-dwlabxbfwpmpbqgzvhgmayanfazd/Build/Products/Debug-iphonesimulator/include -Xcc -I/Users/david/Library/Developer/Xcode/DerivedData/Crasher-dwlabxbfwpmpbqgzvhgmayanfazd/Build/Intermediates/Crasher.build/Debug-iphonesimulator/Crasher.build/DerivedSources/x86_64 -Xcc -I/Users/david/Library/Developer/Xcode/DerivedData/Crasher-dwlabxbfwpmpbqgzvhgmayanfazd/Build/Intermediates/Crasher.build/Debug-iphonesimulator/Crasher.build/DerivedSources -Xcc -DDEBUG=1 -Xcc -working-directory/Users/david/Desktop/Crasher -emit-module-doc-path /Users/david/Library/Developer/Xcode/DerivedData/Crasher-dwlabxbfwpmpbqgzvhgmayanfazd/Build/Intermediates/Crasher.build/Debug-iphonesimulator/Crasher.build/Objects-normal/x86_64/Crasher~partial.swiftdoc -serialize-diagnostics-path /Users/david/Library/Developer/Xcode/DerivedData/Crasher-dwlabxbfwpmpbqgzvhgmayanfazd/Build/Intermediates/Crasher.build/Debug-iphonesimulator/Crasher.build/Objects-normal/x86_64/Crasher.dia -Onone -module-name Crasher -emit-module-path /Users/david/Library/Developer/Xcode/DerivedData/Crasher-dwlabxbfwpmpbqgzvhgmayanfazd/Build/Intermediates/Crasher.build/Debug-iphonesimulator/Crasher.build/Objects-normal/x86_64/Crasher~partial.swiftmodule -emit-dependencies-path /Users/david/Library/Developer/Xcode/DerivedData/Crasher-dwlabxbfwpmpbqgzvhgmayanfazd/Build/Intermediates/Crasher.build/Debug-iphonesimulator/Crasher.build/Objects-normal/x86_64/Crasher.d -emit-reference-dependencies-path /Users/david/Library/Developer/Xcode/DerivedData/Crasher-dwlabxbfwpmpbqgzvhgmayanfazd/Build/Intermediates/Crasher.build/Debug-iphonesimulator/Crasher.build/Objects-normal/x86_64/Crasher.swiftdeps -o /Users/david/Library/Developer/Xcode/DerivedData/Crasher-dwlabxbfwpmpbqgzvhgmayanfazd/Build/Intermediates/Crasher.build/Debug-iphonesimulator/Crasher.build/Objects-normal/x86_64/Crasher.o 
1.  While type-checking 'foo' at /Users/david/Desktop/Crasher/Crasher/Crasher.swift:16:5
2.  While type-checking expression at [/Users/david/Desktop/Crasher/Crasher/Crasher.swift:17:9 - line:17:36] RangeText="(B.self as! Sequence.Type).E"

[belkadan]

I'm not sure we support this kind of dynamic lookup at the moment. What type would the resulting value have?

[belkadan]

(It shouldn't crash, of course.)

[hartbit]

I'm doing something like this only because I'm hacking my way around a missing generics feature in the first place. But I'm expecting to get the Element type of the Sequence (when the associated type is a Sequence type).

[belkadan]

No, what's the static type?

(In this simplified example, the right way to do this is extension A where B: Sequence, but I suspect that doesn't work in your full case.)

[hartbit]

> No, what's the static type?

I'm sorry, I don't understand the question. Can you describe what you mean by static type? I'm sorry, I get confused easily when talking around static/dynamic in terms of types or when dealing with meta-types.

PS: If you know of an article that explains those details, I'd love a link.

[belkadan]

No worries Sequence).Element}}, what does the compiler think the type of t is? If I say let x: Int = t, what does the error message say?

(This is a trick question; the language doesn't currently have an answer.)

For remembering how metatypes work, I recommend Greg's old writeup about Objective-C, http://www.sealiesoftware.com/blog/archive/2009/04/14/objc_explain_Classes_and_metaclasses.html

[hartbit]

Oh yeah, I get why the question is tricky! Would Any.Type be valid? I don't know how the compiler can be any more specific at compile time?

Thanks for the link!

[belkadan]

Any.Type would be valid, but then you couldn't do anything with it. :-) For Element that might be okay, but usually you'd want to actually invoke something on the associated type.

[hartbit]

Couldn't any dynamic dispatch happen on the dynamic type?

[belkadan]

I don't understand what you mean. What dynamic dispatch?

[hartbit]

Sorry, wasn't making any sense. Was thinking in the context of my code which generated the crash. But yeah, `Any.Type` wouldn't be useful :-/

In my code, I cast the result: `(B.self as.Element as) MyType.Type`

[slavapestov]

The code is invalid, but we shouldn't crash.