[SR-13421] Type checker regression and crash in Xcode 12 beta 5

[rastersize]

Previous ID	SR-13421
Radar	rdar://67417121
Original Reporter	@rastersize
Type	Bug

Environment

• Xcode 12 beta 5 (12A8189h)

• Apple Swift version 5.3 (swiftlang-1200.0.28.1 clang-1200.0.30.1) Target: x86_64-apple-darwin19.5.0

• Nimble 8.1.1 and 9.0.0-rc.1

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, 5.3Regression, CompilerCrash, Regression, TypeChecker
Assignee	None
Priority	Medium

md5: 34d150037f0b6c1807d377f1be03a70c

relates to:

• SR-12291 Regression in overload resolution

Issue Description:

The type checker in Swift distributed with Xcode 12 beta 5 fails on existing code (that has worked since at least Xcode 11). For smaller samples the type checker “just” fails with a Ambiguous use of 'expect', however for targets with more cases it causes a crash (see below for a stack trace).

I’ve also filed FB8464226 for this.

What did you do?

I installed Xcode 12 beta 5 and tried to build our existing (test) code:

expect {
    try JSONDecoder().decode(Model.self, from: data)
}.to(throwError())

What did you expect to happen?

I expected the code to compile.

What actually happened instead?

The code failed to compile with a `ambiguous use of 'expect'` error. With these two candidates:

1. Sources/Nimble/DSL.swift#L1-L8

   • public func expect<T>(_ expression: @autoclosure @escaping () throws -> T?, file: FileString = #file, line: UInt = #line) -> Expectation<T>

2. Sources/Nimble/DSL.swift#L10-L17

   • public func expect<T>(_ file: FileString = #file, line: UInt = #line, expression: @escaping () throws -> T?) -> Expectation<T>

Project that demonstrates the issue

https://github.com/rastersize/Xcode12Beta5Nimble

After cloning do the following:

1. Run carthage.sh bootstrap

   • The script works around a Carthage bug with Xcode 12 beta 4+ and universal binaries. As newer versions of Xcode 12 will produce an arm64 slice for both the simulator and device, and a universal binary can’t contain two slices for the same architecture.

2. Open the Xcode project

3. Build for testing

Workaround

Change the call-site of expect to specify using the non-autoclosure function. That is:

expect(expression: {
    try JSONDecoder().decode(SomeModel.self, from: data)
}).to(throwError())

Not as pretty but it works for now.

Stack trace from crash

9.  While type-checking expression at [/Users/<redacted>/DecodableOptionalTests.swift:18:21 - line:18:120] RangeText="expect { try decoder.decode(TestModel.self, from: decodeOptionallyValidData()) }.toNot(throwError()"
0  swift                    0x00000001082a1a85 llvm::sys::PrintStackTrace(llvm::raw_ostream&) + 37
1  swift                    0x00000001082a0a85 llvm::sys::RunSignalHandlers() + 85
2  swift                    0x00000001082a203f SignalHandler(int) + 111
3  libsystem_platform.dylib 0x00007fff712ff5fd _sigtramp + 29
4  libsystem_kernel.dylib   0x00007fff7124b35e __ioctl + 10
5  swift                    0x0000000104aed413 (anonymous namespace)::ExprRewriter::coerceCallArguments(swift::Expr*, swift::AnyFunctionType*, swift::ConcreteDeclRef, swift::ApplyExpr*, llvm::ArrayRef<swift::Identifier>, swift::constraints::ConstraintLocatorBuilder) + 8899
6  swift                    0x0000000104aea352 (anonymous namespace)::ExprRewriter::finishApply(swift::ApplyExpr*, swift::Type, swift::constraints::ConstraintLocatorBuilder, swift::constraints::ConstraintLocatorBuilder) + 11970
7  swift                    0x0000000104af5b5d (anonymous namespace)::ExprRewriter::visitApplyExpr(swift::ApplyExpr*) + 477
8  swift                    0x0000000104accb02 (anonymous namespace)::ExprWalker::walkToExprPost(swift::Expr*) + 18
9  swift                    0x0000000104ac31e3 (anonymous namespace)::ExprWalker::rewriteTarget(swift::constraints::SolutionApplicationTarget) + 371
10 swift                    0x0000000104ac2ed0 swift::constraints::ConstraintSystem::applySolution(swift::constraints::Solution&, swift::constraints::SolutionApplicationTarget) + 6400
11 swift                    0x0000000104cabf1a swift::TypeChecker::typeCheckExpression(swift::constraints::SolutionApplicationTarget&, bool&, swift::OptionSet<swift::TypeCheckExprFlags, unsigned int>) + 1242
12 swift                    0x0000000104cab988 swift::TypeChecker::typeCheckExpression(swift::Expr*&, swift::DeclContext*, swift::TypeLoc, swift::ContextualTypePurpose, swift::OptionSet<swift::TypeCheckExprFlags, unsigned int>) + 360
13 swift                    0x0000000104d90e4b swift::ASTVisitor<(anonymous namespace)::StmtChecker, void, swift::Stmt*, void, void, void, void>::visit(swift::Stmt*) + 9115
14 swift                    0x0000000104d8c69a bool (anonymous namespace)::StmtChecker::typeCheckStmt<swift::BraceStmt>(swift::BraceStmt*&) + 314
15 swift                    0x0000000104d8c373 swift::TypeChecker::typeCheckClosureBody(swift::ClosureExpr*) + 387
16 swift                    0x0000000104ac2f0a swift::constraints::ConstraintSystem::applySolution(swift::constraints::Solution&, swift::constraints::SolutionApplicationTarget) + 6458
17 swift                    0x0000000104cabf1a swift::TypeChecker::typeCheckExpression(swift::constraints::SolutionApplicationTarget&, bool&, swift::OptionSet<swift::TypeCheckExprFlags, unsigned int>) + 1242
18 swift                    0x0000000104cab988 swift::TypeChecker::typeCheckExpression(swift::Expr*&, swift::DeclContext*, swift::TypeLoc, swift::ContextualTypePurpose, swift::OptionSet<swift::TypeCheckExprFlags, unsigned int>) + 360
19 swift                    0x0000000104d90e4b swift::ASTVisitor<(anonymous namespace)::StmtChecker, void, swift::Stmt*, void, void, void, void>::visit(swift::Stmt*) + 9115
20 swift                    0x0000000104d8c69a bool (anonymous namespace)::StmtChecker::typeCheckStmt<swift::BraceStmt>(swift::BraceStmt*&) + 314
21 swift                    0x0000000104d8c373 swift::TypeChecker::typeCheckClosureBody(swift::ClosureExpr*) + 387
22 swift                    0x0000000104ac2f0a swift::constraints::ConstraintSystem::applySolution(swift::constraints::Solution&, swift::constraints::SolutionApplicationTarget) + 6458
23 swift                    0x0000000104cabf1a swift::TypeChecker::typeCheckExpression(swift::constraints::SolutionApplicationTarget&, bool&, swift::OptionSet<swift::TypeCheckExprFlags, unsigned int>) + 1242
24 swift                    0x0000000104cab988 swift::TypeChecker::typeCheckExpression(swift::Expr*&, swift::DeclContext*, swift::TypeLoc, swift::ContextualTypePurpose, swift::OptionSet<swift::TypeCheckExprFlags, unsigned int>) + 360
25 swift                    0x0000000104d90e4b swift::ASTVisitor<(anonymous namespace)::StmtChecker, void, swift::Stmt*, void, void, void, void>::visit(swift::Stmt*) + 9115
26 swift                    0x0000000104d8c69a bool (anonymous namespace)::StmtChecker::typeCheckStmt<swift::BraceStmt>(swift::BraceStmt*&) + 314
27 swift                    0x0000000104d8b0a7 swift::TypeCheckFunctionBodyUntilRequest::evaluate(swift::Evaluator&, swift::AbstractFunctionDecl*, swift::SourceLoc) const + 2231
28 swift                    0x0000000104d93e7d llvm::Expected<swift::TypeCheckFunctionBodyUntilRequest::OutputType> swift::Evaluator::getResultCached<swift::TypeCheckFunctionBodyUntilRequest, (void*)0>(swift::TypeCheckFunctionBodyUntilRequest const&) + 925
29 swift                    0x0000000104d8c148 swift::TypeCheckFunctionBodyUntilRequest::OutputType swift::evaluateOrDefault<swift::TypeCheckFunctionBodyUntilRequest>(swift::Evaluator&, swift::TypeCheckFunctionBodyUntilRequest, swift::TypeCheckFunctionBodyUntilRequest::OutputType) + 440
30 swift                    0x0000000104dc9a84 swift::TypeCheckSourceFileRequest::evaluate(swift::Evaluator&, swift::SourceFile*) const + 1380
31 swift                    0x0000000104dcc699 llvm::Expected<swift::TypeCheckSourceFileRequest::OutputType> swift::Evaluator::getResultUncached<swift::TypeCheckSourceFileRequest>(swift::TypeCheckSourceFileRequest const&) + 953
32 swift                    0x0000000104dc9394 swift::TypeCheckSourceFileRequest::OutputType swift::evaluateOrDefault<swift::TypeCheckSourceFileRequest>(swift::Evaluator&, swift::TypeCheckSourceFileRequest, swift::TypeCheckSourceFileRequest::OutputType) + 164
33 swift                    0x0000000103f44bab swift::CompilerInstance::performSemaUpTo(swift::SourceFile::ASTStage_t) + 6859
34 swift                    0x0000000103e0596d swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 6845
35 swift                    0x0000000103d8a277 main + 1255
36 libdyld.dylib            0x00007fff71106cc9 start + 1
error: Illegal instruction: 4 (in target '<redacted>Tests' from project '<redacted>')

[rastersize]

A colleague of mine noted that this is likely due to the new “forward scan” behavior for trailing closures.

[typesanitizer]

@swift-ci create

[rastersize]

Confirmed still a problem in Xcode 12 beta 6.

[typesanitizer]

cc @xedin