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[SR-12369] Invalid conversions allowed when using ?? #54803

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hamishknight opened this issue Mar 14, 2020 · 3 comments
Closed

[SR-12369] Invalid conversions allowed when using ?? #54803

hamishknight opened this issue Mar 14, 2020 · 3 comments
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@hamishknight
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accepts invalid Bug: Accepts invalid bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself type checker Area → compiler: Semantic analysis

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@hamishknight
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Previous ID SR-12369
Radar None
Original Reporter @hamishknight
Type Bug
Status Closed
Resolution Done
Environment

Swift version 5.2-dev (LLVM a8c5c17, Swift 3a1ce04d31)
Target: x86_64-apple-darwin18.5.0

Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, AcceptsInvalid, TypeChecker
Assignee @hamishknight
Priority Medium

md5: d29192a365bb056a838214da0da4a972

Issue Description:

We correctly prevent the following bridging conversions:

import Foundation

let x = 0 as NSString // error: Cannot convert value of type 'Int' to type 'NSString' in coercion
let y = "" as NSNumber // Cannot convert value of type 'String' to type 'NSNumber' in coercion

But we appear to allow them if the ?? operator is used:

let x = (0 ?? 0) as NSString // Compiles
let y = ("" ?? "") as NSNumber // Also compiles

In an asserts build these hit an assertion in SILGen:

Assertion failed: (inputSubstType->isExactSuperclassOf(outputSubstType) && "should be inheritance relationship between input and output"), function transform, file /Users/hamishknight/Desktop/swift-dev/swift/lib/SILGen/SILGenPoly.cpp, line 498.
Stack dump:
0.  Program arguments: ./swift -frontend -emit-sil /Users/hamishknight/Desktop/Stochastic Projects/newnew/newnew/main.swift -sdk /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk -debug-diagnostic-names -disable-objc-attr-requires-foundation-module
1.  Swift version 5.2-dev (LLVM a8c5c172cc, Swift 3a1ce04d31)
2.  While evaluating request SILGenWholeModuleRequest(SIL Generation for module main)
0  swift                    0x000000010c383405 llvm::sys::PrintStackTrace(llvm::raw_ostream&) + 37
1  swift                    0x000000010c3823b8 llvm::sys::RunSignalHandlers() + 248
2  swift                    0x000000010c3839fc SignalHandler(int) + 268
3  libsystem_platform.dylib 0x00007fff79171b5d _sigtramp + 29
4  swift                    0x000000010eca2ba8 cmark_strbuf__initbuf + 180875
5  libsystem_c.dylib        0x00007fff790316a6 abort + 127
6  libsystem_c.dylib        0x00007fff78ffa20d basename_r + 0
7  swift                    0x000000010c525693 (anonymous namespace)::Transform::transform(swift::Lowering::ManagedValue, swift::Lowering::AbstractionPattern, swift::CanType, swift::Lowering::AbstractionPattern, swift::CanType, swift::SILType, swift::Lowering::SGFContext) (.cold.93) + 35
8  swift                    0x0000000108347743 (anonymous namespace)::Transform::transform(swift::Lowering::ManagedValue, swift::Lowering::AbstractionPattern, swift::CanType, swift::Lowering::AbstractionPattern, swift::CanType, swift::SILType, swift::Lowering::SGFContext) + 12883
9  swift                    0x0000000108343a86 swift::Lowering::SILGenFunction::emitTransformedValue(swift::SILLocation, swift::Lowering::ManagedValue, swift::Lowering::AbstractionPattern, swift::CanType, swift::Lowering::AbstractionPattern, swift::CanType, swift::SILType, swift::Lowering::SGFContext) + 118
10 swift                    0x00000001082b6fd4 emitUnabstractedCast(swift::Lowering::SILGenFunction&, swift::SILLocation, swift::Lowering::ManagedValue, swift::CanType, swift::CanType) + 372
11 swift                    0x00000001082b4267 emitNativeToCBridgedValue(swift::Lowering::SILGenFunction&, swift::SILLocation, swift::Lowering::ManagedValue, swift::CanType, swift::CanType, swift::SILType, swift::Lowering::SGFContext) + 5815
12 swift                    0x00000001082d41f1 swift::Lowering::Conversion::emit(swift::Lowering::SILGenFunction&, swift::SILLocation, swift::Lowering::ManagedValue, swift::Lowering::SGFContext) const + 545
13 swift                    0x00000001082d3f1e swift::Lowering::ConvertingInitialization::finishEmission(swift::Lowering::SILGenFunction&, swift::SILLocation, swift::Lowering::ManagedValue) + 94
14 swift                    0x00000001082d3d85 swift::Lowering::SILGenFunction::emitConvertedRValue(swift::SILLocation, swift::Lowering::Conversion const&, swift::Lowering::SGFContext, llvm::function_ref<swift::Lowering::ManagedValue (swift::Lowering::SILGenFunction&, swift::SILLocation, swift::Lowering::SGFContext)>) + 405
15 swift                    0x00000001082d3bd8 swift::Lowering::SILGenFunction::emitConvertedRValue(swift::Expr*, swift::Lowering::Conversion const&, swift::Lowering::SGFContext) + 104
16 swift                    0x00000001083032d8 tryEmitAsBridgingConversion(swift::Lowering::SILGenFunction&, swift::Expr*, bool, swift::Lowering::SGFContext) + 440
17 swift                    0x00000001082f7025 swift::ASTVisitor<(anonymous namespace)::RValueEmitter, swift::Lowering::RValue, void, void, void, void, void, swift::Lowering::SGFContext>::visit(swift::Expr*, swift::Lowering::SGFContext) + 9685
18 swift                    0x00000001082e78ef swift::Lowering::SILGenFunction::emitExprInto(swift::Expr*, swift::Lowering::Initialization*, llvm::Optional<swift::SILLocation>) + 303
19 swift                    0x00000001082d8a5f swift::Lowering::SILGenFunction::emitPatternBinding(swift::PatternBindingDecl*, unsigned int) + 335
20 swift                    0x00000001082d8b3d swift::Lowering::SILGenFunction::visitPatternBindingDecl(swift::PatternBindingDecl*) + 45
21 swift                    0x0000000108287c12 swift::Lowering::SILGenModule::visitTopLevelCodeDecl(swift::TopLevelCodeDecl*) + 498
22 swift                    0x000000010828827a (anonymous namespace)::SILGenModuleRAII::emitSourceFile(swift::SourceFile*) + 874
23 swift                    0x0000000108289244 swift::SILGenWholeModuleRequest::evaluate(swift::Evaluator&, swift::SILGenDescriptor) const + 180
24 swift                    0x0000000108358ec1 swift::SimpleRequest<swift::SILGenWholeModuleRequest, std::__1::unique_ptr<swift::SILModule, std::__1::default_delete<swift::SILModule> > (swift::SILGenDescriptor), (swift::CacheKind)0>::evaluateRequest(swift::SILGenWholeModuleRequest const&, swift::Evaluator&) + 33
25 swift                    0x000000010828c667 llvm::Expected<swift::SILGenWholeModuleRequest::OutputType> swift::Evaluator::getResultUncached<swift::SILGenWholeModuleRequest>(swift::SILGenWholeModuleRequest const&) + 343
26 swift                    0x00000001082893c4 swift::performSILGeneration(swift::ModuleDecl*, swift::Lowering::TypeConverter&, swift::SILOptions const&) + 116
27 swift                    0x0000000107f16d2d performCompile(swift::CompilerInstance&, swift::CompilerInvocation const&, llvm::ArrayRef<char const*>, int&, swift::FrontendObserver*) + 8717
28 swift                    0x0000000107f13b41 swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 3553
29 swift                    0x0000000107ea6b8d main + 861
30 libdyld.dylib            0x00007fff78f8c3d5 start + 1
31 libdyld.dylib            0x0000000000000008 start + 18446603338486594612
fish: './swift -frontend -emit-sil /Us…' terminated by signal SIGABRT (Abort)

And in a non-asserts build we miscompile.

This also extends to other conversions, such as:

func foo(_ x: String) -> Int {
  return (x ?? "") as Int
}

which also miscompiles in a no-asserts build.

It looks like we're not correctly exploring a type variable's fixed bindings in ConstraintGraph::gatherConstraints.

Unfortunately my attempt to fix this caused the test case for rdar://problem/54274245 to no longer compile:

func rdar54274245(_ arr: [Any]?) {
  _ = (arr ?? []) as [NSObject]
}

But this is because we now correctly re-activate the bridging constraint, which then fails.

The equivalent conversion without ?? already doesn't compile today:

func foo(_ arr: [Any]) {
  _ = arr as [NSObject] // error: cannot convert value of type '[Any]' to type '[NSObject]' in coercion
}
@LucianoPAlmeida
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@hamishknight Are you working on this? If not I can take a look 🙂

@hamishknight
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@LucianoPAlmeida I came up with a fix (which is to always make sure we visit the type variable's fixed bindings in gatherConstraints – currently we can incorrectly bail if we already visited the type variable as an adjacency), but unfortunately that causes a source compatibility regression for the (arr ?? []) as [NSObject] example. I'm planning on asking what we can do about this on Monday, but in the mean time you're more than welcome to take a look if you want 🙂

@hamishknight
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Fixed by #30886

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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accepts invalid Bug: Accepts invalid bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself type checker Area → compiler: Semantic analysis
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@LucianoPAlmeida @hamishknight