swift234

[swiftc] Add test case for crash triggered in swift::NameAliasType::getSinglyDesugaredType()

Stack trace:

```
swift: /path/to/swift/include/swift/AST/Decl.h:2463: swift::Type swift::TypeAliasDecl::getUnderlyingType() const: Assertion `!UnderlyingTy.getType().isNull() && "getting invalid underlying type"' failed.
8  swift           0x0000000001106262 swift::NameAliasType::getSinglyDesugaredType() + 146
9  swift           0x00000000011022e6 swift::TypeBase::getCanonicalType() + 486
10 swift           0x00000000011023fe swift::TypeBase::getCanonicalType() + 766
11 swift           0x00000000010eeb47 swift::removeShadowedDecls(llvm::SmallVectorImpl<swift::ValueDecl*>&, swift::ModuleDecl const*, swift::LazyResolver*) + 311
16 swift           0x00000000010d0c86 swift::lookupVisibleDecls(swift::VisibleDeclConsumer&, swift::DeclContext const*, swift::LazyResolver*, bool, swift::SourceLoc) + 1174
17 swift           0x0000000000edc344 swift::TypeChecker::performTypoCorrection(swift::DeclContext*, swift::DeclRefKind, swift::DeclName, swift::SourceLoc, swift::OptionSet<swift::NameLookupFlags, unsigned int>, swift::LookupResult&, unsigned int) + 260
18 swift           0x0000000000e86f78 swift::TypeChecker::resolveDeclRefExpr(swift::UnresolvedDeclRefExpr*, swift::DeclContext*) + 3864
20 swift           0x000000000104e623 swift::Expr::walk(swift::ASTWalker&) + 19
21 swift           0x0000000000e87797 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>) + 119
22 swift           0x0000000000e8e152 swift::TypeChecker::typeCheckExpression(swift::Expr*&, swift::DeclContext*, swift::TypeLoc, swift::ContextualTypePurpose, swift::OptionSet<swift::TypeCheckExprFlags, unsigned int>, swift::ExprTypeCheckListener*) + 610
23 swift           0x0000000000e8f2a7 swift::TypeChecker::typeCheckBinding(swift::Pattern*&, swift::Expr*&, swift::DeclContext*) + 343
24 swift           0x0000000000e8f4bb swift::TypeChecker::typeCheckPatternBinding(swift::PatternBindingDecl*, unsigned int) + 267
26 swift           0x0000000000e9bbf9 swift::TypeChecker::validateDecl(swift::ValueDecl*, bool) + 4153
27 swift           0x00000000010f220c swift::DeclContext::lookupQualified(swift::Type, swift::DeclName, swift::NLOptions, swift::LazyResolver*, llvm::SmallVectorImpl<swift::ValueDecl*>&) const + 2652
28 swift           0x00000000010f0aa5 swift::UnqualifiedLookup::UnqualifiedLookup(swift::DeclName, swift::DeclContext*, swift::LazyResolver*, bool, swift::SourceLoc, bool, bool) + 2469
29 swift           0x0000000000edaf3b swift::TypeChecker::lookupUnqualified(swift::DeclContext*, swift::DeclName, swift::SourceLoc, swift::OptionSet<swift::NameLookupFlags, unsigned int>) + 187
32 swift           0x0000000000f0b97e swift::TypeChecker::resolveIdentifierType(swift::DeclContext*, swift::IdentTypeRepr*, swift::OptionSet<swift::TypeResolutionFlags, unsigned int>, bool, swift::GenericTypeResolver*, llvm::function_ref<bool (swift::TypeCheckRequest)>*) + 158
34 swift           0x0000000000f0c984 swift::TypeChecker::resolveType(swift::TypeRepr*, swift::DeclContext*, swift::OptionSet<swift::TypeResolutionFlags, unsigned int>, swift::GenericTypeResolver*, llvm::function_ref<bool (swift::TypeCheckRequest)>*) + 164
35 swift           0x0000000000f0b870 swift::TypeChecker::validateType(swift::TypeLoc&, swift::DeclContext*, swift::OptionSet<swift::TypeResolutionFlags, unsigned int>, swift::GenericTypeResolver*, llvm::function_ref<bool (swift::TypeCheckRequest)>*) + 192
38 swift           0x0000000000e9b001 swift::TypeChecker::validateDecl(swift::ValueDecl*, bool) + 1089
43 swift           0x0000000000ea0546 swift::TypeChecker::typeCheckDecl(swift::Decl*, bool) + 150
44 swift           0x0000000000ec37f2 swift::performTypeChecking(swift::SourceFile&, swift::TopLevelContext&, swift::OptionSet<swift::TypeCheckingFlags, unsigned int>, unsigned int, unsigned int) + 994
45 swift           0x0000000000c58c79 swift::CompilerInstance::performSema() + 3289
47 swift           0x00000000007d6eef swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 2863
48 swift           0x00000000007a2ef8 main + 2872
Stack dump:
0.	Program arguments: /path/to/swift/bin/swift -frontend -c -primary-file validation-test/compiler_crashers/28298-swift-namealiastype-getsinglydesugaredtype.swift -target x86_64-unknown-linux-gnu -disable-objc-interop -module-name main -o /tmp/28298-swift-namealiastype-getsinglydesugaredtype-defc2e.o
1.	While type-checking 'A' at validation-test/compiler_crashers/28298-swift-namealiastype-getsinglydesugaredtype.swift:10:1
2.	While type-checking 'e' at validation-test/compiler_crashers/28298-swift-namealiastype-getsinglydesugaredtype.swift:10:9
3.	While resolving type a at [validation-test/compiler_crashers/28298-swift-namealiastype-getsinglydesugaredtype.swift:10:21 - line:10:21] RangeText="a"
4.	While type-checking expression at [validation-test/compiler_crashers/28298-swift-namealiastype-getsinglydesugaredtype.swift:11:7 - line:11:7] RangeText="c"
<unknown>:0: error: unable to execute command: Aborted
<unknown>:0: error: compile command failed due to signal (use -v to see invocation)
```