swift234

Add 💥 (😢 → 58, 😀 → 5107) in swift::GenericSignature::getSubstitutionMap(…)

Add test case for crash triggered in `swift::GenericSignature::getSubstitutionMap(…)`.

Assertion failure in [`lib/AST/GenericSignature.cpp (line 413)`](https://github.com/apple/swift/blob/master/lib/AST/GenericSignature.cpp#L413):

```
Assertion `args.empty() && "did not use all substitutions?!"' failed.

When executing: TypeSubstitutionMap swift::GenericSignature::getSubstitutionMap(ArrayRef<swift::Substitution>) const
```

<details>
<summary>Assertion context:</summary>
```
  // An empty parameter list gives an empty map.
  if (getGenericParams().empty()) {
    assert(args.empty() && "substitutions but no generic params?!");
    return subs;
  }

  // Seed the type map with pre-existing substitutions.
  for (auto depTy : getAllDependentTypes()) {
    auto replacement = args.front().getReplacement();
    args = args.slice(1);

    if (auto subTy = depTy->getAs<SubstitutableType>()) {
      subs[subTy->getCanonicalType().getPointer()] = replacement;
    }
    else if (auto dTy = depTy->getAs<DependentMemberType>()) {
      subs[dTy->getCanonicalType().getPointer()] = replacement;
    }
  }

  assert(args.empty() && "did not use all substitutions?!");
```
</details>
<details>
<summary>Stack trace:</summary>
```
swift: /path/to/swift/lib/AST/GenericSignature.cpp:413: TypeSubstitutionMap swift::GenericSignature::getSubstitutionMap(ArrayRef<swift::Substitution>) const: Assertion `args.empty() && "did not use all substitutions?!"' failed.
8  swift           0x00000000010e5a13 swift::GenericSignature::getSubstitutionMap(llvm::ArrayRef<swift::Substitution>) const + 659
9  swift           0x000000000111fe47 swift::TypeBase::getSuperclass(swift::LazyResolver*) + 215
10 swift           0x00000000011337d2 swift::ConformanceLookupTable::getConformance(swift::NominalTypeDecl*, swift::LazyResolver*, swift::ConformanceLookupTable::ConformanceEntry*) + 290
12 swift           0x0000000001133ef4 swift::ConformanceLookupTable::lookupConformances(swift::NominalTypeDecl*, swift::DeclContext*, swift::LazyResolver*, swift::ConformanceLookupKind, llvm::SmallVectorImpl<swift::ProtocolDecl*>*, llvm::SmallVectorImpl<swift::ProtocolConformance*>*, llvm::SmallVectorImpl<swift::ConformanceDiagnostic>*) + 692
13 swift           0x0000000001116274 swift::DeclContext::getLocalConformances(swift::ConformanceLookupKind, llvm::SmallVectorImpl<swift::ConformanceDiagnostic>*, bool) const + 212
14 swift           0x0000000000efa8fa swift::TypeChecker::findWitnessedObjCRequirements(swift::ValueDecl const*, bool) + 122
26 swift           0x0000000000eb1686 swift::TypeChecker::typeCheckDecl(swift::Decl*, bool) + 150
29 swift           0x0000000000f17bca swift::TypeChecker::typeCheckFunctionBodyUntil(swift::FuncDecl*, swift::SourceLoc) + 346
30 swift           0x0000000000f17a2e swift::TypeChecker::typeCheckAbstractFunctionBodyUntil(swift::AbstractFunctionDecl*, swift::SourceLoc) + 46
31 swift           0x0000000000f185f3 swift::TypeChecker::typeCheckAbstractFunctionBody(swift::AbstractFunctionDecl*) + 179
33 swift           0x0000000000ed38e1 swift::performTypeChecking(swift::SourceFile&, swift::TopLevelContext&, swift::OptionSet<swift::TypeCheckingFlags, unsigned int>, unsigned int, unsigned int) + 1281
34 swift           0x0000000000c60b89 swift::CompilerInstance::performSema() + 3289
36 swift           0x00000000007d8429 swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 2857
37 swift           0x00000000007a4458 main + 2872
Stack dump:
0.	Program arguments: /path/to/swift/bin/swift -frontend -c -primary-file validation-test/compiler_crashers/28355-swift-genericsignature-getsubstitutionmap.swift -target x86_64-unknown-linux-gnu -disable-objc-interop -module-name main -o /tmp/28355-swift-genericsignature-getsubstitutionmap-792793.o
1.	While type-checking 'a' at validation-test/compiler_crashers/28355-swift-genericsignature-getsubstitutionmap.swift:10:1
2.	While type-checking 'A' at validation-test/compiler_crashers/28355-swift-genericsignature-getsubstitutionmap.swift:10:8
<unknown>:0: error: unable to execute command: Aborted
<unknown>:0: error: compile command failed due to signal (use -v to see invocation)
```
</details>