[ASTMangler] Add support for mangling generic typealiases.

[dcci]

rdar://problem/39915946

Replace this paragraph with a description of your changes and rationale. Provide links to external references/discussions if appropriate.

Resolves SR-NNNN.

[dcci]

@swift-ci please test

[dcci]

Type reconstruction will come next, but, even with this patch alone, at least we don't crash when trying to print generic type aliases in lldb anymore :)

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 29fbf7b8cf4d7392f0a9b67dc9b0f28e9a1f43f6

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - 29fbf7b8cf4d7392f0a9b67dc9b0f28e9a1f43f6

[dcci]

@swift-ci please test

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 29fbf7b8cf4d7392f0a9b67dc9b0f28e9a1f43f6

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - 29fbf7b8cf4d7392f0a9b67dc9b0f28e9a1f43f6

[DougGregor]

It's a remangler failure:

/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk -swift-version 4
21:30:35 Remangling failed:
21:30:35 original     = $Ss10DictionaryVy12PackageGraph0B22ContainerConstraintSetV10IdentifieraAE11RequirementayAEQq_AFQa_GGD
21:30:35 remangled    = $Ss10DictionaryVy12PackageGraph0B22ContainerConstraintSetV10IdentifieraAEyAEQq_AFQaG11RequirementaGD

otherwise, the changes generally look correct to be. @eeckstein is more the expert here.

[eeckstein]

lgtm!

[dcci]

This fails on ToT

dtdebugger2:bin davide$ ./swift-demangle '$Ss10DictionaryVy12PackageGraph0B22ContainerConstraintSetV10IdentifieraAE11RequirementayAEQq_AFQa_GGD' -expand -remangle-new
Demangling for $Ss10DictionaryVy12PackageGraph0B22ContainerConstraintSetV10IdentifieraAE11RequirementayAEQq_AFQa_GGD
kind=Global
  kind=TypeMangling
    kind=Type
      kind=BoundGenericStructure
        kind=Type
          kind=Structure
            kind=Module, text="Swift"
            kind=Identifier, text="Dictionary"
        kind=TypeList
          kind=Type
            kind=TypeAlias
              kind=Structure
                kind=Module, text="PackageGraph"
                kind=Identifier, text="PackageContainerConstraintSet"
              kind=Identifier, text="Identifier"
          kind=Type
            kind=TypeAlias
              kind=BoundGenericStructure
                kind=Type
                  kind=Structure
                    kind=Module, text="PackageGraph"
                    kind=Identifier, text="PackageContainerConstraintSet"
                kind=TypeList
                  kind=Type
                    kind=AssociatedTypeRef
                      kind=QualifiedArchetype
                        kind=Number, index=0
                        kind=DeclContext
                          kind=Structure
                            kind=Module, text="PackageGraph"
                            kind=Identifier, text="PackageContainerConstraintSet"
                      kind=Identifier, text="Identifier"
              kind=Identifier, text="Requirement"
$Ss10DictionaryVy12PackageGraph0B22ContainerConstraintSetV10IdentifieraAEyAEQq_AFQaG11RequirementaGD

I guess we weren't producing that name before. I'll take a look at this.

[dcci]

Reduces to just:

extension DictionaryIndex {}

internal enum _VariantDictionaryBuffer<Key: Hashable, Value> {
  internal typealias Index = DictionaryIndex<Key, Value>
}

public struct Dictionary<Key: Hashable, Value> {
  internal typealias _VariantBuffer = _VariantDictionaryBuffer<Key, Value>
}

var Patatino : Dictionary<Int, Int>._VariantBuffer.Index

Looks like we need a special treatment for mangling extensions here?

[dcci]

@swift-ci please test

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - 37a424c8a071b9cd135076a8a59f0aa1395e2f17

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 37a424c8a071b9cd135076a8a59f0aa1395e2f17