[SwiftLexicalLookup] Composite names

[MAJKFL]

This PR introduces notion of composite names to SwiftLexicalLookup. In Swift, it’s possible to have a switch case introducing one name for several enum cases:

switch X {
case .x(let a), .y(let a):
  print(a) // Refers to both introduced names above
}

ASTScope currently deals with this special case by just introducing the first name from the list. Composite names are supposed to instead merge all names with the same semantic meaning into one, unified name representation. It stores an array of related names and, to match the behavior of the compiler, a composite name is represented by the first name.

Combined with some additional minor fixes included in this PR, I was able to finally perform entire Swift compilation with fully enabled validation! There still seem to be some discrepancies when running entire test suite with lit, but I’m happy to see the library finally maturing.

[MAJKFL]

@swift-ci Please test

[ahoppen]

Nice

[ahoppen]

Shouldn’t this be print(a)? x is never defined in this test case.

[MAJKFL]

I purposefully called it x to further indicate that we are not performing name matching in this case. We use useNilAsTheParameter: true for that. This test is supposed to check if we properly partition names equivalent names (like in the first case here).

[ahoppen]

Oh, I missed that and thought that we were looking up x, not that we were collecting all names available at that location. The test makes sense now 😄

[MAJKFL]

@swift-ci Please test

[ahoppen]

Looks good 👍🏽

[ahoppen]

@swift-ci Please test Windows

[DougGregor]

@swift-ci Please test Windows

[MAJKFL]

@swift-ci Please test

[MAJKFL]

@swift-ci Please test Windows

[DougGregor]

@swift-ci Please test Windows

[DougGregor]

@swift-ci Please test Windows

[DougGregor]

@swift-ci please test platform Windows

[DougGregor]

@swift-ci please test platform Windows

[DougGregor]

@swift-ci please test Windows