Rework TypeAttribute bridging facilities.
Eliminate the _fake_ `swift::TypeAttributes`, but just use the normal
`BridgedArrayRef` for briding the attribute list. Introduce
`BridgedTypeOrCustomAttr` tagged pointer which resembles
`swift::TypeOrCustomAttr`.
* Move `AvailabilitySpec` handling logic to AST, so they can be shared
between libParse and ASTGen
* Requestify '-define-availability' arguments parsing and parse them
with 'SwiftParser' according to the 'ParserASTGen' feature flag
* Implement 'AvailableAttr' generation in ASTGen
Since the introduction of custom attributes (as part of property
wrappers), we've modeled the context of expressions within these
attributes as PatternBindingInitializers. These
PatternBindingInitializers would get wired in to the variable
declarations they apply to, establishing the appropriate declaration
context hierarchy. This worked because property wrappers only every
applied to---you guessed it!---properties, so the
PatternBindingInitializer would always get filled in.
When custom attributes were extended to apply to anything for the
purposes of macros, the use of PatternBindingInitializer became less
appropriate. Specifically, the binding declaration would never get
filled in (it's always NULL), so any place in the compiler that
accesses the binding might have to deal with it being NULL, which is a
new requirement. Few did, crashes ensued.
Rather than continue to play whack-a-mole with the abused
PatternBindingInitializer, introduce a new CustomAttributeInitializer
to model the context of custom attribute arguments. When the
attributes are assigned to a declaration that has a
PatternBindingInitializer, we reparent this new initializer to the
PatternBindingInitializer. This helps separate out the logic for
custom attributes vs. actual initializers.
Fixes https://github.com/swiftlang/swift/issues/76409 / rdar://136997841
Use similar scheme as DeclAttribute.
* Create `BridgedTypeAttribute.createSimple()` and
`BridgedTypeAttributes.add()`, instead of
`BridgedTypeAttributes.addSimple()`
* Create `DeclAttributes::createSimple()` to align with `TypeAttribute`
Generate all entries, and ensure we introduce a
PatternBindingInitializer context for non-local
cases. Also use this opportunity to cleanup
`PatternBindingDecl::create`.
* 'ASTGenVisitor' has a reference to a legacy C++ Parser configured for
ASTGen.
* If 'ASTGenVisitor' encounters a AST node that hasn't been migrated,
call parse(Decl|Stmt|Expr|Type) to parse the position using the legacy
parser.
* The legacy parser calls ASTGen's
'swift_ASTGen_build(Decl|Stmt|Expr|Type)' for each ASTNode "parsing"
(unless the call is not directly from the ASTGen.)
rdar://117151886
For nullable nodes, introduce both a non-null and
nullable variant of the bridging wrapper. This
allows us to annotate the necessary parameters
as nullable, but keep the returns of the bridged
`createParsed` methods non-null.
