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
* Make ExportedSourceFile hold any Syntax as the root node
* Move `ExportedSourceFileRequest::evaluate()` to `ParseRequests.cpp`
* Pass the decl context and `GeneatedSourceFileInfo::Kind` to
`swift_ASTGen_parseSourceFile()` to customize the parsing
* Make `ExportedSourceFile` to hold an arbitrary Syntax node
* Move round-trip checking into `ExportedSourceFileRequest::evaluate()`
* Split `parseSourceFileViaASTGen` completely from C++ parsing logic
(in `ParseSourceFileRequest::evaluate()`)
* Remove 'ParserDiagnostics' experimental feature: Now that we have
ParserASTGen mode which includes the swift-syntax parser diagnostics.
