When completing after `names:`, completion should offer the different ways you can specify the names, i.e. `arbitrary`, `named`, etc.
```
@freestanding(declaration, names: #^COMPLETE^#)
```
rdar://108535077
Parse compound and special names in the macro role attributes
(`@freestanding` and `@attached`). This allows both compound names and
initializers, e.g., `init(coding:)`.
Fixes rdar://107967344.
Rename `ResolveAttachedMacroRequest` to `ResolveMacroRequest` and make use of the request in freestanding declaration macro type checking. Add support for type-checking generic arguments on `MacroExpansionDecl`.
The attached and freestanding macro attributes use the same parsing
logic and representation, so generalize the "attached" attribute into
a more general "macro role" attribute.
Describe attached macros with the `@attached` attribute, providing the
macro role and affected names as arguments to the macro. The form of
this macro will remain the same as it gains other kinds of attached
macro roles beyond "accessor".
Remove the "accessors" role from `@declaration`, which will be going
away.
Introduce appropriate name lookup for custom attributes to find macros
at module scope, and prefer those to types of the same name. We don't
do anything with the macros we found other than ignore them, for the
moment.
Add support for freestanding declaration macros.
- Parse `@declaration` attribute.
- Type check and expand `MacroExpansionDecl`.
Known issues:
- Generic macros are not yet handled.
- Expansion does not work when the parent decl context is `BraceStmt`. Need to parse freestanding declaration macro expansions in `BraceStmt` as `MacroExpansionDecl`, and add expanded decls to name lookup.
