Swift macros should be able to use module names as namespaces

[kishikawakatsumi]

Description

The way Swift macros are syntactically defined and their appearance is quite similar to property wrappers and result builders, especially in the case of attached macros. Property wrappers and result builders can be qualified with module names as namespaces to avoid naming collisions.

On the other hand, macros have no way to avoid name collisions when the same macro name exists in different modules, resulting in an "ambiguous use" error. I believe that macros should also be able to use module names to represent their fully qualified names, just like property wrappers and result builders.

For example, property wrappers can be qualified by the module name as follows:

class ViewController: UIViewController {
  @Combine.Published var s = "..."
}

Result builders also can be qualified by the module name as follows.

@SwiftUI.ViewBuilder
func content() -> some View {
  Text("...")
}

Macros should be able to be qualified by the module name as well.

print(#Foundation.URL("https://swift.org/"))

@Swift.Observable
final class Dog {}

[ahoppen]

Tracked in Apple’s issue tracker as rdar://108621205

[ahoppen]

Since name lookup happens inside semantic analysis, which is done after parsing, I’m moving this to the swift repo.