"Add macro implementation" code action triggered from a macro declaration

[DougGregor]

Description

Given a macro declaration like:

@freestanding(expression)
macro stringify(_ value: Int) -> (Int, String) = #externalMacro(module: "MyMacros", type: "StringifyMacro")

Introduce a code action "Add macro implementation" that stubs out the implementation of this macro so it's ready to go in your project.

Ideally, this would do a couple of things:

• Add a macro target MyMacros to the package manifest if it isn't there
• Add MyMacros as a dependency for the current target (that contains this stringify macro declaration) if it isn't there
• Add a dependency on the swift-syntax package to the package manifest if it isn't there
• Add a new file StringifyMacro.swift to the MyMacros target with a StringifyMacro that includes a stubbed-out conformance to ExpressionMacro
• Add/update the list of macros provided by MyMacros with StringifyMacro

[ahoppen]

Synced to Apple’s issue tracker as rdar://128016679

[mateusrodriguesxyz]

Hi @ahoppen! Could you assign this to me, please?