Swift Macros: error - Conformance to 'Prot' is not covered by macro 'macroName'

Question

I'm trying to add protocol conformance with a macro

The macro is defined as:

protocol Prot {}
@attached(extension, conformances: Prot)
public macro MyMacro = #externalMacro(module: "MyMacro", type: "MyMacro")

where MacroName is defined as:

struct MyMacro: ExtensionMacro {
  public static func expansion(of node: AttributeSyntax, 
                               attachedTo declaration: some DeclGroupSyntax,
                               providingExtensionsOf type: some TypeSyntaxProtocol, 
                               conformingTo protocols: [TypeSyntax], in context: some MacroExpansionContext) throws -> [ExtensionDeclSyntax] {
//    guard !protocols.isEmpty else {
//      return []
//    }
    return [try ExtensionDeclSyntax("extension \(type.trimmed): Prot {}") ]
  }
}

The macro expands correctly adding the extension with the protocol conformance declaration correctly However, when I build the code (not the macro plugin, that builds fine) I get an error:

Conformance to 'Prot' is not covered by macro 'MyMacro'

Not sure how to solve this error? Anyone have a hint how to properly add protocol conformance using a macro?

Incidentally, if I uncomment the guard statement I see that protocols is empty

Extensions

681

Posted by

gshaviv

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Answer 1

Just posting here because I have the exact same issue, I don't understand why something so seemingly simple is going wrong and no-one is posting an answer to explain what the problem is

Posted by

Kevinvandenhoek

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Answer 2

@gshaviv try it this way:

public protocol Prot {}
@attached(extension, conformances: Prot, names: arbitrary)
public macro MyMacro() = #externalMacro(module: "MyMacro", type: "MyMacro")

Posted by

anegvonapets

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Swift Macros: error - Conformance to 'Prot' is not covered by macro 'macroName'

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