Emit error for assertMacroExpansion when applying an attached member macro to declaration that can’t have members

[Rajveer100]

Resolves Issue #2206

When we apply an attached member macro to a declaration that cannot have members, assertMacroExpansion fails to emit appropriate diagnostic message.

[ahoppen]

I think you have it the wrong way round. From the issue description

the following test case should emit an error.

Also: Did you run all the other tests? I suspect all member tests will fail with your current changes.

[Rajveer100]

I think you have it the wrong way round. From the issue description

You mean the test itself is wrong or it's in the wrong place?

Also: Did you run all the other tests? I suspect all member tests will fail with your current changes.

Well yes, as I said other member tests are failing.

[ahoppen]

You mean the test itself is wrong or it's in the wrong place?

Yes, having an attached member macro on a variable should emit an error.

[Rajveer100]

Ok so I had mistakenly put a guard instead of if, I am yet to find the trigger for VariableDeclSyntax so I can see the test failing and then add the error message, but the previous errors and tests are good which weren't supposed to fail.

[Rajveer100]

What diagnostic do you recommend adding here? Is there an existing one for such case or we need a custom addition to the enum which we then throw during detection?

[ahoppen]

I would suggest that you add a new diagnostic with any wording you like and then we can iterate from there.

[Rajveer100]

Which property should be checked under MacroExpansion in the below case (directed here from MacroSystem -> expandAttachedMacro -> expandAttachedMacroWithoutCollapsing) if I am under the right place:

case (let attachedMacro as MemberMacro.Type, .member):
// ...

[ahoppen]

In the issue I wrote

specifically, if the declaration is not a DeclGroupSyntax

So that’s the syntax node type I would check.

[Rajveer100]

@ahoppen
According to the issue, as you mentioned:

specifically, if the declaration is not a DeclGroupSyntax

But, the following check exists:

guard let declGroup = declarationNode.asProtocol(DeclGroupSyntax.self)

How does it not throw an error here if the node isn't a DeclGroupSyntax?