How to Typecheck a DefDef

Question

Within an annotation Macro, I'm enumerating members of a class and want the types of the methods that I find.

So I happily iterate over the body of the class, and collect all the DefDef members.

... which I can't typecheck.

For each DefDef I've tried wrapping it in an Expr and using actualType. I've tried duplicating the thing and transplanting it into an ad-hoc class (via quasiquotes). I've tried everything else I can think of :)

The best I can get is either NoType or Any, depending on the technique used. The worst I get is to have an exception thrown at me.

These are simple methods, of the form def foo(i: String) = i, so the return type needs to be inferred, but there's no external information required. There are no abstract types, or type params, or other members of the class involved here. I'd like to handle more advanced cases later, but want to have these trivial examples working first.

In a plugin, this would be simple. I'd just typecheck the entire unit with errors suppressed and get at what I want through the symbols, then reset the tree attributes for subsequent processing. As a macro... I'm stumped.

What am I missing?

Answer 1

In a macro it's the same. Instead of typed as in plugins, you call c.typeCheck, but have to be careful not to fall into a trap (https://github.com/scalamacros/paradise/issues/1) that is supposed to be fixed in 2.10.5 and 2.11.0. After a successful return from a c.typeCheck, you can get access to the symbol and do all the usual stuff.