Missing macros to get Expr and raw source code of method arguments

[alexarchambault]

It's the main issue I ran into when porting sourcecode to dotty. It needs macros to

• get the arguments of ~the root context (like in def foo(a: Int, b: String)(implicit foo: Foo) with the implicit materialization of Foo backed by a macro - how can the macro get Exprs for 2 and "a" in f(2, "a")?). Prevents to have sourcecode.Args work fine.
• get the ~raw code of arguments of the root context (in def foo(s: Seq[Int])(implicit foo: Foo), with the implicit materialization of Foo backed by a macro - how can the macro get a String "(1 to 10).sum" in f((1 to 10).sum)?). Prevents to have sourcecode.Text work fine.

[nicolasstucki]

@alexarchambault is the addition in #5870 enough to implement this macro?

[alexarchambault]

@nicolasstucki I guess it is for the second point. Don't know about the first.

[alexarchambault]

Checking right now for the second point.

[nicolasstucki]

For the first one you should try with (args: Expr[T]).unseal.underlyingArgument

[alexarchambault]

So using sourceCode fails like this (PR).

About Args, I'm not sure how I'm supposed to recover the Expr[_] of the arguments from the root context.

[nicolasstucki]

@alexarchambault could you create a self contained example that shows the desired result?

[nicolasstucki]

This might be used to implement it https://github.com/lampepfl/dotty/blob/master/library/src/scala/compiletime/package.scala#L34