Printing of macro symbols displays like a macrocall

[mbauman]

MWE:

julia> @macroexpand @which @which
:(InteractiveUtils.which(@which, Tuple{LineNumberNode,Module}))

julia> dump(@macroexpand @which @which)
Expr
  head: Symbol call
  args: Array{Any}((3,))
    1: GlobalRef
      mod: Module InteractiveUtils
      name: Symbol which
    2: Symbol @which
    3: Tuple{LineNumberNode,Module} <: Any

This should protect the macro name and print it as a Symbol("@which").

[JeffBezanson]

Looks like a more general problem:

julia> Symbol("##")
Symbol("##")

julia> Expr(:tuple, Symbol("##"))
:((##,))

So there's some code for this, but it's not used inside expressions.

[c42f]

More entertainment:

julia> Expr(:tuple, Symbol("a-b"))
:((a-b,))

[c42f]

So I've got a fix for this over at #23408, but It's worth noting that it dramatically uglifies printing of symbols generated by macro hygiene, even as it makes the resulting Exprs valid.

julia> macro ugly()
           quote
               x = 1
               y = 2
           end
       end
@ugly (macro with 1 method)

julia> @macroexpand @ugly
quote
    #= REPL[30]:3 =#
    $(Symbol("#57#x")) = 1
    #= REPL[30]:4 =#
    $(Symbol("#58#y")) = 2
end

Of course, for non-trivial macros it's a lot worse.

[c42f]

On the up side, the result of printing such expanded forms is actually valid code with those changes.