`combinedef` could/should yield better line numbers

[cstjean]

Motivation and description

Consider this macro, that defines both f as is and f_5 via combinedef

julia> macro return_5(fdef)
       di = splitdef(fdef)
       di[:name] = Symbol(di[:name], :_5)
       di[:body] = quote for _ in 1:5 end; 5 end
       return esc(quote
       $fdef
       $(combinedef(di))
       end)
       end
@return_5 (macro with 1 method)

The uncombined method (bar) has correct line number, but the bar_5 method has a line number from the macro return_5 (it's the di[:body] line). This ruins "Go to definition" features. The user wants to go to bar_5 but gets taken to macro return_5.

julia> @return_5 bar(x) = x+10
bar_5 (generic function with 1 method)

julia> methods(bar)
# 1 method for generic function "bar" from Main:
 [1] bar(x)
     @ REPL[18]:1

julia> methods(bar_5)
# 1 method for generic function "bar_5" from Main:
 [1] bar_5(x)
     @ REPL[17]:4

This can be solved by using @qq begin instead of quote, but A) most people don't know about it and B) @qq is a bit of a blunt tool.

Possible Implementation

1. Find the LineNumberNode in splitdef
2. Store it inside of the dict returned by splitdef
3. Insert it in the new method in combinedef

The LineNumberNode seems to always be the first element of the body's block. It shouldn't be too difficult.

julia> dump(:(f(x) = x+2))
Expr
  head: Symbol =
  args: Array{Any}((2,))
    1: Expr
      head: Symbol call
      args: Array{Any}((2,))
        1: Symbol f
        2: Symbol x
    2: Expr
      head: Symbol block
      args: Array{Any}((2,))
        1: LineNumberNode
          line: Int64 1
          file: Symbol REPL[30]
        2: Expr
          head: Symbol call
          args: Array{Any}((3,))
            1: Symbol +
            2: Symbol x
            3: Int64 2