Nested begin/end indexing no longer supported

[torfjelde]

Back in the day, doing something like x[1][end] was possible, but it no longer is:

julia> AbstractPPL.vinds(:(x[1][end]))
:((((lastindex)(var"##S#319"),),))

which references an undefined variable. This is because of the Base.replace_ref_begin_end!:

julia> Base.replace_ref_begin_end!(:(x[1][end]))
:(let var"##S#320" = x[1]
      var"##S#320"[(lastindex)(var"##S#320")]
  end)

which is then further altered afterwards in

AbstractPPL.jl/src/varname.jl

Lines 357 to 364 in 34fc3e1

	@static if VERSION < v"1.5.0-DEV.666"
	Base.replace_ref_end!(ex)
	else
	Base.replace_ref_begin_end!(ex)
	end
	last = Expr(:tuple, ex.args[2:end]...)
	init = vinds(ex.args[1]).args
	return Expr(:tuple, init..., last)

resulting in the incorrect generated code.

Is this intended?

[phipsgabler]

Not intented, no. Very good point, it seems like this just didn't get properly tested. I guess it needs to be rewritten to

:(let var"##S#320" = x[1]
      VarName{:x}(((lastindex(var"##S#320"),),))
  end)

right?

[torfjelde]

It needs to rewritten to

:(let var"##S#320" = x[1]
      VarName{:x}(((1, ), (lastindex(var"##S#320"),),))
  end)

Essentially doing what Base.replace_ref_begin_end! does but we need to capture the full indexing being used.

[torfjelde]

Seems like we'd have to re-implement Base.replace_ref_begin_end!? It seems a bit complicated though

https://github.com/JuliaLang/julia/blob/bb5b98e72a151c41471d8cc14cacb495d647fb7f/base/views.jl#L17-L75