`n` skips assignments and branches

[bicycle1885]

This behavior is surprising because it suddenly jumps to an unexpected place:

julia> function foo(x)
           println(x)
           y = 0
           if x
               y = 1
           end
           return y
       end
foo (generic function with 1 method)

julia> @enter foo(true)
In foo(x) at REPL[2]:1
 1  function foo(x)
>2      println(x)
 3      y = 0
 4      if x
 5          y = 1
 6      end

About to run: (println)(true)
1|debug> n
true
In foo(x) at REPL[2]:1
 3      y = 0
 4      if x
 5          y = 1
 6      end
>7      return y
 8  end

About to run: return 1
1|debug>
1

[bicycle1885]

This is due to https://github.com/JuliaDebug/JuliaInterpreter.jl/blob/8e7bac93fb03e98ff5bc89097995ada1518d0157/src/commands.jl#L184, which skips assignments and branches because they are neither function calls nor returns. Stopping only at function calls and returns may be a reasonable design choice, but it feels counterintuitive.

[KristofferC]

It should be possible to stop on assignments as well, you would just need to ignore the assignments to temporaries that also exist:

julia> function f()
           x = 1
           sin(x+x)
       end
f (generic function with 1 method)

julia> ci = @code_lowered f()
CodeInfo(
1 ─      x = 1
│   %2 = x + x # <----------------- ignore
│   %3 = Main.sin(%2)
└──      return %3
)

But these look quite different so that should be possible:

julia> ci.code[1] |> dump
Expr
  head: Symbol =
  args: Array{Any}((2,))
    1: Core.SlotNumber
      id: Int64 2
    2: Int64 1

julia> ci.code[2] |> dump
Expr
  head: Symbol call
  args: Array{Any}((3,))
    1: GlobalRef
      mod: Module Main
      name: Symbol +
    2: Core.SlotNumber
      id: Int64 2
    3: Core.SlotNumber
      id: Int64 2