Debugger doesn't skip "preamble" defining destructured args on function entry

[oscardssmith]

This should print 1

julia> function foo((a, b), c)
           a + c
       end
foo (generic function with 1 method)

julia> @enter foo((1,2), 3)
In foo(, c) at REPL[3]:1
 1  function foo((a, b), c)
>2      a + c
 3  end

About to run: indexed_iterate((1, 2), 1)
1|julia> a
ERROR: UndefVarError: `a` not defined in `Main`
Suggestion: check for spelling errors or missing imports.
Stacktrace:
  [1] top-level scope
    @ none:1
  [2] eval
    @ ./boot.jl:430 [inlined]
  [3] eval_code(frame::JuliaInterpreter.Frame, expr::Expr)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/CpHEo/src/utils.jl:722
  [4] eval_code(frame::JuliaInterpreter.Frame, command::String)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/CpHEo/src/utils.jl:695
  [5] _eval_code(frame::JuliaInterpreter.Frame, code::String)
    @ Debugger ~/.julia/packages/Debugger/zdZP1/src/repl.jl:210
  [6] (::Debugger.var"#27#29"{Debugger.DebuggerState})(s::REPL.LineEdit.MIState, buf::IOBuffer, ok::Bool)
    @ Debugger ~/.julia/packages/Debugger/zdZP1/src/repl.jl:193
  [7] #invokelatest#2
    @ ./essentials.jl:1055 [inlined]
  [8] invokelatest
    @ ./essentials.jl:1052 [inlined]
  [9] run_interface(terminal::REPL.Terminals.TextTerminal, m::REPL.LineEdit.ModalInterface, s::REPL.LineEdit.MIState)
    @ REPL.LineEdit ~/.julia/juliaup/julia-1.11.3+0.x64.linux.gnu/share/julia/stdlib/v1.11/REPL/src/LineEdit.jl:2755
 [10] run_interface
    @ ~/.julia/juliaup/julia-1.11.3+0.x64.linux.gnu/share/julia/stdlib/v1.11/REPL/src/LineEdit.jl:2749 [inlined]
 [11] RunDebugger(frame::JuliaInterpreter.Frame, repl::Nothing, terminal::Nothing; initial_continue::Bool)
    @ Debugger ~/.julia/packages/Debugger/zdZP1/src/repl.jl:167
 [12] RunDebugger
    @ ~/.julia/packages/Debugger/zdZP1/src/repl.jl:12 [inlined]
 [13] RunDebugger(frame::JuliaInterpreter.Frame)
    @ Debugger ~/.julia/packages/Debugger/zdZP1/src/repl.jl:12
 [14] macro expansion
    @ ~/.julia/packages/Debugger/zdZP1/src/Debugger.jl:127 [inlined]
 [15] top-level scope
    @ REPL[6]:1

[KristofferC]

The reason for this is:

julia> @code_lowered foo((1,2), 3)
CodeInfo(
1 ─ %1 = Base.indexed_iterate(@_2, 1) <------------------- you are here
│        a = Core.getfield(%1, 1) <------------------- a is defined here
│        @_4 = Core.getfield(%1, 2)
│   %4 = @_4
│   %5 = Base.indexed_iterate(@_2, 2, %4)
│        b = Core.getfield(%5, 1)
│   %7 = Main.:+
│   %8 = a
│   %9 = (%7)(%8, c)
└──      return %9

So a has not been defined on the entrance of the function. It is possible that this "preamble" should be skipped but it is a bit hard from lowered code to know exactly what is "preamble" and what is the actual body. If you step down a bit it is defined:

1|debug>  # L to enter lowered code mode
In foo(, c) at REPL[2]:1
>1  1 ─ %1 = Base.indexed_iterate(@_2, 1)
 2  │        a = Core.getfield(%1, 1)
 3  │        @_4 = Core.getfield(%1, 2)
 4  │   %4 = @_4
 5  │   %5 = Base.indexed_iterate(@_2, 2, %4)

About to run: indexed_iterate((1, 2), 1)
1|debug> se
In foo(, c) at REPL[2]:1
 1  1 ─ %1 = Base.indexed_iterate(@_2, 1)
>2  │        a = Core.getfield(%1, 1)
 3  │        @_4 = Core.getfield(%1, 2)
 4  │   %4 = @_4
 5  │   %5 = Base.indexed_iterate(@_2, 2, %4)
 6  │        b = Core.getfield(%5, 1)

About to run: getfield((1, 2), 1)
1|debug> 
In foo(, c) at REPL[2]:1
 1  1 ─ %1 = Base.indexed_iterate(@_2, 1)
 2  │        a = Core.getfield(%1, 1)
>3  │        @_4 = Core.getfield(%1, 2)
 4  │   %4 = @_4
 5  │   %5 = Base.indexed_iterate(@_2, 2, %4)
 6  │        b = Core.getfield(%5, 1)
 7  │   %7 = $(QuoteNode(+))

About to run: getfield((1, 2), 2)
1|julia> a
1

[KristofferC]

This is the stepping that is done

https://github.com/JuliaDebug/Debugger.jl/blob/6a6beab2f559a5a72d3284c1c6482e0620026db8/src/Debugger.jl#L93-L94

and this case is not handled. I'll move this issue to JuliaInterpreter since these things are implemented there.