Error when trying to showerror: TypeError: in specializations, expected DataType, got Type{Union{}}

[akriegman]

I got the following error. It looks like it's an error with the debugger itself, that happened when it was trying to show an error with my program.

ERROR: TypeError: in specializations, expected DataType, got Type{Union{}}
Stacktrace:
  [1] #specialize_method#317
    @ ./compiler/utilities.jl:224 [inlined]
  [2] specialize_method
    @ ./compiler/utilities.jl:212 [inlined]
  [3] Base.StackTraces.StackFrame(frame::JuliaInterpreter.Frame)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/ZNccU/src/utils.jl:773
  [4] show_backtrace(io::IOContext{IOBuffer}, frame::JuliaInterpreter.Frame)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/ZNccU/src/utils.jl:792
  [5] showerror(io::IOContext{IOBuffer}, ex::TypeError, bt::JuliaInterpreter.Frame; backtrace::Bool)
    @ Base ./errorshow.jl:99
  [6] showerror
    @ ./errorshow.jl:95 [inlined]
  [7] display_error(io::IOContext{IOBuffer}, er::TypeError, frame::JuliaInterpreter.Frame)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/ZNccU/src/utils.jl:808
  [8] (::Debugger.var"#10#19"{REPL.LineEdit.Prompt, Debugger.DebuggerState})(s::REPL.LineEdit.MIState, buf::IOBuffer, ok::Bool)
    @ Debugger ~/.julia/packages/Debugger/wueAn/src/repl.jl:72
  [9] #invokelatest#2
    @ ./essentials.jl:1055 [inlined]
 [10] invokelatest
    @ ./essentials.jl:1052 [inlined]
 [11] run_interface(terminal::REPL.Terminals.TextTerminal, m::REPL.LineEdit.ModalInterface, s::REPL.LineEdit.MIState)
    @ REPL.LineEdit ~/.julia/juliaup/julia-1.11.5+0.aarch64.apple.darwin14/share/julia/stdlib/v1.11/REPL/src/LineEdit.jl:2755
 [12] run_interface
    @ ~/.julia/juliaup/julia-1.11.5+0.aarch64.apple.darwin14/share/julia/stdlib/v1.11/REPL/src/LineEdit.jl:2749 [inlined]
 [13] RunDebugger(frame::JuliaInterpreter.Frame, repl::Nothing, terminal::Nothing; initial_continue::Bool)
    @ Debugger ~/.julia/packages/Debugger/wueAn/src/repl.jl:167
 [14] RunDebugger
    @ ~/.julia/packages/Debugger/wueAn/src/repl.jl:12 [inlined]
 [15] RunDebugger(frame::JuliaInterpreter.Frame)
    @ Debugger ~/.julia/packages/Debugger/wueAn/src/repl.jl:12
 [16] macro expansion
    @ ~/.julia/packages/Debugger/wueAn/src/Debugger.jl:127 [inlined]
 [17] top-level scope
    @ REPL[3]:1

caused by: TypeError: in specializations, expected DataType, got Type{Union{}}
Stacktrace:
  [1] #specialize_method#317
    @ ./compiler/utilities.jl:224 [inlined]
  [2] specialize_method
    @ ./compiler/utilities.jl:212 [inlined]
  [3] Base.StackTraces.StackFrame(frame::JuliaInterpreter.Frame)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/ZNccU/src/utils.jl:773
  [4] show_backtrace(io::IOContext{IOBuffer}, frame::JuliaInterpreter.Frame)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/ZNccU/src/utils.jl:792
  [5] showerror(io::IOContext{IOBuffer}, ex::BoundsError, bt::JuliaInterpreter.Frame; backtrace::Bool)
    @ Base ./errorshow.jl:99
  [6] showerror
    @ ./errorshow.jl:95 [inlined]
  [7] display_error(io::IOContext{IOBuffer}, er::BoundsError, frame::JuliaInterpreter.Frame)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/ZNccU/src/utils.jl:808
  [8] show_breakpoint(io::Base.TTY, bp::JuliaInterpreter.BreakpointRef, state::Debugger.DebuggerState)
    @ Debugger ~/.julia/packages/Debugger/wueAn/src/commands.jl:22
  [9] execute_command(state::Debugger.DebuggerState, v::Val{:c}, cmd::SubString{String})
    @ Debugger ~/.julia/packages/Debugger/wueAn/src/commands.jl:56
 [10] (::Debugger.var"#10#19"{REPL.LineEdit.Prompt, Debugger.DebuggerState})(s::REPL.LineEdit.MIState, buf::IOBuffer, ok::Bool)
    @ Debugger ~/.julia/packages/Debugger/wueAn/src/repl.jl:64
 [11] #invokelatest#2
    @ ./essentials.jl:1055 [inlined]
 [12] invokelatest
    @ ./essentials.jl:1052 [inlined]
 [13] run_interface(terminal::REPL.Terminals.TextTerminal, m::REPL.LineEdit.ModalInterface, s::REPL.LineEdit.MIState)
    @ REPL.LineEdit ~/.julia/juliaup/julia-1.11.5+0.aarch64.apple.darwin14/share/julia/stdlib/v1.11/REPL/src/LineEdit.jl:2755
 [14] run_interface
    @ ~/.julia/juliaup/julia-1.11.5+0.aarch64.apple.darwin14/share/julia/stdlib/v1.11/REPL/src/LineEdit.jl:2749 [inlined]
 [15] RunDebugger(frame::JuliaInterpreter.Frame, repl::Nothing, terminal::Nothing; initial_continue::Bool)
    @ Debugger ~/.julia/packages/Debugger/wueAn/src/repl.jl:167
 [16] RunDebugger
    @ ~/.julia/packages/Debugger/wueAn/src/repl.jl:12 [inlined]
 [17] RunDebugger(frame::JuliaInterpreter.Frame)
    @ Debugger ~/.julia/packages/Debugger/wueAn/src/repl.jl:12
 [18] macro expansion
    @ ~/.julia/packages/Debugger/wueAn/src/Debugger.jl:127 [inlined]
 [19] top-level scope
    @ REPL[3]:1

I tried to debug the debugger with @run @run ... but it just gave me a different error:

Breaking for error:
ERROR: ArgumentError: _deleteend! requires delta in 0:length(a)
Stacktrace:
 [1] _deleteend!(a::Vector{JuliaInterpreter.FrameData}, delta::Int64)
   @ Base array.jl:1204
 [2] empty!(a::Vector{JuliaInterpreter.FrameData})
   @ Base array.jl:2029
 [3] clear_caches()
   @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/ZNccU/src/construct.jl:59
 [4] enter_call_expr(expr::Expr; enter_generated::Bool)
   @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/ZNccU/src/construct.jl:630
 [5] enter_call_expr(expr::Expr)
   @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/ZNccU/src/construct.jl:629
 [6] var"##thunk#270"()
   @ Main ~/.julia/packages/Debugger/wueAn/src/Debugger.jl:91

In _deleteend!(a, delta) at array.jl:1201
 1201  function _deleteend!(a::Vector, delta::Integer)
 1202      delta = Int(delta)
 1203      len = length(a)
>1204      0 <= delta <= len || throw(ArgumentError("_deleteend! requires delta in 0:length(a)"))
 1205      newlen = len - delta
 1206      for i in newlen+1:len
 1207          @inbounds _unsetindex!(a, i)
 1208      end

About to run: throw(ArgumentError("_deleteend! requires delta in 0:length(a)"))
1|debug> bt
[1] _deleteend!(a, delta) at array.jl:1204
  | a::Vector{JuliaInterpreter.FrameData} = <JuliaInterpreter.FrameData[JuliaInterpreter.FrameData(Union{Nothing, Some{Any}}[Some(Core.toInt64), S...>
  | delta::Int64 = 29
  | len::Int64 = 28
  | ::Bool = false
[2] empty!(a) at array.jl:2029
  | a::Vector{JuliaInterpreter.FrameData} = <JuliaInterpreter.FrameData[JuliaInterpreter.FrameData(Union{Nothing, Some{Any}}[Some(Core.toInt64), S...>
[3] clear_caches() at /Users/akriegma/.julia/packages/JuliaInterpreter/ZNccU/src/construct.jl:59
[4] #enter_call_expr#46(enter_generated, , expr) at /Users/akriegma/.julia/packages/JuliaInterpreter/ZNccU/src/construct.jl:630
  | enter_generated::Bool = false
  | ::typeof(JuliaInterpreter.enter_call_expr) = JuliaInterpreter.enter_call_expr
  | expr::Expr = <:((VM(Float32[-0.06815089 0.027055124 0.046305846 -0.02320608 0.0076302057 -0.035288677 0.073490456 -...>
[5] enter_call_expr(expr) at /Users/akriegma/.julia/packages/JuliaInterpreter/ZNccU/src/construct.jl:629
  | expr::Expr = <:((VM(Float32[-0.06815089 0.027055124 0.046305846 -0.02320608 0.0076302057 -0.035288677 0.073490456 -...>
[6] ##thunk#270() at REPL[4]:91
  | theargs::Tuple{VM, Matrix{Float64}} = <(VM(Float32[-0.06815089 0.027055124 0.046305846 -0.02320608 0.0076302057 -0.035288677 0.073490456 -0....>

So with that being the state of things I'm not sure how to gather more information about this error.

[akriegman]

Still struggling with this, it's very frustrating as it's basically impossible to debug. Anyways, I took a closer look at what happens when I try to debug the debugger. It looks like the outer debugger and the inner debugger are trying to modify certain global variables at the same time. I guess that means that the debugger is just not debugable.

1|debug> c
Breaking for error:
ERROR: UndefRefError: access to undefined reference
Stacktrace:
 [1] empty!(h::Dict{Method, JuliaInterpreter.FrameCode})
   @ Base dict.jl:230
 [2] clear_caches()
   @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/construct.jl:60
 [3] enter_call_expr(expr::Expr; enter_generated::Bool, method_table::Nothing)
   @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/construct.jl:636
 [4] enter_call_expr(expr::Expr)
   @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/construct.jl:633
 [5] var"##thunk#233"()
   @ Main ~/.julia/packages/Debugger/kuAYs/src/Debugger.jl:91

In empty!(h) at dict.jl:220
 220  function empty!(h::Dict{K,V}) where V where K
 221      fill!(h.slots, 0x0)
 222      sz = length(h.slots)
 223      for i in 1:sz
 224          _unsetindex!(h.keys, i)
 225          _unsetindex!(h.vals, i)
 226      end
 227      h.ndel = 0
 228      h.count = 0
 229      h.maxprobe = 0
>230      h.age += 1
 231      h.idxfloor = max(1, sz)
 232      return h
 233  end
 234
 235  # get the index where a key is stored, or -1 if not present

About to run: getproperty(Dict{Method, JuliaInterpreter.FrameCode}(), :age)
1|debug> up
In clear_caches() at /Users/akriegma/.julia/packages/JuliaInterpreter/41lEl/src/construct.jl:58
 58  function clear_caches()
 59      empty!(junk_framedata)
>60      empty!(framedict)
 61      empty!(genframedict)
 62      empty!(junk_frames)
 63      for bp in breakpoints()
 64          empty!(bp.instances)
 65      end
 66  end

About to run: empty!(Dict{Method, JuliaInterpreter.FrameCode}())
2|debug>

[KristofferC]

"Nested" interpretation basically doesn't work no, ref JuliaDebug/JuliaInterpreter.jl#228.

[KristofferC]

Do you have example code where this happens?

[akriegman]

Ok I finally figured out what causes this. It's a bounds error. It also turns out that if I had just run the debugger without break_on(:error) then I would've gotten a less opaque error message.

% julia
               _
   _       _ _(_)_     |  Documentation: https://docs.julialang.org
  (_)     | (_) (_)    |
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _  |  |
  | | |_| | | | (_| |  |  Version 1.11.5 (2025-04-14)
 _/ |\__'_|_|_|\__'_|  |  Official https://julialang.org/ release
|__/                   |

julia> using Debugger, StridedViews

julia> StridedView([1], (1,), (0,), -5)[1]
4372037264

julia> @run StridedView([1], (1,), (0,), -5)[1]
ERROR: TypeError: in specializations, expected DataType, got Type{Union{}}
Stacktrace:
  [1] #specialize_method#317
    @ ./compiler/utilities.jl:224 [inlined]
  [2] specialize_method
    @ ./compiler/utilities.jl:212 [inlined]
  [3] Base.StackTraces.StackFrame(frame::JuliaInterpreter.Frame)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/utils.jl:786
  [4] show_backtrace(io::IOContext{IOBuffer}, frame::JuliaInterpreter.Frame)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/utils.jl:805
  [5] showerror(io::IOContext{IOBuffer}, ex::BoundsError, bt::JuliaInterpreter.Frame; backtrace::Bool)
    @ Base ./errorshow.jl:99
  [6] showerror
    @ ./errorshow.jl:95 [inlined]
  [7] display_error(io::IOContext{IOBuffer}, er::BoundsError, frame::JuliaInterpreter.Frame)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/utils.jl:821
  [8] RunDebugger(frame::JuliaInterpreter.Frame, repl::Nothing, terminal::Nothing; initial_continue::Bool)
    @ Debugger ~/.julia/packages/Debugger/kuAYs/src/repl.jl:157
  [9] RunDebugger
    @ ~/.julia/packages/Debugger/kuAYs/src/repl.jl:12 [inlined]
 [10] macro expansion
    @ ~/.julia/packages/Debugger/kuAYs/src/Debugger.jl:137 [inlined]
 [11] top-level scope
    @ REPL[3]:1

caused by: BoundsError: attempt to access MemoryRef{Int64} at index [-4]
Stacktrace:
  [1]
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/builtins.jl:193
  [2]
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/interpret.jl:245
  [3] evaluate_call!(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, call_expr::Expr)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/interpret.jl:242
  [4] eval_rhs(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, node::Expr)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/interpret.jl:399
  [5] step_expr!(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, node::Any, istoplevel::Bool)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/interpret.jl:562
  [6] step_expr!(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, istoplevel::Bool)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/interpret.jl:620
  [7] finish!(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, istoplevel::Bool)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/commands.jl:14
  [8] finish_and_return!(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, istoplevel::Bool)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/commands.jl:30
  [9] evaluate_call!(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, fargs::Vector{…}, enter_generated::Bool)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/interpret.jl:283
 [10]
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/interpret.jl:249
 [11] evaluate_call!(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, call_expr::Expr)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/interpret.jl:242
 [12] eval_rhs(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, node::Expr)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/interpret.jl:399
 [13] step_expr!(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, node::Any, istoplevel::Bool)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/interpret.jl:562
 [14] step_expr!(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, istoplevel::Bool)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/interpret.jl:620
 [15] finish!(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, istoplevel::Bool)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/commands.jl:14
 [16] finish_and_return!(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, istoplevel::Bool)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/commands.jl:30
 [17] evaluate_call!(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, fargs::Vector{…}, enter_generated::Bool)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/interpret.jl:283
 [18]
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/interpret.jl:249
 [19] evaluate_call!(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, call_expr::Expr)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/interpret.jl:242
 [20] eval_rhs(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, node::Expr)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/interpret.jl:399
 [21] step_expr!(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, node::Any, istoplevel::Bool)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/interpret.jl:562
 [22] step_expr!(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, istoplevel::Bool)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/interpret.jl:620
 [23] finish!(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, istoplevel::Bool)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/commands.jl:14
 [24] finish_and_return!(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, istoplevel::Bool)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/commands.jl:30
 [25] evaluate_call!(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, fargs::Vector{…}, enter_generated::Bool)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/interpret.jl:283
 [26]
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/interpret.jl:249
 [27] evaluate_call!(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, call_expr::Expr)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/interpret.jl:242
 [28] eval_rhs(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, node::Expr)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/interpret.jl:399
 [29] step_expr!(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, node::Any, istoplevel::Bool)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/interpret.jl:562
 [30] step_expr!(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, istoplevel::Bool)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/interpret.jl:620
 [31] finish!(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, istoplevel::Bool)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/commands.jl:14
 [32] finish_and_return!
    @ ~/.julia/packages/JuliaInterpreter/41lEl/src/commands.jl:30 [inlined]
 [33] finish_stack!(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, rootistoplevel::Bool)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/commands.jl:65
 [34]
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/commands.jl:546
 [35] debug_command
    @ ~/.julia/packages/JuliaInterpreter/41lEl/src/commands.jl:477 [inlined]
 [36] debug_command(interp::JuliaInterpreter.RecursiveInterpreter, frame::JuliaInterpreter.Frame, cmd::Symbol)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/commands.jl:477
 [37] execute_command(state::Debugger.DebuggerState, v::Val{:c}, cmd::String)
    @ Debugger ~/.julia/packages/Debugger/kuAYs/src/commands.jl:46
 [38] RunDebugger(frame::JuliaInterpreter.Frame, repl::Nothing, terminal::Nothing; initial_continue::Bool)
    @ Debugger ~/.julia/packages/Debugger/kuAYs/src/repl.jl:153
 [39] RunDebugger
    @ ~/.julia/packages/Debugger/kuAYs/src/repl.jl:12 [inlined]
 [40] macro expansion
    @ ~/.julia/packages/Debugger/kuAYs/src/Debugger.jl:137 [inlined]
 [41] top-level scope
    @ REPL[3]:1
Some type information was truncated. Use `show(err)` to see complete types.

julia> break_on(:error)

julia> @run StridedView([1], (1,), (0,), -5)[1]
ERROR: TypeError: in specializations, expected DataType, got Type{Union{}}
Stacktrace:
  [1] #specialize_method#317
    @ ./compiler/utilities.jl:224 [inlined]
  [2] specialize_method
    @ ./compiler/utilities.jl:212 [inlined]
  [3] Base.StackTraces.StackFrame(frame::JuliaInterpreter.Frame)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/utils.jl:786
  [4] show_backtrace(io::IOContext{IOBuffer}, frame::JuliaInterpreter.Frame)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/utils.jl:805
  [5] showerror(io::IOContext{IOBuffer}, ex::TypeError, bt::JuliaInterpreter.Frame; backtrace::Bool)
    @ Base ./errorshow.jl:99
  [6] showerror
    @ ./errorshow.jl:95 [inlined]
  [7] display_error(io::IOContext{IOBuffer}, er::TypeError, frame::JuliaInterpreter.Frame)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/utils.jl:821
  [8] RunDebugger(frame::JuliaInterpreter.Frame, repl::Nothing, terminal::Nothing; initial_continue::Bool)
    @ Debugger ~/.julia/packages/Debugger/kuAYs/src/repl.jl:157
  [9] RunDebugger
    @ ~/.julia/packages/Debugger/kuAYs/src/repl.jl:12 [inlined]
 [10] macro expansion
    @ ~/.julia/packages/Debugger/kuAYs/src/Debugger.jl:137 [inlined]
 [11] top-level scope
    @ REPL[5]:1

caused by: TypeError: in specializations, expected DataType, got Type{Union{}}
Stacktrace:
  [1] #specialize_method#317
    @ ./compiler/utilities.jl:224 [inlined]
  [2] specialize_method
    @ ./compiler/utilities.jl:212 [inlined]
  [3] Base.StackTraces.StackFrame(frame::JuliaInterpreter.Frame)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/utils.jl:786
  [4] show_backtrace(io::IOContext{IOBuffer}, frame::JuliaInterpreter.Frame)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/utils.jl:805
  [5] showerror(io::IOContext{IOBuffer}, ex::BoundsError, bt::JuliaInterpreter.Frame; backtrace::Bool)
    @ Base ./errorshow.jl:99
  [6] showerror
    @ ./errorshow.jl:95 [inlined]
  [7] display_error(io::IOContext{IOBuffer}, er::BoundsError, frame::JuliaInterpreter.Frame)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/41lEl/src/utils.jl:821
  [8] show_breakpoint(io::Base.TTY, bp::JuliaInterpreter.BreakpointRef, state::Debugger.DebuggerState)
    @ Debugger ~/.julia/packages/Debugger/kuAYs/src/commands.jl:22
  [9] execute_command(state::Debugger.DebuggerState, v::Val{:c}, cmd::String)
    @ Debugger ~/.julia/packages/Debugger/kuAYs/src/commands.jl:56
 [10] RunDebugger(frame::JuliaInterpreter.Frame, repl::Nothing, terminal::Nothing; initial_continue::Bool)
    @ Debugger ~/.julia/packages/Debugger/kuAYs/src/repl.jl:153
 [11] RunDebugger
    @ ~/.julia/packages/Debugger/kuAYs/src/repl.jl:12 [inlined]
 [12] macro expansion
    @ ~/.julia/packages/Debugger/kuAYs/src/Debugger.jl:137 [inlined]
 [13] top-level scope
    @ REPL[5]:1

julia>