REPL: call display on the backend

[IanButterworth]

Fixes #57742

With this PR (The last 2 are pasted in in one operation)

% ./julia -q -t8,0

julia> struct Foo end

julia> Base.display(::Foo) = @show Threads.threadid()

julia> Foo()
Threads.threadid() = 1

julia> Foo()
Threads.threadid() = 1

julia> Foo()
Threads.threadid() = 1

julia> Foo()
Threads.threadid() = 1

[IanButterworth]

Though I think handling errors in display might need a tweak.

julia> Base.display(::Foo) = error()

julia> Foo()

julia> Foo()

julia>

[vtjnash]

Branching on whether the parser returned an Expr or a Function seems somewhat unwise, but otherwise the PR seems a good direction

[KristofferC]

I think this broke Debugger.jl.

julia> f(a,b) = a+b
f (generic function with 1 method)

julia> @enter f(4, 5)
In f(a, b) at REPL[4]:1
>1  f(a,b) = a+b

About to run: (+)(4, 5)
1|julia> a < HANGS>
# Force interrupt:
^CERROR: InterruptException:
Stacktrace:
  [1] poptask(W::Base.IntrusiveLinkedListSynchronized{Task})
    @ Base ./task.jl:1012
  [2] wait()
    @ Base ./task.jl:1021
  [3] wait(c::Base.GenericCondition{ReentrantLock}; first::Bool)
    @ Base ./condition.jl:130
  [4] wait
    @ ./condition.jl:125 [inlined]
  [5] take_buffered(c::Channel{Any})
    @ Base ./channels.jl:493
  [6] take!
    @ ./channels.jl:487 [inlined]
  [7] eval_with_backend
    @ ~/.julia/juliaup/julia-1.11.5+0.aarch64.apple.darwin14/share/julia/stdlib/v1.11/REPL/src/REPL.jl:1006 [inlined]
  [8] print_response(errio::IO, response::Any, backend::Union{…}, show_value::Bool, have_color::Bool, specialdisplay::Union{…})
    @ REPL ~/.julia/juliaup/julia-1.11.5+0.aarch64.apple.darwin14/share/julia/stdlib/v1.11/REPL/src/REPL.jl:436
  [9] (::REPL.var"#70#71"{REPL.LineEditREPL, Tuple{Int64, Bool}, Bool, Bool})(io::Any)
    @ REPL ~/.julia/juliaup/julia-1.11.5+0.aarch64.apple.darwin14/share/julia/stdlib/v1.11/REPL/src/REPL.jl:405
 [10] with_repl_linfo(f::Any, repl::REPL.LineEditREPL)
    @ REPL ~/.julia/juliaup/julia-1.11.5+0.aarch64.apple.darwin14/share/julia/stdlib/v1.11/REPL/src/REPL.jl:678

This is what Debugger does: https://github.com/JuliaDebug/Debugger.jl/blob/6a6beab2f559a5a72d3284c1c6482e0620026db8/src/repl.jl#L194.

Should it be changed somehow?

[oscardssmith]

@KristofferC I believe this is fixed by JuliaDebug/Debugger.jl#366 (but I would appreciate review since the intent here is highly unclear)

[IanButterworth]

I think the fix should be to figure out and fix why it's hanging, not avoid that method. But I haven't had time to look into this yet. I don't have any breadcrumbs right now, sorry.

[oscardssmith]

should we revert the backport to 1.11? This is in 1.11.5 (already released), and breaking Debugger is pretty bad...

[IanButterworth]

I think we just need to async call print_response and wait for it