Print a hint if the user types exit in the REPL (implemented by customizing Base.show for typeof(exit))

[DilumAluthge]

This implements the suggestion from triage in #42011 (comment) and #42011 (comment).

[DilumAluthge]

cc: @mkitti

[vtjnash]

Seems okay, but feels a little odd that display will have this text in all cases, not just the REPL. I think this might be better:

diff --git a/stdlib/REPL/src/REPL.jl b/stdlib/REPL/src/REPL.jl
index 3308760046..cb7163aeab 100644
--- a/stdlib/REPL/src/REPL.jl
+++ b/stdlib/REPL/src/REPL.jl
@@ -301,6 +301,9 @@ function print_response(errio::IO, response, show_value::Bool, have_color::Bool,
                         println(errio, "Error showing value of type ", typeof(val), ":")
                         rethrow()
                     end
+                    if response === exit
+                        println("Hint: To exit Julia, use Ctrl-D or type exit() and press enter.")
+                    end
                 end
             end
             break

[mkitti]

To review, we've explored a few ways of doing this, and come full circle:

1. add exit/quit hint #21362
   Similar to this PR
2. REPL-only: Print a hint if the user types exit in the REPL #38307
   Modified display(d::REPLDisplay, mime::MIME"text/plain", x)
3. REPL-only: Print a hint if the user types exit in the REPL #38522
   Added a print_exit_help method called after print_response
4. REPL-only: Print a hint if the user types exit in the REPL using an AST transform #42011
   Used an AST transform in the REPL

julia> function Base.show(io::IO, m::MIME"text/plain", fn::typeof(exit))
           TT = Tuple{IO, MIME"text/plain", Function}
           invoke(show, TT, io, m, fn)
           println(io)
           print(io, "Hint: To exit Julia, use Ctrl-D or type exit() and press enter.")
           return nothing
       end

julia> exit
exit (generic function with 2 methods)
Hint: To exit Julia, use Ctrl-D or type exit() and press enter.

julia> (exit, exit)
(exit, exit)

julia> [exit]
1-element Vector{typeof(exit)}:
 exit

julia> ans[1]
exit (generic function with 2 methods)
Hint: To exit Julia, use Ctrl-D or type exit() and press enter.

[mkitti]

Would making it conditional on Base.isinteractive() help?

[mkitti]

Thinking of the bigger picture here, why doesn't the REPL have it's own MIME type? text/vnd.juliarepl perhaps. The fallback would be to text/plain.

[JeffBezanson]

Was I on that triage call? This is absolutely not the right way to implement this. You don't want to change what the exit function looks like, you just want to hook into the exact repl input exit. For example what if I write Fs = [exit] followed by Fs[1].

[JeffBezanson]

Same thing I posted in 2017 btw.

[vtjnash]

So #42011?

[JeffBezanson]

That's not ideal either; a string operation like how we handle ; seems like the best way. But I don't think this is necessary at all.

[mkitti]

That's not ideal either; a string operation like how we handle ; seems like the best way. But I don't think this is necessary at all.

https://github.com/JuliaLang/julia/pull/38522/files

[JeffBezanson]

While we're at it, we can fix quit too, which does weird things:

julia> f() = quit
f (generic function with 1 method)

julia> f()
ERROR: UndefVarError: quit not defined
suggestion: To exit Julia, use Ctrl-D, or type exit() and press enter.

[mkitti]

@DilumAluthge , Jeff, leading triage, says to go back to #38522 , with the binding resolved enhancement he suggested.

[JeffBezanson]

Same thing for help.