REPL becomes unusable after error

[barucden]

I stumbled upon a (not very critical, just inconvenient) error when using the REPL. Using the following I always get the displayed error.

julia> l = [1 => 2]
1-element Array{Pair{Int64,Int64},1}:
 1 => 2

julia> (x=>y) = l[1]
Error showing value of type UnionAll:
ERROR: 
SYSTEM (REPL): showing an error caused an error
ERROR: 
SYSTEM (REPL): caught exception of type MethodError while trying to handle a nested exception; giving up

After that, the REPL session cannot be used anymore because subsequent calls result in the following.

julia> 1+1
┌ Error: Error in the keymap
│   exception =
│    MethodError: no method matching isspace(::Int64)
│    Closest candidates are:
│      isspace(::AbstractChar) at strings/unicode.jl:466
│    Stacktrace:
│     [1] rstrip(::typeof(isspace), ::String) at ./strings/util.jl:259
│     [2] rstrip(::String) at ./strings/util.jl:263
│     [3] add_history(::REPL.REPLHistoryProvider, ::Any) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/REPL/src/REPL.jl:570
│     [4] add_history(::REPL.LineEdit.PromptState) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/REPL/src/LineEdit.jl:1229
│     [5] add_history(::REPL.LineEdit.MIState) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/REPL/src/LineEdit.jl:208
│     [6] commit_line(::Any) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/REPL/src/LineEdit.jl:1995
│     [7] (::REPL.LineEdit.var"#110#163")(::Any, ::Any, ::Vararg{Any,N} where N) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/REPL/src/LineEdit.jl:2077
│     [8] #invokelatest#1 at ./essentials.jl:710 [inlined]
│     [9] invokelatest at ./essentials.jl:709 [inlined]
│     [10] (::REPL.LineEdit.var"#22#23"{REPL.LineEdit.var"#110#163",String})(::Any, ::Any) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/REPL/src/LineEdit.jl:1364
│     [11] prompt!(::REPL.Terminals.TextTerminal, ::REPL.LineEdit.ModalInterface, ::REPL.LineEdit.MIState) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/REPL/src/LineEdit.jl:2447
│     [12] run_interface(::REPL.Terminals.TextTerminal, ::REPL.LineEdit.ModalInterface, ::REPL.LineEdit.MIState) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/REPL/src/LineEdit.jl:2350
│     [13] run_frontend(::REPL.LineEditREPL, ::REPL.REPLBackendRef) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/REPL/src/REPL.jl:1143
│     [14] (::REPL.var"#38#42"{REPL.LineEditREPL,REPL.REPLBackendRef})() at ./task.jl:356
└ @ REPL.LineEdit /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/REPL/src/LineEdit.jl:2449

My Julia version:

Julia Version 1.5.0
Commit 96786e22cc (2020-08-01 23:44 UTC)
Platform Info:
  OS: Linux (x86_64-pc-linux-gnu)
  CPU: Intel(R) Core(TM) i5-4258U CPU @ 2.40GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-9.0.1 (ORCJIT, haswell)

On the current nighly build (1.6.0-DEV.1065), the result is the same, but the last error is slightly different:

julia> 1+1
┌ Error: Error in the keymap
│   exception =
│    TypeError: in typeassert, expected AbstractChar, got a value of type Int64
│    Stacktrace:
│      [1] rstrip(f::typeof(isspace), s::String)
│        @ Base ./strings/util.jl:259
│      [2] rstrip
│        @ ./strings/util.jl:263 [inlined]
│      [3] add_history(hist::REPL.REPLHistoryProvider, s::REPL.LineEdit.PromptState)
│        @ REPL /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/REPL/src/REPL.jl:547
│      [4] add_history(s::REPL.LineEdit.PromptState)
│        @ REPL.LineEdit /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/REPL/src/LineEdit.jl:1248
│      [5] add_history(::REPL.LineEdit.MIState)
│        @ REPL.LineEdit /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/REPL/src/LineEdit.jl:227
│      [6] commit_line(s::REPL.LineEdit.MIState)
│        @ REPL.LineEdit /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/REPL/src/LineEdit.jl:2075
│      [7] (::REPL.LineEdit.var"#110#163")(::REPL.LineEdit.MIState, ::Any, ::Vararg{Any, N} where N)
│        @ REPL.LineEdit /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/REPL/src/LineEdit.jl:2157
│      [8] #invokelatest#2
│        @ ./essentials.jl:709 [inlined]
│      [9] invokelatest
│        @ ./essentials.jl:708 [inlined]
│     [10] (::REPL.LineEdit.var"#22#23"{REPL.LineEdit.var"#110#163", String})(s::Any, p::Any)
│        @ REPL.LineEdit /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/REPL/src/LineEdit.jl:1414
│     [11] prompt!(term::REPL.Terminals.TextTerminal, prompt::REPL.LineEdit.ModalInterface, s::REPL.LineEdit.MIState)
│        @ REPL.LineEdit /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/REPL/src/LineEdit.jl:2528
│     [12] run_interface(terminal::REPL.Terminals.TextTerminal, m::REPL.LineEdit.ModalInterface, s::REPL.LineEdit.MIState)
│        @ REPL.LineEdit /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/REPL/src/LineEdit.jl:2430
│     [13] run_frontend(repl::REPL.LineEditREPL, backend::REPL.REPLBackendRef)
│        @ REPL /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/REPL/src/REPL.jl:1124
│     [14] (::REPL.var"#44#49"{REPL.LineEditREPL, REPL.REPLBackendRef})()
│        @ REPL ./task.jl:392
└ @ REPL.LineEdit /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/REPL/src/LineEdit.jl:253

[KristofferC]

What happens is that you replace the Pair constructor with nonsense and then the whole of julia comes crashing down (because it uses Pairs internally).

A more MWE would be:

julia> =>
Pair

julia> Pair(a,b) = error()
Error showing value of type UnionAll:
ERROR:
SYSTEM (REPL): showing an error caused an error
ERROR:
SYSTEM (REPL): caught exception of type ErrorException while trying to handle a nested exception; giving up

And since Pair is not a method but a constructor, you don't have to import it like with e.g.

julia> +
+ (generic function with 184 methods)

julia> +(a,b) = error()
ERROR: error in method definition: function Base.+ must be explicitly imported to be extended

I think this could be fixed by making =>(a,b) = Pair(a,b) instead of const => = Pair like it is now?

[KristofferC]

And would you look at that... Closing as dup of #25744