What does this error message mean

lewis · May 11, 2020, 7:07pm

It should be sort of obvious: I am redefining a const somewhere.

Which const could it be?

I have nothing named Variable anywhere. I only have 4 structs anywhere in the code. None redefine another.

What is the reference to “toplevel”?

julia> using CovidSim
Revise.LogRecord(Error, evaluation error starting at /Users/lewis/Dropbox/Online Coursework/Covid/src/toplevel:257, lowered, Revise_e943ed8b, "/Users/lewis/.julia/packages/Revise/MgvIv/src/lowered.jl", 106, (mod=JuliaInterpreter, ex=begin
    #= toplevel:257 =#
    struct Variable
        #= /Users/lewis/.julia/packages/JuliaInterpreter/R1LXQ/src/types.jl:269 =#
        value::Any
        #= /Users/lewis/.julia/packages/JuliaInterpreter/R1LXQ/src/types.jl:270 =#
        name::Symbol
        #= /Users/lewis/.julia/packages/JuliaInterpreter/R1LXQ/src/types.jl:271 =#
        isparam::Bool
        #= /Users/lewis/.julia/packages/JuliaInterpreter/R1LXQ/src/types.jl:272 =#
        is_captured_closure::Bool
    end
end)invalid redefinition of constant Variable
Stacktrace:
 [1] top-level scope at none:0)[ Info: Precompiling CovidSim [top-level]

lewis · May 11, 2020, 7:15pm

Never mind. I “up’ed” my packages; quit Julia; restarted Julia in the same terminal session. I’d been in the same terminal session for about a week. That’s just asking for trouble. Memory corruption or Revise got confused. Quit terminal. Open new terminal. Problem gone.

Don’t worry about this. Long sessions are always risky. Pays to purge every day. And it’s good practice to make things clean and repeatable.

dpsanders · May 11, 2020, 8:39pm

You probably tried to redefine the struct Variable with a different definition. This is not possible in Julia and indeed the only solution is to restart the whole Julia process if you wish to redefine it with the same name.

lewis · May 11, 2020, 8:45pm

I have nothing named “Variable” anywhere in the module. More likely this came from a package.

dpsanders · May 11, 2020, 8:45pm

It’s right there on the 4th line of the code you posted:

julia> using CovidSim
Revise.LogRecord(Error, evaluation error starting at /Users/lewis/Dropbox/Online Coursework/Covid/src/toplevel:257, lowered, Revise_e943ed8b, "/Users/lewis/.julia/packages/Revise/MgvIv/src/lowered.jl", 106, (mod=JuliaInterpreter, ex=begin
    #= toplevel:257 =#
    struct Variable

lewis · May 11, 2020, 8:55pm

I can do a text search across all files in the project. No such thing.

What I pasted is the error message. It refers to something that isn’t present. I suspect it was in a package that was subsequently upgraded, which is why it disappeared when I restarted terminal and Julia—with no change to my code.

Let’s let it go. It’s one those mysteries. If it had persisted, then there’d be something to figure out.

kristoffer.carlsson · May 11, 2020, 9:15pm

The struct Variable is from JuliaInterpreter.jl

github.com

JuliaDebug/JuliaInterpreter.jl/blob/939c0d7c6a4923459b95fbd83bce403dec40195f/src/types.jl#L268


      
          `Variable` is a struct representing a variable with an asigned value.
          By calling the function [`locals`](@ref) on a [`Frame`](@ref) a
          `Vector` of `Variable`'s is returned.
          
          
Important fields:
          - `value::Any`: the value of the local variable.
          - `name::Symbol`: the name of the variable as given in the source code.
          - `isparam::Bool`: if the variable is a type parameter, for example `T` in `f(x::T) where {T} = x`.
          - `is_captured_closure::Bool`: if the variable has been captured by a closure
          """
          struct Variable
              value::Any
              name::Symbol
              isparam::Bool
              is_captured_closure::Bool
          end
          Variable(value, name) = Variable(value, name, false, false)
          Variable(value, name, isparam) = Variable(value, name, isparam, false)
          Base.show(io::IO, var::Variable) = (print(io, var.name, " = "); show(io,var.value))
          Base.isequal(var1::Variable, var2::Variable) =
              var1.value == var2.value && var1.name == var2.name && var1.isparam == var2.isparam &&

and the error you got after updating is because JuliaInterpreter.jl released a new version which included a change to that struct

https://github.com/JuliaDebug/JuliaInterpreter.jl/pull/388/files#diff-1f61f32925620a8c37482af6f9a5d108R272

and Revise/Julia can’t handle hot reloading of struct redefinitions.

lewis · May 11, 2020, 9:29pm

Perfect. The correct answer.

And reload all was all that had to happen.