remove convert method for `Any`?

[JeffBezanson]

As in JuliaData/CategoricalArrays.jl#177, the method

Base.convert(::Type{Any}, ::DataValue{Union{}}) = NA

causes a lot of recompilation. IIUC, NA is a singleton and so this method is not different from the default conversion to Any in Base?

[davidanthoff]

convert(Any, NA) throws a method ambiguity error without it...

[JeffBezanson]

Works for me on master. What's the full error output you get?

[davidanthoff]

julia> convert(Any, NA)
ERROR: MethodError: convert(::Type{Any}, ::DataValue{Union{}}) is ambiguous. Candidates:
  convert(::Type{Union{Missing, T}}, ::DataValue{Union{}}) where T in DataValues at C:\Users\david\.julia\dev\DataValues\src\scalar\core.jl:38
  convert(::Type{Any}, x) in Base at essentials.jl:153
Possible fix, define
  convert(::Type{Any}, ::DataValue{Union{}})
Stacktrace:
 [1] top-level scope at none:0

[pfitzseb]

This also causes issues when trying to put a DataValue{Any} into Any-typed containers, e.g.

julia> dv = DataValue{Any}("asd")
DataValue{Any}("asd")

julia> c = Channel(0)
Channel{Any}(sz_max:0,sz_curr:0)

julia> put!(c, dv)
ERROR: MethodError: convert(::Type{Any}, ::DataValue{Any}) is ambiguous. Candidates:
  convert(::Type{Any}, x) in Base at essentials.jl:170
  convert(::Type{Union{Missing, T}}, value::DataValue{T}) where T in DataValues at /home/pfitzseb/.julia/packages/DataValues/N7oeL/src/scalar/core.jl:40
  convert(::Type{T}, x::T) where T>:Union{Missing, Nothing} in Base at missing.jl:68
To resolve the ambiguity, try making one of the methods more specific, or adding a new method more specific than any of the existing applicable methods.
Stacktrace:
 [1] put!(::Channel{Any}, ::DataValue{Any}) at ./channels.jl:311
 [2] top-level scope at REPL[5]:1

on 1.5 or

julia> dv = DataValue{Any}("asd")
Error showing value of type DataValue{Any}:
ERROR: MethodError: convert(::Type{Any}, ::DataValue{Any}) is ambiguous. Candidates:
  convert(::Type{Any}, x) in Base at essentials.jl:204
  convert(::Type{T}, x::T) where T>:Union{Missing, Nothing} in Base at missing.jl:68
  convert(::Type{T}, x::T) where T>:Nothing in Base at some.jl:35
  convert(::Type{T}, x) where T>:Union{Missing, Nothing} in Base at missing.jl:70
  convert(::Type{T}, x) where T>:Nothing in Base at some.jl:36
  convert(::Type{Union{Missing, T}}, value::DataValue{T}) where T in DataValues at /home/pfitzseb/.julia/packages/DataValues/N7oeL/src/scalar/core.jl:40
To resolve the ambiguity, try making one of the methods more specific, or adding a new method more specific than any of the existing applicable methods.
Stacktrace:
  [1] Base.RefValue{Any}(x::DataValue{Any})
    @ Base ./refvalue.jl:8
  [2] Ref{Any}(x::DataValue{Any})
    @ Base ./refpointer.jl:136
  [3] display(d::REPL.REPLDisplay, mime::MIME{Symbol("text/plain")}, x::Any)
    @ REPL ~/Documents/Git/julia/usr/share/julia/stdlib/v1.7/REPL/src/REPL.jl:212
  [4] display(d::REPL.REPLDisplay, x::Any)
    @ REPL ~/Documents/Git/julia/usr/share/julia/stdlib/v1.7/REPL/src/REPL.jl:225

on master.

That first error is also the cause of julia-vscode/julia-vscode#1940.