Protect cmd_gen against invalidation

[timholy]

This gets used by Base.require, arguably the most painful of all invalidations. CSV is one package that invalidates it.

[KristofferC]

N.b get's invalidated from https://github.com/rofinn/FilePathsBase.jl/blob/0eb6a7a725c57a990b73a411731746705d9b4de6/src/path.jl#L69-L72

[timholy]

Hmm, in my analysis it's

julia> tree
inserting convert(::Type{String}, x::WeakRefStrings.WeakRefString) @ WeakRefStrings ~/.julia/packages/WeakRefStrings/31nkb/src/WeakRefStrings.jl:81 invalidated:
   mt_backedges: 1: MethodInstance for setindex!(::Vector{String}, ::Any, ::Int64) at depth 0 with 24 children blocked 0.05790986799999999 inclusive time for 2 nodes


julia> ascend(root)
Choose a call for analysis (q to quit):
 >   setindex!(::Vector{String}, ::Any, ::Int64)
       getindex(::Type{String}, ::Any)
         arg_gen(::AbstractString)
           cmd_gen(::Tuple{Tuple{Cmd}, Tuple{String}, Tuple{String}, Tuple{SubString{String}}, Tuple{String}, Tuple{String}, Tuple{Nothing}, Tuple{String}, Tuple{String}, Tuple{String}, Tu
             link_image_cmd(::Nothing, ::String)
               link_image(::Nothing, ::String, ::IO, ::IO)
                 link_image(::Nothing, ::String)
                   compilecache(::Base.PkgId, ::String, ::IO, ::IO, ::Bool)
                     compilecache(::Base.PkgId, ::String)
v                      _require(::Base.PkgId, ::Nothing)

This is using the analysis in JuliaData/DataFrames.jl#3285 (comment)

[KristofferC]

Hm, okay but I've seen traces pointing to that method extension elsewhere at least.

[timholy]

Me too. I'm not very familiar with FilePathsBase, but I wonder if the conveniences it offers are so nice as to make the invalidations worth it.