MethodError in diff print: no method matching stat_rep(::Nothing)

[fredrikekre]

ERROR: LoadError: MethodError: no method matching stat_rep(::Nothing)
Closest candidates are:
  stat_rep(::Pkg.Types.PackageSpec; name)
   @ Pkg /opt/julia/julia-1.9.0/share/julia/stdlib/v1.9/Pkg/src/Operations.jl:1991
Stacktrace:
  [1] print_diff
    @ /opt/julia/julia-1.9.0/share/julia/stdlib/v1.9/Pkg/src/Operations.jl:2014 [inlined]
  [2] print_status(env::Pkg.Types.EnvCache, old_env::Pkg.Types.EnvCache, registries::Vector{Pkg.Registry.RegistryInstance}, header::Symbol, uuids::Vector{Base.UUID}, names::Vector{String}; man
ifest::Bool, diff::Bool, ignore_indent::Bool, outdated::Bool, extensions::Bool, io::Base.TTY, mode::Pkg.Types.PackageMode, hidden_upgrades_info::Bool, show_usagetips::Bool)
    @ Pkg.Operations /opt/julia/julia-1.9.0/share/julia/stdlib/v1.9/Pkg/src/Operations.jl:2290**

Julia 1.9 beta3

[KristofferC]

What's the package it is trying to stat_rep? Was it added/removed between the diffs?

[fredrikekre]

$ pkg --project=. add SimpleWeightedGraphs
   Resolving package versions...
    Updating `~/dev/Metis/Project.toml`
  [86223c79] + Graphs v1.7.4
  [093fc24a] ERROR: LoadError: MethodError: no method matching stat_rep(::Nothing)

So I guess package 093fc24a is to blame, which is LightGraphs. I can't reproduce the error now though.

[fredrikekre]

Nevermind, I can.
Manifest.txt
Project.txt

[jakobnissen]

I also encountered this. Here's how I hit the problem:

To reproduce:
I'm on Julia 1.9.0, on Linux x86-64 glibc.
Run the following shell commands:

mkdir foo
cd foo
git clone http://github.com/BioJulia/BioSymbols.jl
cd BioSymbols.jl
git clone http://github.com/BioJulia/FASTX.jl
julia --color=yes --project=FASTX.jl

Then, in Julia:

using Pkg
Pkg.develop(PackageSpec(path="."))

[IanButterworth]

It'd be good to fix this. Just hit it dev-ing a dep

[gdalle]

Do we know why this happens?

[IanButterworth]

Worth noting that this happens with add too

$ mkdir foo
$ cd foo
$ git clone http://github.com/BioJulia/BioSymbols.jl
$ cd BioSymbols.jl
$ git clone http://github.com/BioJulia/FASTX.jl
$ julia --color=yes --project=FASTX.jl
FASTX.jl pkg> add .
...
  [67c07d97] + Automa v1.0.0
  [47718e42] + BioGenerics v0.1.2
  [7e6ae17a] ERROR: MethodError: no method matching stat_rep(::Nothing)
...

[IanButterworth]

This turns out to be because parts of Pkg weren't aware of the way that weakdeps can be listed in both [weakdeps] and [deps] as a way to make them deps on <1.9 and weakdeps on 1.9+

Fix #3591