Description:

The package manager in julia-2:0.5.1-6 is incompatible with libgit2-1:0.25.1-2. Downgrading to libgit2-1:0.24.6-1 resolves the issue. This is noted in https://discourse.julialang.org/t/pkg-update-giterror/3368 and is being reported here for visibility, as those affected are most likely to be Arch users.

Additional info:
* package version(s)
libgit2-1:0.25.1-2
julia-2:0.5.1-6

* config and/or log files etc.
Only attempted on 64 bit packages

Steps to reproduce:

With julia-2:0.5.1-6, the latest as of this report, launch the julia REPL and call the update function of the package manager

$ julia

julia> Pkg.update()
INFO: Updating METADATA...
ERROR: METADATA cannot be updated. Resolve problems manually in /home/d9w/.julia/v0.5/METADATA.
GitError(Code:ERROR, Class:Invalid, Invalid version 0 on git_proxy_options)
in macro expansion at ./libgit2/error.jl:99 [inlined]
in #fetch#55(::Base.LibGit2.FetchOptions, ::String, ::Function, ::Base.LibGit2.GitRemote, ::Array{AbstractString,1}) at ./libgit2/remote.jl:70
in (::Base.LibGit2.#kw##fetch)(::Array{Any,1}, ::Base.LibGit2.#fetch, ::Base.LibGit2.GitRemote, ::Array{AbstractString,1}) at ./<missing>:0
in #fetch#96(::String, ::String, ::Array{AbstractString,1}, ::Nullable{Base.LibGit2.AbstractCredentials}, ::Function, ::Base.LibGit2.GitRepo) at ./libgit2/libgit2.jl:164
in eval_user_input(::Any, ::Base.REPL.REPLBackend) at ./REPL.jl:64
in macro expansion at ./REPL.jl:95 [inlined]
in (::Base.REPL.##3#4{Base.REPL.REPLBackend})() at ./event.jl:68
in eval_user_input(::Any, ::Base.REPL.REPLBackend) at ./REPL.jl:64
in macro expansion at ./REPL.jl:95 [inlined]
in (::Base.REPL.##3#4{Base.REPL.REPLBackend})() at ./event.jl:68

After downgrading to libgit2-1:0.24.6-1, expected behavior is restored.

# cd /var/cache/pacman/pkg
# pacman -U libgit2-1:0.24.6-1-x86_64.pkg.tar.xz
...
(1/1) downgrading libgit2
...
# julia
_
_ _ _(_)_ | A fresh approach to technical computing
(_) | (_) (_) | Documentation: http://docs.julialang.org
_ _ _| |_ __ _ | Type "?help" for help.
| | | | | | |/ _` | |
| | |_| | | | (_| | | Version 0.5.1 (2017-03-05 13:25 UTC)
_/ |\__'_|_|_|\__'_| |
|__/ | x86_64-pc-linux-gnu

julia> Pkg.update()
INFO: Updating METADATA...
INFO: Computing changes...
INFO: No packages to install, update or remove