DeclarativePackages.jl, or jdp for short, allows to declaratively specify which Julia packages a project should use, with exact version or commit details.

jdp will install the specified packages (if necessary) and start Julia with exactly these packages available.

jdp is heavily inspired by the nix package manager.

You need to have git installed. Install the package and link jdp into a directory on your PATH, for example in ~/local/bin:

Pkg.add("DeclarativePackages") 
symlink(Pkg.dir("DeclarativePackages")*"/bin/jdp",  "$(homedir())/local/bin/jdp")

Simply create a DECLARE file in your project's directory and invoke jdp in that directory instead of julia.

Example for a DECLARE file:

# Julia packages:  Packagename [ version or commit hash]
JSON
HDF5 0.4.6
Images 86a43d8368

# Any Git URL:  URL [ version or commit hash ]
https://github.com/JuliaLang/BinDeps.jl.git
https://github.com/timholy/HDF5.jl.git 0.4.6
https://github.com/jakebolewski/LibGit2.jl.git dcbf6f2419f92edeae4014f0a293c66a3c053671

You can change both the name of the DECLARE file as well as the julia binary called via environment variables. All arguments after jdp will be passed on to Julia:

DECLARE=mydeclarations.txt DECLARE_JULIA=/usr/bin/juliafromgit jdp -e "println(123)"

To launch IJulia make sure that IJulia is listed in your DECLARE file and start Julia like this:

jdp -e "using IJulia; notebook()"

If you would like to initially create a DECLARE file based on your currently installed packages, run:

julia -e "using DeclarativePackages; exportDECLARE()"

Finally, git add DECLARE and track the set of installed packages along with your code!

You will see that your DECLARE files get auto-updated if not all packages details are fully specified. There is also an entry for METADATA, the repo where Julia gets the information about available packages from, fixed at a commit.

There are several ways to update a package by editing DECLARE:

• You can change the version number or commit hash.
• You can remove the package and, in the case that another package requires it, have jdp update it to the version Pkg.add() would pick.
• As long as DECLARE contains a line fixing METADATA to a specific commit, packages can only be updated using the versions listed therein.
• You can use METADATA corresponding to a different commit hash (simply change it), or delete the line containing METADATA to pull in the newest METADATA.

If you want to only control a few packages and update the rest automatically, you can keep a second declaration file, e.g. DECLARE.minimal, containing only the minumum you want to specify:

HDF5 0.4.0
Images

Running cp DECLARE.minimal DECLARE; jdp will then update the rest of the required dependencies to the newest versions. And as you have DECLARE in your git repo, you can always go back.

jdp can be influenced using the following environment variables:

• DECLARE_JULIA - path of the Julia executable
• DECLARE - path of the DECLARE file to be used
• DECLARE_VERBOSITY - control dignostic output. 0==quiet, 1==default, 2==debug, 3==chatty
• DECLARE_INCLUDETEST - include all dependencies in the packages' test/REQUIRE files

Remove the symlink to jdp you created during installation, run Pkg.rm("DeclarativePackages") and delete all packages installed by jdp:

chmod -R +w $HOME/.julia/declarative && rm -rf $HOME/.julia/declarative

Normally, Julia has a global, mutable state of installed packages in $HOME/.julia/v0.x.

jdp, in contrast, installs the packages for each unique DECLARE file in a distinct location, marks the installation read-only, and calls Julia with a modified JULIA_PKGDIR. Like this, Julia sees only the packages specified in DECLARE. And different projects and even different branches within a project can easily specify which package versions (or commits) to use.

The packages are actually installed in $HOME/.julia/declarative/HASH/v0.x, where HASH is the md5 hash over the contents of the DECLARE file.

In addition to JULIA_PKGDIR Julia's LOAD_PATH is set to include the src, modules and submodules subdirectories of where jdp was invoked. The first is handy when working on a module while the second or third are a great places to put any git submodules.

Hard links are used for packages at the same commit, resuling in very little disc space used in $HOME/.julia/declarative. You can delete that directory without ill-effect at any time, jdp will re-install packages as needed on the next invokation.

• jdp was tested on Linux and OSX - help adapting it to Windows would be much appreciated!