Introduction

Opam's default solver is designed to maintain a set of packages over time, minimising disruption when installing new programs and finding a compromise solution across all packages (e.g. avoiding upgrading some library to prevent uninstalling another program).

In many situations (e.g. a CI system building in a clean environment, a project-local opam root, or a duniverse build) this is not necessary, and we can get a solution much faster by using a different algorithm.

This package uses 0install's (pure OCaml) solver with opam packages.

Usage

Run the opam-zi binary with the packages you want to install:

$ dune exec -- opam-zi utop
[NOTE] Opam library initialised in 0.16 s
base-bigarray.base base-bytes.base base-threads.base base-unix.base camomile.1.0.2 charInfo_width.1.1.0 conf-m4.1 cppo.1.6.6 dune.2.1.3 dune-configurator.2.1.3 dune-private-libs.2.1.3 lambda-term.2.0.3 lwt.5.1.1 lwt_log.1.1.1 lwt_react.1.1.3 mmap.1.1.0 ocaml.4.09.0 ocaml-base-compiler.4.09.0 ocaml-config.1 ocamlbuild.0.14.0 ocamlfind.1.8.1 ocplib-endian.1.0 react.1.2.1 result.1.4 seq.base topkg.1.0.1 utop.2.4.3 zed.2.0.4
[NOTE] Solve took 0.25 s

It outputs the set of packages that should be installed (but doesn't install them itself). The output is in a format suitable for use as input to opam. e.g.

opam install $(opam-zi utop)

Note that it does not look at the current switch's OCaml version and may therefore choose a newer (or older) one. You can pass the version explicitly to constrain it. e.g.

opam-zi utop ocaml.4.08.1

or

opam-zi utop 'ocaml<4.09'

You can also pass other packages and constraints here too, as with opam itself. opam-zi will optimise the packages in order, so opam-zi foo bar will always pick the newest possible version of foo, even if that means choosing an older version of bar (but it will choose an older version of foo if there is no other way to get bar at all).

Tests

Running make test will run various tests (some fixed and some random) using both opam-zi and opam's solver and compare the results.

When testing changes to the code, you may want to do:

dune exec -- ./test/dump.exe --jobs=NN baseline.csv
[ make changes ]
dune exec -- ./test/dump.exe --jobs=NN new.csv

dump.exe takes each package name in opam-repository and solves for it individually, generating a CSV file with the solutions. NN is the number of processes to use to speed it up; use the number of cores your machine has. Depending on the speed of your computer, this is likely to take several minutes.

You may want to use --root to use a separate opam root directory, e.g.

opam init --no-setup --root ./opam-root /path/to/opam-repository

This means you can upgrade your default opam root without changing the test results.

To compare the results, use:

dune exec -- ./test/diff.exe baseline.csv new.csv

Internals

The core 0install solver does not depend on the rest of 0install and just provides a functor that can be instantiated with whatever package system you like (see Simplifying the Solver With Functors).

• The zi-solver directory contains a copy of 0install's solver directory.
• The lib directory applies this to opam.

zi-solver/s.ml describes the interface required by zi-solver. lib/model.ml maps opam concepts onto 0install ones. It's a little complicated because 0install doesn't support alternatives in dependencies (e.g. ocaml-config depends on "ocaml-base-compiler" | "ocaml-variants" | "ocaml-system"). The mapping introduces a "virtual" package in these cases (so ocaml-config depends on a virtual package that has three available versions, with dependencies on the real packages).

A virtual package is also created if you specify multiple packages on the command-line.

License

This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA