root edited this page Oct 11, 2017 · 10 revisions

Page to sum up the discussions about OPAM. It may be incomplete. Feel free to fill in but please don't change the structure of the page that is meant to drive discussion.

Problems of today we want to solve via a package manager

These are problems encountered by the Coq users and developers we want to tackle, not problems of OPAM in one of its declinations. I take the freedom to rank problems into the more urgent, and the ones I (Enrico) consider less urgent (no matter if a solution for one is also a solution for another).

  1. regular user installing Coq.

    I don't think it applies to a developer, since we know what we are doing. Unfortunately even people using Debian or derivatives regularly need a version of Coq, even a stable one, not packaged. Not a problem for OSX or Windows (in principle you have an official bundle).

  2. regular user installing an ml extension of Coq.

    This problem affects all users. If one is lucky the bundle (as above) ships all the files needed in order to compile the extension (will be the same in 8.5 for windows, don't know for mac), but compilation can still fail in many ways (upgrade of OCaml between Coq and plugin compilation, wrong paths or env variables).

  3. people distributing extensions.

    One can bundle/precompile them for OSX or Window, but this is an effort (e.g. you need a Mac/Windows machine). No bundle for Linux.

  4. dependency resolution in testing.

    Today hard coded in the bench system.

  5. extensions depending on extensions depending on extensions...

    There are a few already, e.g. the Plouffe package depends on Coquelicot, which depends on Ssreflect. I (Guillaume) have a proof that depends on Flocq, Ssreflect, Coquelicot, Mathcomp, Interval, Gappa, and Why3; this is getting painful for the user. "Soon" Ssreflect will be fragmented into ~ 10 smaller libraries.

Maybe problems in the (near) future, desiderata, commodities

  1. standardize the way one distributes/installs an extension (ml or not) for Coq.
  2. distributing the contribs that are not alive (the ones alive are distributed by their authors using the same mechanism)
  3. easy to make coq depend on ocamlc for native_compute
  4. make external libraries as easy to install as the standard library

The tool

OPAM, what offers and at which price.

good

  1. clean environment compatible with OCaml's idiosyncrasies (same version of the compiler for all linked files) and Coq's (same coqtop binary for all .cmxs and .vo linked)
  2. handling dependencies between coq and extensions
  3. handling dependencies between extensions
  4. low cost of packaging (especially extensions built using coq_makefile)

bad

  1. a new tool for (some) users, especially the less technically inclined
  2. complexity of dependency management exposed to the user
  3. compilation time
  4. not for windows (not in time for 8.5, maybe later)
  5. not a complete toolchain (the C compiler needs to be in any case installed in the host system for .ml plugins)
  6. does not interact with system-level package managers (e.g. Debian)

opinions: should we adopt it?

  1. Enrico: no real alternative tool (esp. handling the specificities of ocaml); complexity for the user can be lowered in many ways (extra work, but possible); compilation time not a problem for the regular user (a regular user does not install coq every day). In short the problems it solves are more than the ones it creates (assuming we use opam >= 1.2, lower versions are too broken).
  2. Guillaume: not a panacea, but still much better than not having a package manager.

Proposals so far

Things that have been proposed, some of them already implemented

  1. All extensions' versions for various coq versions in the same coq repo (repo-stable)

    • PROS: 1 repo to add to opam to access everything
    • CONS: quite some complexity for the beginner. (e.g. you see packages you can't install without changing Coq version)
    • CONS: the coq package is not under our direct control. (updates via pull requests to be accepted by non-coq people)

    good documentation could clearly help the beginner. maybe we could get commit rights in the opam official repo.

  2. A repo for Coq version X, containing also the right Coq version

    • PROS: the user only sees a consistent set of packages for his coq version
    • CONS: the coq package is already in the opam standard repo, and some packages depend on it (why3)

    maybe we could have coq both on the official repo and in our repo, but have on our side a coq version with a higher version number to "shadow" the official one if needed.

  3. Embedding opam in Coq

    • PROS: max flexibility, we can hack it
    • CONS: like maintaining a fork
    • CONS: no code yet, not trivial
  4. A specific wrapper for Coq around opam

    • PROS: max flexibility

    • CONS: no code yet, how do we install the wrapper?

      A proof of concept is there: opam-coq-shell_

related proposals

  1. The OSX bundle includes also an opam root
    • PROS: best of both worlds (pre compiled environment, extensible via opam)

    • CONS: a .app/ directory is read only and .opam/ roots are not relocatable

      Enrico: I think the following "hack" is worth trying The bundled OPAM root is built in /Library/coq-$VERSION/opam (i.e. a dir not depending on the user name); such root is then shipped as a .tgz inside the .app bundle; the startup script in the .app/ bundle untars (using sudo_) the opam root if not already there and starts coq from the opam root (eval opam config env; coqide). The user willing to add opam packages jumps to /Library/coq-$VERSION/opam and calls opam via sudo. The drawback is that one has, in the .app/ a tarball that uses some space (but also allows one to restart from scratch by erasing the dir in /Library).

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