[opam-devel] One (or more) opam root per projet?

[Gabriel Scherer]

Dear opam-devel,

Guillaume Claret (one of the Coq developpers) has been experimenting with
using one OPAM root for each of his software projects, instead of using
global switches.

  http://coq-blog.clarus.me/use-opam-for-coq.html

I have a personal preference for keeping using switches that I'm familiar
with and seem more idiomatic in OCaml usage (and also compiling Coq in each
project would remind me too much of my Gentoo years), but Guillaume points
out that it has evolved to be standard usage in the Node/npm community (and
with Python/virtualenv I think), and that it can solve incompatible-version
headaches by having a finer granularity. More generally the rationale seems
to be "local is better than global", which sounds reasonable.

(Besides compilation time and duplication of efforts -- that could be
partially solved if/when binary packages where to see the light -- a good
argument in favor of switches would be the ability to install programs
across multiple switches in the same root, eg. opam compiler-conf and
similiar scripts.)

Do you know of other users having converged towards that per-project
scheme? Is there tool support, or interest in eventually supporting, for
this mode of use in upstream OPAM?
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