Opam removes package when failing to recompile

[thomas-huet]

Trying to install a new package can remove previously installed packages if the installation of the new package fails. I think this behaviour is very unintuitive.

Example:

$ opam install conf-gnutls
The following actions will be performed:
  ∗ install   conf-gnutls     1
  ↻ recompile ocamlnet        4.1.6 [uses conf-gnutls]

...

┌─ The following actions failed
│ λ build conf-gnutls 1
└─ 
┌─ The following changes have been performed (the rest was aborted)
│ ⊘ remove  ocamlnet        4.1.6
└─ 

The installation failed because I was missing some library so I installed the missing library and ran opam install conf-gnutls again but didn't think about reinstalling ocamlnet too.

[AltGr]

We took extra care in opam 2.0.0 to minimise the removals as much as possible, while guaranteeing that the set of installed packages remains consistent at all times. It seems you have hit a bug, or at least a corner case, though, as in your case the removal should certainly only have been done after the conf-gnutls package was successfully built. Could you provide some more context (logs, if possible the files foo-* generated when re-running with the option --cudf foo) to help us debug ?

Thanks for reporting.

[thomas-huet]

Here are the logs and the small foo-* files:
https://gist.github.com/thomas-huet/6dc305ce66a44bf11548b703428941b3
Here are all the foo-* files:
https://github.com/thomas-huet/foo

The steps to reproduce:

• install ocamlnet with opam
• make sure libgnutls28-dev is not installed
• opam install conf-gnutls

[AltGr]

Thanks, that will be very helpful!

[dra27]

This is still a bug in 2.1, and in fact it's got slightly worse. This (opam 2.0.8) doesn't remove ocamlnet:

FROM ocaml/opam
RUN opam install ocamlnet
RUN opam install conf-gnutls

it fails because pkg-config isn't in the image. Fix that by inserting RUN sudo apt-get update && sudo apt-get install -yy pkg-config before the last RUN and you have a reproduction case for this.

However, in opam 2.1 (which you can get by putting RUN sudo ln -f /usr/bin/opam-2.1 /usr/bin/opam && opam update immediately after the FROM), ocamlnet is removed regardless of whether pkg-config is installed or not.