Understand why OPAM won't install a package

I’m trying to install the uri package to play around with it. With 4.06.1, however, I get the following error:

$ opam install -v uri

Your request can't be satisfied:
  - No package matches uri.

No solution found, exiting
'opam install -v uri' failed.

With 4.05.0, the package installs successfully.

The last version of uri, though, seems compatible with OCaml 4.06. My guess is that one of uri's dependencies prevents OPAM from installing on 4.06.1.

Is there a way to get more information out of OPAM in order to understand what’s going on “under the hood”, and why it won’t install the package?

That’s weird, I’m on 4.06.1 and I can opam install uri just fine. What version of opam are you on? Have you done opam update?

My OPAM version is 1.2.2, and repository is up-to-date.

I think you are using the internal solver of opam 1.2.2, don’t. opam conf report should be able to confirm this.

Oh, you’re right! I thought I had aspcud installed.

$ opam conf report

# OPAM config report
# opam-version    1.2.2 
# self-upgrade    no
# os              linux
# external-solver no
# criteria        -removed,-notuptodate,-changed
# jobs            4
# repositories    1* (http)
# pinned          0
# current-switch  4.06.1
# last-update     2018-05-29 08:20

Installing aspcud and retrying did the trick. Thanks!

I get this issue:

bot@4ea62fd207fc:~/pycoq/tutorial$ opam pin -y --switch debug_proj_4.09.1 debug_proj file:///home/bot/pycoq/debug_proj
[NOTE] Package debug_proj is already pinned to file:///home/bot/pycoq/debug_proj (version ~dev).
[debug_proj.~dev] no changes from file:///home/bot/pycoq/debug_proj
debug_proj is now pinned to file:///home/bot/pycoq/debug_proj (version ~dev)

Sorry, no solution found: there seems to be a problem with your request.

[NOTE] Pinning command successful, but your installed packages may be out of sync.

is it similar to this?