安装 opam 包时链接到非标准路径中的库

Question

I am trying to install an opam package (conf-zmq.0.1) in a cluster. I have no root access, and I have manually installed the zmq library in /path/to/libzmq.

The command "opam install zmq" fails at the following point:

[ERROR] The compilation of conf-zmq failed at "/hpc/eb/compilerwrappers/compilers/cc test.c -I/usr/local/include -L/usr/local/lib -lzmq".

This seems simple, but after looking throgh the manual, I have been unable to find how to tell opam to change -L/usr/local/lib to -L/path/to/libzmq.

Any help on this would be very appreciated.

Answer 1

It is not possible to tell opam anything about the C compiler linking rules, neither about OCaml linking rules, or any other compilation rules, as opam is much above this. The responsibility of opam is to find a package with the best suiting version, download it, and install using the build and configuration scripts that are provided by the package maintainer.

Although opam provides facilities for package configuration parameters, the conf-zmq maintainer is not utilizing them and do not provide any parameterization for their package. In fact, there are no other options to pass the installation test of the conf-zmq package, other than installing them in the hardcoded location. You can submit a bug-report or ask the maintainer for further support. You can find all the links in the opam file of the package.

The good news is that there is a workaround. If the package description is broken, then you can always download the package to your local filesystem, fix it, and the pin the fixed version. And opam will now use your local version. If you want to distribute your package, you will need to push your changes upstream of course (if you want it to be available to the general public (ie, via ocaml.org), or just have your own opam repository (that may contain only one package or many packages).

But for starters, here the first drop-in instructions, first obtain the sources either by cloning it from the GitHub repository or just by issuing the following command:

opam source zmq

You can then change your working directory to the folder that opam has created for you, eg, for me it was

cd zmq.5.1.3/

Then (the hardest part) hack the package to make it installable on your system. (The first thing that you need is to drop the dependency on the broken conf-zmq package). Once you're ready, or think that you're ready just do

opam pin add .

opam should pick the package names from the opam files, but if it won't do this see opam pin --help for more options. It will then try to install the pinned package. If it fails, then continue hacking and doing

opam update
opam reinstall zmq # or install

Once the patch is ready, you can either embed it in your automation or create your own opam repository. It is also very easy, just create a new GitHub repo (or clone the ocaml/opam-repository, not recommended) then copy the package definition that you would like to change (for us it would be packages/zmq/zmq.5.1.3/ ) and apply your hacks to the opam and configurations scripts. If your hacks also include changes to the zmq source code, you can format them as patches and add use the patches stanza in your opam file to apply them on the fly.