Re: Finding Dependencies at Run Time

[Julien Lepiller]

My explanation must not have been clear. You can read more on search-paths at 
https://guix.gnu.org/manual/devel/en/html_node/Search-Paths.html#Search-Paths

Basically, it's a declaration on packages that specify which path-like 
environment variables they honor.

When building an environment/profile, guix will look at all the variable 
declarations of packages of that environment and create the corresponding 
variables.

So when building a package, guix creates an environment with all the 
dependencies (inputs) of the package, and the corresponding environment 
variables.

Similarly, when you install say python (that brings in its search-path 
definition) and python-numpy (that provides a python library), guix will know 
to set GUIX_PYTHONPATH properly for using numpy with python. Since numpy 
propagates its dependencies, they are also part of the environment and that's 
how numpy can find them.

Remember the difference between inputs and propagated inputs: they're the same, 
but when you create a profile, inputs are not part of the profile (so they need 
a direct store reference, such as RPATH or a wrapper), whereas propagated 
inputs are part of the profile, so an environment variable allows to find them.

Le 13 juillet 2022 20:51:18 GMT+02:00, Peter Polidoro <peter@polidoro.io> a 
écrit :
>Your explanations are very helpful, thank you, and your links made me realize 
>that devel version of the manual has lots of information that I could not find 
>in the stable version of the manual.
>
>> During the build, search-paths and native-search-paths are used to set up 
>> environment variables. If you use --keep-failed and interrupt a
>> build you'l find them in /tmp/guix-build-…/environment-variables.
>
>So search-paths and native-search-paths are set before the build and unset 
>after the build so they are unavailable during run-time? Or are 
>native-search-paths only available at build-time and search-paths available at 
>both build-time and run-time?
>
>Are the search-paths and native-search-paths absolute path values found by 
>automatically searching the directories in all of the inputs or native inputs, 
>looking for files or directories that match a pattern? So they are a way to 
>map relative paths into absolute paths to the dependency packages?
>
>> For others, the required search paths can be embedded in a wrapper, which 
>> defines environment variables before calling the actual program.
>
>So if a package needs run-time environment variables, then a package should 
>use wrap-program to attach them to a command? These are not found 
>automatically by searching the inputs, they must be manually defined using 
>explicit input paths?
>
>> For propagation, dependencies are found in the environment. It's less "pure" 
>> than the other ways, so we try to avoid resorting to that.
>> Unfortunately some programming languages don't really leave us a choice 
>> (like python…).
>
>So python packages are not using an environment variable, such as PYTHONPATH, 
>to find dependencies? How are they placed together into an environment so they 
>can find each other?