Re: Finding Dependencies at Run Time

[Peter Polidoro <peter@polidoro.io>]

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?