Re: What happens when you build a Guix package at every step?

[david larsson <david.larsson@selfhosted.xyz>]

On 2022-09-25 19:28, jgart wrote:
> What would be the best way to illustrate the levels of nesting and code
> paths that get traversed when building a Guix package?
> 
> I'd like to make some sequence diagram notation or something else to
> better understand what happens in a visual way.
> 
> wdyt

I like your idea! I'm probably not the most qualified person to answer 
it, since I am (also?) mainly using guix as a sparetime "hobby", but 
still very interested in learning more about it on a deeper level, which 
is a challenge. Some visual aids would definitely be helpful.

I think a shell of an answer would be to link together the following 
things in such a diagram:

1. gexps
2. the store
3. derivations
4. build systems
5. a package

Building a package in the repl, kind of illustrates the code paths via 
code modules used:

scheme@(guix-user)> ,use (guix gexp)
scheme@(guix-user)> ,use (guix store)
scheme@(guix-user)> ,use (guix derivations)
scheme@(guix-user)> ,use (gnu packages bash)

However, in my opinion, the reason we look for the diagram is partially 
bcs of that the concepts of the related things are relatively high level 
so that it takes a while to grasp them, just like monads or maybe higher 
order functions.

However, to continue the repl example:

scheme@(guix-user)> (define (sh-symlink)
   (gexp->derivation "sh"
                     #~(symlink (string-append #$bash "/bin/bash")
                                #$output)))
scheme@(guix-user)> (build-derivations (open-connection) 
`(,(run-with-store (open-connection) (sh-symlink))))
$1 = #t

Now if you run just the (run-with-store (open-connection) (sh-symlink)) 
you will see the derivation path output, and if you then open a new 
terminal you can cat /gnu/store/shcvi6d1vgry26sq1i3qdmgsmh0n6wmi-sh.drv 
to see the build script without building it.

Now, to build a "package" after above code is loaded:
scheme@(guix-user)> ,use (guix packages)
scheme@(guix-user)> (build-derivations (open-connection) 
`(,(package-derivation (open-connection) bash)))
substitute: updating substitutes from 'https://ci.guix.gnu.org'... 
100.0%
fetching path 
`/gnu/store/vk4r0x7baig8jnmsqrgrqpyq8qxr4gm3-bash-5.0.16-doc'...
Downloading 
https://ci.guix.gnu.org/nar/lzip/vk4r0x7baig8jnmsqrgrqpyq8qxr4gm3-bash-5.0.16-doc...
bash-5.0.16-doc  290KiB              750KiB/s 00:00 [##################] 
100.0%
$2 = #t

And to only "inspect" it (so you can cat the /gnu/store/paths):
scheme@(guix-user)> (package-derivation (open-connection) bash)
$4 = #<derivation 
/gnu/store/cklj3xvrzrc930qwj1brmwr2dz4zbgd6-bash-5.0.16.drv => 
/gnu/store/vk4r0x7baig8jnmsqrgrqpyq8qxr4gm3-bash-5.0.16-doc 
/gnu/store/v1xc4405s7xilmwhhkdj8z55wa2wlr8y-bash-5.0.16-include 
/gnu/store/87kif0bpf0anwbsaw0jvg8fyciw4sz67-bash-5.0.16 7fc3d283e500>

Concepts:
   - code staging or "delayed evaluation" concepts
   - what is the store and what is a build environment
   - what is a derivation
   - and finally build systems (normal build steps) and a package (incl. 
dependency graphs).

The start reference point: 
https://guix.gnu.org/manual/en/html_node/Defining-Packages.html


I hope above helps.

Best regards,
David