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[bug#49280] [PATCH v2 1/3] gnu: racket: Update to 8.2.

From: Philip McGrath
Subject: [bug#49280] [PATCH v2 1/3] gnu: racket: Update to 8.2.
Date: Sun, 25 Jul 2021 04:22:03 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0

On 7/20/21 5:40 AM, Leo Prikler wrote:
Am Montag, den 19.07.2021, 17:46 -0400 schrieb Philip McGrath:
As you'd probably guess, `lib-search-dirs` and other `-search-dirs`
"config.rktd" entries specify search paths. The `#f` value is used
specify the point at which the default search path should be spliced
into the list: a configuration file can ignore the default altogether
exercise fine-grained control over the search order. Using `#f` also
helps to maintain something closer to a single point of control,
than hard-code the same string constants in several places.
Okay, but for this specific config, we could still splice #f ourselves
(particularly to also get full store paths), or can we not thanks to
the non-constant nature of #f?

Most importantly, the default value is not always a constant: for
example, command-line flags and Racket parameters control whether
user-specific paths are included.
How exactly would this play out?  Would for example one version of #f
contain all of the user-installed packages in ~/.guix-profile whereas
the other would only contain racket's own path?

(For `lib-search-dirs` in particular, it's also worth noting that
these are Racket-specific search directories: it does not control the
use of OS-level defaults for e.g. `dlopen`.)
Perhaps a confusing naming scheme, but okay.

The short answer is that I don't think including #f is causing any problems, whereas trying not to include it seems likely to cause a variety of problems.

I'll try to explain more clearly.

It might be more useful to look at the second patch in the series, which uses the "extend-layer.rkt" script to generate a "config.rkt" file for the `racket` package, and especially the third patch, which replaces this code completely for the `racket-minimal` package:

On 7/19/21 2:31 AM, Philip McGrath wrote:
+         (add-before 'configure 'initialize-config.rktd
             (lambda* (#:key inputs #:allow-other-keys)
-             (chdir "src")
+             (define (write-racket-hash alist)
+               ;; inside must use dotted pair notation
+               (display "#hash(")
+               (for-each (match-lambda
+                           ((k . v)
+                            (format #t "(~s . ~s)" k v)))
+                         alist)
+               (display ")\n"))
+             (mkdir-p "racket/etc")
+             (with-output-to-file "racket/etc/config.rktd"
+               (lambda ()
+                 (write-racket-hash
+                  `((lib-search-dirs
+                     . (#f ,@(map (lambda (lib)
+ (string-append (assoc-ref inputs
+                                                   "/lib"))
+                                  '("openssl"
+                                    "sqlite"))))
+                    (catalogs
+                     . (,(string-append
+                          "";
+                          ,version
+                          "/catalog/")
+                        #f))))))

This code creates a template "config.rktd" file used in the build process: the distributed source tarballs contain such a template already, which is why we didn't need explicitly configure `catalogs` to add the release-pinned package catalog until this change. It is added before the `#f` so that the release catalog is checked before the default catalogs (which point to the latest sources). For `lib-search-dirs`, on the other hand, we want Racket-specific library paths to be tried first, and indeed for layers of a Racket installation to be searched in order, so `#f` is at the head of the list.

The Racket build process extends the template "config.rktd" file based on build options like the `--prefix` passed to `configure`. For example, it configures `lib-dir` to "lib/racket" within the store output directory. (It would be incorrect to set those values in the template "config.rktd" file because it is used in the build process before installation.)

The `#f` entry in `lib-search-dirs` is usually replaced by a user-specific path like "/home/philip/.local/share/racket/8.1/lib" and the installation-wide path specified by the `lib-dir` key, unless one or both are changed. Omitting the `#f` entry means that neither of paths are ever included. I don't know of any real-life circumstance in which one would want such a "config.rktd" file. In particular, missing `#f` entries creates problems for layered installations, which use these search paths to find earlier layers.

There are some other configuration possibilities we may want to explore as Guix's support for Racket packages improves, such as "addon" tethering and customizing the "installation name" or "build stamp". However, this patch series does not attempt to change how Guix's Racket packages work, other than correcting the error I introduced in <>. Racket installed via Guix has the same behavior in this respect as Racket installed via Debian or other package managers, and that's a way of using Racket I think Guix will want to continue to support.


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