Subject: Re: [bug#36563] [PATCH] guix: Add directory to channel.

From: Jan Nieuwenhuizen <[email-masked]>
Date: Sat, 13 Jul 2019 17:37:07 +0200

Ludovic Courtès writes:

Hi!

> That makes a lot of sense to me.
>
> I think that, instead of letting the user specify the right directory in
> ~/.config/guix/channels.scm, it should be the channel author that
> specifies the sub-directory.
>
> There’s already support for a ‘.guix-channel’ file so this is where this
> ‘directory’ thing could be added (actually there’s a FIXME in
> channels.scm about this particular use case :-)).
>
> WDYT?

Yes, I agree that this should be the first option to support.  Attached
is a second attempt: I removed the FIXME and moved `directory' to
channel-metadata.

A downside could be that this could make a channel user dependent on
upstream to provide this `.guix-channel' file; probably best to worry
about that when the need arises :)

Greetings,
janneke

>From 5d78a7eab391ea93c044d85736706b333c2dfee8 Mon Sep 17 00:00:00 2001
From: Jan Nieuwenhuizen <[email-masked]>
Date: Sat, 13 Jul 2019 16:31:50 +0200
Subject: [PATCH] channels: Add optional directory to channel metadata.

* guix/channels.scm (<channel-metadata>): Add directory slot.  Update users.
(read-channel-metadata-from-source): New function.
(standard-module-derivation): Use it.
* doc/guix.texi (Package Modules in a Subdirectory): New subsection.
---
 doc/guix.texi     | 23 ++++++++++++
 guix/channels.scm | 93 ++++++++++++++++++++++++++---------------------
 2 files changed, 75 insertions(+), 41 deletions(-)

diff --git a/doc/guix.texi b/doc/guix.texi
index 5a8ad7ebda..8bc00a5350 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -3921,6 +3921,29 @@ For the sake of reliability and maintainability, you should avoid dependencies
 on channels that you don't control, and you should aim to keep the number of
 dependencies to a minimum.
 
+@cindex subdirectory, channels
+@subsection Package Modules in a Subdirectory
+
+A developer may include a @file{guix} subdirectory in their upstream source
+that contains additional or modified Guix package descriptions.  Typically,
+their toplevel @file{guix.scm} then uses those package definitions:
+
+@lisp
+(define %source-dir (dirname (current-filename)))
+(add-to-load-path (string-append %source-dir "/guix"))
+(use-modules @dots{})
+@dots{}
+@end lisp
+
+By adding a meta-data file @file{.guix-channel} that specifies the
+subdirectory that contains the Guix package descriptions it can be used
+directly as a channel:
+
+@lisp
+(channel
+ (directory "guix"))
+@end lisp
+
 @subsection Replicating Guix
 
 @cindex pinning, channels
diff --git a/guix/channels.scm b/guix/channels.scm
index e6bb9b891b..614639f091 100644
--- a/guix/channels.scm
+++ b/guix/channels.scm
@@ -1,6 +1,7 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2018, 2019 Ludovic Courtès <[email-masked]>
 ;;; Copyright © 2018 Ricardo Wurmus <[email-masked]>
+;;; Copyright © 2019 Jan (janneke) Nieuwenhuizen <[email-masked]>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -107,9 +108,10 @@
   (checkout  channel-instance-checkout))
 
 (define-record-type <channel-metadata>
-  (channel-metadata version dependencies)
+  (channel-metadata version directory dependencies)
   channel-metadata?
   (version       channel-metadata-version)
+  (directory     channel-metadata-directory)
   (dependencies  channel-metadata-dependencies))
 
 (define (channel-reference channel)
@@ -119,18 +121,18 @@
     (#f      `(branch . ,(channel-branch channel)))
     (commit  `(commit . ,(channel-commit channel)))))
 
-(define (read-channel-metadata instance)
-  "Return a channel-metadata record read from the channel INSTANCE's
-description file, or return #F if the channel instance does not include the
-file."
-  (let* ((source (channel-instance-checkout instance))
-         (meta-file (string-append source "/.guix-channel")))
+(define (read-channel-metadata-from-source source)
+  "Return a channel-metadata record read from channel's SOURCE/.guix-channel
+description file, or return #F if SOURCE/.guix-channel does not exist."
+  (let ((meta-file (string-append source "/.guix-channel")))
     (and (file-exists? meta-file)
-         (and-let* ((raw (call-with-input-file meta-file read))
-                    (version (and=> (assoc-ref raw 'version) first))
-                    (dependencies (or (assoc-ref raw 'dependencies) '())))
+         (let* ((raw (call-with-input-file meta-file read))
+                (version (and=> (assoc-ref raw 'version) first))
+                (directory (and=> (assoc-ref raw 'directory) first))
+                (dependencies (or (assoc-ref raw 'dependencies) '())))
            (channel-metadata
             version
+            directory
             (map (lambda (item)
                    (let ((get (lambda* (key #:optional default)
                                 (or (and=> (assoc-ref item key) first) default))))
@@ -144,12 +146,18 @@ file."
                         (commit (get 'commit))))))
                  dependencies))))))
 
+(define (read-channel-metadata instance)
+  "Return a channel-metadata record read from the channel INSTANCE's
+description file, or return #F if the channel instance does not include the
+file."
+  (read-channel-metadata-from-source (channel-instance-checkout instance)))
+
 (define (channel-instance-dependencies instance)
   "Return the list of channels that are declared as dependencies for the given
 channel INSTANCE."
   (match (read-channel-metadata instance)
     (#f '())
-    (($ <channel-metadata> version dependencies)
+    (($ <channel-metadata> version directory dependencies)
      dependencies)))
 
 (define* (latest-channel-instances store channels #:optional (previous-channels '()))
@@ -230,36 +238,39 @@ of COMMIT at URL.  Use NAME as the channel name."
 modules in SOURCE and that depend on DEPENDENCIES, a list of lowerable
 objects.  The assumption is that SOURCE contains package modules to be added
 to '%package-module-path'."
-  ;; FIXME: We should load, say SOURCE/.guix-channel.scm, which would allow
-  ;; channel publishers to specify things such as the sub-directory where .scm
-  ;; files live, files to exclude from the channel, preferred substitute URLs,
-  ;; etc.
-
-  (define build
-    ;; This is code that we'll run in CORE, a Guix instance, with its own
-    ;; modules and so on.  That way, we make sure these modules are built for
-    ;; the right Guile version, with the right dependencies, and that they get
-    ;; to see the right (gnu packages …) modules.
-    (with-extensions dependencies
-      #~(begin
-          (use-modules (guix build compile)
-                       (guix build utils)
-                       (srfi srfi-26))
-
-          (define go
-            (string-append #$output "/lib/guile/" (effective-version)
-                           "/site-ccache"))
-          (define scm
-            (string-append #$output "/share/guile/site/"
-                           (effective-version)))
-
-          (compile-files #$source go
-                         (find-files #$source "\\.scm$"))
-          (mkdir-p (dirname scm))
-          (symlink #$source scm)
-          scm)))
-
-  (gexp->derivation-in-inferior name build core))
+
+  (let* ((metadata (read-channel-metadata-from-source source))
+         (directory (and=> metadata channel-metadata-directory)))
+
+    (define build
+      ;; This is code that we'll run in CORE, a Guix instance, with its own
+      ;; modules and so on.  That way, we make sure these modules are built for
+      ;; the right Guile version, with the right dependencies, and that they get
+      ;; to see the right (gnu packages …) modules.
+      (with-extensions dependencies
+        #~(begin
+            (use-modules (guix build compile)
+                         (guix build utils)
+                         (srfi srfi-26))
+
+            (define go
+              (string-append #$output "/lib/guile/" (effective-version)
+                             "/site-ccache"))
+            (define scm
+              (string-append #$output "/share/guile/site/"
+                             (effective-version)))
+
+            (let* ((subdir (if #$directory
+                               (string-append "/" #$directory)
+                               ""))
+                   (dir (string-append #$source subdir)))
+              (compile-files dir go (find-files dir "\\.scm$"))
+              (mkdir-p (dirname scm))
+              (symlink (string-append #$source subdir) scm))
+
+            scm)))
+
+    (gexp->derivation-in-inferior name build core)))
 
 (define* (build-from-source name source
                             #:key core verbose? commit
-- 
2.21.0

-- 
Jan Nieuwenhuizen <[email-masked]> | GNU LilyPond http://lilypond.org
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