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.

1 files changed, 13 insertions, 0 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index 5a8ad7ebda..458fca20af 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -3921,6 +3921,19 @@ 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 Sub-directory
+
+As a channel author, you may want to keep your channel modules in a
+sub-directory.  If your modules are in the sub-directory @file{guix}, you must
+add a meta-data file @file{.guix-channel} that contains:
+
+@lisp
+(channel
+  (version 0)
+  (directory "guix"))
+@end lisp
+
 @subsection Replicating Guix
 
 @cindex pinning, channels