Make GnuPG automatically find a pinentry installed by Guix. Try using
$HOME or, if that variable is not set, use the system password database,
or fall back to looking in "/".

More information:

https://bugs.gnu.org/24076

diff --git a/common/homedir.c b/common/homedir.c
index 4b6e46e88..f7ae68ba5 100644
--- a/common/homedir.c
+++ b/common/homedir.c
@@ -33,6 +33,7 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <unistd.h>
+#include <pwd.h>
 
 #ifdef HAVE_W32_SYSTEM
 #include <winsock2.h>   /* Due to the stupid mingw64 requirement to
@@ -67,6 +68,10 @@
  * gnupg_homedir and gnupg_set_homedir.  Malloced.  */
 static char *the_gnupg_homedir;
 
+/* The user's home directory. Used in Guix to help GnuPG find the
+ * pinentry. */
+static char *the_user_homedir;
+
 /* Flag indicating that home directory is not the default one.  */
 static byte non_default_homedir;
 
@@ -509,6 +514,25 @@ gnupg_homedir (void)
   return the_gnupg_homedir;
 }
 
+/* Return the user's home directory */
+const char *
+user_homedir (void)
+{
+  const char *dir;
+  dir = getenv("HOME");
+  if (dir == NULL)
+    {
+       struct passwd *pw = NULL;
+       pw = getpwuid (getuid ());
+       if (pw != NULL)
+         dir = pw->pw_dir;
+       else
+         dir = "/";
+    }
+  if (!the_user_homedir)
+    the_user_homedir = make_absfilename (dir, NULL);
+  return the_user_homedir;
+}
 
 /* Return whether the home dir is the default one.  */
 int
@@ -971,6 +995,7 @@ get_default_pinentry_name (int reset)
   } names[] = {
     /* The first entry is what we return in case we found no
        other pinentry.  */
+    { user_homedir, "/.guix-profile/bin/pinentry" },
     { gnupg_bindir, DIRSEP_S "pinentry" EXEEXT_S },
 #ifdef HAVE_W32_SYSTEM
     /* Try Gpg4win directory (with bin and without.) */
ue='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=f72887f6f92b948dd84846770ab76ae2cee8eda4'>root</a>/<a href='/guix/log/gnu?id=f72887f6f92b948dd84846770ab76ae2cee8eda4'>gnu</a>/<a href='/guix/log/gnu/installer?id=f72887f6f92b948dd84846770ab76ae2cee8eda4'>installer</a>/<a href='/guix/log/gnu/installer/services.scm?id=f72887f6f92b948dd84846770ab76ae2cee8eda4'>services.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/installer/services.scm?id=f72887f6f92b948dd84846770ab76ae2cee8eda4&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2023-07-06 15:38:58 +0200'>2023-07-06</span></td><td><a href='/guix/commit/gnu/installer/services.scm?id=961ffca1c75141cbb351d143b22b673638e9659d'>installer: Restore LatGrkCyr-8x16 console font depending on language.</a><span class='msg-avail'>...<span class='msg-tooltip'>Partially-Fixes: &lt;https://issues.guix.gnu.org/64006&gt;

* gnu/installer/services.scm (system-services-&gt;configuration): When the
LANGUAGE environment variable matches a known native console font, wrap the
base services with modify-services, configuring console-font-service-type to
set the native console font on every tty instead of the default console font.

Signed-off-by: Florian Pelz &lt;pelzflorian@pelzflorian.de&gt;
</span></span></td><td>Denys Nykula</td></tr>
<tr><td><span title='2022-11-20 23:20:31 +0100'>2022-11-20</span></td><td><a href='/guix/commit/gnu/installer/services.scm?id=8c7ea71344b91c2c36dfbf6f2bc6daf559b1c696'>installer: Add comment above the 'packages' field.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/installer/services.scm (system-services-&gt;configuration): Add
heading above the 'packages' field.  Rename 'heading' to
'service-heading'.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-08-08 11:54:25 +0200'>2022-08-08</span></td><td><a href='/guix/commit/gnu/installer/services.scm?id=ff9522fb69b9f4a31a5b766029e26dc53a2d1cf8'>installer: Add comments and vertical space to the generated config.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/installer/parted.scm (user-partitions-&gt;configuration): Introduce
vertical space and a comment.
* gnu/installer/services.scm (G_): New macro.
(%system-services): Add comment for OpenSSH.
(system-services-&gt;configuration): Add vertical space and comments.
* gnu/installer/user.scm (users-&gt;configuration): Add comment.
* gnu/installer/steps.scm (format-configuration): Add comment.
(configuration-&gt;file): Expound leading comment.  Pass #:format-comment
to 'pretty-print-with-comments/splice'.
</span></span></td><td>Ludovic Courtès</td></tr>