This is needed to make Mercurial read the HGEXTENSIONPATH to detect
third-party extensions.  It is called HGEXTENSIONPATH and not
HG_EXTENSION_PATH to keep it consistent with other environment variables for
Mercurial, e.g. HGENCODINGAMBIGUOUS, HGEDITOR ...  Hopefully I or someone else
will get this into Mercurial proper.

diff --git a/mercurial/extensions.py b/mercurial/extensions.py
--- a/mercurial/extensions.py
+++ b/mercurial/extensions.py
@@ -13,6 +13,7 @@
 import imp
 import inspect
 import os
+import sys
 
 from .i18n import (
     _,
@@ -108,6 +109,11 @@
 
 def _importh(name):
     """import and return the <name> module"""
+    # Read HGEXTENSIONSPATH environment variable when import extensions.
+    extension_path = os.getenv("HGEXTENSIONSPATH")
+    if extension_path is not None:
+        for path in extension_path:
+            sys.path.append(path)
     mod = __import__(pycompat.sysstr(name))
     components = name.split(b'.')
     for comp in components[1:]:
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<tr><td><span title='2023-08-29 11:42:16 +0200'>2023-08-29</span></td><td><a href='/guix/commit/gnu/home/services/syncthing.scm?id=cf6abf50dbbbd95fef465ab4bb3b608843ac47e1'>home: services: dicod, syncthing: Import (gnu home services shepherd).</a><span class='msg-avail'>...<span class='msg-tooltip'>Fixes &lt;https://issues.guix.gnu.org/65510&gt;.

Without this import, 'shepherd-service-type' is not mapped, leading to
an error about missing 'system' target.

* gnu/home/services/dict.scm,
gnu/home/services/syncthing.scm: Add #:use-module clause.

Reported-by: Morgan Smith &lt;Morgan.J.Smith@outlook.com&gt;
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2023-08-20 22:48:48 +0200'>2023-08-20</span></td><td><a href='/guix/commit/gnu/home/services/syncthing.scm?id=7605c01fccb20b387f5a0d98d6b81074b3039e23'>home: services: Add Syncthing.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/home/services/syncthing.scm: New file.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add it.
* gnu/services/syncthing.scm (&lt;syncthing-configuration&gt;)[home-service?]:
New field.
Adjust 'provision' and 'requirement' depending on 'home-service?', and
likewise for #:user and #:group.
Use 'filter' + 'negate' instead of 'remove'.
* doc/guix.texi (Networking Services): Add note and cross-reference to
"Networking Home Services".
(Networking Home Services): New node.
</span></span></td><td>Ludovic Courtès</td></tr>