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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<div class='path'>path: <a href='/guix/log/?id=7427ff48be0db84a5dfb2283668f08cfdeb5cd4e'>root</a>/<a href='/guix/log/tests?id=7427ff48be0db84a5dfb2283668f08cfdeb5cd4e'>tests</a>/<a href='/guix/log/tests/channels.scm?id=7427ff48be0db84a5dfb2283668f08cfdeb5cd4e'>channels.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/tests/channels.scm?id=7427ff48be0db84a5dfb2283668f08cfdeb5cd4e&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2024-01-31 09:07:25 +0100'>2024-01-31</span></td><td><a href='/guix/commit/tests/channels.scm?id=323b58ac18af8417d5b206288d09d9bb9385d7ae'>channels: ‘latest-channel-instances’ traverses user-provided channels first.</a><span class='msg-avail'>...<span class='msg-tooltip'>Previously, ‘latest-channel-instances’ would perform a depth-first
traversal of channels.  Since dependencies specified in ‘.guix-channel’
are usually less specific that those provided by the user, this would
lead to the use of instances corresponding to those less specific specs,
which in turn might declare dependencies that do not exist for the more
specific instances.

This commit changes ‘latest-channel-instances’ to perform a
breadth-first traversal, thereby giving user-supplied channels higher
precedence over dependencies found via ‘.guix-channel’.

Fixes &lt;https://issues.guix.gnu.org/68822&gt;.

* guix/channels.scm (latest-channel-instances)[ignore?]: Remove.
[instance-name, same-named?, more-specific?]: New procedures.
Rewrite as a breadth-first traversal using a regular loop.
* tests/channels.scm ("latest-channel-instances reads dependencies from most-specific instance"):
New test.

Change-Id: Iba518145cfd209f04293a56246dbfee3b714650b
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2024-01-31 09:07:25 +0100'>2024-01-31</span></td><td><a href='/guix/commit/tests/channels.scm?id=36d654fa540539413b88cf8ec62a0fb55280f820'>channels: Tweak test.</a><span class='msg-avail'>...<span class='msg-tooltip'>* tests/channels.scm ("latest-channel-instances excludes duplicate channel dependencies"):
Use ‘equal?’ rather than ‘string=?’ since we can get #f.

Change-Id: I437b9d7e23200cf0c98b1593e68b1d355bc2de01
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2023-09-26 17:36:59 +0200'>2023-09-26</span></td><td><a href='/guix/commit/tests/channels.scm?id=ba21eeb565fe414b3647173068a0f3eadd174c06'>tests: Assume ‘git’ is always available.</a><span class='msg-avail'>...<span class='msg-tooltip'>* tests/channels.scm (gpg+git-available?): Check for ‘gpg-command’
only.
Remove all ‘test-skip’ statements.
* tests/derivations.scm: Likewise.
* tests/git-authenticate.scm: Likewise.
* tests/git.scm: Likewise.
* tests/import-git.scm: Likewise.
</span></span></td><td>Ludovic Courtès</td></tr>