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:]:
tabs'><tr><td>
<a href='/guix/about/'>about</a><a href='/guix/'>summary</a><a href='/guix/refs/?id=6b83d6060b2fc2ec78a485ae6d75432e31bb00fe'>refs</a><a class='active' href='/guix/log/tests/cran.scm'>log</a><a href='/guix/tree/tests/cran.scm?id=6b83d6060b2fc2ec78a485ae6d75432e31bb00fe'>tree</a><a href='/guix/commit/tests/cran.scm?id=6b83d6060b2fc2ec78a485ae6d75432e31bb00fe'>commit</a><a href='/guix/diff/tests/cran.scm?id=6b83d6060b2fc2ec78a485ae6d75432e31bb00fe'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/tests/cran.scm'>
<input type='hidden' name='id' value='6b83d6060b2fc2ec78a485ae6d75432e31bb00fe'/><select name='qt'>
<option value='grep'>log msg</option>
<option value='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=6b83d6060b2fc2ec78a485ae6d75432e31bb00fe'>root</a>/<a href='/guix/log/tests?id=6b83d6060b2fc2ec78a485ae6d75432e31bb00fe'>tests</a>/<a href='/guix/log/tests/cran.scm?id=6b83d6060b2fc2ec78a485ae6d75432e31bb00fe'>cran.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/cran.scm?id=6b83d6060b2fc2ec78a485ae6d75432e31bb00fe&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2021-12-18 04:09:47 +0100'>2021-12-18</span></td><td><a href='/guix/commit/tests/cran.scm?id=10ceb3e84654e024f14a4b048e7d68492ed9dc7c'>import: cran: Fix description-&gt;package test.</a><span class='msg-avail'>...<span class='msg-tooltip'>This follows up on commit 5cd1019488c44081aaf030fbe8bc357d78daef23.

* tests/cran.scm (description): Include a very long line.
(description-&gt;package): Update the golden description to match the
paragraph filling now performed by BEAUTIFY-DESCRIPTION.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2021-07-11 00:49:16 +0200'>2021-07-11</span></td><td><a href='/guix/commit/tests/cran.scm?id=aa6921634b4ea9988af0e37bfbb56780c431ef64'>import: cran: Emit new-style package inputs.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/import/cran.scm (format-inputs): Emit symbols or
'specification-&gt;package' calls.
(maybe-inputs): Wrap in 'list' instead of 'quasiquote'.
* tests/cran.scm ("description-&gt;package"): Adjust accordingly.
</span></span></td><td>Ludovic Courtès</td></tr>