[PATCH STABLE] procutil: extend gui test to detect wayland session (issue6479)

[Yuya Nishihara]

# HG changeset patch
# User Yuya Nishihara <yuya at tcha.org>
# Date 1612436205 -32400
#      Thu Feb 04 19:56:45 2021 +0900
# Branch stable
# Node ID 6cc6b8610cec85dc624f4bb6568c2fd16ac018d1
# Parent  14feaa5792ed116ec8cc8469fc3de976fb4dd8f5
procutil: extend gui test to detect wayland session (issue6479)

diff --git a/mercurial/utils/procutil.py b/mercurial/utils/procutil.py
--- a/mercurial/utils/procutil.py
+++ b/mercurial/utils/procutil.py
@@ -546,7 +546,11 @@ def _gui():
             # pure build; use a safe default
             return True
     else:
-        return pycompat.iswindows or encoding.environ.get(b"DISPLAY")
+        return (
+            pycompat.iswindows
+            or encoding.environ.get(b"DISPLAY")
+            or encoding.environ.get(b"WAYLAND_DISPLAY")
+        )
 
 
 def gui():