commit 61ef41ebf1ad9ee825c5d793288bf8cb65a462f2
Author: zhoulinhui <df.some@foxmail.com>
Date:   Tue Oct 6 21:09:33 2020 +0800

    Dep's should be restricted by upper-constraints
    
    Tox trying to install latest versions for building docs which may
    not be supported by stable and lower branches, so should be
    restricted by respective version's upper-constraints.txt
    
    Change-Id: I89104a009ad9434e49c77afd32080b79412c467d

diff --git a/tox.ini b/tox.ini
index af793d7..5454e8f 100644
--- a/tox.ini
+++ b/tox.ini
@@ -47,7 +47,9 @@ commands =
     coverage report
 
 [testenv:docs]
-deps = -r{toxinidir}/doc/requirements.txt
+deps =
+    -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+    -r{toxinidir}/doc/requirements.txt
 commands = sphinx-build -a -E -W -d doc/build/doctrees -b html doc/source doc/build/html
 
 [flake8]