Lessen factor use check

Fixes issue 191

2 files changed, 21 insertions, 1 deletions

diff --git a/tests/test_config.py b/tests/test_config.py
index 1c58a4a..f2ecf8c 100644
--- a/tests/test_config.py
+++ b/tests/test_config.py
@@ -960,6 +960,18 @@ class TestConfigTestEnv:
         assert configs["py27"].setenv["X"] == "1"
         assert "X" not in configs["py26"].setenv
 
+    @pytest.mark.issue191
+    def test_factor_use_not_checked(self, newconfig):
+        inisource="""
+            [tox]
+            envlist = py27-{a,b}
+
+            [testenv]
+            deps = b: test
+        """
+        configs = newconfig([], inisource).envconfigs
+        assert set(configs.keys()) == set(['py27-a', 'py27-b'])
+
     def test_period_in_factor(self, newconfig):
         inisource="""
             [tox]
diff --git a/tox/_config.py b/tox/_config.py
index 41f02ec..e93ad26 100644
--- a/tox/_config.py
+++ b/tox/_config.py
@@ -287,10 +287,18 @@ class parseini:
 
         config.envlist, all_envs = self._getenvdata(reader, toxsection)
 
-        # configure testenvs
+        # factors used in config or predefined
         known_factors = self._list_section_factors("testenv")
         known_factors.update(default_factors)
         known_factors.add("python")
+
+        # factors stated in config envlist
+        stated_envlist = reader.getdefault(toxsection, "envlist", replace=False)
+        if stated_envlist:
+            for env in _split_env(stated_envlist):
+                known_factors.update(env.split('-'))
+
+        # configure testenvs
         for name in all_envs:
             section = testenvprefix + name
             factors = set(name.split('-'))