Fix: accept hyphens in generative section names

CONTRIBUTORS

@@ -94,6 +94,7 @@ Stephen Finucane
 Sviatoslav Sydorenko
 Thomas Grainger
 Tim Laurence
+Tyagraj Desigar
 Ville Skyttä
 Xander Johnson
 anatoly techtonik

docs/changelog/1636.bugfix.rst

@@ -0,0 +1 @@
+Allow hyphens and empty factors in generative section name. - by :user:`tyagdit`

src/tox/config/__init__.py

@@ -1420,7 +1420,7 @@ def expand_section_names(config):
         The parser will see it as two different sections: [testenv:py36-cov], [testenv:py37-cov]
 
         """
-        factor_re = re.compile(r"\{\s*([\w\s,]+)\s*\}")
+        factor_re = re.compile(r"\{\s*([\w\s,-]+)\s*\}")
         split_re = re.compile(r"\s*,\s*")
         to_remove = set()
         for section in list(config.sections):

tests/unit/config/test_config.py

@@ -865,10 +865,11 @@ def test_getbool(self, newconfig):
     def test_expand_section_name(self, newconfig):
         config = newconfig(
             """
-            [testenv:custom-{one,two,three}-{four,five}-six]
+            [testenv:custom{,-one,-two,-three}-{four,five}-six]
         """,
         )
         assert "testenv:custom-one-five-six" in config._cfg.sections
+        assert "testenv:custom-four-six" in config._cfg.sections
         assert "testenv:custom-{one,two,three}-{four,five}-six" not in config._cfg.sections