Fix multiple substitution on factor filtering (#2680)

Resolves #2650

docs/changelog/2650.bugfix.rst

@@ -0,0 +1,2 @@
+Fix multiple substitution on factor filtering in ``tox.ini`` when multiple factor filters match
+- by :user:`gaborbernat`.

src/tox/config/loader/ini/factor.py

@@ -21,6 +21,7 @@ def filter_for_env(value: str, name: str | None) -> str:
             for group in factors:
                 if all((a_name in current) ^ negate for a_name, negate in group):
                     overall.append(content)
+                    break  # if any match we use it, and then bail
     result = "\n".join(overall)
     return result
 

tests/config/loader/ini/test_factor.py

@@ -203,3 +203,11 @@ def test_generative_section_name(tox_ini_conf: ToxIniCreator) -> None:
     env_config.add_config(keys="deps-x", of_type=List[str], default=[], desc="deps")
     deps = env_config["deps-x"]
     assert deps == ["flake8"]
+
+
+def test_multiple_factor_match(tox_ini_conf: ToxIniCreator) -> None:
+    config = tox_ini_conf("[testenv]\nconf = a{,-b}: x")
+    env_config = config.get_env("a-b")
+    env_config.add_config(keys="conf", of_type=str, default="", desc="conf")
+    deps = env_config["conf"]
+    assert deps == "x"