Unescaped comma in substitution should not be replaced during INI exp…

…ansion (#2626)

Resolves #2616

docs/changelog/2616.bugfix.rst

@@ -0,0 +1 @@
+Unescaped comma in substitution should not be replaced during INI expansion - by :user:`gaborbernat`.

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

@@ -54,14 +54,14 @@ def replace(conf: Config, loader: IniLoader, value: str, args: ConfigLoadArgs) -
 
 REPLACE_PART = re.compile(
     r"""
-        (?<! \\) {  # Unescaped {
-            ( [^{}] | \\ { | \\ } )*  # Anything except an unescaped { or }
+        (?<!\\) {  # Unescaped {
+            ( [^{},] | \\ { | \\ } )*  # Anything except an unescaped { or }
         (?<! \\) }  # Unescaped }
     |
         (?<! \\) \[ ]  # Unescaped []
     """,
     re.VERBOSE,
-)  # simplified - not verbose version (?<!\\)([^{}]|\\\{|\\\})*(?<!\\)\}|(?<!\\)\[\]
+)
 
 
 def find_replace_part(value: str, end: int) -> tuple[int, int, str | None]:
@@ -70,7 +70,8 @@ def find_replace_part(value: str, end: int) -> tuple[int, int, str | None]:
         return -1, -1, None
     if match.group() == "[]":
         return match.start(), match.end() - 1, "posargs"  # brackets is an alias for positional arguments
-    return match.start(), match.end() - 1, match.group()[1:-1]
+    matched_part = match.group()[1:-1]
+    return match.start(), match.end() - 1, matched_part
 
 
 def _replace_match(conf: Config, loader: IniLoader, value: str, conf_args: ConfigLoadArgs) -> str | None:

tests/config/loader/ini/test_factor.py

@@ -136,6 +136,11 @@ def test_factor_config(tox_ini_conf: ToxIniCreator) -> None:
             assert "Django>=1.6,<1.7" in deps
 
 
+def test_factor_config_do_not_replace_unescaped_comma(tox_ini_conf: ToxIniCreator) -> None:
+    config = tox_ini_conf("[tox]\nenv_list = py37-{base,i18n},b")
+    assert list(config) == ["py37-base", "py37-i18n", "b"]
+
+
 def test_factor_config_no_env_list_creates_env(tox_ini_conf: ToxIniCreator) -> None:
     """If we have a factor that is not specified within the core env-list then that's also an environment"""
     config = tox_ini_conf(