fix config: add deprecation warning for non-string value in string-typed ini option

changelog/14808.deprecation.rst

@@ -0,0 +1 @@
+Passing a non-string value to a ``string``-typed ini option now emits a ``pytest.PytestRemovedIn10Warning``. This affects ``[tool.pytest.ini_options]`` in ``pyproject.toml``, where TOML arrays are kept as lists by ``make_scalar`` instead of being converted to strings. In pytest 10 this will raise a ``TypeError``, matching the behavior of the corresponding TOML config path.

src/_pytest/config/__init__.py

@@ -1878,6 +1878,11 @@ def _getini_ini(
         elif type == "bool":
             return _strtobool(str(value).strip())
         elif type == "string":
+            if not isinstance(value, str):
+                warnings.warn(
+                    _pytest.deprecated.INI_STRING_TYPE_NON_STR_VALUE,
+                    stacklevel=2,
+                )
             return value
         elif type == "int":
             if not isinstance(value, str):

src/_pytest/deprecated.py

@@ -96,6 +96,14 @@
     "See https://docs.pytest.org/en/stable/deprecations.html#the-pastebin-option"
 )
 
+INI_STRING_TYPE_NON_STR_VALUE = PytestRemovedIn10Warning(
+    "Passing a value that is not a string to a 'string'-typed ini option is deprecated.\n"
+    "In a future version this will raise a TypeError, matching the behavior of the "
+    "corresponding TOML config path.\n"
+    "If your plugin intentionally accepts non-string values, declare an explicit type "
+    '(e.g. type="args") instead of relying on the implicit string default.'
+)
+
 # You want to make some `__init__` or function "private".
 #
 #   def my_private_function(some, args):

testing/test_config.py

@@ -1089,6 +1089,30 @@ def pytest_addoption(parser):
         ):
             _ = config.getini("ini_param")
 
+    def test_addini_string_non_str_deprecated(self, pytester: Pytester) -> None:
+        """Passing a non-string value to a 'string'-typed ini option emits a
+        deprecation warning. The value is still returned as-is for now, but will
+        raise TypeError in pytest 10."""
+        pytester.makeconftest(
+            """
+            def pytest_addoption(parser):
+                parser.addini("myname", "", type="string")
+        """
+        )
+        pytester.makepyprojecttoml(
+            """
+            [tool.pytest.ini_options]
+            myname = ["value1", "value2"]
+            """
+        )
+        config = pytester.parseconfig()
+        with pytest.warns(
+            pytest.PytestRemovedIn10Warning,
+            match="Passing a value that is not a string to a 'string'-typed ini option",
+        ):
+            result = config.getini("myname")
+        assert result == ["value1", "value2"]
+
     UNION_CONFTEST = """
         def pytest_addoption(parser):
             parser.addini("ini_param", "", type=int | str, default=None)