Make ConfigSet ABC and add contains to Loader (#2209)

The ConfigSet should be always specialized via subclassing. The contains
is a quality of life imporvement for plugins. Also bumped the tools
while at it.

Signed-off-by: Bernát Gábor <gaborjbernat@gmail.com>

6 files changed, 37 insertions, 7 deletions

diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 72dc1bfd..d6dd3e68 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -12,7 +12,7 @@ repos:
       - id: end-of-file-fixer
       - id: trailing-whitespace
   - repo: https://github.com/asottile/pyupgrade
-    rev: v2.23.3
+    rev: v2.25.0
     hooks:
       - id: pyupgrade
         args: ["--py36-plus"]
@@ -24,7 +24,7 @@ repos:
     hooks:
       - id: isort
   - repo: https://github.com/psf/black
-    rev: 21.7b0
+    rev: 21.8b0
     hooks:
       - id: black
         args:
@@ -44,11 +44,11 @@ repos:
       - id: tox-ini-fmt
         args: [ "-p", "fix" ]
   - repo: https://github.com/asottile/blacken-docs
-    rev: v1.10.0
+    rev: v1.11.0
     hooks:
       - id: blacken-docs
         additional_dependencies:
-          - black==21.7b0
+          - black==21.8b0
   - repo: https://github.com/pre-commit/pygrep-hooks
     rev: v1.9.0
     hooks:
@@ -67,7 +67,7 @@ repos:
       - id: flake8
         additional_dependencies:
         - flake8-bugbear==21.4.3
-        - flake8-comprehensions==3.5
+        - flake8-comprehensions==3.6.1
         - flake8-pytest-style==1.5
         - flake8-spellcheck==0.24
         - flake8-unused-arguments==0.0.6
diff --git a/docs/changelog/2209.bugfix.rst b/docs/changelog/2209.bugfix.rst
new file mode 100644
index 00000000..ec4e97c8
--- /dev/null
+++ b/docs/changelog/2209.bugfix.rst
@@ -0,0 +1,2 @@
+Do not allow constructing ``ConfigSet`` directly and implement ``__contains__`` for ``Loader`` -- by
+:user:`gaborbernat`.
diff --git a/src/tox/config/loader/api.py b/src/tox/config/loader/api.py
index f436a1ff..1f664eb5 100644
--- a/src/tox/config/loader/api.py
+++ b/src/tox/config/loader/api.py
@@ -77,6 +77,9 @@ class Loader(Convert[T]):
     def __repr__(self) -> str:
         return f"{type(self).__name__}"
 
+    def __contains__(self, item: str) -> bool:
+        return item in self.found_keys()
+
     def load(
         self,
         key: str,
@@ -91,8 +94,10 @@ class Loader(Convert[T]):
 
         :param key: the key under it lives
         :param of_type: the type to convert to
+        :param kwargs: keyword arguments to forward
         :param conf: the configuration object of this tox session (needed to manifest the value)
         :param env_name: env name
+        :param chain: a chain of lookups
         :return: the converted type
         """
         if key in self.overrides:
diff --git a/src/tox/config/sets.py b/src/tox/config/sets.py
index dc8c3eea..c11f7d82 100644
--- a/src/tox/config/sets.py
+++ b/src/tox/config/sets.py
@@ -1,3 +1,4 @@
+from abc import ABC, abstractmethod
 from pathlib import Path
 from typing import (
     TYPE_CHECKING,
@@ -27,7 +28,7 @@ if TYPE_CHECKING:
 V = TypeVar("V")
 
 
-class ConfigSet:
+class ConfigSet(ABC):
     """A set of configuration that belong together (such as a tox environment settings, core tox settings)"""
 
     def __init__(self, conf: "Config"):
@@ -118,8 +119,9 @@ class ConfigSet:
         return config_definition.__call__(self._conf, self.loaders, self.name, chain)
 
     @property
+    @abstractmethod
     def name(self) -> Optional[str]:
-        return None
+        raise NotImplementedError
 
     def __repr__(self) -> str:
         return f"{self.__class__.__name__}(loaders={self.loaders!r})"
@@ -197,6 +199,10 @@ class CoreConfigSet(ConfigSet):
     def _on_duplicate_conf(self, key: str, definition: ConfigDefinition[V]) -> None:  # noqa: U100
         pass  # core definitions may be defined multiple times as long as all their options match, first defined wins
 
+    @property
+    def name(self) -> Optional[str]:
+        return None
+
 
 class EnvConfigSet(ConfigSet):
     """Configuration set for a tox environment"""
diff --git a/tests/config/loader/test_memory_loader.py b/tests/config/loader/test_memory_loader.py
index 814148cc..6b35e300 100644
--- a/tests/config/loader/test_memory_loader.py
+++ b/tests/config/loader/test_memory_loader.py
@@ -45,3 +45,9 @@ def test_memory_loader(value: Any, of_type: Type[Any]) -> None:
 def test_memory_found_keys() -> None:
     loader = MemoryLoader(a=1, c=2)
     assert loader.found_keys() == {"a", "c"}
+
+
+def test_memory_loader_contains() -> None:
+    loader = MemoryLoader(a=1)
+    assert "a" in loader
+    assert "b" not in loader
diff --git a/tests/config/test_sets.py b/tests/config/test_sets.py
index 9c03c71d..1f61486b 100644
--- a/tests/config/test_sets.py
+++ b/tests/config/test_sets.py
@@ -3,6 +3,7 @@ from pathlib import Path
 from typing import Callable, Dict, Optional, Set, TypeVar
 
 import pytest
+from pytest_mock import MockerFixture
 
 from tests.conftest import ToxIniCreator
 from tox.config.cli.parser import Parsed
@@ -134,6 +135,7 @@ def test_config_dynamic_not_equal(conf_builder: ConfBuilder) -> None:
 
 def test_define_custom_set(tox_project: ToxProjectCreator) -> None:
     class MagicConfigSet(ConfigSet):
+
         SECTION = "magic"
 
         def __init__(self, conf: Config):
@@ -141,6 +143,10 @@ def test_define_custom_set(tox_project: ToxProjectCreator) -> None:
             self.add_config("a", of_type=int, default=0, desc="number")
             self.add_config("b", of_type=str, default="", desc="string")
 
+        @property
+        def name(self) -> Optional[str]:
+            return self.SECTION
+
     project = tox_project({"tox.ini": "[testenv]\npackage=skip\n[magic]\na = 1\nb = ok"})
     result = project.run()
 
@@ -150,3 +156,8 @@ def test_define_custom_set(tox_project: ToxProjectCreator) -> None:
     assert repr(conf) == "MagicConfigSet(loaders=[IniLoader(section=<Section: magic>, overrides={})])"
 
     assert isinstance(result.state.conf.options, Parsed)
+
+
+def test_do_not_allow_create_config_set(mocker: MockerFixture) -> None:
+    with pytest.raises(TypeError, match="Can't instantiate"):
+        ConfigSet(mocker.create_autospec(Config))  # type: ignore # the type checker also warns that ABC