Do not show inherited keys as unused (#1913)

Signed-off-by: Bernát Gábor <bgabor8@bloomberg.net>

6 files changed, 14 insertions, 9 deletions

diff --git a/docs/changelog/1833.bugfix.rst b/docs/changelog/1833.bugfix.rst
new file mode 100644
index 00000000..c04bfc3c
--- /dev/null
+++ b/docs/changelog/1833.bugfix.rst
@@ -0,0 +1,2 @@
+Show config no longer marks as unused keys that are inherited (e.g. if the key is coming from ``testenv`` section and our
+target is ``testenv:fix``) - by :user:`gaborbernat`.
diff --git a/src/tox/config/loader/api.py b/src/tox/config/loader/api.py
index 4c9fb405..d031ce63 100644
--- a/src/tox/config/loader/api.py
+++ b/src/tox/config/loader/api.py
@@ -51,6 +51,7 @@ class Loader(Convert[T]):
 
     def __init__(self, overrides: List[Override]) -> None:
         self.overrides = {o.key: o for o in overrides}
+        self.parent: Optional["Loader[Any]"] = None
 
     @abstractmethod
     def load_raw(self, key: str, conf: Optional["Config"], env_name: Optional[str]) -> T:  # noqa: U100
diff --git a/src/tox/config/loader/ini/__init__.py b/src/tox/config/loader/ini/__init__.py
index a8867c02..55361dfa 100644
--- a/src/tox/config/loader/ini/__init__.py
+++ b/src/tox/config/loader/ini/__init__.py
@@ -19,12 +19,7 @@ V = TypeVar("V")
 class IniLoader(StrConvert, Loader[str]):
     """Load configuration from an ini section (ini file is a string to string dictionary)"""
 
-    def __init__(
-        self,
-        section: str,
-        parser: ConfigParser,
-        overrides: List[Override],
-    ) -> None:
+    def __init__(self, section: str, parser: ConfigParser, overrides: List[Override]) -> None:
         self._section: SectionProxy = parser[section]
         self._parser = parser
         super().__init__(overrides)
diff --git a/src/tox/config/sets.py b/src/tox/config/sets.py
index 79ef8271..c5d13937 100644
--- a/src/tox/config/sets.py
+++ b/src/tox/config/sets.py
@@ -109,8 +109,11 @@ class ConfigSet:
     def unused(self) -> List[str]:
         """Return a list of keys present in the config source but not used"""
         found: Set[str] = set()
+        # keys within loaders (only if the loader is not a parent too)
+        parents = {id(i.parent) for i in self.loaders if i.parent is not None}
         for loader in self.loaders:
-            found.update(loader.found_keys())
+            if id(loader) not in parents:
+                found.update(loader.found_keys())
         found -= self._defined.keys()
         return sorted(found)
 
diff --git a/src/tox/config/source/tox_ini.py b/src/tox/config/source/tox_ini.py
index 8fd80422..02f97c01 100644
--- a/src/tox/config/source/tox_ini.py
+++ b/src/tox/config/source/tox_ini.py
@@ -53,7 +53,7 @@ class ToxIni(Source):
         except KeyError:
             loaders: List[IniLoader] = []
             self._envs[section] = loaders
-
+            loader: Optional[IniLoader] = None
             if self._parser.has_section(section):
                 loader = IniLoader(
                     section=section,
@@ -73,11 +73,14 @@ class ToxIni(Source):
                 for base in conf["base"]:
                     for section in (base, f"{TEST_ENV_PREFIX}{base}"):
                         if self._parser.has_section(section):
+                            child = loader
                             loader = IniLoader(
                                 section=section,
                                 parser=self._parser,
                                 overrides=override_map.get(section, []),
                             )
+                            if child is not None:
+                                child.parent = loader
                             yield loader
                             loaders.append(loader)
                             break
diff --git a/tests/session/cmd/test_show_config.py b/tests/session/cmd/test_show_config.py
index 6cd90709..b44b43c8 100644
--- a/tests/session/cmd/test_show_config.py
+++ b/tests/session/cmd/test_show_config.py
@@ -62,7 +62,8 @@ def test_show_config_filter_keys(tox_project: ToxProjectCreator) -> None:
 
 
 def test_show_config_unused(tox_project: ToxProjectCreator) -> None:
-    outcome = tox_project({"tox.ini": "[testenv:py]\nmagical=yes\nmagic=yes"}).run("c", "-e", "py")
+    tox_ini = "[testenv]\nok=false\n[testenv:py]\nmagical=yes\nmagic=yes"
+    outcome = tox_project({"tox.ini": tox_ini}).run("c", "-e", "py")
     outcome.assert_success()
     assert "\n# !!! unused: magic, magical\n" in outcome.out