Pylint plugin to check __init__ return type (#50868)

* Pylint plugin to check __init__ return type

* Support *args add **kwargs, type hints

* Use 'in' instead of 'any()'

* Fix last few places

pylint/plugins/hass_constructor.py

@@ -0,0 +1,52 @@
+"""Plugin for constructor definitions."""
+from astroid import ClassDef, Const, FunctionDef
+from pylint.checkers import BaseChecker
+from pylint.interfaces import IAstroidChecker
+from pylint.lint import PyLinter
+
+
+class HassConstructorFormatChecker(BaseChecker):  # type: ignore[misc]
+    """Checker for __init__ definitions."""
+
+    __implements__ = IAstroidChecker
+
+    name = "hass_constructor"
+    priority = -1
+    msgs = {
+        "W0006": (
+            '__init__ should have explicit return type "None"',
+            "hass-constructor-return",
+            "Used when __init__ has all arguments typed "
+            "but doesn't have return type declared",
+        ),
+    }
+    options = ()
+
+    def visit_functiondef(self, node: FunctionDef) -> None:
+        """Called when a FunctionDef node is visited."""
+        if not node.is_method() or node.name != "__init__":
+            return
+
+        # Check that all arguments are annotated.
+        # The first argument is "self".
+        args = node.args
+        annotations = (
+            args.posonlyargs_annotations
+            + args.annotations
+            + args.kwonlyargs_annotations
+        )[1:]
+        if args.vararg is not None:
+            annotations.append(args.varargannotation)
+        if args.kwarg is not None:
+            annotations.append(args.kwargannotation)
+        if not annotations or None in annotations:
+            return
+
+        # Check that return type is specified and it is "None".
+        if not isinstance(node.returns, Const) or node.returns.value != None:
+            self.add_message("hass-constructor-return", node=node)
+
+
+def register(linter: PyLinter) -> None:
+    """Register the checker."""
+    linter.register_checker(HassConstructorFormatChecker(linter))