add mypy plugin

src/idom/mypy.py

@@ -1,36 +1,71 @@
-from typing import Callable, Final
+from __future__ import annotations
+
+from typing import Any, Callable, Final
 
 from mypy.errorcodes import ErrorCode
 from mypy.nodes import ArgKind
 from mypy.plugin import FunctionContext, Plugin
 from mypy.types import CallableType, Instance, Type
 
 
-KEY_IN_RENDER_FUNC: Final = ErrorCode(
+KEY_IN_RENDER_FUNC_ERROR: Final = ErrorCode(
     "idom-key-in-render-func",
     "Component render function has reserved 'key' parameter",
     "IDOM",
 )
 
+NO_STAR_ARGS_ERROR: Final = ErrorCode(
+    "idom-no-star-args",
+    "Children were passed using *args instead of as a list or tuple",
+    "IDOM",
+)
+
 
 class MypyPlugin(Plugin):
     """MyPy plugin for IDOM"""
 
+    def __init__(self, *args: Any, **kwargs: Any) -> None:
+        super().__init__(*args, **kwargs)
+        self._idom_component_function_names: set[str] = set()
+
     def get_function_hook(self, fullname: str) -> Callable[[FunctionContext], Type]:
         if fullname == "idom.core.component.component":
-            return self.component_decorator_hook
+            return self._idom_component_decorator_hook
+        elif fullname in self._idom_component_function_names:
+            return self._idom_component_function_hook
         return super().get_function_hook(fullname)
 
-    def component_decorator_hook(self, ctx: FunctionContext) -> CallableType:
+    def _idom_component_function_hook(self, ctx: FunctionContext) -> CallableType:
+        if any(ArgKind.ARG_STAR in arg_kinds for arg_kinds in ctx.arg_kinds):
+            ctx.api.msg.fail(
+                "Cannot pass variable number of children to component using *args",
+                ctx.context,
+                code=NO_STAR_ARGS_ERROR,
+            )
+            ctx.api.msg.note(
+                "You can pass a sequence of children directly to a component. That is, "
+                "`example(*children)` will be treated the same as `example(children)`. "
+                'Bear in mind that all children in such a sequence must have a  "key" '
+                "that uniquely identifies each child amongst its siblings.",
+                ctx.context,
+                code=NO_STAR_ARGS_ERROR,
+            )
+        return ctx.default_return_type
+
+    def _idom_component_decorator_hook(self, ctx: FunctionContext) -> CallableType:
         if not ctx.arg_types or not ctx.arg_types[0]:
             return ctx.default_return_type
+
         render_func: CallableType = ctx.arg_types[0][0]
 
+        if render_func.definition:
+            self._idom_component_function_names.add(render_func.definition.fullname)
+
         if render_func.argument_by_name("key") is not None:
             ctx.api.msg.fail(
                 "Component render function has reserved 'key' parameter",
                 ctx.context,
-                code=KEY_IN_RENDER_FUNC,
+                code=KEY_IN_RENDER_FUNC_ERROR,
             )
             return ctx.default_return_type
 

temp.py

@@ -0,0 +1,9 @@
+from idom import component
+
+
+@component
+def temp(x: int, y: int) -> None:
+    return None
+
+
+temp(*[1, 2])