core: user overloads to type @warn_if_empty properly..

my/core/common.py

@@ -282,9 +282,22 @@ def _warn_iterator(it):
     if not emitted:
         warnings.warn(f"Function hasn't emitted any data, make sure your config paths are correct")
 
-# todo need to popretly restrict to a container... ugh
+
-C = TypeVar('C')
+# TODO ugh, so I want to express something like:
-def _warn_iterable(it: C) -> C:
+# X = TypeVar('X')
+# C = TypeVar('C', bound=Iterable[X])
+# _warn_iterable(it: C) -> C
+# but apparently I can't??? ugh.
+# https://github.com/python/typing/issues/548
+# I guess for now overloads are fine...
+
+from typing import overload
+X = TypeVar('X')
+@overload
+def _warn_iterable(it: List[X]    ) -> List[X]    : ...
+@overload
+def _warn_iterable(it: Iterable[X]) -> Iterable[X]: ...
+def _warn_iterable(it):
     if isinstance(it, Sized):
         sz = len(it)
         if sz == 0:
@@ -294,11 +307,14 @@ def _warn_iterable(it: C) -> C:
         return _warn_iterator(it)
 
 
-CC = TypeVar('CC')
+@overload
-def warn_if_empty(f: CC) -> CC:
+def warn_if_empty(f: Callable[[], List[X]]    ) -> Callable[[], List[X]]    : ...
+@overload
+def warn_if_empty(f: Callable[[], Iterable[X]]) -> Callable[[], Iterable[X]]: ...
+def warn_if_empty(f):
     from functools import wraps
-    @wraps(f) # type: ignore[arg-type]
+    @wraps(f)
     def wrapped(*args, **kwargs):
-        res = f(*args, **kwargs) # type: ignore[call-arg, operator]
+        res = f(*args, **kwargs)
         return _warn_iterable(res)
-    return wrapped # type: ignore[return-value]
+    return wrapped

tests/misc.py

@@ -63,6 +63,15 @@ def test_warn_if_empty() -> None:
     def empty() -> List[str]:
         return []
 
+    # should be rejected by mypy!
+    # todo how to actually test it?
+    # @warn_if_empty
+    # def baad() -> float:
+    #     return 0.00
+
+    # reveal_type(nonempty)
+    # reveal_type(empty)
+
     with warnings.catch_warnings(record=True) as w:
         assert list(nonempty()) == ['a', 'aba']
         assert len(w) == 0
@@ -80,6 +89,8 @@ def test_warn_iterable() -> None:
     # reveal_type(i2)
     x1 = _warn_iterable(i1)
     x2 = _warn_iterable(i2)
+    # vvvv this should be flagged by mypy
+    # _warn_iterable(123)
     # reveal_type(x1)
     # reveal_type(x2)
     with warnings.catch_warnings(record=True) as w: