handle FunctionLikes + re-add test

python · hauntsaninja · Sep 3, 2021 · May 29, 2021 · Jun 18, 2021 · Jun 25, 2021
commit dc70b7cac6385ccf210fd2518bf5c868569e3578
diff --git a/mypy/checker.py b/mypy/checker.py
@@ -3998,13 +3998,18 @@ def _check_for_truthy_type(self, t: Type, expr: Expression) -> None:
         if not state.strict_optional:
             return  # if everything can be None, all bets are off
         if self._is_truthy_instance(t):
-            self.msg.note(
+            self.msg.fail(
                 '{} which does not implement __bool__ or __len__ '
                 'so it will always be true in boolean context'.format(self._format_expr_name(expr, t)), expr,
                 code=codes.IMPLICIT_BOOL,
             )
-        elif isinstance(t, UnionType) and all(self._is_truthy_instance(t) for t in t.items):
-            self.msg.note(
+        elif isinstance(t, FunctionLike):
+            self.msg.fail(
+                f'function "{t}" will always be true in boolean context', expr,
+                code=codes.IMPLICIT_BOOL,
+            )
+        elif isinstance(t, UnionType) and all(self._is_truthy_instance(t) or isinstance(t, FunctionLike) for t in t.items):
+            self.msg.fail(
                 "{} none of which implement __bool__ or __len__ "
                 "so it will always be true in boolean context".format(self._format_expr_name(expr, t)), expr,
                 code=codes.IMPLICIT_BOOL,

diff --git a/test-data/unit/check-errorcodes.test b/test-data/unit/check-errorcodes.test
@@ -807,3 +807,61 @@ from typing_extensions import TypedDict
 
 Foo = TypedDict("Bar", {})  # E: First argument "Bar" to TypedDict() does not match variable name "Foo"  [name-match]
 [builtins fixtures/dict.pyi]
+[case testImplicitBool]
+# flags: --enable-error-code implicit-bool
+from typing import List, Union
+
+class Foo:
+    pass
+
+
+foo = Foo()
+if foo:  # E: "__main__.foo" has type "__main__.Foo" which does not implement __bool__ or __len__ so it will always be true in boolean context  [implicit-bool]
+    pass
+
+zero = 0
+if zero:
+    pass
+
+
+false = False
+if false:
+    pass
+
+
+null = None
+if null:
+    pass
+
+
+s = ''
+if s:
+    pass
+
+
+good_union: Union[str, int] = 5
+if good_union:
+    pass
+
+
+bad_union: Union[Foo, object] = Foo()
+if bad_union:  # E: "__main__.bad_union" has type "Union[__main__.Foo, builtins.object]" none of which implement __bool__ or __len__ so it will always be true in boolean context  [implicit-bool]
+    pass
+
+
+def f():
+    pass
+
+
+if f:  # E: function "def () -> Any" will always be true in boolean context  [implicit-bool]
+    pass
+
+
+lst: List[int] = []
+if lst:
+    pass
+
+
+conditional_result = 'foo' if f else 'bar'  # E: function "def () -> Any" will always be true in boolean context  [implicit-bool]
+
+[builtins fixtures/list.pyi]
diff --git a/test-data/unit/fixtures/list.pyi b/test-data/unit/fixtures/list.pyi
@@ -30,7 +30,7 @@ class function: pass
 class int:
     def __bool__(self) -> bool: pass
 class float: pass
-class str: pass
+class str(Sequence[str]): pass
 class bool(int): pass
 
 property = object() # Dummy definition.