Throw shade at bad boi callables.

This commit improves the readability of exceptions raised by edge-case
`@beartype`-decorated callables annotated by one or more forward
references while also failing to define the `__module__` dunder
attribute, resolving issue #381 kindly submitted by dynamical Bostonian
and bonafide real-life main character @femtomc (McCoy R. Becker). For
unknown (and probably indefensible) reasons, the third-party
`markdown-exec` package appears to define such horrifying callables.
When confronted with such horrifying callables, the `@beartype`
decorator now raises human-readable exceptions resembling:

```python
beartype.roar.BeartypeDecorHintForwardRefException: Function muh_func()
parameter "muh_arg" forward reference type hint "MuhType" unresolvable,
as "muh_func.__module__" dunder attribute undefined (e.g., due to
<function muh_func at 0x7f030d402160> being defined only dynamically
in-memory). So much bad stuff is happening here all at once that
@beartype can no longer cope with the explosion in badness.
```

Flex those burly exception messages, @beartype! Flex 'em! (*A flexible lexicon on iconic nicks!*)

beartype/_check/forward/fwdmain.py

@@ -31,8 +31,9 @@
     get_func_globals,
     get_func_locals,
 )
-from beartype._util.module.utilmodget import get_object_module_name
+from beartype._util.module.utilmodget import get_object_module_name_or_none
 from beartype._util.py.utilpyversion import IS_PYTHON_AT_MOST_3_9
+from beartype._util.utilobject import get_object_name
 from builtins import __dict__ as func_builtins  # type: ignore[attr-defined]
 
 # ....................{ RESOLVERS                          }....................
@@ -249,13 +250,6 @@ def resolve_hint(
         # Localize metadata for readability and efficiency. Look. Just do it.
         cls_stack = decor_meta.cls_stack
 
-        # Fully-qualified name of the module declaring the decorated callable,
-        # which also serves as the name of this module and thus global scope.
-        func_module_name = get_object_module_name(func)  # type: ignore[operator]
-
-        # Global scope of the decorated callable.
-        func_globals = get_func_globals(func=func, exception_cls=exception_cls)
-
         # If the decorated callable is nested (rather than global) and thus
         # *MAY* have a non-empty local nested scope...
         if decor_meta.func_wrappee_is_nested:
@@ -438,6 +432,38 @@ def resolve_hint(
         else:
             func_locals = DICT_EMPTY
 
+        # Fully-qualified name of the module declaring the decorated callable if
+        # that callable defines the "__module__" dunder attribute *OR* "None"
+        # (i.e., if that callable fails to define that attribute).
+        func_module_name = get_object_module_name_or_none(func)  # type: ignore[operator]
+
+        # If the decorated callable fails to define the "__module__" dunder
+        # attribute, there exists *NO* known module against which to resolve
+        # this stringified type hint. Since this implies that this hint *CANNOT*
+        # be reliably resolved, raise an exception.
+        #
+        # Note that this is an uncommon edge case that nonetheless occurs
+        # frequently enough to warrant explicit handling by raising a more
+        # human-readable exception than would otherwise be raised (e.g., if the
+        # lower-level get_object_module_name() getter were called instead
+        # above). Notably, the third-party "markdown-exec" package behaved like
+        # this -- and possibly still does. See also:
+        #     https://github.com/beartype/beartype/issues/381
+        if not func_module_name:
+            raise exception_cls(
+                f'{exception_prefix}forward reference type hint "{hint}" '
+                f'unresolvable, as '
+                f'"{get_object_name(func)}.__module__" dunder attribute '
+                f'undefined (e.g., due to {repr(func)} being defined only '
+                f'dynamically in-memory). '
+                f'So much bad stuff is happening here all at once that '
+                f'@beartype can no longer cope with the explosion in badness.'
+            )
+        # Else, the decorated callable defines that attribute.
+
+        # Global scope of the decorated callable.
+        func_globals = get_func_globals(func=func, exception_cls=exception_cls)
+
         # Forward scope compositing this global and local scope of the decorated
         # callable as well as dynamically replacing each unresolved attribute of
         # this stringified type hint with a forward reference proxy resolving

beartype_test/a00_unit/a70_decor/a40_code/a90_pep/pep484/test_pep484ref.py

@@ -142,6 +142,20 @@ def test_pep484_ref_decor_fail() -> None:
     from beartype.roar import BeartypeDecorHintForwardRefException
     from beartype_test._util.pytroar import raises_uncached
 
+    # ..................{ CALLABLES                          }..................
+    def of_oceans(mountainous_waste: 'ToMutualWar'):
+        '''
+        Arbitrary callable annotated by an **unresolvable relative forward
+        reference** (i.e., unqualified name of a user-defined type that is
+        *never* defined in either local or global scope).
+        '''
+
+        return mountainous_waste
+
+    # Maliciously delete the "__module__" dunder attribute of that callable to
+    # exercise an edge case below.
+    del of_oceans.__module__
+
     # ..................{ FAIL                               }..................
     #FIXME: Uncomment if and when a future Python release unconditionally
     #enables some variant of PEP 563... yet again.
@@ -182,6 +196,14 @@ def deep_hearts_core(i_hear_it: (
             'While.I.stand.on.the.roadway.or.on.the.pavements.0grey')):
             return i_hear_it
 
+    # Assert @beartype raises the expected exception when decorating a callable
+    # annotated by a syntactically valid forward reference type hint when the
+    # caller maliciously deletes the "__module__" dunder attribute of that
+    # callable *AFTER* defining that callable but before decorating that
+    # callable by @beartype.
+    with raises_uncached(exception_cls):
+        beartype(of_oceans)
+
 
 def test_pep484_ref_call_fail() -> None:
     '''