Fix relative-beyond-top-level false positive (#1186)

* Fix ``relative-beyond-top-level`` false positive

ChangeLog

@@ -36,6 +36,10 @@ Release date: TBA
 
 * Improve brain for ``typing.Callable`` and ``typing.Type``.
 
+* Fix bug with importing namespace packages with relative imports
+
+  Closes PyCQA/pylint#5059
+
 
 What's New in astroid 2.8.0?
 ============================

astroid/nodes/scoped_nodes.py

@@ -43,6 +43,7 @@
 import builtins
 import io
 import itertools
+import os
 import typing
 from typing import List, Optional, TypeVar
 
@@ -732,10 +733,17 @@ def relative_to_absolute_name(self, modname, level):
         if level:
             if self.package:
                 level = level - 1
+                package_name = self.name.rsplit(".", level)[0]
+            elif not os.path.exists("__init__.py") and os.path.exists(
+                modname.split(".")[0]
+            ):
+                level = level - 1
+                package_name = ""
+            else:
+                package_name = self.name.rsplit(".", level)[0]
             if level and self.name.count(".") < level:
                 raise TooManyLevelsError(level=level, name=self.name)
 
-            package_name = self.name.rsplit(".", level)[0]
         elif self.package:
             package_name = self.name
         else:
@@ -744,7 +752,7 @@ def relative_to_absolute_name(self, modname, level):
         if package_name:
             if not modname:
                 return package_name
-            return f"{package_name}.{modname}"
+            return f"{package_name}.{modname.split('.')[0]}"
         return modname
 
     def wildcard_import_names(self):

tests/testdata/python3/data/beyond_top_level/import_package.py

@@ -0,0 +1,3 @@
+from namespace_package import top_level_function
+
+top_level_function.do_something()

tests/testdata/python3/data/beyond_top_level/namespace_package/lower_level/helper_function.py

@@ -0,0 +1,5 @@
+from ..plugin_api import top_message
+
+
+def plugin_message(msg):
+    return "plugin_message: %s" % top_message(msg)

tests/testdata/python3/data/beyond_top_level/namespace_package/plugin_api.py

@@ -0,0 +1,2 @@
+def top_message(msg):
+    return "top_message: %s" % msg

tests/testdata/python3/data/beyond_top_level/namespace_package/top_level_function.py

@@ -0,0 +1,5 @@
+from .lower_level.helper_function import plugin_message
+
+
+def do_something():
+    return plugin_message("called by do_something")

tests/unittest_inference.py

@@ -6535,5 +6535,10 @@ def play():
     assert next(node.infer()).pytype() == ".B"
 
 
+def test_namespace_package() -> None:
+    """check that a file using namespace packages and relative imports is parseable"""
+    resources.build_file("data/beyond_top_level/import_package.py")
+
+
 if __name__ == "__main__":
     unittest.main()