Provide first component of dotted path to namespace searches (#1575)

* Use first component of dotted path only in namespace searches

* Add test and catch KeyError instead of altering search strategy

Author: jacobtylerwalls

astroid/interpreter/_import/util.py

@@ -18,17 +18,18 @@ def is_namespace(modname: str) -> bool:
     # That's unacceptable here, so we fallback to _find_spec_from_path(), which does
     # not, but requires instead that each single parent ('astroid', 'nodes', etc.)
     # be specced from left to right.
-    processed_components = []
-    last_parent = None
-    for component in modname.split("."):
-        processed_components.append(component)
-        working_modname = ".".join(processed_components)
+    components = modname.split(".")
+    for i in range(1, len(components) + 1):
+        working_modname = ".".join(components[:i])
         try:
-            found_spec = _find_spec_from_path(working_modname, last_parent)
+            # Search under the highest package name
+            # Only relevant if package not already on sys.path
+            # See https://github.com/python/cpython/issues/89754 for reasoning
+            # Otherwise can raise bare KeyError: https://github.com/python/cpython/issues/93334
+            found_spec = _find_spec_from_path(working_modname, components[0])
         except ValueError:
             # executed .pth files may not have __spec__
             return True
-        last_parent = working_modname
 
     if found_spec is None:
         return False

tests/testdata/python3/data/parent_of_homonym/__init__.py

@@ -0,0 +1,2 @@
+This submodule should have the same name as a directory in the root of the project that
+is _NOT_ a python module. For this reason, it's currently called "doc".

tests/testdata/python3/data/parent_of_homonym/doc/README.md

@@ -120,6 +120,11 @@ def test_identify_old_namespace_package_protocol(self) -> None:
             util.is_namespace("tests.testdata.python3.data.path_pkg_resources_1")
         )
 
+    def test_submodule_homonym_with_non_module(self) -> None:
+        self.assertFalse(
+            util.is_namespace("tests.testdata.python3.data.parent_of_homonym.doc")
+        )
+
     def test_implicit_namespace_package(self) -> None:
         data_dir = os.path.dirname(resources.find("data/namespace_pep_420"))
         contribute = os.path.join(data_dir, "contribute_to_namespace")