Fix discovery of modules in namespace packages

Instead of relying on `__init__.py` files, stop at the first parent
directory that is in `sys.path`. This gives the shortest module name
under which the file can really be imported. (Unless there are name
conflicts in `sys.path`, which is arguably a misconfiguration; this
is caught by the location check in `module_tree`.)

src/slotscheck/discovery.py

@@ -2,6 +2,7 @@
 
 import importlib
 import pkgutil
+import sys
 from dataclasses import dataclass, field, replace
 from functools import partial, reduce
 from importlib.util import find_spec
@@ -299,15 +300,19 @@ def _is_package(p: AbsPath) -> bool:
     return p.is_dir() and (p / _INIT_PY).is_file()
 
 
-def find_modules(p: AbsPath) -> Iterable[ModuleLocated]:
+def find_modules(
+    p: AbsPath, python_path: Optional[FrozenSet[AbsPath]] = None
+) -> Iterable[ModuleLocated]:
     "Recursively find modules at given path. Nonexistent Path is ignored"
+    if python_path is None:
+        python_path = frozenset(map(Path, sys.path))
     if p.name == _INIT_PY:
-        yield from find_modules(p.parent)
+        yield from find_modules(p.parent, python_path)
     elif _is_module(p):
-        parents = [p] + list(takewhile(_is_package, p.parents))
+        parents = [p, *takewhile(lambda p: p not in python_path, p.parents)]
         yield ModuleLocated(
             ".".join(p.stem for p in reversed(parents)),
-            (p / "__init__.py" if _is_package(p) else p),
+            (p / _INIT_PY if _is_package(p) else p),
         )
     elif p.is_dir():
-        yield from flatten(map(find_modules, p.iterdir()))
+        yield from flatten(find_modules(sp, python_path) for sp in p.iterdir())

tests/src/conftest.py

@@ -13,9 +13,9 @@
 @pytest.fixture(scope="session", autouse=True)
 def add_pypath() -> Iterator[None]:
     "Add example modules to the python path"
-    sys.path.insert(0, str(EXAMPLES_DIR))
+    sys.path[:0] = [str(EXAMPLES_DIR), str(EXAMPLES_DIR / "other")]
     yield
-    sys.path.remove(str(EXAMPLES_DIR))
+    del sys.path[:2]
 
 
 @pytest.fixture(autouse=True)

tests/src/test_discovery.py

@@ -370,32 +370,34 @@ def test_given_nonpython_file(self):
     def test_given_python_file(self):
         location = EXAMPLES_DIR / "files/subdir/myfile.py"
         result = list(find_modules(location))
-        assert result == [ModuleLocated("myfile", location)]
+        assert result == [ModuleLocated("files.subdir.myfile", location)]
 
     def test_given_python_root_module(self):
         location = EXAMPLES_DIR / "files/subdir/some_module/"
         result = list(find_modules(location))
         assert result == [
-            ModuleLocated("some_module", location / "__init__.py")
+            ModuleLocated("files.subdir.some_module", location / "__init__.py")
         ]
 
     def test_given_dir_containing_python_files(self):
         location = EXAMPLES_DIR / "files/my_scripts/"
         result = list(find_modules(location))
         assert len(result) == 4
         assert set(result) == {
-            ModuleLocated("bla", location / "bla.py"),
-            ModuleLocated("foo", location / "foo.py"),
-            ModuleLocated("foo", location / "sub/foo.py"),
-            ModuleLocated("mymodule", location / "mymodule/__init__.py"),
+            ModuleLocated("files.my_scripts.bla", location / "bla.py"),
+            ModuleLocated("files.my_scripts.foo", location / "foo.py"),
+            ModuleLocated("files.my_scripts.sub.foo", location / "sub/foo.py"),
+            ModuleLocated(
+                "files.my_scripts.mymodule", location / "mymodule/__init__.py"
+            ),
         }
 
     def test_given_file_within_module(self):
         location = EXAMPLES_DIR / "files/subdir/some_module/sub/foo.py"
         result = list(find_modules(location))
         assert result == [
             ModuleLocated(
-                "some_module.sub.foo",
+                "files.subdir.some_module.sub.foo",
                 EXAMPLES_DIR / "files/subdir/some_module/sub/foo.py",
             )
         ]
@@ -404,13 +406,17 @@ def test_given_submodule(self):
         location = EXAMPLES_DIR / "files/subdir/some_module/sub"
         result = list(find_modules(location))
         assert result == [
-            ModuleLocated("some_module.sub", location / "__init__.py")
+            ModuleLocated(
+                "files.subdir.some_module.sub", location / "__init__.py"
+            )
         ]
 
     def test_given_init_py(self):
         location = EXAMPLES_DIR / "files/subdir/some_module/sub/__init__.py"
         result = list(find_modules(location))
-        assert result == [ModuleLocated("some_module.sub", location)]
+        assert result == [
+            ModuleLocated("files.subdir.some_module.sub", location)
+        ]
 
 
 class TestConsolidate: