Make _EditableFinder case-sensitive on case-insensitive filesystems (for certain editable installations)

newsfragments/3995.bugfix.rst

@@ -0,0 +1 @@
+Made imports in editable installs case-sensitive on case-insensitive filesystems -- by :user:`aganders3`

setuptools/command/editable_wheel.py

@@ -744,7 +744,7 @@ def _get_root(self):
 
 _FINDER_TEMPLATE = """\
 import sys
-from importlib.machinery import ModuleSpec
+from importlib.machinery import ModuleSpec, PathFinder
 from importlib.machinery import all_suffixes as module_suffixes
 from importlib.util import spec_from_file_location
 from itertools import chain
@@ -758,10 +758,15 @@ def _get_root(self):
 class _EditableFinder:  # MetaPathFinder
     @classmethod
     def find_spec(cls, fullname, path=None, target=None):
+        # Top-level packages and modules (we know these exist in the FS)
+        if fullname in MAPPING:
+            pkg_path = MAPPING[fullname]
+            return cls._find_spec(fullname, Path(pkg_path))
+
+        # Nested modules (apparently required for namespaces to work)
         for pkg, pkg_path in reversed(list(MAPPING.items())):
-            if fullname == pkg or fullname.startswith(f"{{pkg}}."):
-                rest = fullname.replace(pkg, "", 1).strip(".").split(".")
-                return cls._find_spec(fullname, Path(pkg_path, *rest))
+            if fullname.startswith(f"{{pkg}}."):
+                return cls._find_nested_spec(fullname, pkg, pkg_path)
 
         return None
 
@@ -773,6 +778,20 @@ def _find_spec(cls, fullname, candidate_path):
             if candidate.exists():
                 return spec_from_file_location(fullname, candidate)
 
+    @classmethod
+    def _find_nested_spec(cls, fullname, parent, parent_path):
+        '''
+        To avoid problems with case sensitivity in the file system we delegate to the
+        importlib.machinery implementation.
+        '''
+        rest = fullname.replace(parent, "", 1).strip(".")
+        nested = PathFinder.find_spec(rest, path=[parent_path])
+        return nested and spec_from_file_location(
+            fullname,
+            nested.origin,
+            submodule_search_locations=nested.submodule_search_locations
+        )
+
 
 class _EditableNamespaceFinder:  # PathEntryFinder
     @classmethod

setuptools/tests/test_editable_install.py

@@ -577,6 +577,88 @@ def test_similar_name(self, tmp_path):
             with pytest.raises(ImportError, match="foobar"):
                 import_module("foobar")
 
+    def test_case_sensitivity(self, tmp_path):
+        files = {
+            "foo": {
+                "__init__.py": "",
+                "lowercase.py": "x = 1",
+                "bar": {
+                    "__init__.py": "",
+                    "lowercase.py": "x = 2",
+                },
+            },
+        }
+        jaraco.path.build(files, prefix=tmp_path)
+        mapping = {
+            "foo": str(tmp_path / "foo"),
+        }
+        template = _finder_template(str(uuid4()), mapping, {})
+        with contexts.save_paths(), contexts.save_sys_modules():
+            sys.modules.pop("foo", None)
+
+            self.install_finder(template)
+            with pytest.raises(ImportError, match="\'FOO\'"):
+                import_module("FOO")
+
+            with pytest.raises(ImportError, match="\'foo\\.LOWERCASE\'"):
+                import_module("foo.LOWERCASE")
+
+            with pytest.raises(ImportError, match="\'foo\\.bar\\.Lowercase\'"):
+                import_module("foo.bar.Lowercase")
+
+            with pytest.raises(ImportError, match="\'foo\\.BAR\'"):
+                import_module("foo.BAR.lowercase")
+
+            with pytest.raises(ImportError, match="\'FOO\'"):
+                import_module("FOO.bar.lowercase")
+
+            mod = import_module("foo.lowercase")
+            assert mod.x == 1
+
+            mod = import_module("foo.bar.lowercase")
+            assert mod.x == 2
+
+    def test_namespace_case_sensitivity(self, tmp_path):
+        files = {
+            "pkg": {
+                "__init__.py": "a = 13",
+                "foo": {
+                    "__init__.py": "b = 37",
+                    "bar.py": "c = 42",
+                },
+            },
+        }
+        jaraco.path.build(files, prefix=tmp_path)
+
+        mapping = {"ns.othername": str(tmp_path / "pkg")}
+        namespaces = {"ns": []}
+
+        template = _finder_template(str(uuid4()), mapping, namespaces)
+        with contexts.save_paths(), contexts.save_sys_modules():
+            for mod in ("ns", "ns.othername"):
+                sys.modules.pop(mod, None)
+
+            self.install_finder(template)
+            pkg = import_module("ns.othername")
+            expected = str((tmp_path / "pkg").resolve())
+            assert_path(pkg, expected)
+            assert pkg.a == 13
+
+            foo = import_module("ns.othername.foo")
+            assert foo.b == 37
+
+            bar = import_module("ns.othername.foo.bar")
+            assert bar.c == 42
+
+            with pytest.raises(ImportError, match="\'NS\'"):
+                import_module("NS.othername.foo")
+
+            with pytest.raises(ImportError, match="\'ns\\.othername\\.FOO\\'"):
+                import_module("ns.othername.FOO")
+
+            with pytest.raises(ImportError, match="\'ns\\.othername\\.foo\\.BAR\\'"):
+                import_module("ns.othername.foo.BAR")
+
 
 def test_pkg_roots(tmp_path):
     """This test focus in getting a particular implementation detail right.