Add better support for packages with files outside site-packages

importlib_metadata/__init__.py

@@ -19,7 +19,7 @@
 import collections
 
 from . import _meta
-from .compat import py39
+from .compat import py39, py311
 from ._collections import FreezableDefaultDict, Pair
 from ._compat import (
     NullFinder,
@@ -570,9 +570,8 @@ def _read_files_egginfo_installed(self):
             return
 
         paths = (
-            (subdir / name)
-            .resolve()
-            .relative_to(self.locate_file('').resolve())
+            py311.relative_fix((subdir / name).resolve())
+            .relative_to(self.locate_file('').resolve(), walk_up=True)
             .as_posix()
             for name in text.splitlines()
         )

importlib_metadata/compat/py311.py

@@ -0,0 +1,22 @@
+import os
+import pathlib
+import sys
+import types
+
+
+def wrap(path):  # pragma: no cover
+    """
+    Workaround for https://github.com/python/cpython/issues/84538
+    to add backward compatibility for walk_up=True.
+    An example affected package is dask-labextension, which uses
+    jupyter-packaging to install JupyterLab javascript files outside
+    of site-packages.
+    """
+
+    def relative_to(root, *, walk_up=False):
+        return pathlib.Path(os.path.relpath(path, root))
+
+    return types.SimpleNamespace(relative_to=relative_to)
+
+
+relative_fix = wrap if sys.version_info < (3, 12) else lambda x: x

newsfragments/455.bugfix.rst

@@ -0,0 +1 @@
+When reading installed files from an egg, use ``relative_to(walk_up=True)`` to honor files installed outside of the installation root.

tests/fixtures.py

@@ -233,6 +233,40 @@ def main():
     }
 
 
+class EggInfoPkgPipInstalledExternalDataFiles(OnSysPath, SiteBuilder):
+    files: FilesSpec = {
+        "egg_with_module_pkg.egg-info": {
+            "PKG-INFO": "Name: egg_with_module-pkg",
+            # SOURCES.txt is made from the source archive, and contains files
+            # (setup.py) that are not present after installation.
+            "SOURCES.txt": """
+                egg_with_module.py
+                setup.py
+                egg_with_module.json
+                egg_with_module_pkg.egg-info/PKG-INFO
+                egg_with_module_pkg.egg-info/SOURCES.txt
+                egg_with_module_pkg.egg-info/top_level.txt
+            """,
+            # installed-files.txt is written by pip, and is a strictly more
+            # accurate source than SOURCES.txt as to the installed contents of
+            # the package.
+            "installed-files.txt": """
+                ../../../etc/jupyter/jupyter_notebook_config.d/relative.json
+                /etc/jupyter/jupyter_notebook_config.d/absolute.json
+                ../egg_with_module.py
+                PKG-INFO
+                SOURCES.txt
+                top_level.txt
+            """,
+            # missing top_level.txt (to trigger fallback to installed-files.txt)
+        },
+        "egg_with_module.py": """
+            def main():
+                print("hello world")
+            """,
+    }
+
+
 class EggInfoPkgPipInstalledNoModules(OnSysPath, SiteBuilder):
     files: FilesSpec = {
         "egg_with_no_modules_pkg.egg-info": {

tests/test_api.py

@@ -29,6 +29,7 @@ class APITests(
     fixtures.EggInfoPkg,
     fixtures.EggInfoPkgPipInstalledNoToplevel,
     fixtures.EggInfoPkgPipInstalledNoModules,
+    fixtures.EggInfoPkgPipInstalledExternalDataFiles,
     fixtures.EggInfoPkgSourcesFallback,
     fixtures.DistInfoPkg,
     fixtures.DistInfoPkgWithDot,