Add better support for packages with files outside site-packages

importlib_metadata/__init__.py

@@ -562,15 +562,31 @@ def _read_files_egginfo_installed(self):
         if not text or not subdir:
             return
 
+        site_path = self.locate_file('').resolve()
         paths = (
-            (subdir / name)
-            .resolve()
-            .relative_to(self.locate_file('').resolve())
-            .as_posix()
+            self._relative_to(
+                (subdir / name).resolve(),
+                site_path,
+            ).as_posix()
             for name in text.splitlines()
         )
         return map('"{}"'.format, paths)
 
+    def _relative_to(self, path, root):
+        """
+        Workaround for https://bugs.python.org/issue23082 where ".."
+        isn't added by pathlib.Path.relative_to() when path is not
+        a subpath of root.
+
+        One example of such a package is dask-labextension, which uses
+        jupyter-packaging to install JupyterLab javascript files outside
+        of site-packages.
+        """
+        try:
+            return path.relative_to(root)
+        except ValueError:
+            return pathlib.Path(os.path.relpath(path, root))
+
     def _read_files_egginfo_sources(self):
         """
         Read SOURCES.txt and return lines in a similar CSV-parsable

importlib_metadata/_meta.py

@@ -65,3 +65,5 @@ def read_text(self, encoding=None) -> str: ...  # pragma: no cover
     def read_bytes(self) -> bytes: ...  # pragma: no cover
 
     def exists(self) -> bool: ...  # pragma: no cover
+
+    def resolve(self) -> bool: ...  # pragma: no cover

tests/fixtures.py

@@ -250,6 +250,40 @@ 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,