Fallback to a placeholder if a distribution's location is None

news/11704.bugfix.rst

@@ -0,0 +1,2 @@
+Fix an issue when an already existing in-memory distribution would cause
+exceptions in ``pip install``

src/pip/_internal/req/req_install.py

@@ -195,7 +195,11 @@ def __str__(self) -> str:
         else:
             s = "<InstallRequirement>"
         if self.satisfied_by is not None:
-            s += " in {}".format(display_path(self.satisfied_by.location))
+            if self.satisfied_by.location is not None:
+                location = display_path(self.satisfied_by.location)
+            else:
+                location = "<memory>"
+            s += f" in {location}"
         if self.comes_from:
             if isinstance(self.comes_from, str):
                 comes_from: Optional[str] = self.comes_from

tests/functional/test_install.py

@@ -2351,3 +2351,45 @@ def test_install_8559_wheel_package_present(
         allow_stderr_warning=False,
     )
     assert DEPRECATION_MSG_PREFIX not in result.stderr
+
+
+@pytest.mark.skipif(
+    sys.version_info < (3, 11),
+    reason="3.11 required to find distributions via importlib metadata",
+)
+def test_install_existing_memory_distribution(script: PipTestEnvironment) -> None:
+    sitecustomize_text = textwrap.dedent(
+        """
+        import sys
+        from importlib.metadata import Distribution, DistributionFinder
+
+
+        EXAMPLE_METADATA = '''Metadata-Version: 2.1
+        Name: example
+        Version: 1.0.0
+
+        '''
+
+        class ExampleDistribution(Distribution):
+            def locate_file(self, path):
+                return path
+
+            def read_text(self, filename):
+                if filename == 'METADATA':
+                    return EXAMPLE_METADATA
+
+
+        class CustomFinder(DistributionFinder):
+            def find_distributions(self, context=None):
+                return [ExampleDistribution()]
+
+
+        sys.meta_path.append(CustomFinder())
+        """
+    )
+    with open(script.site_packages_path / "sitecustomize.py", "w") as sitecustomize:
+        sitecustomize.write(sitecustomize_text)
+
+    result = script.pip("install", "example")
+
+    assert "Requirement already satisfied: example in <memory>" in result.stdout