apport_python_hook: Fix FileNotFoundError if cwd was deleted

Run following Shell script:

```sh
echo "raise ValueError()" > /tmp/failure.py
mkdir /tmp/foo
cd /tmp/foo/
rmdir /tmp/foo/
python3 ../failure.py
```

Then Apport's Python hook fails:

```
Traceback (most recent call last):
  File "../failure.py", line 1, in <module>
    raise ValueError()
ValueError
Error in sys.excepthook:
Traceback (most recent call last):
  File "<frozen importlib._bootstrap_external>", line 1372, in _path_importer_cache
KeyError: '..'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "apport_python_hook.py", line 55, in apport_excepthook
    if not enabled():
  File "apport_python_hook.py", line 24, in enabled
    import re
  File "<frozen importlib._bootstrap>", line 1027, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1002, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 945, in _find_spec
  File "<frozen importlib._bootstrap_external>", line 1439, in find_spec
  File "<frozen importlib._bootstrap_external>", line 1408, in _get_spec
  File "<frozen importlib._bootstrap_external>", line 1374, in _path_importer_cache
  File "<frozen importlib._bootstrap_external>", line 1350, in _path_hooks
  File "<frozen importlib._bootstrap_external>", line 1632, in path_hook_for_FileFinder
  File "<frozen importlib._bootstrap_external>", line 1505, in __init__
FileNotFoundError: [Errno 2] No such file or directory

Original exception was:
Traceback (most recent call last):
  File "../failure.py", line 1, in <module>
    raise ValueError()
ValueError
```

Bug: https://launchpad.net/bugs/1979637
Signed-off-by: Benjamin Drung <[email protected]>

apport_python_hook.py

@@ -20,10 +20,10 @@ def enabled():
 
     # This doesn't use apport.packaging.enabled() because it is too heavyweight
     # See LP: #528355
-    # pylint: disable=import-outside-toplevel; for Python starup time
-    import re
-
     try:
+        # pylint: disable=import-outside-toplevel; for Python starup time
+        import re
+
         with open(CONFIG) as f:
             conf = f.read()
         return re.search(r"^\s*enabled\s*=\s*0\s*$", conf, re.M) is None
@@ -55,15 +55,15 @@ def apport_excepthook(exc_type, exc_obj, exc_tb):
         if not enabled():
             return
 
-        import io
-        import os
-        import re
-        import traceback
-
         try:
+            import io
+            import os
+            import re
+            import traceback
+
             import apport.report
             from apport.fileutils import get_recent_crashes, likely_packaged
-        except ImportError:
+        except (ImportError, IOError):
             return
 
         # apport will look up the package from the executable path.

tests/integration/test_python_crashes.py

@@ -12,6 +12,7 @@
 
 import atexit
 import os
+import re
 import shutil
 import stat
 import subprocess
@@ -26,6 +27,8 @@
 
 
 class T(unittest.TestCase):
+    maxDiff = None
+
     @classmethod
     def setUpClass(cls):
         cls.env = os.environ | local_test_environment()
@@ -295,6 +298,58 @@ def _assert_no_reports(self):
             len(reports), 0, "no crash reports present (cwd: %s)" % os.getcwd()
         )
 
+    def test_deleted_working_directory(self):
+        """Relative Python script from deleted working directory."""
+        orig_cwd = os.getcwd()
+        try:
+            with tempfile.TemporaryDirectory(dir="/var/tmp") as tmpdir:
+                deleted_dir = os.path.join(tmpdir, "gone")
+                os.mkdir(deleted_dir)
+                os.chdir(deleted_dir)
+                os.rmdir(deleted_dir)
+
+                with open(os.path.join(tmpdir, "script.py"), "w") as script:
+                    script.write(
+                        "import apport_python_hook\n"
+                        "apport_python_hook.install()\n"
+                        "raise ValueError()\n"
+                    )
+
+                env = os.environ.copy()
+                env["PYTHONPATH"] = orig_cwd
+                process = subprocess.run(
+                    ["python3", "../script.py"],
+                    env=env,
+                    stdout=subprocess.PIPE,
+                    stderr=subprocess.PIPE,
+                )
+        finally:
+            os.chdir(orig_cwd)
+
+        # Workaround for pytest bug.
+        # See https://github.com/pytest-dev/pytest-cov/issues/541
+        stderr = re.sub(
+            r"^Error processing [A-Za-z0-9 /-]*init_cov_core.pth:\n[\S\W]*\n"
+            r"pytest-cov: Failed to setup subprocess coverage.*\n",
+            "",
+            process.stderr.decode(),
+        )
+
+        self.assertEqual(
+            stderr,
+            textwrap.dedent(
+                """\
+                Traceback (most recent call last):
+                  File "../script.py", line 3, in <module>
+                    raise ValueError()
+                ValueError
+                """
+            ),
+        )
+        self.assertEqual(process.stdout.decode(), "")
+        self.assertEqual(process.returncode, 1)
+        self._assert_no_reports()
+
     def test_interactive(self):
         """interactive Python sessions never generate a report."""