[PATCH v2 2/6] iotests: add warning for rogue 'qemu' packages

[John Snow]

Add a warning for when 'iotests' runs against a qemu namespace that
isn't the one in the source tree. This might occur if you have
(accidentally) installed the Python namespace package to your local
packages.

(I'm not going to say that this is because I bit myself with this,
but you can fill in the blanks.)

In the future, we will pivot to always preferring a specific installed
instance of qemu python packages managed directly by iotests. For now
simply warn if there is an ambiguity over which instance that iotests
might use.

Example: If a user has navigated to ~/src/qemu/python and executed
`pip install .`, you will see output like this when running `./check`:

WARNING: 'qemu' python packages will be imported from outside the source tree 
('/home/jsnow/src/qemu/python')
         Importing instead from 
'/home/jsnow/.local/lib/python3.9/site-packages/qemu'

Signed-off-by: John Snow <jsnow@redhat.com>
---
 tests/qemu-iotests/testenv.py | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/tests/qemu-iotests/testenv.py b/tests/qemu-iotests/testenv.py
index 99a57a69f3a..1c0f6358538 100644
--- a/tests/qemu-iotests/testenv.py
+++ b/tests/qemu-iotests/testenv.py
@@ -16,6 +16,8 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #
 
+import importlib.util
+import logging
 import os
 import sys
 import tempfile
@@ -112,6 +114,27 @@ def init_directories(self) -> None:
         # Path where qemu goodies live in this source tree.
         qemu_srctree_path = Path(__file__, '../../../python').resolve()
 
+        # Warn if we happen to be able to find qemu namespace packages
+        # (using qemu.qmp as a bellwether) from an unexpected location.
+        # i.e. the package is already installed in the user's environment.
+        try:
+            qemu_spec = importlib.util.find_spec('qemu.qmp')
+        except ModuleNotFoundError:
+            qemu_spec = None
+
+        if qemu_spec and qemu_spec.origin:
+            spec_path = Path(qemu_spec.origin)
+            try:
+                _ = spec_path.relative_to(qemu_srctree_path)
+            except ValueError:
+                self._logger.warning(
+                    "WARNING: 'qemu' python packages will be imported from"
+                    " outside the source tree ('%s')",
+                    qemu_srctree_path)
+                self._logger.warning(
+                    "         Importing instead from '%s'",
+                    spec_path.parents[1])
+
         self.pythonpath = os.pathsep.join(filter(None, (
             self.source_iotests,
             str(qemu_srctree_path),
@@ -230,6 +253,7 @@ def __init__(self, imgfmt: str, imgproto: str, aiomode: str,
 
         self.build_root = os.path.join(self.build_iotests, '..', '..')
 
+        self._logger = logging.getLogger('qemu.iotests')
         self.init_directories()
         self.init_binaries()
 
-- 
2.31.1