.dir-locals: include QEMU code in PYTHONPATH

When editing python code the linters tools have a hard time with our
imports as they can't be found. To ease this we can expand a
PYTHONPATH in .dir-locals so at least Emacs users can have less
warnings in their editor.

I still get complaints from python-mypy about missing library stubs
that mean it can't do proper type analysis though.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-ID: <20261019192704.3220373-4-alex.bennee@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

.dir-locals.el

@@ -1,2 +1,8 @@
 ((c-mode . ((c-file-style . "stroustrup")
-	    (indent-tabs-mode . nil))))
+	    (indent-tabs-mode . nil)))
+ (python-mode .
+              ((eval . (when-let* ((root (locate-dominating-file default-directory ".dir-locals.el")))
+                         (setq-local process-environment (copy-sequence process-environment))
+                         (setenv "PYTHONPATH"
+                                 (concat (expand-file-name "python" root) ":"
+                                         (expand-file-name "tests/functional" root))))))))