Force QT_LOGGING_RULES in testlib's selftest

On some systems (e.g. Debian/buster) a standard Qt package may install
a qtlogging.ini file, e.g. in /etc/xdg/QtProject/, which suppresses
QDEBUG output.  A ~/.config/QtProject/qtlogging.ini could interfere
similarly.  This can break the selftest, when run with expected_*
files generated without such interference.  Likewise, if those
expected_* files are generated on a system such similar, they won't
work on CI.  Given that this caused confusion and delay with
integrating the latest set of updates to the expected_* files, it
seemed best to save others from similar bafflement.

So set a standard value for QT_LOGGING_RULES in both the selftest and
the generator script, so we get consistency.

Change-Id: I649e2f1f6ead21edf8af051aaee286e369fed064
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@qt.io>

tests/auto/testlib/selftests/generate_expected_output.py

@@ -252,7 +252,13 @@ def generateTestData(testname, clean,
 
 def main(name, *args):
     """Minimal argument parsing and driver for the real work"""
-    os.environ['LC_ALL'] = 'C'
+    os.environ.update(
+        LC_ALL = 'C', # Use standard locale
+        # Avoid interference from any qtlogging.ini files, e.g. in
+        # /etc/xdg/QtProject/, (must match tst_selftests.cpp's
+        # processEnvironment()'s value):
+        QT_LOGGING_RULES = '*.debug=true;qt.qpa.screen=false')
+
     herePath = os.getcwd()
     cleaner = Cleaner(herePath, name)
 

tests/auto/testlib/selftests/tst_selftests.cpp

@@ -568,6 +568,10 @@ static QProcessEnvironment processEnvironment()
             if (useVariable)
                 result.insert(key, systemEnvironment.value(key));
         }
+        // Avoid interference from any qtlogging.ini files, e.g. in /etc/xdg/QtProject/:
+        result.insert(QStringLiteral("QT_LOGGING_RULES"),
+                      // Must match generate_expected_output.py's main()'s value:
+                      QStringLiteral("*.debug=true;qt.qpa.screen=false"));
     }
     return result;
 }