tst_QLocale: fix restoration of default locale after tests change it

Use qScopeGuard() to ensure we always restore cleanly. Some of them
didn't even need to set default locale, and one only needed a minor
tweak to save the need for it.  Remove tst_QLocale's red-flag comments
about its tests that exercise setDefault(), since they should now be
harmless and not care about their order relative to other tests.

Change-Id: I552218989c66c4e7b238b3a949a6aeae3a7c2825
Reviewed-by: Tor Arne Vestbø <[email protected]>

tests/auto/corelib/text/qlocale/tst_qlocale.cpp

@@ -161,16 +161,12 @@ private slots:
     void lcsToCode();
     void codeToLcs();
 
-    // *** ORDER-DEPENDENCY *** (This Is Bad.)
-    // Test order is determined by order of declaration here: *all* tests that
-    // QLocale::setDefault() *must* appear *after* all other tests !
-    void defaulted_ctor(); // This one must be the first of these.
+    void defaulted_ctor();
     void legacyNames();
     void unixLocaleName_data();
     void unixLocaleName();
     void testNames_data();
     void testNames();
-    // DO NOT add tests here unless they QLocale::setDefault(); see above.
 private:
     QString m_decimal, m_thousand, m_sdate, m_ldate, m_time;
     QString m_sysapp;
@@ -391,6 +387,9 @@ void tst_QLocale::ctor_match_land()
 void tst_QLocale::defaulted_ctor()
 {
     QLocale priorDefault;
+    const auto restoreDefault = qScopeGuard([priorDefault]() {
+        QLocale::setDefault(priorDefault);
+    });
     QLocale::Language defaultLanguage = priorDefault.language();
     QLocale::Territory defaultTerritory = priorDefault.territory();
 
@@ -501,6 +500,7 @@ void tst_QLocale::defaulted_ctor()
     TEST_CTOR(Swedish, AnyTerritory, QLocale::Swedish, QLocale::Sweden);
     TEST_CTOR(Uzbek, AnyTerritory, QLocale::Uzbek, QLocale::Uzbekistan);
 
+#undef CHECK_DEFAULT
 #undef TEST_CTOR
 #define TEST_CTOR(req_lc, exp_lang, exp_country) \
     do { \
@@ -512,7 +512,6 @@ void tst_QLocale::defaulted_ctor()
         QCOMPARE(qHash(l), qHash(m)); \
     } while (false)
 
-    QLocale::setDefault(QLocale(QLocale::C));
     const QString empty;
 
     TEST_CTOR("C", C, AnyTerritory);
@@ -583,7 +582,6 @@ void tst_QLocale::defaulted_ctor()
     TEST_CTOR("ru_Cyrl", Russian, CyrillicScript, RussianFederation);
 
 #undef TEST_CTOR
-#undef CHECK_DEFAULT
 }
 
 #if QT_CONFIG(process)
@@ -746,8 +744,6 @@ void tst_QLocale::systemLocale()
 
 void tst_QLocale::legacyNames()
 {
-    QLocale::setDefault(QLocale(QLocale::C));
-
 #define TEST_CTOR(req_lc, exp_lang, exp_country) \
     do { \
         const QLocale l(req_lc); \
@@ -821,8 +817,8 @@ void tst_QLocale::unixLocaleName_data()
     ADDROW("C_any", C, AnyTerritory, "C");
     ADDROW("en_any", English, AnyTerritory, "en_US");
     ADDROW("en_GB", English, UnitedKingdom, "en_GB");
-    ADDROW("ay_GB", Aymara, UnitedKingdom, "C");
 #undef ADDROW
+    QTest::newRow("ay_GB") << QLocale::Aymara << QLocale::UnitedKingdom << QLocale().name();
 }
 
 void tst_QLocale::unixLocaleName()
@@ -836,8 +832,6 @@ void tst_QLocale::unixLocaleName()
         return copy.replace(u'_', ch);
     };
 
-    QLocale::setDefault(QLocale(QLocale::C));
-
     const QLocale locale(lang, land);
     QCOMPARE(locale.name(), expect);
     QCOMPARE(locale.name(QLocale::TagSeparator::Dash), expected(u'-'));
@@ -3073,8 +3067,6 @@ void tst_QLocale::testNames_data()
     QTest::addColumn<QLocale::Language>("language");
     QTest::addColumn<QLocale::Territory>("country");
 
-    QLocale::setDefault(QLocale(QLocale::C)); // Ensures predictable fall-backs
-
 #ifdef QT_BUILD_INTERNAL
     bool ok = QLocaleData::allLocaleDataRows([](qsizetype index, const QLocaleData &item) {
         const QByteArray lang =