QProgressDialog: make the cancel button retranslate on LanguageChange

It is documented to be, and the LanguageChange event is caught and processed.
However, retranslateStrings() uses QProgressDialog::setCancelButtonText(),
which unconditionally sets useDefaultCancelText=true, blocking any further
changes to the button text by subsequent LanguageChange events.

The fix is to use extracted QProgressDialogPrivate::setCancelButtonText()
which - quite intentionally - doesn't set useDefaultCancelText.

Task-number: QTBUG-40504
Change-Id: I6e701deda10c454cb088c0b0778ac2d6adff574a
Reviewed-by: David Faure <david.faure@kdab.com>

2 files changed, 46 insertions, 2 deletions

diff --git a/src/widgets/dialogs/qprogressdialog.cpp b/src/widgets/dialogs/qprogressdialog.cpp
index d160ab0ae1..35a75adea2 100644
--- a/src/widgets/dialogs/qprogressdialog.cpp
+++ b/src/widgets/dialogs/qprogressdialog.cpp
@@ -179,9 +179,8 @@ void QProgressDialogPrivate::layout()
 
 void QProgressDialogPrivate::retranslateStrings()
 {
-    Q_Q(QProgressDialog);
     if (useDefaultCancelText)
-        q->setCancelButtonText(QProgressDialog::tr("Cancel"));
+        setCancelButtonText(QProgressDialog::tr("Cancel"));
 }
 
 void QProgressDialogPrivate::_q_disconnectOnClose()
diff --git a/tests/auto/widgets/dialogs/qprogressdialog/tst_qprogressdialog.cpp b/tests/auto/widgets/dialogs/qprogressdialog/tst_qprogressdialog.cpp
index 4ff158f632..86b9d7eee2 100644
--- a/tests/auto/widgets/dialogs/qprogressdialog/tst_qprogressdialog.cpp
+++ b/tests/auto/widgets/dialogs/qprogressdialog/tst_qprogressdialog.cpp
@@ -50,6 +50,7 @@
 #include <qlabel.h>
 #include <qpointer.h>
 #include <qthread.h>
+#include <qtranslator.h>
 
 class tst_QProgressDialog : public QObject
 {
@@ -63,6 +64,7 @@ private Q_SLOTS:
     void task198202();
     void QTBUG_31046();
     void settingCustomWidgets();
+    void i18n();
 };
 
 void tst_QProgressDialog::cleanup()
@@ -234,5 +236,48 @@ void tst_QProgressDialog::settingCustomWidgets()
 #endif
 }
 
+class QTestTranslator : public QTranslator
+{
+    const QString m_str;
+public:
+    explicit QTestTranslator(QString str) : m_str(qMove(str)) {}
+
+    QString translate(const char *, const char *sourceText, const char *, int) const Q_DECL_OVERRIDE
+    { return m_str + sourceText + m_str; }
+
+    bool isEmpty() const Q_DECL_OVERRIDE { return false; }
+};
+
+template <typename Translator>
+class QTranslatorGuard {
+    Translator t;
+public:
+    template <typename Arg>
+    explicit QTranslatorGuard(Arg a) : t(qMove(a))
+    { qApp->installTranslator(&t); }
+    ~QTranslatorGuard()
+    { qApp->removeTranslator(&t); }
+};
+
+void tst_QProgressDialog::i18n()
+{
+    QProgressDialog dlg;
+    QPushButton *btn = dlg.findChild<QPushButton*>();
+    QVERIFY(btn);
+    const QString xxx = QStringLiteral("xxx");
+    {
+        QTranslatorGuard<QTestTranslator> guard(xxx);
+        {
+            QPushButton *btn = dlg.findChild<QPushButton*>();
+            QVERIFY(btn);
+            QTRY_COMPARE(btn->text(), QProgressDialog::tr("Cancel"));
+            QVERIFY(btn->text().startsWith(xxx));
+        }
+    }
+    QVERIFY(btn);
+    QTRY_COMPARE(btn->text(), QProgressDialog::tr("Cancel"));
+    QVERIFY(!btn->text().startsWith(xxx));
+}
+
 QTEST_MAIN(tst_QProgressDialog)
 #include "tst_qprogressdialog.moc"