Silently strip leading dot off QFileDialog default suffixes.

Change-Id: Ie41fafe8c2ce7e8ac8dd595ca3809c1da3b386f4
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>

dist/changes-5.2.0

@@ -29,3 +29,5 @@ QtWidgets
 - [QTBUG-4206] QTableView resizeToContents will now adjust to actual contents
   and not just visible area. QHeaderView::setAutoResizePrecision() has been
   introduced to control how precise the autoResize should be.
+
+- QFileDialog::setDefaultSuffix() removes leading dot characters.

src/gui/kernel/qplatformdialoghelper.cpp

@@ -495,6 +495,8 @@ QStringList QFileDialogOptions::nameFilters() const
 void QFileDialogOptions::setDefaultSuffix(const QString &suffix)
 {
     d->defaultSuffix = suffix;
+    if (d->defaultSuffix.size() > 1 && d->defaultSuffix.startsWith(QLatin1Char('.')))
+        d->defaultSuffix.remove(0, 1); // Silently change ".txt" -> "txt".
 }
 
 QString QFileDialogOptions::defaultSuffix() const

src/widgets/dialogs/qfiledialog.cpp

@@ -1552,6 +1552,8 @@ bool QFileDialog::confirmOverwrite() const
     filename if it has no suffix already. The suffix is typically
     used to indicate the file type (e.g. "txt" indicates a text
     file).
+
+    If the first character is a dot ('.'), it is removed.
 */
 void QFileDialog::setDefaultSuffix(const QString &suffix)
 {

tests/auto/widgets/dialogs/qfiledialog/tst_qfiledialog.cpp

@@ -621,6 +621,8 @@ void tst_QFiledialog::defaultSuffix()
     QCOMPARE(fd.defaultSuffix(), QString());
     fd.setDefaultSuffix("txt");
     QCOMPARE(fd.defaultSuffix(), QString("txt"));
+    fd.setDefaultSuffix(".txt");
+    QCOMPARE(fd.defaultSuffix(), QString("txt"));
     fd.setDefaultSuffix(QString());
     QCOMPARE(fd.defaultSuffix(), QString());
 }