desktop: overwrite drag & drop in TagWidget

The interaction of Qt's drag & drop with GroupedLineEdit was
exceedingly weird. The user was able to scroll the viewport
making the text invisible.

This implements a very primitive alternative drag & drop
functionality: dropped text is regarged as a distinct tag.
This means that it is not possible to modify existing tags
by dropping in the middle of them. Arguably, this might even
be better than arbitrary drag & drop. But even if not perfect,
this fixes a very nasty UI behavior.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

CHANGELOG.md

@@ -1,3 +1,4 @@
+- desktop: fix crash on drag&drop into tag widgets [#3030]
 - macOS: fix issue with HID dive computers like Suunto Eon Core/Steel [#2999]
 - windows: add missing modern Vista theme
 - mobile: add location service warning as required by Google Play

desktop-widgets/tagwidget.cpp

@@ -3,6 +3,7 @@
 #include "mainwindow.h"
 #include "tab-widgets/maintab.h"
 #include <QCompleter>
+#include <QMimeData>
 
 TagWidget::TagWidget(QWidget *parent) : GroupedLineEdit(parent), m_completer(NULL), lastFinishedTag(false)
 {
@@ -211,3 +212,43 @@ void TagWidget::focusOutEvent(QFocusEvent *ev)
 	GroupedLineEdit::focusOutEvent(ev);
 	emit editingFinished();
 }
+
+// Implement simple drag and drop: text dropped onto the widget
+// will be added as a new tag at the end. This overrides
+// Qt's implementation which resulted in weird UI behavior,
+// as the user may succeed in scrolling the view port.
+static void handleDragEvent(QDragMoveEvent *e)
+{
+	if (e->mimeData()->hasFormat(QStringLiteral("text/plain")))
+		e->acceptProposedAction();
+}
+
+void TagWidget::dragEnterEvent(QDragEnterEvent *e)
+{
+	handleDragEvent(e);
+}
+
+void TagWidget::dragMoveEvent(QDragMoveEvent *e)
+{
+	handleDragEvent(e);
+}
+
+void TagWidget::dragLeaveEvent(QDragLeaveEvent *)
+{
+}
+
+void TagWidget::dropEvent(QDropEvent *e)
+{
+	e->acceptProposedAction();
+
+	QString newTag = e->mimeData()->text().trimmed();
+	if (newTag.isEmpty())
+		return;
+
+	QString s = text().trimmed();
+	if (!s.isEmpty())
+		s += ", ";
+	s += newTag;
+	setText(s);
+	emit editingFinished();
+}

desktop-widgets/tagwidget.h

@@ -26,7 +26,11 @@ slots:
 	void completionHighlighted(const QString &text);
 
 protected:
-	void keyPressEvent(QKeyEvent *e);
+	void keyPressEvent(QKeyEvent *e) override;
+	void dragEnterEvent(QDragEnterEvent *e) override;
+	void dragLeaveEvent(QDragLeaveEvent *e) override;
+	void dragMoveEvent(QDragMoveEvent *e) override;
+	void dropEvent(QDropEvent *e) override;
 private:
 	void focusOutEvent(QFocusEvent *ev) override;
 	QCompleter *m_completer;