[LyX/master] #12818 correct evaluation of message box result info

[Stephan Witt]

commit b924db72c5bc7e194d1b6a2b0e55f0427fa366b6
Author: Stephan Witt <switt at lyx.org>
Date:   Sun Jul 16 16:48:49 2023 +0200

    #12818 correct evaluation of message box result info
    
    The help page of int QMessageBox::exec() (​https://doc.qt.io/qt-6/qmessagebox.html#exec) says:
    When using a QMessageBox with standard buttons, this function returns a StandardButton value indicating the standard button that was clicked.
    When using QMessageBox with custom buttons, this function returns an opaque value; use clickedButton() to determine which button was clicked.
---
 src/frontends/alert.h         |    6 ++++--
 src/frontends/qt/GuiAlert.cpp |   36 +++++++++++++++++++++++++-----------
 2 files changed, 29 insertions(+), 13 deletions(-)

diff --git a/src/frontends/alert.h b/src/frontends/alert.h
index 20da436..a4556ca 100644
--- a/src/frontends/alert.h
+++ b/src/frontends/alert.h
@@ -19,6 +19,8 @@ namespace lyx {
 namespace frontend {
 namespace Alert {
 
+typedef unsigned short buttonid;
+
 /**
  * Prompt for a question. Returns 0-3 for the chosen button.
  * Set default_button and cancel_button to reasonable values. b1-b3
@@ -30,8 +32,8 @@ namespace Alert {
  * "Yes" or "No", I will personally come around to your house and
  * slap you with fish, and not in an enjoyable way either.
  */
-int prompt(docstring const & title, docstring const & question,
-	   int default_button, int cancel_button,
+buttonid prompt(docstring const & title, docstring const & question,
+	   buttonid default_button, buttonid cancel_button,
 	   docstring const & b0, docstring const & b1,
 	   docstring const & b2 = empty_docstring(),
 	   docstring const & b3 = empty_docstring());
diff --git a/src/frontends/qt/GuiAlert.cpp b/src/frontends/qt/GuiAlert.cpp
index 93b8e1d..85a5e22 100644
--- a/src/frontends/qt/GuiAlert.cpp
+++ b/src/frontends/qt/GuiAlert.cpp
@@ -75,8 +75,8 @@ docstring toPlainText(docstring const & msg)
 }
 
 
-int doPrompt(docstring const & title, docstring const & question,
-		  int default_button, int cancel_button,
+buttonid doPrompt(docstring const & title, docstring const & question,
+		  buttonid default_button, buttonid cancel_button,
 		  docstring const & b1, docstring const & b2,
 		  docstring const & b3, docstring const & b4)
 {
@@ -108,7 +108,7 @@ int doPrompt(docstring const & title, docstring const & question,
 
 	// FIXME replace that with guiApp->currentView()
 	//LYXERR0("FOCUS: " << qApp->focusWidget());
-	QPushButton * b[4] = { 0, 0, 0, 0 };
+	QPushButton * b[4] = { nullptr, nullptr, nullptr, nullptr };
 	QMessageBox msg_box(QMessageBox::Information,
 			toqstr(title), toqstr(question),
 			QMessageBox::NoButton, qApp->focusWidget());
@@ -120,23 +120,37 @@ int doPrompt(docstring const & title, docstring const & question,
 		b[2] = msg_box.addButton(toqstr(b3), QMessageBox::ActionRole);
 	if (!b4.empty())
 		b[3] = msg_box.addButton(toqstr(b4), QMessageBox::ActionRole);
-	msg_box.setDefaultButton(b[default_button]);
-	msg_box.setEscapeButton(static_cast<QAbstractButton *>(b[cancel_button]));
-	int res = msg_box.exec();
+	if (default_button < size(b) && nullptr != b[default_button])
+		msg_box.setDefaultButton(b[default_button]);
+	if (cancel_button < size(b) && nullptr != b[cancel_button])
+		msg_box.setEscapeButton(static_cast<QAbstractButton *>(b[cancel_button]));
+	msg_box.exec();
+	const QAbstractButton * button = msg_box.clickedButton();
 
 	qApp->restoreOverrideCursor();
 
 	if (long_op)
 		theApp()->startLongOperation();
 
-	// Qt bug: can return -1 on cancel or WM close, despite the docs.
-	if (res == -1)
-		res = cancel_button;
+	size_t res = cancel_button;
+
+	if (button == nullptr)
+		return res;
+	else {
+		// Convert selection of the button into an integer
+		for (size_t i = 0; i < size(b); i++) {
+			if (button == b[i]) {
+				res = i;
+				break;
+			}
+		}
+	}
+
 	return res;
 }
 
-int prompt(docstring const & title, docstring const & question,
-		  int default_button, int cancel_button,
+buttonid prompt(docstring const & title, docstring const & question,
+		  buttonid default_button, buttonid cancel_button,
 		  docstring const & b0, docstring const & b1,
 		  docstring const & b2, docstring const & b3)
 {