qt: Ignore gcc 12.1 optimization bug with Qt

The Qt implicit casts from QByteArray to QString all use
size = -1, meaning to the end of the string.

This causes gcc 12.1 with -O2 to produce a very dubious stringop-overread
warning, by computing both sides of a branch even when it shouldn't:

/usr/include/qt5/QtCore/qstring.h:706:69: error: ‘size_t strlen(const char*)’ reading 1 or more bytes from a region of size 0 [-Werror=stringop-overread]
  706 |         return fromUtf8_helper(str, (str && size == -1) ? int(strlen(str)) : size);
      |                                                               ~~~~~~^~~~~

There's also a similar error with QByteArray.constData(), even though
isEmpty() should return True when the QByteArray is NULL.
(Adding isNull() prevents the warning but is redundant.)

Use DIAG_OFF and DIAG_ON to ignore the warning on GCC 12.1 and higher.
Fix #18090.

ui/qt/about_dialog.cpp

@@ -461,8 +461,18 @@ void AboutDialog::updateWiresharkText()
     /* Save the info for the clipboard copy */
     clipboardInfo = "";
     clipboardInfo += vcs_version_info_str + "\n\n";
+    /* XXX: GCC 12.1 has a bogus stringop-overread warning using the Qt
+     * conversions from QByteArray to QString at -O2 and higher due to
+     * computing a branch that will never be taken.
+     */
+#if WS_IS_AT_LEAST_GNUC_VERSION(12,1)
+DIAG_OFF(stringop-overread)
+#endif
     clipboardInfo += gstring_free_to_qbytearray(get_compiled_version_info(gather_wireshark_qt_compiled_info)) + "\n";
     clipboardInfo += gstring_free_to_qbytearray(get_runtime_version_info(gather_wireshark_runtime_info));
+#if WS_IS_AT_LEAST_GNUC_VERSION(12,1)
+DIAG_ON(stringop-overread)
+#endif
 }
 
 void AboutDialog::on_copyToClipboard_clicked()

ui/qt/follow_stream_dialog.cpp

@@ -891,7 +891,17 @@ FollowStreamDialog::showBuffer(char *buffer, size_t nchars, gboolean is_from_ser
             int len = current_pos + base64_raw_len < nchars ? base64_raw_len : (int) nchars - current_pos;
             QByteArray base64_data(&buffer[current_pos], len);
 
+            /* XXX: GCC 12.1 has a bogus stringop-overread warning using the Qt
+             * conversions from QByteArray to QString at -O2 and higher due to
+             * computing a branch that will never be taken.
+             */
+#if WS_IS_AT_LEAST_GNUC_VERSION(12,1)
+DIAG_OFF(stringop-overread)
+#endif
             yaml_text += "      " + base64_data.toBase64() + "\n";
+#if WS_IS_AT_LEAST_GNUC_VERSION(12,1)
+DIAG_ON(stringop-overread)
+#endif
 
             current_pos += len;
             (*global_pos) += len;

ui/qt/show_packet_bytes_dialog.cpp

@@ -801,7 +801,17 @@ void ShowPacketBytesDialog::updatePacketBytes(void)
         while (pos < len) {
             QByteArray base64_data = field_bytes_.mid(pos, base64_raw_len);
             pos += base64_data.length();
+            /* XXX: GCC 12.1 has a bogus stringop-overread warning using the Qt
+             * conversions from QByteArray to QString at -O2 and higher due to
+             * computing a branch that will never be taken.
+             */
+#if WS_IS_AT_LEAST_GNUC_VERSION(12,1)
+DIAG_OFF(stringop-overread)
+#endif
             text.append("  " + base64_data.toBase64() + "\n");
+#if WS_IS_AT_LEAST_GNUC_VERSION(12,1)
+DIAG_ON(stringop-overread)
+#endif
         }
 
         ui->tePacketBytes->setLineWrapMode(QTextEdit::NoWrap);

ui/qt/wireshark_main_window_slots.cpp

@@ -950,7 +950,17 @@ void WiresharkMainWindow::startCapture(QStringList interfaces _U_) {
                     /* Not the first selected interface; is its capture filter
                        the same as the one the other interfaces we've looked
                        at have? */
+                    /* XXX: GCC 12.1 has a bogus warning at -O2 and higher
+                     * even though the isEmpty() check guarantees that
+                     * filter_ba.constData() is never NULL or empty.
+                     */
+#if WS_IS_AT_LEAST_GNUC_VERSION(12,1)
+DIAG_OFF(stringop-overread)
+#endif
                     if (strcmp(interface_opts->cfilter, filter_ba.constData()) != 0) {
+#if WS_IS_AT_LEAST_GNUC_VERSION(12,1)
+DIAG_ON(stringop-overread)
+#endif
                         /* No, so not all selected interfaces have the same capture
                            filter. */
                         filter_ba.clear();