With libqrencode installed:
mkdir buildcmake && cd buildcmake
cmake -GNinja ..
ninja
./src/qt/bitcoin-qt
Go the the `Receive` tab and click the `Request payment` button.
A QR code should be displayed.
rm -rf *
cmake -GNinja -DENABLE_QRCODE=OFF ..
ninja
./src/qt/bitcoin-qt
Go the the `Receive` tab and click the `` button.
The QR code should not be displayed.
Uninstall libqrencode. On Debian: `sudo apt remove libqrencode*`
rm -rf *
cmake -GNinja -DENABLE_QRCODE=ON ..
CMake should output an error:
```
QR support requested but cannot be built as it requires libqrencode to
be installed. Use -DENABLE_QRCODE=OFF
```