CRS transform exception bricks map canvas

[uclaros]

Describe the bug
If a crs transform exception is thrown, QGIS can be stuck in an strange state where the map canvas can be panned or zoomed but the layers panel has no effect on layers visibility any more!

How to Reproduce

1. Open the attached project tmp_project.zip
2. Right click on layer dem_tfw > Layer CRS > Set to EPSG:4326 (wrong on purpose)
3. Uncheck any layer to turn off its visibility
4. An exception messagebox informs that Could not transform bounding box to target CRS
5. The map canvas is now at a stuck state. You can zoom / pan but layers panel does nothing.
6. Close QGIS (discard project)
7. Same exception messagebox, we cannot quit!
8. Remove the layer or correctly set CRS to EPSG:2100
9. Map canvas is still stuck, at least we can exit!

QGIS and OS versions
677ccf5 on debian testing

[nyalldawson]

You should see the full stacketrace dumped to console when this happens -- are you able to copy and paste that?

[uclaros]

This is all I get with QGIS_DEBUG=9

../src/core/qgscoordinatetransform.cpp:545 : (transformBoundingBox) [0ms] Entering transformBoundingBox...
Critical: Caught unhandled QgsException:  "Could not transform bounding box to target CRS"
Stacktrace (piped through c++filt):
./output/bin/qgis(+0xcfc8)[0x55701fd80fc8]
./output/bin/qgis(+0xd513)[0x55701fd81513]
/lib/x86_64-linux-gnu/libQt5Core.so.5(+0xc47c8)[0x7f1dc69c87c8]
/lib/x86_64-linux-gnu/libQt5Core.so.5(qt_message_output(QtMsgType, QMessageLogContext const&, QString const&)+0xd)[0x7f1dc69c9d4d]
/lib/x86_64-linux-gnu/libQt5Core.so.5(QDebug::~QDebug()+0x68)[0x7f1dc6ac93a8]
/home/uclaros/dev/QGIS/build-master-Debug/output/lib/libqgis_core.so.3.17.0(QgsApplication::notify(QObject*, QEvent*)+0x180)[0x7f1dc512b4da]
/lib/x86_64-linux-gnu/libQt5Core.so.5(QCoreApplication::notifyInternal2(QObject*, QEvent*)+0x12a)[0x7f1dc6bb1f2a]
/lib/x86_64-linux-gnu/libQt5Core.so.5(QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*)+0x171)[0x7f1dc6bb4961]
/lib/x86_64-linux-gnu/libQt5Core.so.5(+0x305df3)[0x7f1dc6c09df3]
/lib/x86_64-linux-gnu/libglib-2.0.so.0(g_main_context_dispatch+0x25b)[0x7f1dbc7afbdb]
/lib/x86_64-linux-gnu/libglib-2.0.so.0(+0x51e88)[0x7f1dbc7afe88]
/lib/x86_64-linux-gnu/libglib-2.0.so.0(g_main_context_iteration+0x2f)[0x7f1dbc7aff3f]
/lib/x86_64-linux-gnu/libQt5Core.so.5(QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>)+0x5f)[0x7f1dc6c0947f]
/lib/x86_64-linux-gnu/libQt5Core.so.5(QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>)+0x12b)[0x7f1dc6bb08eb]
/lib/x86_64-linux-gnu/libQt5Core.so.5(QCoreApplication::exec()+0x90)[0x7f1dc6bb8b60]
./output/bin/qgis(+0x14ade)[0x55701fd88ade]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xea)[0x7f1dc414bd0a]
./output/bin/qgis(+0xb06a)[0x55701fd7f06a]

[nyalldawson]

Are you running a debug build?

[uclaros]

Yup

[nyalldawson]

Ok, got it. It's master only.