QT Py SAMD21: Specific error in REPL in Thonny causes hard crash and damages unprotected bootloader

[dhalbert]

8.1.0
QT Py SAMD21
Thonny

https://forums.adafruit.com/viewtopic.php?p=973733

import board
import busio
uart = busio.UART(board.TX, board.RX, baudrate=4800, bits=7, parity=EVEN, stop=2, timeout=0.5)

Note that EVEN is undefined, so it shouldn't get to the constructor call.

Doing the above in the REPL causes the error to be reported followed by a safe mode crash, repeated attempts to reconnect from Thonny. For the user, with an unprotected bootloader, it bricked the board.

When used with pico or other terminal program, nothing unusual happens. The above example just generates

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'EVEN' is not defined

With a protected bootloader, the board was not bricked, but still need to figure out what is causing this serious error.

[dhalbert]

thonny issue: thonny/thonny#2914

[dhalbert]

Still reproducible with 9.2.7 and 10.0.0-alpha.2. Note that simplifying this to say, the imports plus uart = busio.UART(board.TX, board.RX, parity=EVEN) does not provoke the error. So this particular sample of code is tickling a bug.