Python syntax tree broken after edit that should have no effect

[microbit-matt-hillsdon]

Using lang-python, start with this program:

#Amount of text here is significant !

while True:
    if function_call_quite_long():
        if True:
            pass
        else:
            pass

Delete the "else: pass" part. Reinstate it as it was.

Note that the syntax tree now has what I think are error nodes and is different from the original syntax tree.

Original syntax tree toString():

Script(Comment,WhileStatement(while,Boolean,Body(":",IfStatement(if,CallExpression(VariableName,ArgList("(",")")),Body(":",IfStatement(if,Boolean,Body(":",PassStatement(pass)),else,Body(":",PassStatement(pass)))))))) 

Syntax tree toString() after:

Script(Comment,WhileStatement(while,Boolean,Body(":",IfStatement(if,CallExpression(VariableName,ArgList("(",")")),Body(":",IfStatement(if,Boolean,Body(":",PassStatement(pass))),⚠),⚠,else,Body(":",PassStatement(pass)))))) 

There's a sandbox here with a reproduction that dumps out the syntax tree in a debug view plugin:

https://codesandbox.io/s/python-if-else-bug-xs85w

It was hard to further minimise the code. The length of the comment and the function call seemed to be significant, so I wondered whether it might be an incremental parse issue of some sort.

[marijnh]

That was indeed a bug in the incremental parsing. Upgrading to lezer 0.13.5 should help.

[microbit-matt-hillsdon]

I've confirmed that 0.13.5 fixes the reproduction above and my more involved original scenario. Thank you.