Currently, if you enter an invalid expression (for example bad as the expression for a snapshot or {bad} as the message for a logpoint) the php interpreter will fail, either throwing an exception or a segmentation fault, when it reaches the breakpoint

This is very bad news for running the debugger in production. You can easily break production by adding a breakpoint (snapshot or logpoint) with invalid expressions.

The behaviour should be the same as the current behaviour for conditions. If you enter an invalid condition this is just ignored. Or perhaps some kind of error is recorded for snapshots and logpoints, but never crash the app