By "empty traceback" I mean a traceback all of whose entries have been
filtered/cut/pruned out.
Currently, if an empty traceback needs to be repr'ed, the last entry
before the filtering is used instead (added in
accd962c9f).
Showing a hidden frame is not so good IMO. This commit does the
following instead:
1. Shows details of the exception.
2. Shows a message about how the full trace can be seen.
Example:
```
_____________ test _____________
E ZeroDivisionError: division by zero
All traceback entries are hidden. Pass `--full-trace` to see hidden and internal frames.
```
Also handles `--tb=native`, though there the `--full-trace` bit is not
shown.
This commit contains some pieces from
431ec6d34e (which has been reverted).
Helps towards fixing issue # 1904.
Co-authored-by: Felix Hofstätter <Felhof1@hotmail.com>
e3b1799766