- `RUST_BACKTRACE=full` prints all the informations (old behaviour)
- `RUST_BACKTRACE=(0|no)` disables the backtrace.
- `RUST_BACKTRACE=<everything else>` (including `1`) shows a simplified
backtrace, without the function addresses and with cleaned filenames
and symbols. Also removes some unneded frames at the beginning and the
end.
Fixes#37783.
PR is #38165.