There was an issue with the script when passing optional rustfmt configs
without specifying a commit hash. Because these optional values are
passed via positional arguments the configs ($4) would be used in place
of the commit hash ($3). Now that we set a default value for the
optional commit hash we avoid this problem.
The `set -e` option is used to immediately exit if any command exits
with a non zero exit status. This will help us catch errors in the
script, for example, needing the `LD_LIBRARY_PATH` to be set.
There were some upstream changes made a while back that requires this to
be set when building rustfmt from source like we do in the
`check_diff.sh` script.
See issue 5675 for more details.
This new action is intended to help us maintainers determine when feature
branches cause breaking formatting changes by running rustfmt (master)
and the feature branch on various rust repositories.
Over time I expect the list of checked projects to increase.
With this action in place we can more easily test that a new feature or
bug fix doesn't introduce breaking changes. Although this action needs to
be manually triggered right now, we might consider adding it to our CI
runs in the future.
