Elpi: fix catastrophic backtracking

[jeanas]

Closes #2053

[birkenfeld]

The reformatting makes it basically impossible to see what has really changed.

Please don't apply black to the Pygments codebase, as you can see we have a pretty different style.

[jeanas]

The reformatting makes it basically impossible to see what has really changed.

Please don't apply black to the Pygments codebase, as you can see we have a pretty different style.

OK, I'll back the formatting out. Note, though, that it is in a separate commit for the purpose of review (I've been trained rigorously to use atomic commits, but maybe that is not usual here?).

[birkenfeld]

As far as I can see, the formatting changes in the first commit ("minor changes") which also has a bunch of other (useful) things?

[birkenfeld]

I've been trained rigorously to use atomic commits, but maybe that is not usual here?

Of course it's useful, but even with atomic commits I wouldn't expect to see a wholesale reformatting in a PR to fix a bug :-)

[jeanas]

I have refactored this PR to include only the bugfix.

[birkenfeld]

Thanks a lot!