Remove the limit on input size for diff gen

[its-the-shrimp]

I'm using this version of trybuild for my tests as the lack of diffs for non-trivial compiler outputs is extremely annoying, as those are the ones where proper diffs are the most important.

I found that the removed if condition is 4 years old, I wonder if the concern is still up to date

[dtolnay]

This is to protect from dtolnay/dissimilar#12.

Switching to a more robust diff algorithm would be a more viable option.

[its-the-shrimp]

Would you accept a PR replacing dissimilar with diffy? It seems to be more mature

[dtolnay]

That crate is specifically for generating (and coloring) .patch file format, which is not the format that I would prefer trybuild's output to take. It is not compatible with intraline highlighting. The use case that .patch files are designed for is very different. It is optimized for applying one set of changes to a source file that already contains a different set of changes, e.g. in the context of source control. The crate also has many fewer downloads than dissimilar. I am not confident that it would turn out to be mature in practical usage.