Only rescue LoadError for linguist

[calebhearth]

Currently this also catches a LoadError for rugged, a dependency Linguist
added but didn't add to its gemspec.

github-linguist/linguist#1600
github-linguist/linguist#1601

[jch]

Thanks for the pull, but I'd rather see this fixed upstream in linguist rather than here.

[calebhearth]

It's being fixed there, but you're also being potentially overzealous in your rescue.

[calebhearth]

Or rather, there are PRs to fix it.

[jch]

@calebthompson it sounds like rugged is a required dependency of linguist. With those fixes in place, why would there be a load error for rugged if the fixes are made upstream? Wouldn't attempting to load linguist fail if rugged wasn't installed?

I see that this would fix older versions of linguist, but I want to avoid more error handling for external dependencies. For 2.0, I have some ideas about defining adaptors for external dependencies so we can encapsulate these checks outside of the filter classes.

[calebhearth]

Sorry, I just realized I left out important information here.

I found the problem in Linguist while trying to update Html Pipeline. I had trouble debugging it because of the rescue LoadError, and wouldn't have found the problem (upstream) at all if I hadn't added a require: to my project's Gemfile, because Html Pipeline was eating the LoadError (with the error message about 'rugged') and giving me a different message about not being having the github-linguist dependency.

So the bug this pull request solves is that our approach to having this gem's users handle dependencies also hides useful errors that don't result from not having its (direct) dependencies resolved.

[jch]

Html Pipeline was eating the LoadError (with the error message about 'rugged') and giving me a different message about not being having the github-linguist dependency.

Ah, that is a good point. What do you think of updating the rescue message to output the raw error message then? Something along the lines of:

rescue LoadError => e
  abort "Missing dependency for SyntaxHighlightFilter. See README.md for details.\n#{e.message}"
end

If that sounds good, could you make the changes to the other filters as well?

[calebhearth]

I'm fine with that, but I'll have to come back to the change.