AO3-7561 Fix 500 when trying to /comments/show_comments on nothing

[danderson]

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Issue

https://otwarchive.atlassian.net/browse/AO3-7561

Purpose

Fixes a 500 when attempting to view comments without passing any query parameters. With this change, the user is instead redirected back from whence they came, with a flash error noting that you can't view comments on nothing.

Testing Instructions

Navigate to http://archiveofourown.org/comments/show_comments. Without this change, will 500. With this change, will redirect to the homepage with an error flash.

References

https://otwarchive.atlassian.net/browse/AO3-7556 is a similar issue in a different route, with a similar fix. Assuming I didn't screw up this one, I can send a followup PR with that fix too.

Credit

David Anderson (he/him)

Misc notes

This is my first PR to otwarchive. There were no first timer issues open, so I picked a recent Difficulty=Easy bug instead to get my feet wet and figure out the dev workflow.

I chose to handle the nil in the show_comments logic, rather than in the redirect_to_all_comments helper where the 500 triggered. This seems to match the local coding style for handling nil commentables (e.g. new and create), and the helper is also called from places where the commentable is a DB object or similar, and silently swallowing an error in those codepaths didn't seem right.

[danderson]

The couple force pushes were to fix rubocop complaints, which all concerned the preexisting code that I moved into the else branch. The fixes are straightforward, but I did have to switch a use of ts() to t() and add a translation string. Those lint fixes aren't very related to the purpose of the PR, so lemme know if you want them split out, and how?

[ASalbenblatt]

Just one small thing to fix, otherwise it looks good. I also marked your issues as In Review on Jira so no one accidentally picks them up. Someone with more perms should be along soon to help get your account connected so you can update them yourself :)
Also including the ts() to t() conversion in this pr is absolutely expected and a-ok

[ASalbenblatt]

Looks good! Thanks!

[sarken]

Hi, David Anderson!

Thank you so much for this pull request. I've left a quick comment about the error message i18n. Once that's addressed, I think this will be ready to merge.

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[danderson]

Thanks for the review! Changes done, assuming CI is happy with what I did.

I emailed otw-coders@ with account info for Jira.

[sarken]

Thank you! (Your Jira permissions should be all set now as well.)