Avoid creating a new empty talk page when removing a template from a non-existent page

[gabina]

What this PR does

In some cases, such as an assignment being added and then removed again before the edit job is run, the dashboard may create a page that doesn't exist already, but make it empty. Ideally, this should not happen.

This PR starts handing the specific situation of trying to remove a template from a page that doesn't exist in WikiAssignmentOutput, and add a unit spec for the new build_talk_page_update behavior.

The idea is to make build_talk_page_update return nil when:

1. the talk page doesn't exist already (get_page_content returns empty string) and,
2. the update is to remove the assignments (@assignments is an empty collection)

This way update_assignments_for_article won't make the post_whole_page call, avoiding the creation of the empty page.

Prior to this PR, build_talk_page_update returned an empty string. This shall have caused update_assignments_for_article to call post_whole_page with empty content, resulting in the creation of an empty page.

Closes #2412

Screenshots

Open questions and concerns

The mentioned issue says that "edits should never create an empty page". This PR only takes into account one specific case of edits (trying to remove templates when the talk page doesn't exist). It might make sense to keep the issue open, as there could be other instances of edits that result in creating empty pages, which have not been addressed in this PR.

[gabina]

Some concerns:

The issue mentions that edits shouldn't create empty pages and, in such cases, "it should just leave the page as a redlink". I don't fully understand what the "redlink" refers to, so the PR may be missing something.

I didn't set my dev environment to make live edits on Wikipedia for this PR (as I considered it a bit risky), so it could be valuable to add an end-to-end test for this. However, I would need guidance for doing that.

[ragesoss]

@gabina a "redlink" just means a page that does not exist on Wikipedia. If you link to a page title that does not actually exist, instead of the normal blue color, the link is rendered in red on Wikipedia to indicate that the page has not been created yet.

[ragesoss]

This looks like it will work, but it it's a little confusing to me. It would be clearer, in my opinion, to follow the structure of the other guard statements that are already present: return nil if [some condition].

I'm guessing that you're trying to work around complexity warnings from Rubocop here; if so, I suggest extracting lines 44-46 into a helper method; all that code is basically answering the same question: is it a real, existing article? I'd suggest something like return nil unless is_normal_article?

For the new check, I think a comment along with something like return nil if @assignment.empty? && initial_page_content.empty? will be easy enough to understand.

[gabina]

Yep, exactly, I was trying to deal with Cyclomatic Complexity while trying to modify the least amount of existing code. I like your suggestions, addressed changes on 89a3501

[gabina]

Another option would be to use the negation of or operator, but I feel like and operator is usually easier to understand:
!(article_content.blank? || includes_disambiguation_template?(article_content))

[ragesoss]

Your implementation looks good to me.

[gabina]

@gabina a "redlink" just means a page that does not exist on Wikipedia. If you link to a page title that does not actually exist, instead of the normal blue color, the link is rendered in red on Wikipedia to indicate that the page has not been created yet.

Gotcha, thank you. I understand that I don't need to do any extra check then.

[gabina]

CI failed due to what I believe to be a flaky test

Finished in 33 minutes 37 seconds (files took 13.59 seconds to load)
1827 examples, 1 failure, 17 pending

Failed examples:

rspec ./spec/lib/importers/revision_score_importer_spec.rb:205 # RevisionScoreImporter.update_revision_scores_for_all_wikis imports data and calcuates an article completeness score for available wikis