SafeNames does not abbreviate first names

[islemaster]

FND-1146: Fix the name abbreviation logic on section login page.

There were some documented problems with name abbreviations when one first-name was a strict subset of another. For instance, for the set of names Anna, Annabel, Annabelle, Brad, Bradford, Bradlee, Bradley, Branford, Maria, Mariamu the login page would show the following:

Notice that Anna and Maria have been reduced to one character, and Annabel has oddly been truncated to five characters.

The logic abbreviating names here is designed to find the smallest unique prefix that can be used to tell two students with the same name apart; for example, reducing Tom Sawyer, Tom Smith to Tom Sa, Tom Sm. However, we never want to abbreviate a first name, and if the first name is already unique, we should be able to use it without trying to compute a minimum prefix.

We already had logic to that effect here:

    # If the first name is unique, simply use that
    return first_name if trie.words(first_name).count == 1

But trie.words gets all the words that start with a particular string. If you put in John Smith and Johnny Smith then trie.words("John").count is 2 even though the first name is unique.

I've added a different check for first-name-uniqueness to fix this behavior. Now the login page looks like this:

Testing story

I've extended the existing test with new assertions capturing known problem cases.

Reviewer Checklist:

• Tests provide adequate coverage
• Code is well-commented
• New features are translatable or updates will not break translations
• Relevant documentation has been added or updated
• User impact is well-understood and desirable
• Pull Request is labeled appropriately
• Follow-up work items (including potential tech debt) are tracked and linked

[islemaster]

Captured this because I found it to be an interesting and useful behavior - I think this is a better outcome than John, John, John Smy.

[Hamms]

LGTM!

[Hamms]

concise!