Show and sort by downloads on reverse dependency page

[LeopoldArkham]

Fixes #495

I swapped the redundant arrow link on the right for the download count, I don't think anybody used it (?).

[LeopoldArkham]

@carols10cents Ok, it works now. I had to abuse the CI because the tests won't run on my machine.
Let me know how it looks.

[carols10cents]

@LeopoldArkham Hm, why doesn't the ordering in SQL work?

[LeopoldArkham]

@carols10cents Whenever a query contains a DISTINCT ON statement and an ORDER BY clause, the leftmost argument to ORDER BY has to be the same as the one to DISTINCT.

So since we're DISTINCT ON crate_name, I can only ORDER BY crate_name. I think it would be possible to do in all SQL with a sub-query, but this seemed like a clearer and more maintainable way.

If there's a policy against this (or I'm missing something), I can go back and look into it.

(Didn't mean to close)

[carols10cents]

Oh! There's no policy or anything, it's just that SQL is really good at ordering things really fast :)

So the reason a reverse dependency might be duplicated is if a crate lists another crate as a dependency multiple times, such as target-specific dependencies. So for crate A, it might depend on crate B twice, so crate B's reverse dependencies would have duplicate listing of A. However, in both listings of A, the number of crates.downloads for A will be the same. So we should be able to add crate_downloads to the list of columns specified in the DISTINCT clause, and meet the necessary criteria for the ordering, like this:

SELECT DISTINCT ON (crate_downloads, crate_name)
    dependencies.*,
    crates.downloads AS crate_downloads,
    crates.name AS crate_name
FROM dependencies
INNER JOIN versions
ON versions.id = dependencies.version_id
INNER JOIN crates
ON crates.id = versions.crate_id
WHERE dependencies.crate_id = 2
AND versions.num = crates.max_version
ORDER BY crate_downloads DESC;

What do you think? Is there anything I'm missing? (it's entirely possible!)

[LeopoldArkham]

No, you're totally right, thank you! I had misunderstood the behavior of DISTINCT ON when provided with more than 1 argument. (See? No programming Sunday evenings.)

I also got the test suite to (mostly) work, so we should be OK.

[LeopoldArkham]

^ I jinxed myself.
Although it's the yarn install that failed. Gonna close and re-open to trigger a rebuild.

[carols10cents]

Looks great, works like a charm!!! 🍀 Sorry I took so long to review this, thank you for your patience!! ❤️

[LeopoldArkham]

And you for yours!