rustdoc: Fix duplicated impls with generics

[ollie27]

The same type can appear multiple times in impls so we need to use a set
to avoid adding it multiple times.

Fixes: #45584

[rust-highfive]

r? @frewsxcv

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[frewsxcv]

reassigning to someone from dev-tools team

[GuillaumeGomez]

I think that the order won't be kept with only the set. You need both a Vec and a Set.

[frewsxcv]

I'm not sure about a FxHashSet but order is preserved with a BTreeSet

[QuietMisdreavus]

Right, but is that the order of the DefIds or the order of the pushes? Anyway, it shouldn't matter because the Set in question isn't the global set but a local list of items to add a single impl to. The order in which you choose lists to push to shouldn't matter if there's only one item you're pushing at a time.

[ollie27]

I think that the order won't be kept with only the set.

The order of what? This is just gathering DefIds to use as keys to insert into a HashMap and it doesn't matter what order we insert into the HashMap. FxHashSet is deterministic if that's what you're worried about.

[carols10cents]

review ping @QuietMisdreavus or @GuillaumeGomez!

[QuietMisdreavus]

@bors r+

Sorry for letting this get stale!

[bors]

📌 Commit 676b4bb has been approved by QuietMisdreavus

[bors]

⌛ Testing commit 676b4bb with merge 3e7f501...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: QuietMisdreavus
Pushing 3e7f501 to master...