data_structures: Add deterministic FxHashMap and FxHashSet wrappers

[shivan1b]

StableMap
A wrapper for FxHashMap that allows to insert, remove, get, get_mut and convert a hashmap into a sorted vector using the method into_sorted_vector but no iteration support.

StableSet
A wrapper for FxHashSet that allows to insert, remove, get and convert a hashset into a sorted vector using the method into_sorted_vector but no iteration support.

Addresses issue #63713

[rust-highfive]

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[shivan1b]

Hi @bjorn3!
Could you please check if this meets the requirements of the corresponding issue?
Please note that this does not have the "convertion to a sorted vec." support. I learned the basics of HashMap and checked a few functions, not sure which function does this exactly, could you please point me to that?
Thank you.

[shivan1b]

r? @bjorn3

[Mark-Simulacrum]

Please note that the examples above are NOT a part of the commit message.

But they will be if we decide to merge this (bors includes PR message in merge commit).

---

I'd also like to see this called something like StableMap perhaps or DeterministicMap, since otherwise the determinism aspect is a bit lost in the naming (and since we're likely almost universally using this once we migrate the compiler, it would be good to separate it a bit).

---

[Mark-Simulacrum]

We'll probably want a Set variant of the map as well.

---

For sorted vector support something like the following would work:

fn into_sorted_vector(self) -> Vec<(K, V)> /* or Vec<T> */
where K: PartialOrd,
           V: PartialOrd,
{
    let mut v = self.base.into_iter().collect::<Vec<_>>();
    v.unstable_sort(); // this is interesting in that it's unstable but we're not actually adding instability here since the underlying map already has an unstable iteration order
    v
}

[bjorn3]

Please rustfmt dfx.rs (but not the rest of the files, so you will need to run rustfmt /path/to/dfx.rs instead of cargo fmt.)

Apart from a few nits this looks good. @Mark-Simulacrum should this PR contain a first user of the new api, or can that be done in a follow-up?

[shivan1b]

Please note that the examples above are NOT a part of the commit message.

But they will be if we decide to merge this (bors includes PR message in merge commit).

Right. Forgot about it. I shall remove them before merging unless you think it makes sense to have them as a part of commit message?

I'd also like to see this called something like StableMap perhaps or DeterministicMap, since otherwise the determinism aspect is a bit lost in the naming (and since we're likely almost universally using this once we migrate the compiler, it would be good to separate it a bit).

Shall I go with DeterministickMap then? Should the module name also be changed from dfx to deterministic_map ?

[bjorn3]

I prefer StableMap as it is shorter, which means it is more likely to be picked over FxHashMap.

[shivan1b]

We'll probably want a Set variant of the map as well.

Sure. Should I be creating a separate issue for this?

For sorted vector support something like the following would work:

fn into_sorted_vector(self) -> Vec<(K, V)> /* or Vec<T> */
where K: PartialOrd,
           V: PartialOrd,
{
    let mut v = self.base.into_iter().collect::<Vec<_>>();
    v.unstable_sort(); // this is interesting in that it's unstable but we're not actually adding instability here since the underlying map already has an unstable iteration order
    v
}

Thank you very much!

[Mark-Simulacrum]

I think adding the set in this PR makes sense; it should be minimally difficult to do so, hopefully.

Right. Forgot about it. I shall remove them before merging unless you think it makes sense to have them as a part of commit message?

Yeah, I don't think the examples are too useful.

Apart from a few nits this looks good. @Mark-Simulacrum should this PR contain a first user of the new api, or can that be done in a follow-up?

I think that moving the compiler over can be done in followup PRs. It'll likely be fairly straightforward (mostly just search and replace on FxHash{Map,Set}).

[Alexendoo]

Ping from triage, any updates? @cramertj

[Mark-Simulacrum]

r? @Mark-Simulacrum

r=me with commits squashed into one

[JohnCSimon]

Ping from triage:
This is marked as "waiting on author"
@shivan1b can you address the comments from @Mark-Simulacrum ?
Thanks.

[shivan1b]

Sorry @JohnCSimon for having missed that.
r? @Mark-Simulacrum

[Mark-Simulacrum]

@bors r+ rollup

Thanks!

[bors]

📌 Commit 800bd3a has been approved by Mark-Simulacrum