Replace some u64 hashes with Hash64

[saethlin]

I introduced the Hash64 and Hash128 types in #110083, essentially as a mechanism to prevent hashes from landing in our leb128 encoding paths. If you just have a u64 or u128 field in a struct then derive Encodable/Decodable, that number gets leb128 encoding. So if you need to store a hash or some other value which behaves very close to a hash, don't store it as a u64.

This reverts part of #117603, which turned an encoded Hash64 into a u64.

Based on #110083, I don't expect this to be perf-sensitive on its own, though I expect that it may help stabilize some of the small rmeta size fluctuations we currently see in perf reports.

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[rustbot]

rust-analyzer is developed in its own repository. If possible, consider making this change to rust-lang/rust-analyzer instead.

cc @rust-lang/rust-analyzer

[Veykril]

rust-analyzer can't depend on rustc_data_structures since it doesn't compile on stable

[Noratrieb]

time to put the wrapper in rustc_index :3

[saethlin]

Actually I was thinking about creating rustc_nightly_data_structures but I haven't looked at how much of rustc_data_structures needs nightly yet.

[workingjubilee]

Potentially silly alternative: byte arrays?

[saethlin]

In practice, all the little helper methods that permit numeric operations while keeping the containment of "do not encode me with leb128" are quite useful in the compiler. And these types get passed around a lot so I think it would be a silly maintenance issue to have multiple of them. I'll just figure out how to put these helper types in a crate that r-a can use.

[workingjubilee]

Sounds good.

Also, @saethlin can you add this to the docs for Hash64? And likewise for Hash128.

+/// A hashed u64 encoded with a stable size that is more compact than u64's ULEB128 encoding
 #[derive(Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord, Default)]
 pub struct Hash64 {

That way it appears in hover-docs.

[workingjubilee]

Any variation on that sentence you want is fine, as long as it is a single one so that it consistently renders correctly.

[rustbot]

These commits modify the Cargo.lock file. Unintentional changes to Cargo.lock can be introduced when switching branches and rebasing PRs.

If this was unintentional then you should revert the changes before this PR is merged.
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[saethlin]

I factored this now so that the HashN types are in a new crate called rustc_hashes. I think this works? The diff touches a lot of files now which is unfortunate, but any proper solution to code sharing with r-a like this is going to have to touch a lot of files. Happy to try out another strategy if people think it will turn out better.

Also, the Encodable/Decodable impls for these types now live in rustc_serialize, which is producing a strange diff visualization.

[workingjubilee]

Thanks, that's great!

This should be fine.

@bors r+ rollup

[bors]

📌 Commit 7b99665 has been approved by workingjubilee

It is now in the queue for this repository.

[workingjubilee]

Wait, I just remembered, there's a test to update, lemme check...

@bors r-

[workingjubilee]

I believe rustc_hashes should be added to https://github.com/rust-lang/rust/blob/master/tests/run-make/rustc-crates-on-stable/rmake.rs

[rustbot]

This PR modifies tests/run-make/. If this PR is trying to port a Makefile
run-make test to use rmake.rs, please update the
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so we can track our progress. You can either modify the tracking issue
directly, or you can comment on the tracking issue and link this PR.

cc @jieyouxu

[saethlin]

Since you wanted to mark this for rollup, I'll wait until CI passes to re-add it to the queue

[workingjubilee]

@bors r+

[bors]

📌 Commit 4cf2186 has been approved by workingjubilee

It is now in the queue for this repository.