Extract rustc stable hasher into it's own crate

[Urgau]

Proposal

Extract the StableHasher (struct), StableHasherResult (trait) and SipHasher128 (struct) from rustc_data_structures into their own (new) crate rustc-stable-hash, similar to rustc-hash, so they can be used by other projects.

In particular, this would be useful for Cargo, which needs a cross-platform independent stable hasher for the trim-paths feature, rust-lang/cargo#13171 (comment).

The plan is to create a separate repo rustc-stable-hash (already done), create the infra¹, import those parts¹, publish the crate, use the new crate in rustc_data_structures.

Mentors or Reviewers

My-self, @Urgau.

Process

The main points of the Major Change Process are as follows:

• File an issue describing the proposal.
• A compiler team member or contributor who is knowledgeable in the area can second by writing @rustbot second.
  • Finding a "second" suffices for internal changes. If however, you are proposing a new public-facing feature, such as a -C flag, then full team check-off is required.
  • Compiler team members can initiate a check-off via @rfcbot fcp merge on either the MCP or the PR.
• Once an MCP is seconded, the Final Comment Period begins. If no objections are raised after 10 days, the MCP is considered approved.

You can read more about Major Change Proposals on forge.

Comments

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.

Footnotes

1. https://github.com/rust-lang/rustc-stable-hash/pull/1 ↩ ↩²

[rustbot]

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.

Concerns or objections to the proposal should be discussed on Zulip and formally registered here by adding a comment with the following syntax:

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<description of the concern> 

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See documentation at https://forge.rust-lang.org

cc @rust-lang/compiler @rust-lang/compiler-contributors

[oli-obk]

@rustbot second

[apiraino]

@rustbot label -final-comment-period +major-change-accepted