Document layout guarantee of TypeId

[apiraino]

Meeting proposal info

• Title: Document layout guarantee of TypeId
• Type: technical

Summary

A TypeId represents a globally unique identifier for a type.

Stabilizing and documenting its layout is useful for FFI use-cases where a TypeId may be stored within a foreign data structure or buffer.

The initial proposal is to set a fixed size of 16 bytes. Preliminary discussion from T-compiler pointed out (comment) that a more flexible solution supporting more architectures.

Stakeholders / interested parties

RfL (Rust for Linux) for example would benefit from that, see discussion on the LKML, cc: @dakr @Darksonn

Project Bevy chimed in as well with some thoughts, see comment, backlink to Bevy Discord (login required) cc @alice-i-cecile

Requirements for the meeting to happen

• T-lang should decide on a threat-model (see discussion)
• T-libs seems to defer T-compiler for a decision, see comment

Expected outcome of the meeting

Agreement about the layout and size of TypeId, an actionable to write documentation.

Meeting proposal date(s)

TODO

Relevant links

• library: core: document layout guarantee of `TypeId` by dakr · Pull Request #148265 · rust-lang/rust
• Discussion in T-compiler triage meeting
• Discussion on Zulip in #rust-for-linux
• LKML discussion

About this issue

This issue corresponds to a meeting proposal for the compiler team
steering meeting. It corresponds to a possible topic of
discussion. You can read more about the steering meeting procedure
here.

Comment policy

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details. Feel free to subscribe to updates. We'll post comments when
reviewing the proposal in meetings or making a scheduling decision.
In the meantime, if you have questions or ideas, ping the proposers
on Zulip (or elsewhere).