Description
Proposal
Relevant PR rust-lang/rust#100719
Some intrinsics of the core library are usable in safe context, despite being declared as extern "rust-intrinsic" functions. This concerns intrinsics such as rotate_left, which are indeed not "unsafe" functions in themselves. However, the list of these safe intrinsics is not directly apparent within the core library source code (the explanation is however present in the documentation). In order to mark an intrinsic as safe or unsafe, the compiler instead relies on a hardcoded list of symbols as shown here.
Since the safety of these intrinsics is sometimes subject to changes, it is hard to keep up with the list of safe and unsafe intrinsics, which is why the addition of a source-level #[rustc_safe_intrinsic] attribute would lighten the mental load.
Such attributes already exist: For example, some intrinsics are usable in constant contexts. Because the intrinsics are declared as extern, the syntax also forbids the usage of the const keyword. Hence, #[rustc_const_stable] and #[rustc_const_unstable], among other things, serve to mark these intrinsic functions as constant.
Mentors or Reviewers
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 mergeon either the MCP or the PR.
- Finding a "second" suffices for internal changes. If however, you are proposing a new public-facing feature, such as a
- Once an MCP is seconded, the Final Comment Period begins. If no objections are raised after 10 days, the MCP is considered approved.
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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.