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Support slices in type reflection #151118

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@BD103 BD103 commented Jan 14, 2026 •
edited by rustbot
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Tracking issue: #146922

This PR adds support for inspecting slices [T] through type reflection. It does so by adding the new Slice struct + variant, which is very similar to Array but without the len field:

pub struct Slice {
    pub element_ty: TypeId,
}

Here is an example reflecting a slice:

match const { Type::of::<[u8]>() }.kind {
    TypeKind::Slice(slice) => assert_eq!(slice.element_ty, TypeId::of::<u8>()),
    _ => unreachable!(),
}

In addition to this, I also re-arranged the type info unit tests.

r? @oli-obk

BD103 added 2 commits January 14, 2026 10:08
@BD103
feat: support slices in reflection type info
91d3f18
@BD103
refactor: put type info unit tests in the same order as TypeKind enum
ea67602 
The current order is:

- Tuple
- Array
- Slice
- Leaf
- Other

Both `core::mem::type_info` and `rustc_const_eval::const_eval::type_info` follow this order, so the `core` unit tests should as well.
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rustbot commented Jan 14, 2026

The reflection data structures are tied exactly to the implementation
in the compiler. Make sure to also adjust rustc_const_eval/src/const_eval/type_info.rs

cc @oli-obk

Some changes occurred to the CTFE machinery

cc @RalfJung, @oli-obk, @lcnr

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Jan 14, 2026
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rustbot commented Jan 14, 2026

oli-obk is not on the review rotation at the moment.
They may take a while to respond.

@SpriteOvO SpriteOvO added A-type-system Area: Type system F-type_info #![feature(type_info)] labels Jan 14, 2026
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A-type-system Area: Type system F-type_info #![feature(type_info)] S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue.

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