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Support slices in type reflection #151118

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@BD103 BD103 commented Jan 14, 2026 •
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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

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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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oli-obk commented Jan 18, 2026

Needs a rebase. Otherwise lgtm

@SpriteOvO SpriteOvO added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jan 18, 2026
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@SpriteOvO SpriteOvO added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jan 19, 2026
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oli-obk commented Jan 20, 2026

@bors delegate+

r=me after rebase

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rust-bors bot commented Jan 20, 2026

✌️ @BD103, you can now approve this pull request!

If @oli-obk told you to "r=me" after making some further change, then please make that change and post @bors r=oli-obk.

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rustbot commented Jan 21, 2026

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

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BD103 commented Jan 21, 2026

@bors r=oli-obk

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rust-bors bot commented Jan 21, 2026

📌 Commit a509588 has been approved by oli-obk

It is now in the queue for this repository.

@rust-bors rust-bors bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jan 21, 2026
JonathanBrouwer added a commit to JonathanBrouwer/rust that referenced this pull request Jan 21, 2026
@JonathanBrouwer
Rollup merge of rust-lang#151118 - BD103:reflect-slices, r=oli-obk
7690c9a 
Support slices in type reflection

Tracking issue: rust-lang#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:

```rust
pub struct Slice {
    pub element_ty: TypeId,
}
```

Here is an example reflecting a slice:

```rust
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
@JonathanBrouwer JonathanBrouwer mentioned this pull request Jan 21, 2026
Closed
jhpratt added a commit to jhpratt/rust that referenced this pull request Jan 22, 2026
@jhpratt
Rollup merge of rust-lang#151118 - BD103:reflect-slices, r=oli-obk
a4cf93b 
Support slices in type reflection

Tracking issue: rust-lang#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:

```rust
pub struct Slice {
    pub element_ty: TypeId,
}
```

Here is an example reflecting a slice:

```rust
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
@jhpratt jhpratt mentioned this pull request Jan 22, 2026
Open
JonathanBrouwer added a commit to JonathanBrouwer/rust that referenced this pull request Jan 22, 2026
@JonathanBrouwer
Rollup merge of rust-lang#151118 - BD103:reflect-slices, r=oli-obk
f3e98e5 
Support slices in type reflection

Tracking issue: rust-lang#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:

```rust
pub struct Slice {
    pub element_ty: TypeId,
}
```

Here is an example reflecting a slice:

```rust
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
@JonathanBrouwer JonathanBrouwer mentioned this pull request Jan 22, 2026
Closed
rust-bors bot pushed a commit that referenced this pull request Jan 22, 2026
@bors
Auto merge of #151480 - jhpratt:rollup-kUkiF2m, r=jhpratt
d29e478 
Rollup of 4 pull requests

Successful merges:

 - #151118 (Support slices in type reflection)
 - #151439 (Bump bootstrap compiler to 1.94)
 - #151442 (Port `#![crate_type]` to the attribute parser)
 - #151457 (Improve error message for assert!() macro in functions returning bool)

r? @ghost
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A-type-system Area: Type system F-type_info #![feature(type_info)] S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. 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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