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Support arrays in type reflection #151031

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@BD103 BD103 commented Jan 12, 2026 •
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Tracking issue: #146922

This PR adds support for inspecting arrays [T; N] through type reflection. It does so by adding TypeKind::Array and the Array struct:

pub struct Array {
    pub element_ty: TypeId,
    pub len: usize,
}

This can be used to inspect arrays like so:

match const { Type::of::<[u16; 4]>() }.kind {
    TypeKind::Array(array) => {
        assert_eq!(array.element_ty, TypeId::of::<u16>());
        assert_eq!(array.len, 4);
    }
    _ => unreachable!(),
}

r? @oli-obk

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rustbot commented Jan 12, 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 12, 2026
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rustbot commented Jan 12, 2026

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

BD103
BD103 commented Jan 12, 2026
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compiler/rustc_const_eval/src/const_eval/type_info.rs
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Please pay special attention to my changes in this file, as this is where I feel least confident in my understanding of the code!

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@JayanAXHF JayanAXHF added the A-type-system Area: Type system label Jan 12, 2026
@SpriteOvO SpriteOvO added the F-type_info #![feature(type_info)] label Jan 13, 2026
oli-obk
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BD103 commented Jan 13, 2026

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@rustbot rustbot 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 13, 2026
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rustbot commented Jan 13, 2026

Reminder, once the PR becomes ready for a review, use @rustbot ready.

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BD103 commented Jan 13, 2026

@rustbot ready

@rustbot rustbot 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 13, 2026
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oli-obk commented Jan 13, 2026

@bors r+ rollup

@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 13, 2026
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rust-bors bot commented Jan 13, 2026

📌 Commit 71f8ea9 has been approved by oli-obk

It is now in the queue for this repository.

GuillaumeGomez added a commit to GuillaumeGomez/rust that referenced this pull request Jan 13, 2026
@GuillaumeGomez
Rollup merge of rust-lang#151031 - reflect-arrays, r=oli-obk
662658c 
Support arrays in type reflection

Tracking issue: rust-lang#146922

This PR adds support for inspecting arrays `[T; N]` through type reflection. It does so by adding `TypeKind::Array` and the `Array` struct:

```rust
pub struct Array {
    pub element_ty: TypeId,
    pub len: usize,
}
```

This can be used to inspect arrays like so:

```rust
match const { Type::of::<[u16; 4]>() }.kind {
    TypeKind::Array(array) => {
        assert_eq!(array.element_ty, TypeId::of::<u16>());
        assert_eq!(array.len, 4);
    }
    _ => unreachable!(),
}
```

r? @oli-obk
@GuillaumeGomez GuillaumeGomez mentioned this pull request Jan 13, 2026
Closed
GuillaumeGomez added a commit to GuillaumeGomez/rust that referenced this pull request Jan 13, 2026
@GuillaumeGomez
Rollup merge of rust-lang#151031 - reflect-arrays, r=oli-obk
a8e3ce5 
Support arrays in type reflection

Tracking issue: rust-lang#146922

This PR adds support for inspecting arrays `[T; N]` through type reflection. It does so by adding `TypeKind::Array` and the `Array` struct:

```rust
pub struct Array {
    pub element_ty: TypeId,
    pub len: usize,
}
```

This can be used to inspect arrays like so:

```rust
match const { Type::of::<[u16; 4]>() }.kind {
    TypeKind::Array(array) => {
        assert_eq!(array.element_ty, TypeId::of::<u16>());
        assert_eq!(array.len, 4);
    }
    _ => unreachable!(),
}
```

r? @oli-obk
@GuillaumeGomez GuillaumeGomez mentioned this pull request Jan 13, 2026
Open
rust-bors bot pushed a commit that referenced this pull request Jan 14, 2026
@bors
Auto merge of #151087 - GuillaumeGomez:rollup-vIdiReJ, r=GuillaumeGomez
4931e09 
Rollup of 13 pull requests

Successful merges:

 - #150587 (triagebot: add A-rustdoc-js autolabel)
 - #150677 (Improve std::path::Path::join documentation)
 - #150737 (diagnostics: make implicit Sized bounds explicit in E0277)
 - #150771 (Remove legacy homu `try` and `auto` branch mentions)
 - #150840 (Make `--print=check-cfg` output compatible `--check-cfg` arguments)
 - #150915 (Regression test for type params on eii)
 - #151017 (Port the rustc dump attributes to the attribute parser)
 - #151019 (Make `Type::of` support unsized types)
 - #151031 (Support arrays in type reflection)
 - #151043 (armv7-unknown-linux-uclibceabihf.md: Fix bootstrap.toml syntax)
 - #151052 (ui: add regression test for macro resolution ICE (issue #150711))
 - #151053 (Reduce flakyness for `tests/rustdoc-gui/notable-trait.goml`)
 - #151055 (Emit error instead of delayed bug when meeting mismatch type for const array)

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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