Support primitives in type info reflection #151123

SpriteOvO · 2026-01-14T16:08:10Z

Tracking issue: #146922 #![feature(type_info)]

This PR supports {bool,char,int,uint,float,str} primitive types for feature type_info reflection.

rustbot · 2026-01-14T16:08:14Z

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 · 2026-01-14T16:08:18Z

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

SpriteOvO

I also added a ty: TypeId to all primitive variants to represent their own type. The rationale is that users won't need to manually retrieve the TypeId when accessing type info (especially through Type::of::<T>() usage). I'm not sure if this approach is advisable, and whether it's necessary to also provide a ty: TypeId for other variants like Tuple and Array.

View changes since this review

SpriteOvO · 2026-01-14T16:42:37Z

library/core/src/mem/type_info.rs

+    /// The type id of signed integer type.
+    pub ty: TypeId,
+    /// The bit width of the signed integer type.
+    pub bit_width: usize,


I'm not sure whether we should use usize or u64 here to represent the bit width.

Besides, as Option is not used here, reflection on isize and usize will fall into the Int and Uint variants, and users cannot distinguish between them, which may be an issue.

Is it necessary for end users to distinguish between {u,i}size and {u,i}int? If yes, should we add a separate field or add distinct variants to indicate it?

I think having a single Int variant that has a signed: bool field is nicer. It avoids some recurring matches that do Int(_) | Uint(_)

I'm not sure whether we should use usize or u64 here to represent the bit width.

My expectation would be u32 matching the associated {u,i}N::BITS¹²³ constant that already exists on the integer types.

Footnotes

https://doc.rust-lang.org/std/primitive.i8.html#associatedconstant.BITS ↩

https://doc.rust-lang.org/std/primitive.i128.html#associatedconstant.BITS ↩

https://doc.rust-lang.org/std/primitive.usize.html#associatedconstant.BITS ↩

@Skgland Nice point. I found some previous discussions regarding the type of ::BITS constant. And during the stabilization of ::BITS, the choice of u32 affected some ecosystem crates (#81654), but soon after, these crates all accepted the u32 type.

So I think it makes sense to keep the type consistent with ::BITS here. Then I'd also like to change the name from bit_width to bits, also for consistency.

If there is no objection, I will make this change in a follow-up PR later (as this PR is already r+).

UPDATE: Follow-up PR #151235

Support {bool,char,int,uint,float,str} primitive types for feature `type_info` reflection.

SpriteOvO · 2026-01-15T11:10:51Z

I also added a ty: TypeId to all primitive variants to represent their own type. The rationale is that users won't need to manually retrieve the TypeId when accessing type info (especially through Type::of::<T>() usage). I'm not sure if this approach is advisable, and whether it's necessary to also provide a ty: TypeId for other variants like Tuple and Array.

In that case, it might be better to place ty: TypeId under struct Type rather than under enum TypeKind's variants I think.

oli-obk

Yea I think we can leave off the extra TypeId field. I understand that reflection libraries have that on their Opaque variant, but they can still do that when processing the rustc reflection info. I'd rather users invoke TypeId::of manually when they also need the type id

View changes since this review

oli-obk · 2026-01-15T11:58:04Z

library/core/src/mem/type_info.rs

+    /// The type id of signed integer type.
+    pub ty: TypeId,
+    /// The bit width of the signed integer type.
+    pub bit_width: usize,


I think having a single Int variant that has a signed: bool field is nicer. It avoids some recurring matches that do Int(_) | Uint(_)

tests/ui/reflection/dump.rs

SpriteOvO · 2026-01-15T22:12:11Z

@rustbot review

Removed ty: TypeId from variants, merged variant Uint into Int.

oli-obk · 2026-01-16T07:25:50Z

@bors r+ rollup

rust-bors · 2026-01-16T07:25:52Z

📌 Commit b2a7b18 has been approved by oli-obk

It is now in the queue for this repository.

@oli-obk

Support primitives in type info reflection Tracking issue: rust-lang#146922 `#![feature(type_info)]` This PR supports {`bool`,`char`,`int`,`uint`,`float`,`str`} primitive types for feature `type_info` reflection. r? @oli-obk

@ghost

Rollup of 6 pull requests Successful merges: - #145354 (Cache derive proc macro expansion with incremental query) - #151123 (Support primitives in type info reflection) - #151178 (simplify words initialization using Rc::new_zeroed) - #151187 (Use `default_field_values` more in `Resolver`) - #151197 (remove lcnr from compiler review rotation) - #151203 (Revert `QueryStackFrame` split) r? @ghost

@oli-obk

Rollup merge of #151123 - type-info-primitives, r=oli-obk Support primitives in type info reflection Tracking issue: #146922 `#![feature(type_info)]` This PR supports {`bool`,`char`,`int`,`uint`,`float`,`str`} primitive types for feature `type_info` reflection. r? @oli-obk

@Skgland

Change field `bit_width: usize` to `bits: u32` in type info Follow-up rust-lang#151123 (comment). Quotes: @Skgland: > > I'm not sure whether we should use `usize` or `u64` here to represent the bit width. > > My expectation would be `u32` matching the associated `{u,i}N::BITS`[^1][^2][^3] constant that already exists on the integer types. > > [^1]: https://doc.rust-lang.org/std/primitive.i8.html#associatedconstant.BITS > [^2]: https://doc.rust-lang.org/std/primitive.i128.html#associatedconstant.BITS > [^3]: https://doc.rust-lang.org/std/primitive.usize.html#associatedconstant.BITS @SpriteOvO: > I found some [previous discussions](rust-lang#76492 (comment)) regarding the type of `::BITS` constant. And during the stabilization of `::BITS`, the choice of `u32` affected some ecosystem crates (rust-lang#81654), but soon after, these crates all accepted the `u32` type. > > So I think it makes sense to keep the type consistent with `::BITS` here. Then I'd also like to change the name from `bit_width` to `bits`, also for consistency. r? @oli-obk

@Skgland

Change field `bit_width: usize` to `bits: u32` in type info Follow-up rust-lang#151123 (comment). Quotes: @Skgland: > > I'm not sure whether we should use `usize` or `u64` here to represent the bit width. > > My expectation would be `u32` matching the associated `{u,i}N::BITS`[^1][^2][^3] constant that already exists on the integer types. > > [^1]: https://doc.rust-lang.org/std/primitive.i8.html#associatedconstant.BITS > [^2]: https://doc.rust-lang.org/std/primitive.i128.html#associatedconstant.BITS > [^3]: https://doc.rust-lang.org/std/primitive.usize.html#associatedconstant.BITS @SpriteOvO: > I found some [previous discussions](rust-lang#76492 (comment)) regarding the type of `::BITS` constant. And during the stabilization of `::BITS`, the choice of `u32` affected some ecosystem crates (rust-lang#81654), but soon after, these crates all accepted the `u32` type. > > So I think it makes sense to keep the type consistent with `::BITS` here. Then I'd also like to change the name from `bit_width` to `bits`, also for consistency. r? @oli-obk

@Skgland

Rollup merge of #151235 - type-info-rename-bits, r=oli-obk Change field `bit_width: usize` to `bits: u32` in type info Follow-up #151123 (comment). Quotes: @Skgland: > > I'm not sure whether we should use `usize` or `u64` here to represent the bit width. > > My expectation would be `u32` matching the associated `{u,i}N::BITS`[^1][^2][^3] constant that already exists on the integer types. > > [^1]: https://doc.rust-lang.org/std/primitive.i8.html#associatedconstant.BITS > [^2]: https://doc.rust-lang.org/std/primitive.i128.html#associatedconstant.BITS > [^3]: https://doc.rust-lang.org/std/primitive.usize.html#associatedconstant.BITS @SpriteOvO: > I found some [previous discussions](#76492 (comment)) regarding the type of `::BITS` constant. And during the stabilization of `::BITS`, the choice of `u32` affected some ecosystem crates (#81654), but soon after, these crates all accepted the `u32` type. > > So I think it makes sense to keep the type consistent with `::BITS` here. Then I'd also like to change the name from `bit_width` to `bits`, also for consistency. r? @oli-obk

SpriteOvO added the F-type_info #![feature(type_info)] label Jan 14, 2026

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SpriteOvO force-pushed the type-info-primitives branch 3 times, most recently from 7fccb29 to 1066081 Compare January 14, 2026 16:13

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SpriteOvO force-pushed the type-info-primitives branch from 1066081 to 8281828 Compare January 14, 2026 16:15

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SpriteOvO force-pushed the type-info-primitives branch from 8d00b3b to 80ae7d8 Compare January 14, 2026 18:14

Support primitives in type info reflection

79ec275

Support {bool,char,int,uint,float,str} primitive types for feature `type_info` reflection.

SpriteOvO force-pushed the type-info-primitives branch from 80ae7d8 to 79ec275 Compare January 14, 2026 18:15

SpriteOvO mentioned this pull request Jan 14, 2026

Support ADT types in type info reflection #151142

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SpriteOvO added 2 commits January 15, 2026 22:58

Remove their own TypeId from type info for primitives

5c057ad

Merge type info variant Uint into Int

b2a7b18

SpriteOvO force-pushed the type-info-primitives branch from ee3618c to b2a7b18 Compare January 15, 2026 22:05

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This was referenced Jan 16, 2026

Rollup of 6 pull requests #151208

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Rollup of 6 pull requests #151210

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SpriteOvO deleted the type-info-primitives branch January 16, 2026 20:22

SpriteOvO mentioned this pull request Jan 17, 2026

Change field bit_width: usize to bits: u32 in type info #151235

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Support primitives in type info reflection #151123

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