Move Region from rustc_middle to rustc_type_ir by Jamesbarford · Pull Request #154989 · rust-lang/rust

Jamesbarford · 2026-04-08T14:47:55Z

General notes

Probably best reviewed commit by commit. I've tried where to make the changes as isolated as possible.

For the pub struct Region if we use Interned<...> in the definition then we'd need to add a lifetime to the Interner trait. As such I opted for a type InternedRegionKind which is Interned<'tcx, RegionKind<'tcx>> in the implementation. To allow calling the kind() method I implemented inherent::IntoKind for Interned<'tcx, T>.
All methods from the Region trait in inherent have been moved to compiler/rustc_type_ir/src/sty/mod.rs.
Had to implement Lift manually.
I'm not sure the implementation of kind() is correct or even should be implemented for Interned<...>?
In order for the struct to be printable in pretty.rs I've used an intermediary struct; RegionDisplay so we can still access ty::tls::with
Similarly there is an intermediary struct for diagnostics; RegionDiagArg
Moved the impls to the owning crate and add a small abstraction needed for decode to still re-intern Region

error[E0210]: type parameter `E` must be used as the type parameter for some local type (e.g., `MyStruct<E>`)
   --> compiler/rustc_middle/src/ty/codec.rs:162:12
    |
162 | impl<'tcx, E: TyEncoder<'tcx>> Encodable<E> for ty::Region<'tcx> {
    |            ^ type parameter `E` must be used as the type parameter for some local type
    |
    = note: implementing a foreign trait is only possible if at least one of the types for which it is implemented is local
    = note: only traits defined in the current crate can be implemented for a type parameter

error[E0210]: type parameter `D` must be used as the type parameter for some local type (e.g., `MyStruct<D>`)
   --> compiler/rustc_middle/src/ty/codec.rs:301:12
    |
301 | impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for ty::Region<'tcx> {
    |            ^ type parameter `D` must be used as the type parameter for some local type
    |
    = note: implementing a foreign trait is only possible if at least one of the types for which it is implemented is local
    = note: only traits defined in the current crate can be implemented for a type parameter

`compiler/rustc_middle/src/ty/region.rs`

Generally anything that needed to access fields on TyCtxt have been made methods on the interner.

interner.lifetimes.anon_re_bounds.get(debruijn.as_usize()) for getting an interned lifetime, is now a trait method on Interner; fn get_anon_re_bounds_lifetime(...)
fn intern_region(...) now a trait method on Interner
interner.lifetimes.anon_re_canonical_bounds.get(debruijn.as_usize()) required
for fn new_canonical_bound(...). Is now fn get_anon_re_canonical_bounds_lifetime(...)
interner.lifetimes.re_static has become fn get_re_static_lifetime() for method fn new_static((..)

r? @lcnr

rustbot · 2026-04-08T14:47:59Z

changes to the core type system

cc @lcnr

HIR ty lowering was modified

cc @fmease

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

lcnr · 2026-04-09T07:54:13Z

compiler/rustc_type_ir/src/sty/mod.rs

+        // Use a pre-interned one when possible.
+        if let BoundRegion { var, kind: BoundRegionKind::Anon } = bound_region
+            // This
+            && let Some(inner) = interner.get_anon_re_bounds_lifetime(debruijn.as_usize())


View changes since the review

i feel like these interning opts should not be in rustc_type_ir, so maybe add Interner::intern_bound_region and call that directly?

lcnr · 2026-04-09T07:54:18Z

compiler/rustc_type_ir/src/sty/mod.rs

+    #[inline]
+    pub fn new_canonical_bound(interner: I, var: BoundVar) -> Self {
+        // Use a pre-interned one when possible.
+        if let Some(re) = interner.get_anon_re_canonical_bounds_lifetime(var.as_usize()) {


View changes since the review

same here

lcnr

I don't fully get the changes to InternerDecoder

we should keep Region<I>: Display around by implementing it via IrPrint 🤔 having RegionDisplay seems unnecessary, we already have this IrPrint handling for other types, don't we?

IntoDiagArg is defined outside of rustc_middle? Maybe we should make it generic over I as well?

View changes since this review

compiler/rustc_type_ir/src/binder.rs

lcnr · 2026-04-09T07:55:56Z

compiler/rustc_type_ir/src/binder.rs

+
+    fn lift_to_interner(self, interner: U) -> Option<Self::Lifted> {
+        Some(BoundRegion { var: self.var, kind: self.kind.lift_to_interner(interner)? })
+    }


compiler/rustc_type_ir/src/inherent.rs

lcnr · 2026-04-09T07:56:37Z

compiler/rustc_type_ir/src/region_kind.rs


 impl<I: Interner> Eq for RegionKind<I> {}

+impl<I: Interner, U: Interner> Lift<U> for RegionKind<I>


also not derived?

lcnr · 2026-04-09T07:57:27Z

compiler/rustc_middle/src/ty/structural_impls.rs

+//     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+//         write!(f, "{:?}", self.kind())
+//     }
+// }


lcnr · 2026-04-09T07:58:31Z

compiler/rustc_middle/src/ty/structural_impls.rs

    rustc_hir::Safety,
    rustc_middle::mir::ConstValue,
+    rustc_span::ErrorGuaranteed,
+    rustc_span::Symbol,


the alternative would be to restrict the region lift impl to not actually change these types

lcnr · 2026-04-09T08:06:56Z

For the pub struct Region if we use Interned<...> in the definition then we'd need to add a lifetime to the Interner trait. As such I opted for a type InternedRegionKind which is Interned<'tcx, RegionKind<'tcx>> in the implementation. To allow calling the kind() method I implemented inherent::IntoKind for Interned<'tcx, T>.

Interned itself is a type from rustc_middle anyways, is it not? 🤔 I would expect us to instead of type Interned<T> to trait Interner and have region be struct Region<I: Interner>(I::Interned<RegionKind>)

Had to implement Lift manually.

do we have some Lift_Generic derive or whatever? I feel like we should?

rustbot · 2026-04-09T10:19:13Z

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

lcnr · 2026-04-10T12:53:20Z

compiler/rustc_middle/src/ty/context/impl_interner.rs

 use std::{debug_assert_matches, fmt};

 use rustc_abi::ExternAbi;
+use rustc_data_structures::intern::Interned;


View changes since the review

we should not use rustc_data_structures::intern, but instead, an associated type type Interned<T: ...>; on the trait Interner as r-a uses a different interning strategy

I've tried the below;

// compiler/rustc_type_ir/src/interner.rs pub trait Interner: Sized + Copy + /* etc... */ { type Interned<T>; } // compiler/rustc_middle/src/ty/context/impl_interner.rs impl<'tcx> Interner for TyCtxt<'tcx> { // Attempt 1: type Interned<T> = rustc_data_structures::intern::Interned<'tcx, T>; // Attempt 2: type Interned<T: 'tcx> = rustc_data_structures::intern::Interned<'tcx, T>; }

Attempt 1 fails with;

error[E0309]: the parameter type `T` may not live long enough --> compiler/rustc_middle/src/ty/context/impl_interner.rs:35:5 | 30 | impl<'tcx> Interner for TyCtxt<'tcx> { | ---- the parameter type `T` must be valid for the lifetime `'tcx` as defined here... ... 35 | type Interned<T> = rustc_data_structures::intern::Interned<'tcx, T>; | ^^^^^^^^^^^^^^^^ ...so that the type `T` will meet its required lifetime bounds... | note: ...that is required by this bound --> compiler/rustc_data_structures/src/intern.rs:26:28 | 26 | pub struct Interned<'a, T>(pub &'a T, pub private::PrivateZst); | ^^^^^^^^^ help: consider adding an explicit lifetime bound | 35 | type Interned<T: 'tcx> = rustc_data_structures::intern::Interned<'tcx, T>; | ++++++

Which leads to Attempt 2 which fails with;

error[E0276]: impl has stricter requirements than trait --> compiler/rustc_middle/src/ty/context/impl_interner.rs:35:22 | 35 | type Interned<T: 'tcx> = rustc_data_structures::intern::Interned<'tcx, T>; | ^^^^ impl has extra requirement `T: 'tcx`

I'm not sure if I'm missing something? It looks like my problem where I tried to use Interned from rustc_data_structures needing a lifetime added to Interner?

ah yeah 😅 can you add type InternedRegionKind instead 😭

This is annoying limitation of Rust and I don't quite know whether to avoid this for now.

`rustc_type_ir` methods for the struct.

…e already been ported to ir

struct

rustbot · 2026-04-14T11:51:10Z

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.

rustbot assigned lcnr Apr 8, 2026

This comment has been minimized.

Sign in to view

lcnr reviewed Apr 9, 2026

View reviewed changes

Jamesbarford force-pushed the chore/move-region-to-ir branch from fc9ac0c to 39c966a Compare April 9, 2026 10:19

rustbot added the T-clippy Relevant to the Clippy team. label Apr 9, 2026

Jamesbarford force-pushed the chore/move-region-to-ir branch from 39c966a to 7c825ed Compare April 9, 2026 14:12

This comment has been minimized.

Sign in to view

Jamesbarford force-pushed the chore/move-region-to-ir branch from 6de045f to 89ecd54 Compare April 10, 2026 11:43

lcnr reviewed Apr 10, 2026

View reviewed changes

This comment has been minimized.

Sign in to view

Jamesbarford added 6 commits April 14, 2026 09:06

Created a new Struct Region2 and implemented inherent

421b2a3

`rustc_type_ir` methods for the struct.

Create methods and trait methods for Region, I::Region -> Region<I>

fac4e48

Create extension traits, use them and remove implementations that hav…

e906306

…e already been ported to ir

Implement Debug for Region correctly

92dc393

Add lift implementations to fix compiler errors

4af3c9e

Add a facade struct in rustc_middle so we can still print out the

118c0f5

struct

Jamesbarford added 13 commits April 14, 2026 09:07

move Region codec impls out of rustc_middle

91261a0

fix for mismatching return type, just return one Option<Region<...>>

16ec5f1

More imports for trait extensions

8c16d9b

more importing of extension traits and using .to_string() for formatting

9909cc4

Fix for diagnostic by creating an intermediary struct

e3fef43

More importing of extension traits

1f443a7

Remove used import of trait extension

b2ad9b1

PR-Feedback; remove manual Lift implementations

6e0b4f4

Remove commented out code

3685c2d

PR-Feedback; Make interning methods on Interner

adcb2e7

PR-Feedback; fix for printing Region

317320f

fix clippy

7db503d

Fixing ci issues

706e15e

Jamesbarford force-pushed the chore/move-region-to-ir branch from 89ecd54 to 706e15e Compare April 14, 2026 11:51


		impl<I: Interner> Eq for RegionKind<I> {}

		impl<I: Interner, U: Interner> Lift<U> for RegionKind<I>

Uh oh!

Conversation

Jamesbarford commented Apr 8, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

General notes

compiler/rustc_middle/src/ty/region.rs

Uh oh!

rustbot commented Apr 8, 2026

Uh oh!

This comment has been minimized.

This comment has been minimized.

This comment has been minimized.

lcnr Apr 9, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

lcnr Apr 9, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

lcnr left a comment • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

lcnr commented Apr 9, 2026

Uh oh!

rustbot commented Apr 9, 2026

Uh oh!

This comment has been minimized.

This comment has been minimized.

This comment has been minimized.

This comment has been minimized.

lcnr Apr 10, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

This comment has been minimized.

rustbot commented Apr 14, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants

Jamesbarford commented Apr 8, 2026 •

edited by rustbot

Loading

`compiler/rustc_middle/src/ty/region.rs`

lcnr Apr 9, 2026 •

edited by rustbot

Loading

lcnr Apr 9, 2026 •

edited by rustbot

Loading

lcnr left a comment •

edited by rustbot

Loading

lcnr Apr 10, 2026 •

edited by rustbot

Loading