Move Const from rustc_middle to rustc_type_ir

[Jamesbarford]

Split by commit;

• Firstly move the type and methods
• From I::Const -> Const<I>
• Import ConstExt in all places that require the extension trait methods in compiler
• Import ConstExt in all places that require the extension trait methods in clippy

r? @lcnr

[rustbot]

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

Some changes occurred in compiler/rustc_sanitizers

cc @rcvalle

Some changes occurred in match lowering

cc @Nadrieril

Some changes occurred in match checking

cc @Nadrieril

clippy is developed in its own repository. If possible, consider making this change to rust-lang/rust-clippy instead.

cc @rust-lang/clippy

Some changes occurred to the CTFE machinery

cc @RalfJung, @oli-obk, @lcnr

Some changes occurred in rustc_ty_utils::consts.rs

cc @BoxyUwU

Some changes occurred in exhaustiveness checking

cc @Nadrieril

changes to the core type system

cc @lcnr

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri

HIR ty lowering was modified

cc @fmease

[lcnr]

why do we need manual impls instead of the macro here again?

View changes since the review

[Jamesbarford]

nop_lift does;

 assert!(tcx.interners.$set.contains_pointer_to(&InternedInSet(&*self.0.0)));

Whereas we need;

assert!(tcx.interners.const_.contains_pointer_to(&InternedInSet(&*self.0)));

[lcnr]

hmm, why does moving Const change this access pattern from .0.0 to just .0 🤔 that's not immediately obvious to me.

Please add that as a comment if it can't be avoided

[Jamesbarford]

I'm not sure why;

nop_lift! { const_; Const<'a> => Const<'tcx> }

Given the following definitions

// rustc_type_ir/src/sty/consts.rs
pub struct Const<I: Interner>(pub I::InternedConstKind);

// rustc_middle/rustc_middle/src/ty/context/impl_interner.rs
type InternedConstKind = Interned<'tcx, WithCachedTypeInfo<ty::ConstKind<'tcx>>>;

// rustc_middle/src/ty/consts.rs
pub type Const<'tcx> = ir::Const<TyCtxt<'tcx>>;

Walking through how I think the above would work, which could be wrong, I'd have thought the following code snippet would be true;

pub type Const<'tcx> = struct Const<TyCtxt<'tcx>>(pub TyCtxt<'tcx>::InternedConst);

// which in turn becomes
pub type Const<'tcx> = struct Const<TyCtxt<'tcx>>(pub  Interned<'tcx, WithCachedTypeInfo<ty::ConstKind<'tcx>>>);

Which is the same as what we have before all be it the definition is composed from different modules and associated types. The rust-analyser LSP I have setup agrees with with me that my intuition is correct.

However I get a bunch of cascading errors. Of which this one seems the most likely culprit. So I did what the compiler error told me to do; implement Lift for WithCachedTypeInfo<...>.

error[E0277]: the trait bound `Interned<'tcx, _>: Lift<TyCtxt<'tcx>>` is not satisfied
    --> compiler/rustc_middle/src/ty/context.rs:1894:54
     |
1894 | struct InternedInSet<'tcx, T: ?Sized + PointeeSized>(&'tcx T);
     |                                                      ^^^^^^^ unsatisfied trait bound
     |
help: the trait `Lift<TyCtxt<'tcx>>` is not implemented for `Interned<'tcx, rustc_type_ir::WithCachedTypeInfo<rustc_type_ir::ConstKind<context::TyCtxt<'tcx>>>>`
      but trait `Lift<TyCtxt<'_>>` is implemented for `Interned<'_, rustc_type_ir::RegionKind<context::TyCtxt<'_>>>`
    --> compiler/rustc_middle/src/ty/context.rs:1721:1

[lcnr]

instead mark with type_visitable(ignored) 🤔

View changes since the review

[lcnr]

same here

View changes since the review

[lcnr]

when do we want to Debug that 🤔 does this PR change the debug output for some types?

View changes since the review

[Jamesbarford]

In impl_interner.rs we have;

impl<'tcx> Interner for TyCtxt<'tcx> {
    // lots of `type <name> = <concrete>;`
    type InternedConstKind = Interned<'tcx, WithCachedTypeInfo<ty::ConstKind<'tcx>>>;

And then later in the file have;

impl<'tcx, T: std::fmt::Debug + Clone + Copy> rustc_type_ir::intern::Interned<TyCtxt<'tcx>>
    for Interned<'tcx, T>
{
    type Value = T;
    fn get(self) -> T {
        *self.0
    }
}

Interned has the trait bound Debug. This is because as the InternedConstKind and InternedRegionKind implement Lift which has the trait bound Debug.

As InternedConstKind is different to InternedRegionKind I had to add Debug to WithCachedTypeInfo

[lcnr]

why does that impl have a Debug bound?

[Jamesbarford]

We can get rid of it for trait Interned but trait Lift: std::fmt::Debug and we implement Lift for WithCachedTypeInfo<ConstKind>

[lcnr]

nits, otherwise this is looking good

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[rustbot]

rustc_codegen_cranelift is developed in its own repository. If possible, consider making this change to rust-lang/rustc_codegen_cranelift instead.

cc @bjorn3

rustc_codegen_gcc is developed in its own repository. If possible, consider making this change to rust-lang/rustc_codegen_gcc instead.

cc @antoyo, @GuillaumeGomez

[lcnr]

alright, r=me after rebase + final nit then

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[rustbot]

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.