Internal Tracking Issue for the AliasTerm refactor

This is a tracking issue for a refactoring of the way aliases are represented in the type system.

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Steps

move DefId of type aliases into AliasTyKind ty::Alias refactor #154758
do the same for constants, updating AliasTerm AliasTerm refactor #155392
Use special DefIds for aliases #155981
merge AliasTy and AliasTerm and have a single Alias type generic over the kind.
remove AliasTerm::def_id() and AliasTy::def_id as not all variants will ahve DefIds in the future, instead track the current variant more explicitly
- TypeError use more specific DefIds, requires change to Relate impl of AliasTy
replace uses of tcx.mk_ty_from_kind with calls to a more specific constructor method

we should change these types as follows

pub struct Alias<I: Interner, K> {
    pub kind: K,
    pub args: I::GenericArgs,
    pub(crate) _use_alias_new_instead: (),
}

// same for const
type AliasTy<I: Interner> = Alias<I, AliasTyKind<I>>;

with this we can now update NormalizesTo to also be generic over the kind, and e.g. for normalize_anon_const have the argument be Goal<I, ty::NormalizesTo<I, I::UnevaluatedConstId>>, cc #155981

@BoxyUwU

cc @BoxyUwU @WaffleLapkin

CC related tracking issue #154941

woops 😅

re: the step "merge AliasTy and AliasTerm and have a single Alias type generic over the kind", UnevaluatedConst should also be included in this bucket. Relatedly/tangentially, there is currently a const generics work item to rename UnevaluatedConst to AliasConst: rust-lang/project-const-generics#115

(const items are surprisingly similar to type aliases, and generally can be thought of as the same kind of thing!)

Rollup merge of rust-lang#157653 - khyperia:AliasTerm-def_id, r=BoxyUwU

Unrolled build for #157653

Rollup merge of rust-lang#156538 - Jamesbarford:chore/merge-AliasTy-A…

Rollup merge of #157653 - khyperia:AliasTerm-def_id, r=BoxyUwU

Auto merge of #158013 - khyperia:AliasTy-def_id, r=BoxyUwU

Rollup merge of rust-lang#162797 - khyperia:yeet-opt_def_id, r=BoxyUw…

Unrolled build for #162797 in rollup 163002

Rollup merge of #162797 - khyperia:yeet-opt_def_id, r=BoxyUwU,bit-aloo

Rollup merge of rust-lang#157653 - khyperia:AliasTerm-def_id, r=BoxyUwU

Auto merge of rust-lang#158013 - khyperia:AliasTy-def_id, r=BoxyUwU

Rollup merge of rust-lang#162797 - khyperia:yeet-opt_def_id, r=BoxyUw…

Rollup merge of #157653 - khyperia:AliasTerm-def_id, r=BoxyUwU

Auto merge of #158013 - khyperia:AliasTy-def_id, r=BoxyUwU

Rollup merge of #162797 - khyperia:yeet-opt_def_id, r=BoxyUwU,bit-aloo

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Internal Tracking Issue for the `AliasTerm` refactor #156181

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Internal Tracking Issue for the AliasTerm refactor #156181

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lcnr commented on May 5, 2026

lcnr commented on May 5, 2026

fmease commented on May 5, 2026

lcnr commented on May 5, 2026

khyperia commented on Jun 10, 2026

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Internal Tracking Issue for the `AliasTerm` refactor #156181