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Make SemIR::TypeType be an empty FacetType instruction (#7813)

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The type `type` is now a `FacetType` inst with no constraints. This
brings the model implemented in the toolchain into better alignment with
the language design. The `SemIR::TypeType` struct remains as a scope for
holding the `TypeInstId`, `ConstantId`, and `TypeId` constants, but is
not an `InstKind` anymore.

The `TypeType` inst looks a lot like singletons, but there are many
`FacetType` insts so it doesn't quite fit that model. So we put it
alongside singletons with a fixed inst id but refer to it as a more
general "builtin" inst that is not a singleton.
`Namespace::PackageInstId` is similar, and we group it with `TypeType`
conceptually as another builtin instruction with a fixed id.

No conversion is needed anymore to use a `type` as a facet, since types
also have a `FacetType` type. This simplifies and removes a number of
helpers and branches throughout the code.

The `TypeType` inst is now part of the constant store, so we end up
printing it in the constants block in every test. But it's also named
`type` rather than `%type` to preserve the majority of existing
formatting behaviour, though this does look different from other
constants.

Assisted-by: Opus 5 was used to generate a first draft and validate the
refactoring. Though nearly everything non-trivial the tool wrote has
been modified or rewritten.
This commit is contained in:
Dana Jansens
2026-09-22 15:04:40 +00:00
committed by GitHub
parent 83ca5b71e3
commit fcae9610bd
795 changed files with 9505 additions and 8048 deletions
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toolchain/check/deduce.cpp
+3 -3
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@@ -306,11 +306,11 @@ auto DeductionContext::Deduce() -> bool {
if (context().types().Is<SemIR::PatternType>(param_type_id)) {
param_type_id =
SemIR::ExtractScrutineeType(context().sem_ir(), param_type_id);
} else if (context().types().IsFacetType(param_type_id)) {
} else if (context().types().Is<SemIR::FacetType>(param_type_id)) {
// Given `fn F[G: Interface](g: G)`, the type of `g` is `G as type`. For
// deduction, we want to ignore the `as type`, and check that the argument
// can convert to the FacetType of the canonical facet value.
param_id = GetCanonicalFacetOrTypeValue(context(), param_id);
// can convert to the FacetType of the canonical facet.
param_id = GetCanonicalFacet(context(), param_id);
param = context().insts().Get(param_id);
param_type_id = param.type_id();
}