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Dana Jansens
fcae9610bd
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.