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

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
@@ -75,6 +75,7 @@ fn StarstWith(a: str, b: str) -> bool {
// CHECK:STDOUT: --- pass_and_return.carbon
// CHECK:STDOUT:
// CHECK:STDOUT: constants {
// CHECK:STDOUT: type: type = facet_type <type> [concrete]
// CHECK:STDOUT: %F.type: type = fn_type @F [concrete]
// CHECK:STDOUT: %empty_tuple.type: type = tuple_type () [concrete]
// CHECK:STDOUT: %F: %F.type = struct_value () [concrete]
@@ -164,6 +165,7 @@ fn StarstWith(a: str, b: str) -> bool {
// CHECK:STDOUT: --- call_base_method.carbon
// CHECK:STDOUT:
// CHECK:STDOUT: constants {
// CHECK:STDOUT: type: type = facet_type <type> [concrete]
// CHECK:STDOUT: %str: type = class_type @String [concrete]
// CHECK:STDOUT: %empty_tuple.type: type = tuple_type () [concrete]
// CHECK:STDOUT: %pattern_type.adf: type = pattern_type %str [concrete]