Switch TypeId::TypeType to TypeType::SingletonTypeId, and similar

toolchain/check/call.cpp

@@ -97,7 +97,7 @@ static auto PerformCallToGenericClass(Context& context, SemIR::LocId loc_id,
     return SemIR::InstId::BuiltinErrorInst;
   }
   return context.GetOrAddInst<SemIR::ClassType>(
-      loc_id, {.type_id = SemIR::TypeId::TypeType,
+      loc_id, {.type_id = SemIR::TypeType::SingletonTypeId,
                .class_id = class_id,
                .specific_id = *callee_specific_id});
 }
@@ -202,7 +202,7 @@ auto PerformCall(Context& context, SemIR::LocId loc_id, SemIR::InstId callee_id,
     case SemIR::InitRepr::Incomplete:
       // Don't form an initializing expression with an incomplete type.
       // CheckFunctionReturnType will have diagnosed this for us if needed.
-      return_info.type_id = SemIR::TypeId::Error;
+      return_info.type_id = SemIR::ErrorInst::SingletonTypeId;
       break;
   }
 

toolchain/check/context.cpp

@@ -61,10 +61,10 @@ Context::Context(const Lex::TokenizedBuffer& tokens, DiagnosticEmitter& emitter,
   // special `TypeId` values.
   type_ids_for_type_constants_.Insert(
       SemIR::ConstantId::ForTemplateConstant(SemIR::InstId::BuiltinErrorInst),
-      SemIR::TypeId::Error);
+      SemIR::ErrorInst::SingletonTypeId);
   type_ids_for_type_constants_.Insert(
       SemIR::ConstantId::ForTemplateConstant(SemIR::InstId::BuiltinTypeType),
-      SemIR::TypeId::TypeType);
+      SemIR::TypeType::SingletonTypeId);
 
   // TODO: Remove this and add a `VerifyOnFinish` once we properly push and pop
   // in the right places.
@@ -492,7 +492,7 @@ auto Context::AppendLookupScopesForConstant(
     }
     return true;
   }
-  if (base_const_id == SemIR::ConstantId::Error) {
+  if (base_const_id == SemIR::ErrorInst::SingletonConstantId) {
     // Lookup into this scope should fail without producing an error.
     scopes->push_back(LookupScope{.name_scope_id = SemIR::NameScopeId::Invalid,
                                   .specific_id = SemIR::SpecificId::Invalid});
@@ -761,9 +761,9 @@ auto Context::SetBlockArgResultBeforeConstantUse(SemIR::InstId select_id,
     const_id = constant_values().Get(literal.value().value.ToBool() ? if_true
                                                                     : if_false);
   } else {
-    CARBON_CHECK(cond_const_id == SemIR::ConstantId::Error,
+    CARBON_CHECK(cond_const_id == SemIR::ErrorInst::SingletonConstantId,
                  "Unexpected constant branch condition.");
-    const_id = SemIR::ConstantId::Error;
+    const_id = SemIR::ErrorInst::SingletonConstantId;
   }
 
   if (const_id.is_constant()) {
@@ -908,7 +908,7 @@ class TypeCompleter {
         }
         // For a pointer representation, the pointee also needs to be complete.
         if (value_rep.kind == SemIR::ValueRepr::Pointer) {
-          if (value_rep.type_id == SemIR::TypeId::Error) {
+          if (value_rep.type_id == SemIR::ErrorInst::SingletonTypeId) {
             break;
           }
           auto pointee_type_id =
@@ -1295,7 +1295,8 @@ auto Context::GetTypeIdForTypeConstant(SemIR::ConstantId constant_id)
   auto type_id =
       insts().Get(constant_values().GetInstId(constant_id)).type_id();
   // TODO: For now, we allow values of facet type to be used as types.
-  CARBON_CHECK(IsFacetType(type_id) || constant_id == SemIR::ConstantId::Error,
+  CARBON_CHECK(IsFacetType(type_id) ||
+                   constant_id == SemIR::ErrorInst::SingletonConstantId,
                "Forming type ID for non-type constant of type {0}",
                types().GetAsInst(type_id));
 
@@ -1308,15 +1309,16 @@ auto Context::FacetTypeFromInterface(SemIR::InterfaceId interface_id,
   SemIR::FacetTypeId facet_type_id = facet_types().Add(
       SemIR::FacetTypeInfo{.impls_constraints = {{interface_id, specific_id}},
                            .other_requirements = false});
-  return {.type_id = SemIR::TypeId::TypeType, .facet_type_id = facet_type_id};
+  return {.type_id = SemIR::TypeType::SingletonTypeId,
+          .facet_type_id = facet_type_id};
 }
 
 // Gets or forms a type_id for a type, given the instruction kind and arguments.
 template <typename InstT, typename... EachArgT>
 static auto GetTypeImpl(Context& context, EachArgT... each_arg)
     -> SemIR::TypeId {
   // TODO: Remove inst_id parameter from TryEvalInst.
-  InstT inst = {SemIR::TypeId::TypeType, each_arg...};
+  InstT inst = {SemIR::TypeType::SingletonTypeId, each_arg...};
   return context.GetTypeIdForTypeConstant(
       TryEvalInst(context, SemIR::InstId::Invalid, inst));
 }

toolchain/check/context.h

@@ -362,12 +362,12 @@ class Context {
       -> SemIR::TypeId {
     return TryToCompleteType(type_id, diagnoser, abstract_diagnoser)
                ? type_id
-               : SemIR::TypeId::Error;
+               : SemIR::ErrorInst::SingletonTypeId;
   }
 
   // Returns whether `type_id` represents a facet type.
   auto IsFacetType(SemIR::TypeId type_id) -> bool {
-    return type_id == SemIR::TypeId::TypeType ||
+    return type_id == SemIR::TypeType::SingletonTypeId ||
            types().Is<SemIR::FacetType>(type_id);
   }
 

toolchain/check/convert.cpp

@@ -550,7 +550,7 @@ static auto ConvertStructToClass(Context& context, SemIR::StructType src_type,
   CARBON_CHECK(dest_class_info.inheritance_kind != SemIR::Class::Abstract);
   auto object_repr_id =
       dest_class_info.GetObjectRepr(context.sem_ir(), dest_type.specific_id);
-  if (object_repr_id == SemIR::TypeId::Error) {
+  if (object_repr_id == SemIR::ErrorInst::SingletonTypeId) {
     return SemIR::InstId::BuiltinErrorInst;
   }
   auto dest_struct_type =
@@ -866,7 +866,7 @@ static auto PerformBuiltinConversion(Context& context, SemIR::LocId loc_id,
     }
   }
 
-  if (target.type_id == SemIR::TypeId::TypeType) {
+  if (target.type_id == SemIR::TypeType::SingletonTypeId) {
     // A tuple of types converts to type `type`.
     // TODO: This should apply even for non-literal tuples.
     if (auto tuple_literal = value.TryAs<SemIR::TupleLiteral>()) {
@@ -913,7 +913,7 @@ static auto PerformCopy(Context& context, SemIR::InstId expr_id)
     -> SemIR::InstId {
   auto expr = context.insts().Get(expr_id);
   auto type_id = expr.type_id();
-  if (type_id == SemIR::TypeId::Error) {
+  if (type_id == SemIR::ErrorInst::SingletonTypeId) {
     return SemIR::InstId::BuiltinErrorInst;
   }
 
@@ -943,8 +943,9 @@ auto Convert(Context& context, SemIR::LocId loc_id, SemIR::InstId expr_id,
 
   // Start by making sure both sides are valid. If any part is invalid, the
   // result is invalid and we shouldn't error.
-  if (sem_ir.insts().Get(expr_id).type_id() == SemIR::TypeId::Error ||
-      target.type_id == SemIR::TypeId::Error) {
+  if (sem_ir.insts().Get(expr_id).type_id() ==
+          SemIR::ErrorInst::SingletonTypeId ||
+      target.type_id == SemIR::ErrorInst::SingletonTypeId) {
     return SemIR::InstId::BuiltinErrorInst;
   }
 
@@ -1215,10 +1216,11 @@ auto ConvertCallArgs(Context& context, SemIR::LocId call_loc_id,
 
 auto ExprAsType(Context& context, SemIR::LocId loc_id, SemIR::InstId value_id)
     -> TypeExpr {
-  auto type_inst_id =
-      ConvertToValueOfType(context, loc_id, value_id, SemIR::TypeId::TypeType);
+  auto type_inst_id = ConvertToValueOfType(context, loc_id, value_id,
+                                           SemIR::TypeType::SingletonTypeId);
   if (type_inst_id == SemIR::InstId::BuiltinErrorInst) {
-    return {.inst_id = type_inst_id, .type_id = SemIR::TypeId::Error};
+    return {.inst_id = type_inst_id,
+            .type_id = SemIR::ErrorInst::SingletonTypeId};
   }
 
   auto type_const_id = context.constant_values().Get(type_inst_id);
@@ -1227,7 +1229,7 @@ auto ExprAsType(Context& context, SemIR::LocId loc_id, SemIR::InstId value_id)
                       "cannot evaluate type expression");
     context.emitter().Emit(loc_id, TypeExprEvaluationFailure);
     return {.inst_id = SemIR::InstId::BuiltinErrorInst,
-            .type_id = SemIR::TypeId::Error};
+            .type_id = SemIR::ErrorInst::SingletonTypeId};
   }
 
   return {.inst_id = type_inst_id,

toolchain/check/convert.h

@@ -104,7 +104,7 @@ auto ConvertCallArgs(Context& context, SemIR::LocId call_loc_id,
 struct TypeExpr {
   // The converted expression of type `type`, or `InstId::BuiltinErrorInst`.
   SemIR::InstId inst_id;
-  // The corresponding type, or `TypeId::Error`.
+  // The corresponding type, or `ErrorInst::SingletonTypeId`.
   SemIR::TypeId type_id;
 };
 

toolchain/check/eval.cpp

@@ -198,7 +198,7 @@ static auto GetPhase(EvalContext& eval_context, SemIR::ConstantId constant_id)
     -> Phase {
   if (!constant_id.is_constant()) {
     return Phase::Runtime;
-  } else if (constant_id == SemIR::ConstantId::Error) {
+  } else if (constant_id == SemIR::ErrorInst::SingletonConstantId) {
     return Phase::UnknownDueToError;
   } else if (constant_id.is_template()) {
     return Phase::Template;
@@ -246,16 +246,17 @@ static auto MakeConstantResult(Context& context, SemIR::Inst inst, Phase phase)
       return context.constants().GetOrAdd(inst,
                                           SemIR::ConstantStore::IsSymbolic);
     case Phase::UnknownDueToError:
-      return SemIR::ConstantId::Error;
+      return SemIR::ErrorInst::SingletonConstantId;
     case Phase::Runtime:
       return SemIR::ConstantId::NotConstant;
   }
 }
 
 // Forms a `constant_id` describing why an evaluation was not constant.
 static auto MakeNonConstantResult(Phase phase) -> SemIR::ConstantId {
-  return phase == Phase::UnknownDueToError ? SemIR::ConstantId::Error
-                                           : SemIR::ConstantId::NotConstant;
+  return phase == Phase::UnknownDueToError
+             ? SemIR::ErrorInst::SingletonConstantId
+             : SemIR::ConstantId::NotConstant;
 }
 
 // Converts a bool value into a ConstantId.
@@ -460,14 +461,14 @@ static auto ReplaceFieldWithConstantValue(EvalContext& eval_context,
 // If the specified fields of the given typed instruction have constant values,
 // replaces the fields with their constant values and builds a corresponding
 // constant value. Otherwise returns `ConstantId::NotConstant`. Returns
-// `ConstantId::Error` if any subexpression is an error.
+// `ErrorInst::SingletonConstantId` if any subexpression is an error.
 //
 // The constant value is then checked by calling `validate_fn(typed_inst)`,
 // which should return a `bool` indicating whether the new constant is valid. If
 // validation passes, `transform_fn(typed_inst)` is called to produce the final
 // constant instruction, and a corresponding ConstantId for the new constant is
 // returned. If validation fails, it should produce a suitable error message.
-// `ConstantId::Error` is returned.
+// `ErrorInst::SingletonConstantId` is returned.
 template <typename InstT, typename ValidateFn, typename TransformFn,
           typename... EachFieldIdT>
 static auto RebuildIfFieldsAreConstantImpl(
@@ -482,7 +483,7 @@ static auto RebuildIfFieldsAreConstantImpl(
                                      &phase) &&
        ...)) {
     if (phase == Phase::UnknownDueToError || !validate_fn(typed_inst)) {
-      return SemIR::ConstantId::Error;
+      return SemIR::ErrorInst::SingletonConstantId;
     }
     return MakeConstantResult(eval_context.context(), transform_fn(typed_inst),
                               phase);
@@ -603,7 +604,7 @@ static auto PerformArrayIndex(EvalContext& eval_context, SemIR::ArrayIndex inst)
         eval_context.emitter().Emit(
             inst.index_id, ArrayIndexOutOfBounds,
             {.type = index->type_id, .value = index_val}, aggregate_type_id);
-        return SemIR::ConstantId::Error;
+        return SemIR::ErrorInst::SingletonConstantId;
       }
     }
   }
@@ -670,7 +671,7 @@ static auto MakeIntTypeResult(Context& context, SemIRLoc loc,
       .int_kind = int_kind,
       .bit_width_id = width_id};
   if (!ValidateIntType(context, loc, result)) {
-    return SemIR::ConstantId::Error;
+    return SemIR::ErrorInst::SingletonConstantId;
   }
   return MakeConstantResult(context, result, phase);
 }
@@ -798,7 +799,7 @@ static auto PerformBuiltinBinaryIntOp(Context& context, SemIRLoc loc,
     case SemIR::BuiltinFunctionKind::IntUMod:
       if (context.ints().Get(rhs.int_id).isZero()) {
         DiagnoseDivisionByZero(context, loc);
-        return SemIR::ConstantId::Error;
+        return SemIR::ErrorInst::SingletonConstantId;
       }
       break;
     default:
@@ -830,7 +831,7 @@ static auto PerformBuiltinBinaryIntOp(Context& context, SemIRLoc loc,
             builtin_kind == SemIR::BuiltinFunctionKind::IntLeftShift,
             {.type = rhs.type_id, .value = rhs_orig_val});
         // TODO: Is it useful to recover by returning 0 or -1?
-        return SemIR::ConstantId::Error;
+        return SemIR::ErrorInst::SingletonConstantId;
       }
 
       if (builtin_kind == SemIR::BuiltinFunctionKind::IntLeftShift) {
@@ -1110,7 +1111,7 @@ static auto MakeConstantForBuiltinCall(Context& context, SemIRLoc loc,
         break;
       }
       if (!ValidateFloatBitWidth(context, loc, arg_ids[0])) {
-        return SemIR::ConstantId::Error;
+        return SemIR::ErrorInst::SingletonConstantId;
       }
       return context.constant_values().Get(
           SemIR::InstId::BuiltinLegacyFloatType);
@@ -1224,7 +1225,7 @@ static auto MakeConstantForCall(EvalContext& eval_context, SemIRLoc loc,
   //
   // TODO: Use a better representation for this.
   if (call.args_id == SemIR::InstBlockId::Invalid) {
-    return SemIR::ConstantId::Error;
+    return SemIR::ErrorInst::SingletonConstantId;
   }
 
   // Find the constant value of the callee.
@@ -1257,7 +1258,7 @@ static auto MakeConstantForCall(EvalContext& eval_context, SemIRLoc loc,
       ReplaceFieldWithConstantValue(eval_context, &call, &SemIR::Call::args_id,
                                     &phase);
   if (phase == Phase::UnknownDueToError) {
-    return SemIR::ConstantId::Error;
+    return SemIR::ErrorInst::SingletonConstantId;
   }
 
   // If any operand of the call is non-constant, the call is non-constant.
@@ -1294,10 +1295,11 @@ static auto MakeFacetTypeResult(Context& context,
                                 const SemIR::FacetTypeInfo& info, Phase phase)
     -> SemIR::ConstantId {
   SemIR::FacetTypeId facet_type_id = context.facet_types().Add(info);
-  return MakeConstantResult(context,
-                            SemIR::FacetType{.type_id = SemIR::TypeId::TypeType,
-                                             .facet_type_id = facet_type_id},
-                            phase);
+  return MakeConstantResult(
+      context,
+      SemIR::FacetType{.type_id = SemIR::TypeType::SingletonTypeId,
+                       .facet_type_id = facet_type_id},
+      phase);
 }
 
 // Implementation for `TryEvalInst`, wrapping `Context` with `EvalContext`.
@@ -1485,7 +1487,7 @@ static auto TryEvalInstInContext(EvalContext& eval_context,
       // A non-generic class declaration evaluates to the class type.
       return MakeConstantResult(
           eval_context.context(),
-          SemIR::ClassType{.type_id = SemIR::TypeId::TypeType,
+          SemIR::ClassType{.type_id = SemIR::TypeType::SingletonTypeId,
                            .class_id = class_decl.class_id,
                            .specific_id = SemIR::SpecificId::Invalid},
           Phase::Template);
@@ -1702,10 +1704,10 @@ static auto TryEvalInstInContext(EvalContext& eval_context,
       if (auto facet_type = base_facet_inst.TryAs<SemIR::FacetType>()) {
         info = GetConstantFacetTypeInfo(eval_context, facet_type->facet_type_id,
                                         &phase);
-      } else if (base_facet_type_id == SemIR::TypeId::Error) {
-        return SemIR::ConstantId::Error;
+      } else if (base_facet_type_id == SemIR::ErrorInst::SingletonTypeId) {
+        return SemIR::ErrorInst::SingletonConstantId;
       } else {
-        CARBON_CHECK(base_facet_type_id == SemIR::TypeId::TypeType,
+        CARBON_CHECK(base_facet_type_id == SemIR::TypeType::SingletonTypeId,
                      "Unexpected type_id: {0}, inst: {1}", base_facet_type_id,
                      base_facet_inst);
       }
@@ -1747,7 +1749,7 @@ static auto TryEvalInstInContext(EvalContext& eval_context,
                               !value.value.ToBool());
       }
       if (phase == Phase::UnknownDueToError) {
-        return SemIR::ConstantId::Error;
+        return SemIR::ErrorInst::SingletonConstantId;
       }
       break;
     }

toolchain/check/function.cpp

@@ -26,8 +26,8 @@ auto CheckFunctionTypeMatches(Context& context,
       new_function.GetDeclaredReturnType(context.sem_ir());
   auto prev_return_type_id =
       prev_function.GetDeclaredReturnType(context.sem_ir(), prev_specific_id);
-  if (new_return_type_id == SemIR::TypeId::Error ||
-      prev_return_type_id == SemIR::TypeId::Error) {
+  if (new_return_type_id == SemIR::ErrorInst::SingletonTypeId ||
+      prev_return_type_id == SemIR::ErrorInst::SingletonTypeId) {
     return false;
   }
   if (!context.types().AreEqualAcrossDeclarations(new_return_type_id,

toolchain/check/handle_alias.cpp

@@ -61,7 +61,7 @@ auto HandleParseNode(Context& context, Parse::AliasId /*node_id*/) -> bool {
     CARBON_DIAGNOSTIC(AliasRequiresNameRef, Error,
                       "alias initializer must be a name reference");
     context.emitter().Emit(expr_node, AliasRequiresNameRef);
-    alias_type_id = SemIR::TypeId::Error;
+    alias_type_id = SemIR::ErrorInst::SingletonTypeId;
     alias_value_id = SemIR::InstId::BuiltinErrorInst;
   }
   auto alias_id = context.AddInst<SemIR::BindAlias>(

toolchain/check/handle_array.cpp

@@ -54,7 +54,7 @@ auto HandleParseNode(Context& context, Parse::ArrayExprId node_id) -> bool {
       context, context.insts().GetLocId(bound_inst_id), bound_inst_id,
       context.GetBuiltinType(SemIR::BuiltinInstKind::IntLiteralType));
   context.AddInstAndPush<SemIR::ArrayType>(
-      node_id, {.type_id = SemIR::TypeId::TypeType,
+      node_id, {.type_id = SemIR::TypeType::SingletonTypeId,
                 .bound_id = bound_inst_id,
                 .element_type_id = element_type_id});
   return true;

toolchain/check/handle_binding_pattern.cpp

@@ -307,8 +307,8 @@ auto HandleParseNode(Context& context, Parse::AddrId node_id) -> bool {
         context.insts().Get(param_pattern_id).type_id());
     if (pointer_type) {
       auto addr_pattern_id = context.AddPatternInst<SemIR::AddrPattern>(
-          node_id,
-          {.type_id = SemIR::TypeId::AutoType, .inner_id = param_pattern_id});
+          node_id, {.type_id = SemIR::AutoType::SingletonTypeId,
+                    .inner_id = param_pattern_id});
       context.node_stack().Push(node_id, addr_pattern_id);
     } else {
       CARBON_DIAGNOSTIC(