Clean up singleton TypeId use (#6300)

#6289 absentmindedly added fields in more places, and this is undoing
that plus further fixes.

This does some cleanup of types with relation to singletons. For
`TypeType` and `ErrorInst`, they're always complete due to a
`SetComplete` call in `file.cpp`. For `CppVoidType`, it's intended to be
incomplete by construction, and so a `TypeId` should be okay. The intent
though on not generally providing these had been that `GetSingletonType`
needs to be called to get a type to be marked as complete.

In the case of `AutoType`, removing `TypeId`does change a small printing
detail. I think that's old legacy that's just been carried forward.

Otherwise, for both `InstType` and `AutoType`, I've added
`GetSingletonType` calls where they were used in order to ensure
completeness is applied correctly. These calls cause small SemIR
permutations.

This causes `AutoType` to be seen by lowering, so I'm adding a
placeholder for it. Also merging two functions that look like they're
identical in intent -- not sure why they're separate.

---------

Co-authored-by: Dana Jansens <[email protected]>

Author: jonmeow

toolchain/check/action.cpp

@@ -7,6 +7,7 @@
 #include "toolchain/base/kind_switch.h"
 #include "toolchain/check/generic_region_stack.h"
 #include "toolchain/check/inst.h"
+#include "toolchain/check/type.h"
 #include "toolchain/sem_ir/constant.h"
 #include "toolchain/sem_ir/id_kind.h"
 #include "toolchain/sem_ir/inst.h"
@@ -134,7 +135,8 @@ static auto RefineOperand(Context& context, SemIR::LocId loc_id,
           context,
           SemIR::LocIdAndInst(
               loc_id,
-              SemIR::RefineTypeAction{.type_id = SemIR::InstType::TypeId,
+              SemIR::RefineTypeAction{.type_id = GetSingletonType(
+                                          context, SemIR::InstType::TypeInstId),
                                       .inst_id = *inst_id,
                                       .inst_type_inst_id = type_inst_id}),
           type_inst_id);

toolchain/check/convert.cpp

@@ -1459,9 +1459,10 @@ auto Convert(Context& context, SemIR::LocId loc_id, SemIR::InstId expr_id,
     auto target_type_inst_id = context.types().GetInstId(target.type_id);
     return AddDependentActionSplice(
         context, loc_id,
-        SemIR::ConvertToValueAction{.type_id = SemIR::InstType::TypeId,
-                                    .inst_id = expr_id,
-                                    .target_type_inst_id = target_type_inst_id},
+        SemIR::ConvertToValueAction{
+            .type_id = GetSingletonType(context, SemIR::InstType::TypeInstId),
+            .inst_id = expr_id,
+            .target_type_inst_id = target_type_inst_id},
         target_type_inst_id);
   }
 
@@ -1735,7 +1736,7 @@ auto ExprAsType(Context& context, SemIR::LocId loc_id, SemIR::InstId value_id,
                 bool diagnose) -> TypeExpr {
   auto type_inst_id =
       ConvertToValueOfType(context, loc_id, value_id, SemIR::TypeType::TypeId);
-  if (type_inst_id == SemIR::ErrorInst::InstId) {
+  if (type_inst_id == SemIR::ErrorInst::TypeInstId) {
     return {.inst_id = SemIR::ErrorInst::TypeInstId,
             .type_id = SemIR::ErrorInst::TypeId};
   }

toolchain/check/eval.cpp

@@ -987,10 +987,9 @@ static auto PerformCheckedCharConvert(Context& context, SemIR::LocId loc_id,
 static auto MakeIntTypeResult(Context& context, SemIR::LocId loc_id,
                               SemIR::IntKind int_kind, SemIR::InstId width_id,
                               Phase phase) -> SemIR::ConstantId {
-  auto result = SemIR::IntType{
-      .type_id = GetSingletonType(context, SemIR::TypeType::TypeInstId),
-      .int_kind = int_kind,
-      .bit_width_id = width_id};
+  auto result = SemIR::IntType{.type_id = SemIR::TypeType::TypeId,
+                               .int_kind = int_kind,
+                               .bit_width_id = width_id};
   if (!ValidateIntType(context, loc_id, result)) {
     return SemIR::ErrorInst::ConstantId;
   }
@@ -1002,10 +1001,9 @@ static auto MakeIntTypeResult(Context& context, SemIR::LocId loc_id,
 static auto MakeFloatTypeResult(Context& context, SemIR::LocId loc_id,
                                 SemIR::InstId width_id, Phase phase)
     -> SemIR::ConstantId {
-  auto result = SemIR::FloatType{
-      .type_id = GetSingletonType(context, SemIR::TypeType::TypeInstId),
-      .bit_width_id = width_id,
-      .float_kind = SemIR::FloatKind::None};
+  auto result = SemIR::FloatType{.type_id = SemIR::TypeType::TypeId,
+                                 .bit_width_id = width_id,
+                                 .float_kind = SemIR::FloatKind::None};
   if (!ValidateFloatTypeAndSetKind(context, loc_id, result)) {
     return SemIR::ErrorInst::ConstantId;
   }
@@ -2085,8 +2083,10 @@ static auto TryEvalTypedInst(EvalContext& eval_context, SemIR::InstId inst_id,
         // The result is an instruction.
         return MakeConstantResult(
             eval_context.context(),
-            SemIR::InstValue{.type_id = SemIR::InstType::TypeId,
-                             .inst_id = result_inst_id},
+            SemIR::InstValue{
+                .type_id = GetSingletonType(eval_context.context(),
+                                            SemIR::InstType::TypeInstId),
+                .inst_id = result_inst_id},
             Phase::Concrete);
       }
       // Couldn't perform the action because it's still dependent.

toolchain/check/handle_binding_pattern.cpp

@@ -412,7 +412,8 @@ auto HandleParseNode(Context& context, Parse::AddrId node_id) -> bool {
     if (pointer_type) {
       auto addr_pattern_id = AddPatternInst<SemIR::AddrPattern>(
           context, node_id,
-          {.type_id = GetPatternType(context, SemIR::AutoType::TypeId),
+          {.type_id = GetPatternType(
+               context, GetSingletonType(context, SemIR::AutoType::TypeInstId)),
            .inner_id = param_pattern_id});
       context.node_stack().Push(node_id, addr_pattern_id);
     } else {

toolchain/check/member_access.cpp

@@ -461,13 +461,13 @@ auto PerformMemberAccess(Context& context, SemIR::LocId loc_id,
   if (required) {
     return HandleAction<SemIR::AccessMemberAction>(
         context, loc_id,
-        {.type_id = SemIR::InstType::TypeId,
+        {.type_id = GetSingletonType(context, SemIR::InstType::TypeInstId),
          .base_id = base_id,
          .name_id = name_id});
   } else {
     return HandleAction<SemIR::AccessOptionalMemberAction>(
         context, loc_id,
-        {.type_id = SemIR::InstType::TypeId,
+        {.type_id = GetSingletonType(context, SemIR::InstType::TypeInstId),
          .base_id = base_id,
          .name_id = name_id});
   }