Use separate ConversionKind instead of bool flag

Author: geoffromer

toolchain/check/convert.cpp

@@ -730,6 +730,7 @@ static auto IsValidExprCategoryForConversionTarget(
     case ConversionTarget::Value:
       return category == SemIR::ExprCategory::Value;
     case ConversionTarget::ValueOrRef:
+    case ConversionTarget::RefParam:
     case ConversionTarget::Discarded:
       return category == SemIR::ExprCategory::Value ||
              category == SemIR::ExprCategory::DurableRef ||
@@ -1396,13 +1397,13 @@ auto Convert(Context& context, SemIR::LocId loc_id, SemIR::InstId expr_id,
     if (lookup_result) {
       has_ref_tag = true;
       if (lookup_result.value() == Context::RefTag::Present &&
-          !target.require_ref_tag) {
+          target.kind != ConversionTarget::RefParam) {
         CARBON_DIAGNOSTIC(RefTagNoRefParam, Error,
                           "`ref` tag is not an argument to a `ref` parameter");
         context.emitter().Emit(expr_id, RefTagNoRefParam);
       }
     } else {
-      if (target.require_ref_tag) {
+      if (target.kind == ConversionTarget::RefParam) {
         CARBON_DIAGNOSTIC(RefParamNoRefTag, Error,
                           "argument to `ref` parameter not marked with `ref`");
         context.emitter().Emit(expr_id, RefParamNoRefTag);
@@ -1597,7 +1598,8 @@ auto Convert(Context& context, SemIR::LocId loc_id, SemIR::InstId expr_id,
       // If a reference expression is an acceptable result, we're done.
       if (target.kind == ConversionTarget::ValueOrRef ||
           target.kind == ConversionTarget::Discarded ||
-          target.kind == ConversionTarget::CppThunkRef) {
+          target.kind == ConversionTarget::CppThunkRef ||
+          target.kind == ConversionTarget::RefParam) {
         break;
       }
 

toolchain/check/convert.h

@@ -21,6 +21,8 @@ struct ConversionTarget {
     ValueOrRef,
     // Convert to a durable reference of type `type_id`.
     DurableRef,
+    // Convert to a reference, suitable for binding to a reference parameter.
+    RefParam,
     // Convert to a reference of type `type_id`, for use as the argument to a
     // C++ thunk.
     CppThunkRef,
@@ -57,8 +59,6 @@ struct ConversionTarget {
   // should be false.
   bool diagnose = true;
 
-  bool require_ref_tag = false;
-
   // Are we converting this value into an initializer for an object?
   auto is_initializer() const -> bool {
     return kind == Initializer || kind == FullInitializer;

toolchain/check/pattern_match.cpp

@@ -374,12 +374,13 @@ auto MatchContext::DoEmitPatternMatch(Context& context,
       // We should already have a durable reference (in the case of a
       // VarParamPattern, that's handled by the enclosing VarPattern), but we
       // may need to adjust its type.
-      auto scrutinee_ref_id = Convert(
-          context, SemIR::LocId(entry.scrutinee_id), entry.scrutinee_id,
-          {.kind = ConversionTarget::ValueOrRef,
-           .type_id = scrutinee_type_id,
-           .require_ref_tag =
-               std::is_same_v<RefParamPatternT, SemIR::RefParamPattern>});
+      auto conversion_kind =
+          std::is_same_v<RefParamPatternT, SemIR::RefParamPattern>
+              ? ConversionTarget::RefParam
+              : ConversionTarget::ValueOrRef;
+      auto scrutinee_ref_id =
+          Convert(context, SemIR::LocId(entry.scrutinee_id), entry.scrutinee_id,
+                  {.kind = conversion_kind, .type_id = scrutinee_type_id});
 
       switch (SemIR::GetExprCategory(context.sem_ir(), scrutinee_ref_id)) {
         case SemIR::ExprCategory::Error: