Repository: carbon-language/carbon-lang
File: toolchain/check/cpp/import.cpp (C++)

Code before:
      AddImportIRInst(context.sem_ir(), cpp_loc);

  SemIR::TypeId type_id = MapType(context, loc_id, type).type_id;
  if (!type_id.has_value()) {
    return SemIR::ErrorInst::InstId;
  }

  SemIR::InstId inst_id = SemIR::InstId::None;
  if (ap_value.isInt()) {
    int64_t value = ap_value.getInt().getExtValue();
    if (type->isBooleanType()) {
      inst_id = AddInstInNoBlock(
          context,
          MakeImportedLocIdAndInst<SemIR::BoolLiteral>(
              context, imported_loc_id,
              {.type_id = type_id, .value = SemIR::BoolValue::From(value)}));
    } else {
      IntId int_id = context.ints().Add(value);
      inst_id = AddInstInNoBlock(context,
                                 MakeImportedLocIdAndInst<SemIR::IntValue>(
                                     context, imported_loc_id,
                                     {.type_id = type_id, .int_id = int_id}));
    }
  } else {
    // TODO: support other types.
    return SemIR::ErrorInst::InstId;
  }

  context.imports().push_back(inst_id);
  return inst_id;
}

// Maps a Clang literal expression to a Carbon constant.
// TODO: Add support for all constant types for which a C++ to Carbon type
// mapping exists.
static auto MapConstant(Context& context, SemIR::LocId loc_id,
                        clang::Expr* expr) -> SemIR::InstId {
  CARBON_CHECK(expr, "empty expression");

  if (auto* string_literal = dyn_cast<clang::StringLiteral>(expr)) {
    if (!string_literal->isOrdinary() && !string_literal->isUTF8()) {
      context.TODO(loc_id,
                   llvm::formatv("Unsupported: string literal type: {0}",
                                 expr->getType()));
      return SemIR::ErrorInst::InstId;
    }
    StringLiteralValueId string_id =
        context.string_literal_values().Add(string_literal->getString());
    auto inst_id =
        MakeStringLiteral(context, Parse::StringLiteralId::None, string_id);
    return inst_id;

Review comment (suggestion):
As above, we should either produce a diagnostic here or return something other than `ErrorInst::InstId`.

Code after:

  if (auto* string_literal = dyn_cast<clang::StringLiteral>(expr)) {
    if (!string_literal->isOrdinary() && !string_literal->isUTF8()) {
      context.TODO(loc_id,
                   llvm::formatv("Unsupported: string literal type: {0}",
                                 expr->getType()));
      return SemIR::ErrorInst::InstId;
    }
    StringLiteralValueId string_id =
        context.string_literal_values().Add(string_literal->getString());
    auto inst_id =
        MakeStringLiteral(context, Parse::StringLiteralId::None, string_id);
    return inst_id;
  } else if (isa<clang::CXXNullPtrLiteralExpr>(expr)) {
    auto type_id = MapNullptrType(context, loc_id).type_id;
    return GetOrAddInst<SemIR::UninitializedValue>(context, SemIR::LocId::None,
                                                   {.type_id = type_id});
  }

  SemIR::TypeId type_id = MapType(context, loc_id, expr->getType()).type_id;
  if (!type_id.has_value()) {
    context.TODO(loc_id, llvm::formatv("Unsupported: C++ literal's type `{0}` "
                                       "could not be mapped to a Carbon type",
                                       expr->getType().getAsString()));
    return SemIR::ErrorInst::InstId;
  }

  SemIR::InstId inst_id = SemIR::InstId::None;
  SemIR::ImportIRInstId imported_loc_id =
      AddImportIRInst(context.sem_ir(), expr->getExprLoc());

  if (auto* integer_literal = dyn_cast<clang::IntegerLiteral>(expr)) {
    IntId int_id =
        context.ints().Add(integer_literal->getValue().getSExtValue());
    inst_id = AddInstInNoBlock(
        context,
        MakeImportedLocIdAndInst<SemIR::IntValue>(
            context, imported_loc_id, {.type_id = type_id, .int_id = int_id}));
  } else if (auto* bool_literal = dyn_cast<clang::CXXBoolLiteralExpr>(expr)) {
    inst_id = AddInstInNoBlock(
        context,
        MakeImportedLocIdAndInst<SemIR::BoolLiteral>(
            context, imported_loc_id,
            {.type_id = type_id,
             .value = SemIR::BoolValue::From(bool_literal->getValue())}));
  } else if (auto* float_literal = dyn_cast<clang::FloatingLiteral>(expr)) {
    FloatId float_id = context.floats().Add(float_literal->getValue());
    inst_id = AddInstInNoBlock(context,
                               MakeImportedLocIdAndInst<SemIR::FloatValue>(
                                   context, imported_loc_id,
                                   {.type_id = type_id, .float_id = float_id}));