Repository: carbon-language/carbon-lang
File: toolchain/sem_ir/function.cpp (C++)

Code before:
  }

  // Identify the function we're calling by its type.
  auto fn_type_inst_id =
      sem_ir.types().GetTypeInstId(sem_ir.insts().Get(val_id).type_id());

  if (auto cpp_overload_set_type =
          sem_ir.insts().TryGetAs<CppOverloadSetType>(fn_type_inst_id)) {
    CARBON_CHECK(!fn.resolved_specific_id.has_value(),
                 "Only `SpecificFunction` will be resolved, not C++ overloads");
    return CalleeCppOverloadSet{
        .cpp_overload_set_id = cpp_overload_set_type->overload_set_id,
        .self_id = fn.self_id};
  }

  if (auto impl_fn_type =
          sem_ir.insts().TryGetAs<FunctionTypeWithSelfType>(fn_type_inst_id)) {
    // Combine the associated function's `Self` with the interface function
    // data.
    fn.self_type_id = impl_fn_type->self_id;
    fn_type_inst_id = impl_fn_type->interface_function_type_id;
  }

  auto fn_type_val_id =
      sem_ir.constant_values().GetConstantInstId(fn_type_inst_id);
  if (fn_type_val_id == SemIR::ErrorInst::InstId) {
    return CalleeError();
  }
  auto fn_type = sem_ir.insts().TryGetAs<FunctionType>(fn_type_val_id);
  if (!fn_type) {
    return CalleeNonFunction();
  }

  fn.function_id = fn_type->function_id;
  fn.enclosing_specific_id = fn_type->specific_id;
  return fn;
}

auto GetCalleeAsFunction(const File& sem_ir, InstId callee_id,
                         SpecificId caller_specific_id) -> CalleeFunction {
  auto callee = GetCallee(sem_ir, callee_id, caller_specific_id);
  CARBON_CHECK(std::holds_alternative<CalleeFunction>(callee));
  return std::get<CalleeFunction>(callee);
}

auto DecomposeVirtualFunction(const File& sem_ir, InstId fn_decl_id,
                              SpecificId base_class_specific_id)
    -> DecomposedVirtualFunction {
  // Remap the base's vtable entry to the appropriate constant usable in
  // the context of the derived class (for the specific for the base
  // class, for instance).

Review comment (suggestion):
```suggestion
  if (fn_type_val_id == ErrorInst::InstId) {
```

Code after:
  }

  // Identify the function we're calling by its type.
  auto fn_type_inst_id =
      sem_ir.types().GetTypeInstId(sem_ir.insts().Get(val_id).type_id());

  if (auto cpp_overload_set_type =
          sem_ir.insts().TryGetAs<CppOverloadSetType>(fn_type_inst_id)) {
    CARBON_CHECK(!fn.resolved_specific_id.has_value(),
                 "Only `SpecificFunction` will be resolved, not C++ overloads");
    return CalleeCppOverloadSet{
        .cpp_overload_set_id = cpp_overload_set_type->overload_set_id,
        .self_id = fn.self_id};
  }

  if (auto impl_fn_type =
          sem_ir.insts().TryGetAs<FunctionTypeWithSelfType>(fn_type_inst_id)) {
    // Combine the associated function's `Self` with the interface function
    // data.
    fn.self_type_id = impl_fn_type->self_id;
    fn_type_inst_id = impl_fn_type->interface_function_type_id;
  }

  auto fn_type_val_id =
      sem_ir.constant_values().GetConstantInstId(fn_type_inst_id);
  if (fn_type_val_id == ErrorInst::InstId) {
    return CalleeError();
  }
  auto fn_type = sem_ir.insts().TryGetAs<FunctionType>(fn_type_val_id);
  if (!fn_type) {
    return CalleeNonFunction();
  }

  fn.function_id = fn_type->function_id;
  fn.enclosing_specific_id = fn_type->specific_id;
  return fn;
}

auto GetCalleeAsFunction(const File& sem_ir, InstId callee_id,
                         SpecificId caller_specific_id) -> CalleeFunction {
  auto callee = GetCallee(sem_ir, callee_id, caller_specific_id);
  CARBON_CHECK(std::holds_alternative<CalleeFunction>(callee));
  return std::get<CalleeFunction>(callee);
}

auto DecomposeVirtualFunction(const File& sem_ir, InstId fn_decl_id,
                              SpecificId base_class_specific_id)
    -> DecomposedVirtualFunction {
  // Remap the base's vtable entry to the appropriate constant usable in
  // the context of the derived class (for the specific for the base
  // class, for instance).