src: avoid unnecessary string allocations in SPrintF impl

If we can use a `std::string_view` instead of a `std::string`, let's just do that instead. PR-URL: #60052 Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Rafael Gonzaga <rafael.nunu@hotmail.com>

Author: addaleax

src/debug_utils-inl.h

@@ -11,25 +11,41 @@
 
 namespace node {
 
+template <typename T>
+concept StringViewConvertible = requires(T a) {
+ {
+ a.ToStringView()
+ } -> std::convertible_to<std::string_view>;
+ };
+template <typename T>
+concept StringConvertible = requires(T a) {
+ {
+ a.ToString()
+ } -> std::convertible_to<std::string>;
+ };
+
 struct ToStringHelper {
  template <typename T>
- static std::string Convert(
- const T& value,
- std::string(T::* to_string)() const = &T::ToString) {
- return (value.*to_string)();
+ requires(StringConvertible<T>) && (!StringViewConvertible<T>)
+ static std::string Convert(const T& value) {
+ return value.ToString();
  }
+ template <typename T>
+ requires StringViewConvertible<T>
+ static std::string_view Convert(const T& value) {
+ return value.ToStringView();
+ }
+
  template <typename T,
  typename test_for_number = typename std::
  enable_if<std::is_arithmetic<T>::value, bool>::type,
  typename dummy = bool>
  static std::string Convert(const T& value) { return std::to_string(value); }
- static std::string Convert(const char* value) {
+ static std::string_view Convert(const char* value) {
  return value != nullptr ? value : "(null)";
  }
  static std::string Convert(const std::string& value) { return value; }
- static std::string Convert(std::string_view value) {
- return std::string(value);
- }
+ static std::string_view Convert(std::string_view value) { return value; }
  static std::string Convert(bool value) { return value ? "true" : "false"; }
  template <unsigned BASE_BITS,
  typename T,
@@ -50,18 +66,23 @@ struct ToStringHelper {
  template <unsigned BASE_BITS,
  typename T,
  typename = std::enable_if_t<!std::is_integral_v<T>>>
- static std::string BaseConvert(T& value) { // NOLINT(runtime/references)
+ static auto BaseConvert(T&& value) {
  return Convert(std::forward<T>(value));
  }
 };
 
 template <typename T>
-std::string ToString(const T& value) {
+auto ToStringOrStringView(const T& value) {
  return ToStringHelper::Convert(value);
 }
 
+template <typename T>
+std::string ToString(const T& value) {
+ return std::string(ToStringOrStringView(value));
+}
+
 template <unsigned BASE_BITS, typename T>
-std::string ToBaseString(const T& value) {
+auto ToBaseString(const T& value) {
  return ToStringHelper::BaseConvert<BASE_BITS>(value);
 }
 
@@ -106,7 +127,7 @@ std::string COLD_NOINLINE SPrintFImpl( // NOLINT(runtime/string)
  case 'i':
  case 'u':
  case 's':
- ret += ToString(arg);
+ ret += ToStringOrStringView(arg);
  break;
  case 'o':
  ret += ToBaseString<3>(arg);

src/debug_utils.h

@@ -26,6 +26,8 @@ class Environment;
 
 template <typename T>
 inline std::string ToString(const T& value);
+template <typename T>
+inline auto ToStringOrStringView(const T& value);
 
 // C++-style variant of sprintf()/fprintf() that:
 // - Returns an std::string