std::source_location make constexpr size wrong at compile time.

[Ghost-LZW]

background: want to get compile time type name without rtti.

#include <iostream>
#include <string_view>
#include <source_location>
#include <utility>

template<typename T>
void foo() {
  constexpr std::string_view func_name =
      std::source_location::current().function_name();
  constexpr size_t type_anchor_idx = func_name.find_first_of('=');
  constexpr size_t type_end_idx = func_name.find_last_of(']');
  constexpr auto type_str =
      func_name.substr(type_anchor_idx + 2, type_end_idx - type_anchor_idx - 2);
  std::cerr << type_anchor_idx << ' ' << type_end_idx << std::endl;
  std::cerr << func_name.data() << '\n' << type_str.data() << std::endl;
  std::cerr << type_str.size() << ' '
            << std::make_index_sequence<type_str.size()>().size() << std::endl;
}

int main() {
  foo<int>();
}
/*
14 19
void foo() [T = int]
int]
3 9
*/

https://godbolt.org/z/r45d8cjsr

expect output is

14 19
void foo() [T = int]
int]
3 3

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: lzw (Ghost-LZW)

background: want to get compile time type name without rtti.

#include <iostream>
#include <string_view>
#include <source_location>
#include <utility>

template<typename T>
void foo() {
  constexpr std::string_view func_name =
      std::source_location::current().function_name();
  constexpr size_t type_anchor_idx = func_name.find_first_of('=');
  constexpr size_t type_end_idx = func_name.find_last_of(']');
  constexpr auto type_str =
      func_name.substr(type_anchor_idx + 2, type_end_idx - type_anchor_idx - 2);
  std::cerr << type_anchor_idx << ' ' << type_end_idx << std::endl;
  std::cerr << func_name.data() << '\n' << type_str.data() << std::endl;
  std::cerr << type_str.size() << ' '
            << std::make_index_sequence<type_str.size()>().size() << std::endl;
}

int main() {
  foo<int>();
}
/*
14 19
void foo() [T = int]
int]
3 9
*/

https://godbolt.org/z/r45d8cjsr

expect output is

14 19
void foo() [T = int]
int]
3 3

[llvmbot]

@llvm/issue-subscribers-c-20

Author: lzw (Ghost-LZW)

background: want to get compile time type name without rtti.

#include <iostream>
#include <string_view>
#include <source_location>
#include <utility>

template<typename T>
void foo() {
  constexpr std::string_view func_name =
      std::source_location::current().function_name();
  constexpr size_t type_anchor_idx = func_name.find_first_of('=');
  constexpr size_t type_end_idx = func_name.find_last_of(']');
  constexpr auto type_str =
      func_name.substr(type_anchor_idx + 2, type_end_idx - type_anchor_idx - 2);
  std::cerr << type_anchor_idx << ' ' << type_end_idx << std::endl;
  std::cerr << func_name.data() << '\n' << type_str.data() << std::endl;
  std::cerr << type_str.size() << ' '
            << std::make_index_sequence<type_str.size()>().size() << std::endl;
}

int main() {
  foo<int>();
}
/*
14 19
void foo() [T = int]
int]
3 9
*/

https://godbolt.org/z/r45d8cjsr

expect output is

14 19
void foo() [T = int]
int]
3 3

[tbaederr]

Here with fewer dependencies:

#include <iostream>
#include <source_location>

template<int N>
constexpr int f() {
  return N;
}



template<typename T>
void foo() {
  constexpr std::string_view func_name = std::source_location::current().function_name();

  std::cout << func_name.size() << "\n";
  std::cout << f<func_name.size()>() << '\n';
}

int main() {
  foo<int>();
}

Prints

20
10

[shafik]

CC @cor3ntin @Fznamznon

[cor3ntin]

Without dependencies https://compiler-explorer.com/z/nnYjoc3K9