С23 is not supported by CDT parser/indexer/analyser without LSP

[Karlson2k]

Describe the bug
I'm using latest Eclipse (2025-09) CDT with GCC-16 (which defaults to C23), Makefile project and no LSP editor.
Syntax highlighter (and CDT code analyser) indicates errors on every bool, true, false, constexpr.

To Reproduce
Steps to reproduce the behavior:

1. Create Makefile project in Eclipse CDT
2. Add .c file with C23 code (any of bool, true, false, constexpr), for example:

int main(int argc, char **argv) {
  constexpr int a_cnst = (int) false;
  bool b_var = true;
  return b_var ? a_cnst : argc;
}

4. See detected "errors" for every mentioned keyword

Expected behavior
bool, true, false, constexpr should not be detected as "errors" even when no header is included.

Screenshots

Version Information (please complete the following information):

• GNU/Linux, Gentoo
• Eclipse Version: 2025-09 (4.37.0)
• CDT Version: 12.2.0.202506091931

[jonahgraham]

С23 is not supported by CDT parser/indexer/analyser without LSP

This is an accurate summary. Thank you for providing an explicit test case of something in C23 that is unsupported.

[Karlson2k]

The extended list of keywords added by C23:

• bool
• true
• false
• constexpr
• nullptr
• alignas()
• alignof()
• static_assert()
• thread_local
• typeof()
• typeof_unqual()
• _BitInt(N)
• _Decimal32
• _Decimal64
• _Decimal128

Also new semantic for auto