[BUG] `constexpr` anonymous object rejected as function or type

[JohelEGP]

Title: constexpr anonymous object rejected as function or type.

Minimal reproducer (https://cpp2.godbolt.org/z/9d7f8v8Pa):

main: () = {
  _: int == 0;
}

Commands:

cppfront main.cpp2
clang++18 -std=c++23 -stdlib=libc++ -lc++abi -pedantic-errors -Wall -Wextra -Wconversion -Werror=unused-result -I . main.cpp

Expected result: A better error message, or a valid program.

Actual result and error: main.cpp2(2,3): error: '_' (wildcard) may not be the name of a function or type - it may only be used as the name of an anonymous object or anonymous namespace

[ntrel]

If you remove the _, you get error: syntax error at '==' - did you mean '='? (at '==').

It would indeed be useful to be able to ensure compile-time evaluation of an expression by using :== expr.

[hsutter]

Thanks!