FMT_STRING issue w/ clang, spdlog 1.15.1 and external fmt 11.1.3

[abrownsword]

In straightforward spdlog-using code (that was changed a couple of years back to use FMT_STRING everywhere), after updating to spdlog 1.15.1 and an external fmt 11.1.3, I'm seeing this across the entire codebase. Building with Clang 19.1.6 set to C++20 using gnu stdlibc++ on Ubuntu 24.04:

error: implicit instantiation of undefined template 'fmt::detail::type_is_unformattable_for<FMT_COMPILE_STRING, char>'
     |     type_is_unformattable_for<T, char_type> _;

The line of code is (but this occurs identically on several hundred logging calls):

logger->debug(FMT_STRING("my string"));

I have seen various reported issues in fmt & spdlog repos saying this was fixed via issue fmtlib/fmt#4177 ... however I am on the latest code and am still seeing this issue. Removing FMT_STRING at any given callsite eliminates the error, but I'm not excited about making such a sweeping change across the codebase (and it would make reverting much harder). The macro still seems to be supported, however it appears to be broken.

[gabime]

What would be the fix ?

[abrownsword]

I don't know, but a couple of direct uses of fmt::format(FMT_STRING("..."), ...) in the same file as the above error compile fine.

[gabime]

It works as long as there are params. Not related to direct uses.
Fwiw “replace all” works pretty well with any IDE :)

[abrownsword]

Ah yes, I hadn't noticed that the failure cases were all without args. Perhaps an additional overload of info/debug/warn/etc is required then?

As I mentioned above making a sweeping change increases the difficulty of reverting to an older version if some other issue is discovered.

[gabime]

So perhaps redefine the macro after including spdlog.h or replace all code with custom macro name that does nothing, so it would be easy to revert