.clang-format:

Language:        Cpp
...

c1.h:

[Xml::Serialization::XmlTypeAttribute("Label")]
public ref struct Label
{
}

c2.h:

void Foo(System::Collections::Generic::IDictionary< K, V >^ d)
{
  for each(auto kvp in d)
  {
  }
}

With clang-format versions 15 and 16 (didn't test older ones):

> clang-format.exe --style=file c1.h
Configuration file(s) do(es) not support Objective-C: C:\temp\clangformat\.clang-format

> clang-format.exe --style=file c2.h
Configuration file(s) do(es) not support Objective-C: C:\temp\clangformat\.clang-format

The above is for C++/CLI code, but there have been other reports in the past where special cases in plain C and C++ result in the same problem: https://bugs.llvm.org/show_bug.cgi?id=48580.

With that in mind I'm wondering: instead of trying to fix this on a per-case basis, or using workarounds like renaming to .hpp or using stdin+make sure working directory is ok to pick up the .clang-format+ --assume-filename=.hpp, would it be an acceptable solution to instead make the --assume-filename argument also work for files?