[bug?] Ambiguous template specialization with a custom formatter for a template class

[nlg550]

Hello,

I was integrating the {fmt} library into my project and encounter the following issue: the compilation fails due to ambiguous partial template specialization when I include fmt/ranges.h and a template class have the methods begin(), end() and a custom formatter defined. For example,

#include <vector>

#include <fmt/format.h>
#include <fmt/ranges.h>

template<typename T>
struct Matrix {
	using iterator = typename std::vector<T>::iterator;
	
	int nrows;
	int ncols;
	std::vector<T> internal;
	
	Matrix(int rows, int cols, std::initializer_list<T> ilist) : nrows(rows), ncols(cols), internal(ilist)
	{}
	
	T operator()(int i, int j) const {
		return internal[j + i * ncols];
	}
	
	iterator begin() {
		return internal.begin();
	}
	
	iterator end() {
		return internal.end();
	}
};

template<typename T>
struct fmt::formatter<Matrix<T>>
{
	formatter<T> entry_fmt;
	
	template<typename ParseContext>
	constexpr auto parse(ParseContext& ctx) {
		return entry_fmt.parse(ctx);
	}
	
	template<typename FormatContext>
	auto format(const Matrix<T>& mat, FormatContext& ctx) {
		auto output = ctx.out();
		
		for (int i = 0; i < mat.nrows; ++i) {
			for (int j = 0; j < mat.ncols; ++j) {
				output = entry_fmt.format(mat(i, j), ctx);
				format_to(output, " ");
			}
			
			format_to(output, "\n");
		}
		
		return output;
	}
};

int main(int argc, char* argv[]) {
    Matrix<float> mat1(3, 3, {1, 2, 3, 4, 5, 6, 7, 8, 9});
	fmt::print("{}", mat1);
	
    return EXIT_SUCCESS;
}

Live demo: https://godbolt.org/z/nY4771soe

Naturally, removing the fmt/ranges.h header, everything works as expected. However, the issue arises when you have multiple classes: one using a custom formatter like this and another that uses a range formatter.

[vitaut]

Same as #751.