When I compile vroom using clang++ (command make CXX=clang++), the compiler outputs a warning:

structures/vroom/input/input.cpp:681:41: warning: braces around scalar initializer [-Wbraced-scalar-init]
            d_m->second = Matrix<Cost>({{0}});
                                        ^~~

I believe this is a valid warning as the Matrix's constructor accepts a scalar and the braces are redundant.

For the record, I'm using clang version 13.0.1.