If the function you trying to keep is in non-pub module, it will be removed.
Maybe you could move it out of private module: <https://rust.godbolt.org/z/PYPbG8>.
There's also an `#[used]`[1] attribute, but only for static items.
If your use case is special, consider open a feature request in
Rust repo.
The only thing that worked was adding a linker argumment: "-C", "link_args=--undefined=<name_of_function>"
That will force the linker to assume it's referenced.