result code = -1
standard error = {
tests/diagnostics/autodiff-data-flow-2.slang(18): error 41020: derivative cannot be propagated through call to non-backward-differentiable function `f`, use 'no_diff' to clarify intention.
    float val = f(x + 1); // Error: f must also be backward-differentiable
                 ^
}
standard output = {
}