Values returned by prox! function

[BenjaminPINEAU]

For a given function $h$, prox! functions from ShiftedProximalOperators return the value of the proximal operator while prox! function from ProximalOperator return the value of $h$ evaluate in $\mathrm{prox}_h$.

To be consistent, I think that prox! function from ShiftedProximalOperators should also return the (shifted) value of $h$.
For exemple, the Moreau envelope in ProximalOperator uses the value of $h$ as the return value of the prox function:

function (f::MoreauEnvelope)(x)
    R = eltype(x)
    buf = similar(x)
    g_prox = prox!(buf, f.g, x, f.lambda)
    return g_prox + R(1) / (2 * f.lambda) * norm(buf .- x)^2
end

The return value will be incorrect if the function is derived from ShiftedProximalOperators.