Why does THIS allocate? No hairs were harmed in this experiment ('cause I am bald...)

General Usage
7

My problem is actually still somewhere (as @Benny just demonstrated cross3 has been falsely blamed by me). My full MWE is

module mcs002xxx
using LinearAlgebra
using Statistics
using InteractiveUtils

function cross3!(
    result::AbstractVector{T1},
    theta::AbstractVector{T2},
    v::Tuple{T3, T3, T3},
) where {T1, T2, T3}
    @assert (length(theta) == 3) && (length(v) == 3) "Inputs must be 3-vectors"
    result[1] = -theta[3] * v[2] + theta[2] * v[3]
    result[2] = theta[3] * v[1] - theta[1] * v[3]
    result[3] = -theta[2] * v[1] + theta[1] * v[2]
    return result
end

@views function gen_iso_csmat!(csmatout::Matrix{T}, XYZ::Matrix{T}, tangents::Matrix{T}, feid::IT, qpid::IT) where {T, IT}
    sdim, mdim = size(tangents)
    if sdim == mdim # finite element embedded in space of the same dimension
        for i in 1:size(csmatout, 1), j in 1:size(csmatout, 2)
            csmatout[i, j] = (i == j ? one(T) : zero(T))
        end
    else # lower-dimensional finite element embedded in space of higher dimension
        @assert 0 < mdim < sdim
        @assert 0 < sdim
        csmatout[:, 1] = tangents[:, 1]
        csmatout[:, 1] /= norm(csmatout[:, 1])
        if mdim == 1 # curve-like finite element in 2d or 3d
            # all done
        elseif mdim == 2 # surface-like finite element in 3d
            e2 = (tangents[1, 2], tangents[2, 2], tangents[3, 2])
            cross3!(csmatout[:, 2], csmatout[:, 1], e2)
            csmatout[:, 2] /= norm(csmatout[:, 2])
        end
    end
    return csmatout
end

function doit()
    XYZ = reshape([0.2, 0.3, 0.4], 1, 3)
    tangents = reshape([1.0, 0.0, 0.0], 3, 1)
    m = zeros(3, 3)

    @time begin @views let
            cross3!(m[:, 2], m[:, 1], (1.0, 0.0, 0.010))
        end
    end

    @time gen_iso_csmat!(m, XYZ, tangents, 0, 0)

    true
end
doit()
nothing
end

I get

julia> include("C:\\Users\\pkonl\\Documents\\00WIP\\FinEtools.jl\\playn.jl")                                                    
WARNING: replacing module mcs002xxx.                                                                                            
  0.000001 seconds                                                                                                              
  0.000002 seconds (1 allocation: 80 bytes)                                                                                     
Main.mcs002xxx

which means gen_iso_csmat! allocates. The path actually does not involve cross3!: the empty block # all done is hit.