Error when using AD on eigen

[lijas]

This has worked before, but seems to be broken now.
Probably related to JuliaDiff/ForwardDiff.jl#703 , but I don't understand how to fix it.

# add Tensors 
using Tensors    
function myfunk(e)
      p, n = Tensors.eigen(e)
      return otimes(n[:,1])
end;
e = rand(SymmetricTensor{2,3});
Tensors.gradient(myfunk, e)

Gives this error:

ERROR: setindex!(::StaticArraysCore.SMatrix{3, 3, Float64, 9}, value, ::Int) is not defined.
 Hint: Use `MArray` or `SizedArray` to create a mutable static array

[KnutAM]

Realized that this actually works due to JuliaDiff/ForwardDiff.jl#703, but the problem is that that one isn't released in ForwardDiff, because ForwardDiff is stuck on 0.10 and seems to be very unclear when changes on master will be released...

I could get the above example to work by (need to trick Tensors.jl to allow (ForwardDiff v0.11.0-DEV)

• Add Tensors to global (shared) environment
• Add ForwardDiff#master to current environment
• Run code above