Would more detailed error message of SpaceMismatch be possible

[Chenqitrg]

Hi developers,

Would a more detailed error message of SpaceMismatch in a tensor contraction be possible? The current one only reports those incompatible spaces, but currently I always need to add more tests mannually to find out tensors and legs that those incompatible spaces belongs to.

So will a more detailed output be more helpful? For example,

ERROR: SpaceMismatch("(Vect[IsingAnyon](:I=>1) ⊗ Vect[IsingAnyon](:σ=>1)') ≠ (Vect[IsingAnyon](:σ=>1) ⊗ Vect[IsingAnyon](:σ=>1)')")

may be more detailed output by

The x-th graded space of the domain of the tensor T: Vect[IsingAnyon](:I=>1) ⊗ Vect[IsingAnyon](:σ=>1)') is incompatible with the y-th graded space of the codomain of the tensor K: Vect[IsingAnyon](:σ=>1) ⊗ Vect[IsingAnyon](:σ=>1)')

Then the bug can be immediately traced.

[lkdvos]

I'm not sure if this helps your specific case, but there is a neat trick in the context of the @tensor (and I think also @planar) calls. If you add the contractcheck = true annotation before the contraction, it will tell you which label has mismatching sizes:

using TensorKit
V = ComplexSpace(2)
W = ComplexSpace(3)
t1 = rand(V, W)
t2 = rand(V, V)

julia> @tensor contractcheck = true t3[i j] := t1[i k] * t2[k l]
ERROR: SpaceMismatch: incompatible spaces for k: ℂ^3 ≠ ℂ^2
[...]

I tend to find this more helpful since it tells you about the label of the input tensors, and not the spaces of the intermediate tensors that might appear in the decomposition of a network contraction into pairwise contractions.

[Chenqitrg]

Thank you, this is indeed helpful.