Fix reindex! function to do nothing if reindex is not necessary

src/Quantum.jl

@@ -153,7 +153,13 @@ Tenet.select(tn::Quantum, ::Val{:index}, site::Site) = tn[site]
 Tenet.select(tn::Quantum, ::Val{:tensor}, site::Site) = select(TensorNetwork(tn), :any, tn[site]) |> only
 
 function reindex!(a::Quantum, ioa, b::Quantum, iob)
-    ioa ∈ [:inputs, :outputs] || error("Invalid argument: :$ioa")
+    sitesa = if ioa === :inputs
+        inputs(a)
+    elseif ioa === :outputs
+        outputs(a)
+    else
+        error("Invalid argument: :$ioa")
+    end
 
     sitesb = if iob === :inputs
         inputs(b)
@@ -163,6 +169,10 @@ function reindex!(a::Quantum, ioa, b::Quantum, iob)
         error("Invalid argument: :$iob")
     end
 
+    if sitesa == sitesb
+        return b
+    end
+
     replacements = map(sitesb) do site
         select(b, :index, site) => select(a, :index, ioa != iob ? site' : site)
     end