accounts/abi: support nested nested array args

Previously, the code only considered the outer-size of the array,
ignoring the size of the contents. This was fine for most types,
but nested arrays are packed directly into it, and count towards
the total size. This resulted in arguments following a nested
array to replicate some of the binary contents of the array.

The fix: for arrays, calculate their complete contents size:
 count the arg.Type.Elem.Size when Elem is an Array, and
 repeat when their child is an array too, etc.
The count is the number of 32 byte elements, similar to how it
 previously counted, but nested.

accounts/abi/argument.go

@@ -169,6 +169,21 @@ func (arguments Arguments) unpackAtomic(v interface{}, marshalledValues []interf
 	return set(elem, reflectValue, arguments.NonIndexed()[0])
 }
 
+// Computes the full size of an array;
+// i.e. counting nested arrays, which count towards size for unpacking.
+func getArraySize(arr *Type) int {
+	size := arr.Size
+	// Arrays can be nested, with each element being the same size
+	arr = arr.Elem
+	for arr.T == ArrayTy {
+		// Keep multiplying by elem.Size while the elem is an array.
+		size *= arr.Size
+		arr = arr.Elem
+	}
+	// Now we have the full array size, including its children.
+	return size
+}
+
 // UnpackValues can be used to unpack ABI-encoded hexdata according to the ABI-specification,
 // without supplying a struct to unpack into. Instead, this method returns a list containing the
 // values. An atomic argument will be a list with one element.
@@ -181,9 +196,14 @@ func (arguments Arguments) UnpackValues(data []byte) ([]interface{}, error) {
 			// If we have a static array, like [3]uint256, these are coded as
 			// just like uint256,uint256,uint256.
 			// This means that we need to add two 'virtual' arguments when
-			// we count the index from now on
-
-			virtualArgs += arg.Type.Size - 1
+			// we count the index from now on.
+			//
+			// Array values nested multiple levels deep are also encoded inline:
+			// [2][3]uint256: uint256,uint256,uint256,uint256,uint256,uint256
+			//
+			// Calculate the full array size to get the correct offset for the next argument.
+			// Decrement it by 1, as the normal index increment is still applied.
+			virtualArgs += getArraySize(&arg.Type) - 1
 		}
 		if err != nil {
 			return nil, err