Consider the following definitions:
```
(defcstruct test-struct
(:array-field (:array :int 1))
(:bool-field :boolean))
```
The following would be expected to work:
```
(with-foreign-object (test-obj '(:struct test-struct))
(setf (mem-ref test-obj '(:struct test-struct)) '(:array-field #(0) :bool-field nil)))
```
However, each of those fails in different ways. The array field errors out:
```
(with-foreign-object (test-obj '(:struct test-struct))
(setf (mem-ref test-obj '(:struct test-struct)) '(:array-field #(0))))
```
```
The value
#.(SB-SYS:INT-SAP #X7FCDDCA105B0)
is not of type
ARRAY
when binding ARRAY
[Condition of type TYPE-ERROR]
Backtrace:
0: (AREF #.(SB-SYS:INT-SAP #X7FCDDCA105B0) 0) [more]
1: (LISP-ARRAY-TO-FOREIGN #.(SB-SYS:INT-SAP #X7FCDDCA105B0) #.(SB-SYS:INT-SAP #X7FCDE3B5FFE0) (:ARRAY :INT 1))
2: ((:METHOD (SETF CFFI::FOREIGN-STRUCT-SLOT-VALUE) (T T CFFI::AGGREGATE-STRUCT-SLOT)) #.(SB-SYS:INT-SAP #X7FCDDCA105B0) #.(SB-SYS:INT-SAP #X7FCDE3B5FFE0) #<CFFI::AGGREGATE-STRUCT-SLOT {1005854CC3}>) [fa..
3: (CFFI::FOREIGN-SLOT-SET #.(SB-SYS:INT-SAP #X7FCDDCA105B0) #.(SB-SYS:INT-SAP #X7FCDE3B5FFE0) (:STRUCT TEST-STRUCT) :ARRAY-FIELD)
4: ((:METHOD TRANSLATE-INTO-FOREIGN-MEMORY (LIST CFFI::FOREIGN-STRUCT-TYPE T)) (:ARRAY-FIELD #(0)) #<TEST-STRUCT-TCLASS TEST-STRUCT> #.(SB-SYS:INT-SAP #X7FCDE3B5FFE0)) [fast-method]
...
```
The bool field gets set to `t` instead of `nil`:
```
(with-foreign-object (test-obj '(:struct test-struct))
(setf (mem-ref test-obj '(:struct test-struct)) '(:bool-field nil))
(foreign-slot-value test-obj '(:struct test-struct) :bool-field))
```
returns T.
These are both caused by an extra call to `convert-to-foreign` inside of `(translate-to-foreign-memory list foreign-struct-type t)`. In the array case, `convert-to-foreign` converts the array to a pointer, rather than initializing the slot directly. (This also seems to cause the allocated array to leak; I believe the same behavior occurs with nested structs.) In the :boolean case, `convert-to-foreign` converts `nil` to `0`; when it gets assigned to the slot, `translate-to-foreign` gets called again, and since `0` is truthy, the actual assigned value is `1`. Naively removing that call makes both of the above cases work correctly, but breaks nested struct initialization; this seems to be because structs are treated as aggregates to be initialized from a pointer, even though with the new :struct specifiers they are initialized by value instead, and the extra call to `convert-from-foreign` seems to paper over that inconsistency.
