Change to C99 and add weak references

test/alloc.h

@@ -8,7 +8,7 @@
 #include <stdlib.h>
 #include <string.h>
 
-#if __has_attribute(unused)
+#if defined(__has_attribute) && __has_attribute(unused)
 #    define UNUSED __attribute__((unused))
 #else
 #    define UNUSED
@@ -67,8 +67,8 @@ static UNUSED char *counting_strdup(const char *str) {
 }
 
 static UNUSED const RefcountAllocator COUNTING_ALLOCATOR = {
-    .malloc = counting_malloc,
-    .free = counting_free,
+    .malloc.no_data = counting_malloc,
+    .free.no_data = counting_free,
 };
 
 #endif

test/test_refcount.c

@@ -113,6 +113,42 @@ int main(int argc, const char **argv) {
 
     assert(refcount_context_garbage_collect(c) == 26);
 
+    a = make_a(c, 0, "a");
+
+    RefcountWeakref *w = refcount_context_make_weakref(c, a);
+    assert(w);
+    assert(refcount_context_num_refs(c, a) == 0);
+
+    b = refcount_context_strengthen(c, w);
+    assert(b);
+    assert(a == b);
+    assert(refcount_context_num_refs(c, a) == 1);
+
+    refcount_context_ref(c, a);
+    assert(refcount_context_num_refs(c, a) == 2);
+
+    RefcountWeakref *x = refcount_context_weaken(c, a);
+    w = refcount_context_make_weakref(c, a);
+    assert(refcount_context_num_refs(c, a) == 1);
+    assert(w != x);
+    refcount_context_destroy_weakref(c, x);
+
+    refcount_context_ref(c, a);
+    assert(refcount_context_num_refs(c, a) == 2);
+
+    x = refcount_context_weaken(c, a);
+    assert(refcount_context_num_refs(c, a) == 1);
+    assert(w != x);
+    assert(refcount_context_weakref_is_valid(c, w));
+    assert(refcount_context_weakref_is_valid(c, x));
+
+    assert(!refcount_context_unref(c, a));
+    assert(!refcount_context_weakref_is_valid(c, w));
+    assert(!refcount_context_weakref_is_valid(c, x));
+
+    refcount_context_destroy_weakref(c, w);
+    refcount_context_destroy_weakref(c, x);
+
     refcount_context_destroy(c);
 
     check_allocator_status();