refactor: tests work, all fine

src/arraylist.c

@@ -27,9 +27,11 @@ static ArrayListErr arraylist_grow(ArrayList *arr);
 static ArrayListErr arraylist_shrink(ArrayList *arr);
 
 ArrayListErr arraylist_init(ArrayList **arr, size_t capacity, size_t elem_size) {
-    if (arr == NULL || *arr == NULL) {
+    if (arr == NULL) {
         return ARRLIST_NULL_ARG;
     }
+    
+    *arr = NULL;
 
     if (capacity == 0) {
         return ARRLIST_INVALID_CAPACITY;
@@ -44,7 +46,7 @@ ArrayListErr arraylist_init(ArrayList **arr, size_t capacity, size_t elem_size)
     }
 
     ArrayList *new_arr = malloc(sizeof(ArrayList));
-    if (arr == NULL) {
+    if (new_arr == NULL) {
         return ARRLIST_BAD_ALLOC;
     }
 
@@ -54,8 +56,8 @@ ArrayListErr arraylist_init(ArrayList **arr, size_t capacity, size_t elem_size)
     new_arr->borrows = 0;
     new_arr->buffer = malloc(capacity * elem_size);
     if (new_arr->buffer == NULL) {
-        free(arr);
-        return NULL;
+        free(new_arr);
+        return ARRLIST_BAD_ALLOC;
     }
 
     *arr = new_arr;
@@ -435,19 +437,19 @@ ArrayListErr arraylist_reserve(ArrayList *arr, size_t size_to_reserve) {
 }
 
 ArrayListErr arraylist_slice(ArraySlice **slice, ArrayList *arr, size_t start, size_t len) {
-    if (arr == NULL) {
+    if (arr == NULL || slice == NULL) {
         return ARRLIST_NULL_ARG;
     }
 
-    if (arr->len == 0 || len == 0) {
+    if (arr->len == 0) {
         return ARRLIST_INVALID_ARR;
     }
 
-    if (start > SIZE_MAX / arr->elem_size || len > SIZE_MAX / arr->elem_size) {
+    if (start > SIZE_MAX - len) {
         return ARRLIST_INVALID_CAPACITY;
     }
 
-    if (start + len > arr->len) {
+    if (start + len > arr->len || len == 0) {
         return ARRLIST_INVALID_START;
     }
 
@@ -460,26 +462,27 @@ ArrayListErr arraylist_slice(ArraySlice **slice, ArrayList *arr, size_t start, s
     new_slice->start = start;
     new_slice->end = start + len;
     new_slice->current = start;
-    new_slice->is_safe = false;
+    new_slice->is_safe = true;
 
+    arr->borrows++;
     *slice = new_slice;
     return ARRLIST_OK;
 }
 
 ArrayListErr arraylist_slice_unsafe(ArraySlice **slice, ArrayList *arr, size_t start, size_t len) {
-    if (arr == NULL) {
+    if (arr == NULL || slice == NULL) {
         return ARRLIST_NULL_ARG;
     }
 
-    if (arr->len == 0 || len == 0) {
+    if (arr->len == 0) {
         return ARRLIST_INVALID_ARR;
     }
 
-    if (start > SIZE_MAX / arr->elem_size || len > SIZE_MAX / arr->elem_size) {
+    if (start > SIZE_MAX - len) {
         return ARRLIST_INVALID_CAPACITY;
     }
 
-    if (start + len > arr->len) {
+    if (start + len > arr->len || len == 0) {
         return ARRLIST_INVALID_START;
     }
 
@@ -589,7 +592,7 @@ ArrayListErr arrayslice_to_arraylist(ArrayList **arr, const ArraySlice *slice) {
         return ARRLIST_NULL_ARG;
     }
 
-    if (arr == NULL || *arr == NULL) {
+    if (arr == NULL) {
         return ARRLIST_NULL_ARG;
     }