[libcxx-commits] [libcxx] [libc++] Fix {deque, vector}::append_range assuming too much about the types (PR #162438)

[Louis Dionne via libcxx-commits]

================
@@ -489,7 +490,21 @@ class vector {
 #if _LIBCPP_STD_VER >= 23
   template <_ContainerCompatibleRange<_Tp> _Range>
   _LIBCPP_HIDE_FROM_ABI constexpr void append_range(_Range&& __range) {
-    insert_range(end(), std::forward<_Range>(__range));
+    if constexpr (ranges::forward_range<_Range> || ranges::sized_range<_Range>) {
+      auto __size = ranges::distance(__range);
+      if (__size < __cap_ - __end_) {
----------------
ldionne wrote:

```suggestion
      auto __len = ranges::distance(__range);
      if (__len < __cap_ - __end_) {
```

`__size_` will be a member variable of the vector with size-based vector, and it's also confusing with `size()`. I read it incorrectly initially. `__len` says that it's a length or size, but it's different enough from `size()` so that there's no confusion possible.

https://github.com/llvm/llvm-project/pull/162438