[libcxx-commits] [libcxx] [libc++] Fix wraparound issue with -fsanitize=integer in string operator>> (PR #106263)

[Louis Dionne via libcxx-commits]

================
@@ -1211,12 +1211,12 @@ operator>>(basic_istream<_CharT, _Traits>& __is, basic_string<_CharT, _Traits, _
     try {
 #endif
       __str.clear();
-      streamsize __n = __is.width();
-      if (__n <= 0)
-        __n = __str.max_size();
-      if (__n <= 0)
-        __n = numeric_limits<streamsize>::max();
-      streamsize __c            = 0;
+      using _Size = typename basic_string<_CharT, _Traits, _Allocator>::size_type;
+      static_assert(numeric_limits<_Size>::max() >= numeric_limits<streamsize>::max(),
----------------
ldionne wrote:

The other alternative would be to use `streamsize` for the counter and do something like:

```
streamsize const __width = __is.width();
streamsize const __n = __width <= 0 ? std::clamp(__str.max_size(), 0, numeric_limits<streamsize>::max()) : __width;
```

WDYT?

https://github.com/llvm/llvm-project/pull/106263