[libc++][hardening] Use static_assert for __(static_)bounded_iter

[frederick-vs-ja]

We can't static_assert __libcpp_is_contiguous_iterator for __wrap_iter currently because __wrap_iter is also used for wrapping user-defined fancy pointers.

Fixes #115002.

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: A. Jiang (frederick-vs-ja)

Changes

We can't static_assert __libcpp_is_contiguous_iterator for __wrap_iter currently because __wrap_iter is also used for wrapping user-defined fancy pointers.

Fixes #115002.

---

Full diff: https://github.com/llvm/llvm-project/pull/115304.diff

2 Files Affected:

• (modified) libcxx/include/__iterator/bounded_iter.h (+5-2)
• (added) libcxx/test/libcxx/iterators/contiguous_iterators.verify.cpp (+22)

diff --git a/libcxx/include/__iterator/bounded_iter.h b/libcxx/include/__iterator/bounded_iter.h
index 5a86bd98e71940..70638da001e52a 100644
--- a/libcxx/include/__iterator/bounded_iter.h
+++ b/libcxx/include/__iterator/bounded_iter.h
@@ -47,8 +47,11 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 //    pointer, it is undefined at the language level (see [expr.add]). If
 //    bounded iterators exhibited this undefined behavior, we risk compiler
 //    optimizations deleting non-redundant bounds checks.
-template <class _Iterator, class = __enable_if_t< __libcpp_is_contiguous_iterator<_Iterator>::value > >
+template <class _Iterator>
 struct __bounded_iter {
+  static_assert(__libcpp_is_contiguous_iterator<_Iterator>::value,
+                "Only contiguous iterators can be adapted by __bounded_iter.");
+
   using value_type        = typename iterator_traits<_Iterator>::value_type;
   using difference_type   = typename iterator_traits<_Iterator>::difference_type;
   using pointer           = typename iterator_traits<_Iterator>::pointer;
@@ -247,7 +250,7 @@ struct __bounded_iter {
 private:
   template <class>
   friend struct pointer_traits;
-  template <class, class>
+  template <class>
   friend struct __bounded_iter;
   _Iterator __current_;       // current iterator
   _Iterator __begin_, __end_; // valid range represented as [begin, end]
diff --git a/libcxx/test/libcxx/iterators/contiguous_iterators.verify.cpp b/libcxx/test/libcxx/iterators/contiguous_iterators.verify.cpp
new file mode 100644
index 00000000000000..c211104bef7273
--- /dev/null
+++ b/libcxx/test/libcxx/iterators/contiguous_iterators.verify.cpp
@@ -0,0 +1,22 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+
+// <iterator>
+
+// __bounded_iter<_Iter>
+
+// Verify that __bounded_iter does not accept non-contiguous iterators as determined by __libcpp_is_contiguous_iterator.
+// static_assert should be used, see https://github.com/llvm/llvm-project/issues/115002.
+// __wrap_iter cannot be so handled because it may directly wrap user-defined fancy pointers in libc++'s vector.
+
+#include <deque>
+#include <vector>
+
+// expected-error-re@*:* {{static assertion failed due to requirement {{.*}}Only contiguous iterators can be adapted by __bounded_iter.}}
+std::__bounded_iter<std::deque<int>::iterator> bit;

[ldionne]

Can you also modify __static_bounded_iter now that it landed? See #115322.