[libc++][test] Fix overload_compare_iterator::iterator_category

[frederick-vs-ja]

overload_compare_iterator only supports operations required for forward iterators. On the other hand, it is used for output iterators of uninitialized memory algorithms, which requires it to be forward iterator.

As a result, overload_compare_iterator<I>::iterator_category should always be std::forward_iterator_tag if we don't extend its ability. The correct iterator_category can prevent standard library implementations like MSVC STL attempting random access operations on overload_compare_iterator.

Fixes #74756.

[llvmbot]

@llvm/pr-subscribers-libcxx

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

Changes

overload_compare_iterator only supports operations required for forward iterators. On the other hand, it is used for output iterators of uninitialized memory algorithms, which requires it to be forward iterator.

As a result, overload_compare_iterator<I>::iterator_category should always be std::forward_iterator_tag if we don't extends its ability. The correct iterator_category can prevent standard library implementations like MSVC STL to attempt random access operations on it.

Fixes #74756.

---

Full diff: https://github.com/llvm/llvm-project/pull/112165.diff

1 Files Affected:

• (modified) libcxx/test/std/utilities/memory/specialized.algorithms/overload_compare_iterator.h (+6-1)

diff --git a/libcxx/test/std/utilities/memory/specialized.algorithms/overload_compare_iterator.h b/libcxx/test/std/utilities/memory/specialized.algorithms/overload_compare_iterator.h
index d5dcb08c37ed6f..f3b37292e717a1 100644
--- a/libcxx/test/std/utilities/memory/specialized.algorithms/overload_compare_iterator.h
+++ b/libcxx/test/std/utilities/memory/specialized.algorithms/overload_compare_iterator.h
@@ -12,6 +12,7 @@
 
 #include <iterator>
 #include <memory>
+#include <type_traits>
 
 #include "test_macros.h"
 
@@ -21,11 +22,15 @@
 // See https://github.com/llvm/llvm-project/issues/69334 for details.
 template <class Iterator>
 struct overload_compare_iterator {
+  static_assert(
+      std::is_base_of<std::forward_iterator_tag, typename std::iterator_traits<Iterator>::iterator_category>::value,
+      "overload_compare_iterator can only adapt forward iterators");
+
   using value_type        = typename std::iterator_traits<Iterator>::value_type;
   using difference_type   = typename std::iterator_traits<Iterator>::difference_type;
   using reference         = typename std::iterator_traits<Iterator>::reference;
   using pointer           = typename std::iterator_traits<Iterator>::pointer;
-  using iterator_category = typename std::iterator_traits<Iterator>::iterator_category;
+  using iterator_category = std::forward_iterator_tag;
 
   overload_compare_iterator() = default;
 

[philnik777]

This shouldn't be marked [NFC], since it fixes a bug in the test suite. Other than that LGTM.