[libcxx-commits] [PATCH] D130835: [libc++] Fix a hard error in `contiguous_iterator<NoOperatorArrowIter>`.

[Konstantin Varlamov via Phabricator via libcxx-commits]

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Evaluating `contiguous_iterator` on an iterator that satisfies all the
constraints except the `to_address` constraint and doesn't have
`operator->` defined results in a hard error. This is because
`to_address` doesn't SFINAE away when given a type it cannot handle.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D130835

Files:
  libcxx/include/__memory/pointer_traits.h
  libcxx/test/std/iterators/iterator.requirements/iterator.concepts/iterator.concept.random.access/contiguous_iterator.compile.pass.cpp


Index: libcxx/test/std/iterators/iterator.requirements/iterator.concepts/iterator.concept.random.access/contiguous_iterator.compile.pass.cpp
===================================================================
--- libcxx/test/std/iterators/iterator.requirements/iterator.concepts/iterator.concept.random.access/contiguous_iterator.compile.pass.cpp
+++ libcxx/test/std/iterators/iterator.requirements/iterator.concepts/iterator.concept.random.access/contiguous_iterator.compile.pass.cpp
@@ -13,6 +13,7 @@
 
 #include <iterator>
 #include <compare>
+#include <memory>
 
 #include "test_iterators.h"
 
@@ -208,3 +209,45 @@
 // Template param is used instead of element_type.
 static_assert(std::random_access_iterator<template_and_no_element_type<int>>);
 static_assert(std::contiguous_iterator<template_and_no_element_type<int>>);
+
+template <bool DisableArrow, bool DisableToAddress = true>
+struct no_operator_arrow {
+    typedef std::contiguous_iterator_tag    iterator_category;
+    typedef int                             value_type;
+    typedef int                             element_type;
+    typedef std::ptrdiff_t                  difference_type;
+    typedef int*                            pointer;
+    typedef int&                            reference;
+    typedef no_operator_arrow               self;
+
+    no_operator_arrow();
+
+    reference operator*() const;
+    pointer operator->() const requires (!DisableArrow);
+    auto operator<=>(const self&) const = default;
+
+    self& operator++();
+    self operator++(int);
+
+    self& operator--();
+    self operator--(int);
+
+    self& operator+=(difference_type n);
+    self operator+(difference_type n) const;
+    friend self operator+(difference_type n, self x);
+
+    self& operator-=(difference_type n);
+    self operator-(difference_type n) const;
+    difference_type operator-(const self& n) const;
+
+    reference operator[](difference_type n) const;
+};
+
+template<>
+struct std::pointer_traits<no_operator_arrow</*DisableArrow=*/true, /*DisableToAddress=*/false>> {
+  static constexpr int *to_address(const no_operator_arrow<true, false>&);
+};
+
+static_assert(std::contiguous_iterator<no_operator_arrow</*DisableArrow=*/false>>);
+static_assert(!std::contiguous_iterator<no_operator_arrow</*DisableArrow=*/true>>);
+static_assert(std::contiguous_iterator<no_operator_arrow</*DisableArrow=*/true, /*DisableToAddress=*/false>>);
Index: libcxx/include/__memory/pointer_traits.h
===================================================================
--- libcxx/include/__memory/pointer_traits.h
+++ libcxx/include/__memory/pointer_traits.h
@@ -171,9 +171,26 @@
     return __p;
 }
 
+template <class _Pointer, class = void>
+struct _HasToAddress : false_type {};
+
+template <class _Pointer>
+struct _HasToAddress<_Pointer,
+    decltype((void)&pointer_traits<_Pointer>::to_address)
+> : true_type {};
+
+template <class _Pointer, class = void>
+struct _HasArrow : false_type {};
+
+template <class _Pointer>
+struct _HasArrow<_Pointer,
+    decltype((void)declval<const _Pointer&>().operator->())
+> : true_type {};
+
 // enable_if is needed here to avoid instantiating checks for fancy pointers on raw pointers
 template <class _Pointer, class = __enable_if_t<
-    !is_pointer<_Pointer>::value && !is_array<_Pointer>::value && !is_function<_Pointer>::value
+    !is_pointer<_Pointer>::value && !is_array<_Pointer>::value && !is_function<_Pointer>::value &&
+    (_HasArrow<_Pointer>::value || _HasToAddress<_Pointer>::value)
 > >
 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
 typename decay<decltype(__to_address_helper<_Pointer>::__call(declval<const _Pointer&>()))>::type
@@ -208,7 +225,7 @@
 
 template <class _Pointer>
 inline _LIBCPP_INLINE_VISIBILITY constexpr
-auto to_address(const _Pointer& __p) noexcept {
+auto to_address(const _Pointer& __p) noexcept -> decltype(std::__to_address(__p)) {
     return _VSTD::__to_address(__p);
 }
 #endif


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