Improve `views::drop(_while)` and `views::take(_while)` tests (#3390)

Co-authored-by: Stephan T. Lavavej <stl@nuwen.net>

tests/std/tests/P0896R4_views_drop/test.cpp

@@ -289,6 +289,55 @@ constexpr bool test_one(Rng&& rng, Expected&& expected) {
         }
     }
 
+#if _HAS_CXX23
+    using ranges::const_iterator_t, ranges::const_sentinel_t, ranges::cbegin, ranges::cend;
+
+    // Validate view_interface::cbegin
+    STATIC_ASSERT(CanMemberCBegin<R> == input_range<V>);
+    STATIC_ASSERT(same_as<const_iterator_t<R>, const_iterator_t<V>>);
+    STATIC_ASSERT(CanMemberCBegin<const R&> == (random_access_range<const V> && sized_range<const V>) );
+    if (forward_range<V>) { // intentionally not if constexpr
+        const same_as<const_iterator_t<R>> auto i = r.cbegin();
+        if (!is_empty) {
+            assert(*i == *cbegin(expected));
+        }
+
+        if constexpr (copyable<V>) {
+            auto r2                                    = r;
+            const same_as<const_iterator_t<R>> auto i2 = r2.cbegin();
+            if (!is_empty) {
+                assert(*i2 == *i);
+            }
+        }
+
+        if constexpr (random_access_range<const V> && sized_range<const V>) {
+            STATIC_ASSERT(same_as<const_iterator_t<const R>, const_iterator_t<const V>>);
+            const same_as<const_iterator_t<const R>> auto i3 = as_const(r).cbegin();
+            if (!is_empty) {
+                assert(*i3 == *i);
+            }
+        }
+    }
+
+    // Validate view_interface::cend
+    STATIC_ASSERT(CanMemberCEnd<R> == input_range<V>);
+    STATIC_ASSERT(same_as<const_sentinel_t<R>, const_sentinel_t<V>>);
+    STATIC_ASSERT(CanMemberCEnd<const R&> == (random_access_range<const V> && sized_range<const V>) );
+    if (!is_empty) {
+        same_as<const_sentinel_t<R>> auto i = r.cend();
+        if constexpr (bidirectional_range<R> && common_range<R>) {
+            assert(*prev(i) == *prev(cend(expected)));
+        }
+
+        if constexpr (random_access_range<const V> && sized_range<const V>) {
+            same_as<const_sentinel_t<const R>> auto i2 = as_const(r).cend();
+            if constexpr (bidirectional_range<const R> && common_range<const R>) {
+                assert(*prev(i2) == *prev(cend(expected)));
+            }
+        }
+    }
+#endif // _HAS_CXX23
+
     // Validate view_interface::data
     STATIC_ASSERT(CanMemberData<R> == contiguous_range<V>);
     STATIC_ASSERT(CanData<R&> == contiguous_range<V>);

tests/std/tests/P0896R4_views_drop_while/test.cpp

@@ -213,6 +213,51 @@ constexpr bool test_one(Rng&& rng, Expected&& expected) {
         STATIC_ASSERT(!CanEnd<const R>);
     }
 
+#if _HAS_CXX23
+    using ranges::const_iterator_t, ranges::const_sentinel_t, ranges::cbegin, ranges::cend;
+
+    // Validate view_interface::cbegin
+    STATIC_ASSERT(CanMemberCBegin<R> == ranges::input_range<V>);
+    if (forward_range<V>) { // intentionally not if constexpr
+        const same_as<const_iterator_t<R>> auto i = r.cbegin();
+        if (!is_empty) {
+            assert(*i == *cbegin(expected));
+            assert(*r.cbegin() == *cbegin(expected));
+        }
+
+        if constexpr (copyable<V>) {
+            auto r2                                    = r;
+            const same_as<const_iterator_t<R>> auto i2 = r2.cbegin();
+            if (!is_empty) {
+                assert(*i2 == *i);
+                assert(*r2.cbegin() == *i2);
+            }
+        }
+
+        STATIC_ASSERT(!CanCBegin<const R>);
+    }
+
+    // Validate view_interface::cend
+    STATIC_ASSERT(CanMemberCEnd<R> == ranges::input_range<V>);
+    if (!is_empty) {
+        if constexpr (common_range<V>) {
+            same_as<const_iterator_t<R>> auto i = r.cend();
+            if constexpr (bidirectional_range<V>) {
+                assert(*prev(i) == *prev(cend(expected)));
+            }
+        } else {
+            [[maybe_unused]] same_as<const_sentinel_t<R>> auto s = r.cend();
+        }
+
+        if constexpr (bidirectional_range<V> && common_range<V> && copyable<V>) {
+            auto r2 = r;
+            assert(*prev(r2.cend()) == *prev(cend(expected)));
+        }
+
+        STATIC_ASSERT(!CanCEnd<const R>);
+    }
+#endif // _HAS_CXX23
+
     // Validate view_interface::data
     STATIC_ASSERT(CanMemberData<R> == contiguous_range<V>);
     STATIC_ASSERT(CanData<R&> == contiguous_range<V>);

tests/std/tests/P0896R4_views_take/test.cpp

@@ -321,6 +321,86 @@ constexpr bool test_one(Rng&& rng, Expected&& expected) {
         }
     }
 
+#if _HAS_CXX23
+    using ranges::const_iterator_t, ranges::const_sentinel_t, ranges::cbegin, ranges::cend;
+
+    // Validate view_interface::cbegin
+    STATIC_ASSERT(CanMemberCBegin<R>);
+    if constexpr (random_access_range<V> && sized_range<V>) {
+        STATIC_ASSERT(same_as<const_iterator_t<R>, const_iterator_t<V>>);
+    } else {
+        STATIC_ASSERT(same_as<const_iterator_t<R>, const_iterator<counted_iterator<iterator_t<V>>>>);
+    }
+    STATIC_ASSERT(CanMemberCBegin<const R&> == input_range<const V>);
+    if (forward_range<V>) { // intentionally not if constexpr
+        const same_as<const_iterator_t<R>> auto i = r.cbegin();
+        if (!is_empty) {
+            assert(*i == *cbegin(expected));
+        }
+
+        if constexpr (copyable<V>) {
+            auto r2                                    = r;
+            const same_as<const_iterator_t<R>> auto i2 = r2.cbegin();
+            if (!is_empty) {
+                assert(*i2 == *i);
+            }
+        }
+
+        if constexpr (range<const V>) {
+            if constexpr (random_access_range<const V> && sized_range<const V>) {
+                STATIC_ASSERT(same_as<const_iterator_t<const R>, const_iterator_t<const V>>);
+            } else {
+                STATIC_ASSERT(
+                    same_as<const_iterator_t<const R>, const_iterator<counted_iterator<iterator_t<const V>>>>);
+            }
+
+            const same_as<const_iterator_t<const R>> auto i3 = as_const(r).cbegin();
+            if (!is_empty) {
+                assert(*i3 == *i);
+            }
+        }
+    }
+
+    // Validate view_interface::cend
+    STATIC_ASSERT(CanMemberCEnd<R>);
+    if constexpr (sized_range<V>) {
+        if constexpr (random_access_range<V>) {
+            STATIC_ASSERT(same_as<const_sentinel_t<R>, const_iterator_t<V>>);
+        } else {
+            STATIC_ASSERT(same_as<const_sentinel_t<R>, default_sentinel_t>);
+        }
+    } else {
+        // Not much we can do here
+        STATIC_ASSERT(!same_as<const_sentinel_t<R>, const_iterator_t<V>>);
+        STATIC_ASSERT(!same_as<const_sentinel_t<R>, default_sentinel_t>);
+        STATIC_ASSERT(is_class_v<const_sentinel_t<R>>);
+    }
+    STATIC_ASSERT(CanCEnd<const R&> == range<const V>);
+    if (!is_empty) {
+        same_as<const_sentinel_t<R>> auto s = r.cend();
+        if constexpr (bidirectional_range<R> && common_range<R>) {
+            assert(*prev(s) == *prev(cend(expected)));
+        }
+
+        if constexpr (range<const V>) {
+            same_as<const_sentinel_t<const R>> auto sc = as_const(r).cend();
+            if constexpr (bidirectional_range<const R> && common_range<const R>) {
+                assert(*prev(sc) == *prev(cend(expected)));
+            }
+
+            if (forward_range<V>) { // intentionally not if constexpr
+                // Compare with const / non-const iterators
+                const same_as<const_iterator_t<R>> auto i        = r.cbegin();
+                const same_as<const_iterator_t<const R>> auto ic = as_const(r).cbegin();
+                assert(s != i);
+                assert(s != ic);
+                assert(sc != i);
+                assert(sc != ic);
+            }
+        }
+    }
+#endif // _HAS_CXX23
+
     // Validate view_interface::data
     STATIC_ASSERT(CanMemberData<R> == contiguous_range<V>);
     STATIC_ASSERT(CanData<R&> == contiguous_range<V>);

tests/std/tests/P0896R4_views_take_while/test.cpp

@@ -239,7 +239,7 @@ constexpr bool test_one(Rng&& rng, Expected&& expected) {
                 assert(sc == s.base());
                 assert(sc == sc.base());
             } else if constexpr (forward_range<V> && is_lvalue_reference_v<Rng>) {
-                auto full_range   = views::take_while(rng, [](auto const&) { return true; });
+                auto full_range   = views::take_while(rng, [](const auto&) { return true; });
                 const auto length = 8; // NB: depends on the test data
                 assert(full_range.end() == next(full_range.begin(), length));
                 assert(full_range.end() == next(as_const(full_range).begin(), length));
@@ -258,6 +258,90 @@ constexpr bool test_one(Rng&& rng, Expected&& expected) {
         }
     }
 
+#if _HAS_CXX23
+    using ranges::const_iterator_t, ranges::const_sentinel_t, ranges::cbegin, ranges::cend;
+
+    // Validate view_interface::cbegin
+    STATIC_ASSERT(CanMemberCBegin<R>);
+    STATIC_ASSERT(CanMemberCBegin<const R> == ranges::range<const R>);
+    STATIC_ASSERT(indirect_unary_predicate<const Pred, const_iterator_t<const V>>);
+    if (forward_range<V>) { // intentionally not if constexpr
+        const same_as<const_iterator_t<R>> auto i = r.cbegin();
+        if (!is_empty) {
+            assert(*i == *cbegin(expected));
+            assert(*r.cbegin() == *cbegin(expected));
+        }
+
+        if constexpr (copyable<V>) {
+            auto r2                                    = r;
+            const same_as<const_iterator_t<R>> auto i2 = r2.cbegin();
+            if (!is_empty) {
+                assert(*i2 == *i);
+                assert(*r2.cbegin() == *i2);
+            }
+        }
+
+        const same_as<const_iterator_t<const R>> auto ic = as_const(r).cbegin();
+        if (!is_empty) {
+            assert(*ic == *cbegin(expected));
+            assert(*as_const(r).cbegin() == *cbegin(expected));
+        }
+
+        if constexpr (copyable<V>) {
+            auto rc2                                          = as_const(r);
+            const same_as<const_iterator_t<const R>> auto ic2 = rc2.cbegin();
+            if (!is_empty) {
+                assert(*ic2 == *ic);
+                assert(*rc2.cbegin() == *ic2);
+            }
+        }
+    }
+
+    // Validate view_interface::cend
+    STATIC_ASSERT(CanMemberCEnd<R>);
+    STATIC_ASSERT(CanMemberCEnd<const R> == ranges::range<const R>);
+    STATIC_ASSERT(indirect_unary_predicate<const Pred, const_iterator_t<const V>>);
+    STATIC_ASSERT(CanCEnd<const R&> == CanMemberCEnd<const R>);
+    STATIC_ASSERT(!common_range<R>);
+    STATIC_ASSERT(!common_range<const R>);
+    if (!is_empty) {
+        same_as<const_sentinel_t<R>> auto s        = r.cend();
+        same_as<const_sentinel_t<const R>> auto sc = as_const(r).cend();
+
+        if (forward_range<V>) { // intentionally not if constexpr
+            // Compare with const / non-const iterators
+            assert(s != r.cbegin());
+            assert(s != as_const(r).cbegin());
+            assert(sc != r.cbegin());
+            assert(sc != as_const(r).cbegin());
+
+            // Compare with end of range
+            if constexpr (common_range<V>) {
+                assert(s == s.base());
+                assert(s == sc.base());
+                assert(sc == s.base());
+                assert(sc == sc.base());
+            } else if constexpr (forward_range<V> && is_lvalue_reference_v<Rng>) {
+                auto full_range   = views::take_while(rng, [](const auto&) { return true; });
+                const auto length = 8; // NB: depends on the test data
+                assert(full_range.cend() == next(full_range.cbegin(), length));
+                assert(full_range.cend() == next(as_const(full_range).cbegin(), length));
+                assert(as_const(full_range).cend() == next(full_range.cbegin(), length));
+                assert(as_const(full_range).cend() == next(as_const(full_range).cbegin(), length));
+            }
+
+            // Compare with iterator whose predicate evaluates to false
+            if constexpr (forward_range<V>) {
+                const auto length = 4; // NB: depends on the test data
+                assert(s == next(r.cbegin(), length));
+                assert(s == next(as_const(r).cbegin(), length));
+                assert(sc == next(r.cbegin(), length));
+                assert(sc == next(as_const(r).cbegin(), length));
+            }
+        }
+    }
+#endif // _HAS_CXX23
+
     // Validate view_interface::data
     if constexpr (CanData<R&>) {
         const same_as<remove_reference_t<ranges::range_reference_t<V>>*> auto ptr1 = r.data();