QList: implement operator<=> for iterators

This fixes an annoying warning with MSVC where it did already compile
  iterator <=> iterator
by way of the deprecated operator*(). GCC and Clang did not compile the
above, though they do compile the other ordering operators.

Fixes: QTBUG-120924
Change-Id: Ie13bf48bc506e7dd719efffdeae55f0735148976
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
Reviewed-by: Rym Bouabid <rym.bouabid@qt.io>

src/corelib/tools/qlist.h

@@ -142,6 +142,10 @@ public:
         inline T &operator*() const { return *i; }
         inline T *operator->() const { return i; }
         inline T &operator[](qsizetype j) const { return *(i + j); }
+#ifdef __cpp_lib_three_way_comparison
+        friend constexpr auto operator<=>(iterator, iterator) noexcept = default;
+        friend constexpr bool operator==(iterator, iterator) noexcept = default;
+#else
         inline constexpr bool operator==(iterator o) const { return i == o.i; }
         inline constexpr bool operator!=(iterator o) const { return i != o.i; }
         inline constexpr bool operator<(iterator other) const { return i < other.i; }
@@ -154,6 +158,7 @@ public:
         inline constexpr bool operator<=(const_iterator other) const { return i <= other.i; }
         inline constexpr bool operator>(const_iterator other) const { return i > other.i; }
         inline constexpr bool operator>=(const_iterator other) const { return i >= other.i; }
+#endif // __cpp_lib_three_way_comparison
         inline constexpr bool operator==(pointer p) const { return i == p; }
         inline constexpr bool operator!=(pointer p) const { return i != p; }
         inline iterator &operator++() { ++i; return *this; }
@@ -213,6 +218,14 @@ public:
         inline const T &operator*() const { return *i; }
         inline const T *operator->() const { return i; }
         inline const T &operator[](qsizetype j) const { return *(i + j); }
+#ifdef __cpp_lib_three_way_comparison
+        friend constexpr auto operator<=>(const_iterator, const_iterator) noexcept = default;
+        friend constexpr auto operator<=>(const_iterator a, iterator b) noexcept
+        { return a <=> const_iterator(b); }
+        friend constexpr bool operator==(const_iterator, const_iterator) noexcept = default;
+        friend constexpr bool operator==(const_iterator a, iterator b) noexcept
+        { return a == const_iterator(b); }
+#else
         inline constexpr bool operator==(const_iterator o) const { return i == o.i; }
         inline constexpr bool operator!=(const_iterator o) const { return i != o.i; }
         inline constexpr bool operator<(const_iterator other) const { return i < other.i; }
@@ -225,6 +238,7 @@ public:
         inline constexpr bool operator<=(iterator other) const { return i <= other.i; }
         inline constexpr bool operator>(iterator other) const { return i > other.i; }
         inline constexpr bool operator>=(iterator other) const { return i >= other.i; }
+#endif // __cpp_lib_three_way_comparison
         inline constexpr bool operator==(pointer p) const { return i == p; }
         inline constexpr bool operator!=(pointer p) const { return i != p; }
         inline const_iterator &operator++() { ++i; return *this; }

tests/auto/corelib/tools/qlist/CMakeLists.txt

@@ -18,6 +18,7 @@ qt_internal_add_test(tst_qlist
         QT_NO_STRICT_QLIST_ITERATORS # doesn't exist, except for this test
     LIBRARIES
         Qt::CorePrivate
+        Qt::TestPrivate
 )
 
 qt_internal_add_test(tst_qlist_strict_iterators
@@ -28,6 +29,7 @@ qt_internal_add_test(tst_qlist_strict_iterators
         tst_QList=tst_QList_strict_iterators
     LIBRARIES
         Qt::CorePrivate
+        Qt::TestPrivate
 )
 
 ## Scopes:

tests/auto/corelib/tools/qlist/tst_qlist.cpp

@@ -6,13 +6,14 @@
 #    undef QT_STRICT_QLIST_ITERATORS
 #  endif
 #endif
+#include <qlist.h>
 
 #include <QTest>
 #include <QAtomicInt>
+#include <QAtomicScopedValueRollback>
 #include <QThread>
 #include <QSemaphore>
-#include <QAtomicScopedValueRollback>
+#include <QtTest/private/qcomparisontesthelper_p.h>
-#include <qlist.h>
 
 #include <cstdio>
 #include <QtCore/q20memory.h>
@@ -2616,10 +2617,23 @@ void tst_QList::iterators() const
 
     QCOMPARE(v.begin(), v.end());
     QCOMPARE(v.rbegin(), v.rend());
+    QT_TEST_ALL_COMPARISON_OPS(v.begin(), v.end(), Qt::strong_ordering::equal);
+    QT_TEST_ALL_COMPARISON_OPS(v.rbegin(), v.rend(), Qt::strong_ordering::equal);
+    QT_TEST_ALL_COMPARISON_OPS(v.cbegin(), v.end(), Qt::strong_ordering::equal);
+    QT_TEST_ALL_COMPARISON_OPS(v.crbegin(), v.rend(), Qt::strong_ordering::equal);
+    QT_TEST_ALL_COMPARISON_OPS(v.begin(), v.cend(), Qt::strong_ordering::equal);
+    QT_TEST_ALL_COMPARISON_OPS(v.rbegin(), v.crend(), Qt::strong_ordering::equal);
 
     qsizetype idx = 0;
     for (; idx < 10; ++idx)
         v.push_back(idx);
+    QCOMPARE_LT(v.begin(), v.end());
+    QT_TEST_ALL_COMPARISON_OPS(v.begin(), v.end(), Qt::strong_ordering::less);
+    QT_TEST_ALL_COMPARISON_OPS(v.rbegin(), v.rend(), Qt::strong_ordering::less);
+    QT_TEST_ALL_COMPARISON_OPS(v.cbegin(), v.end(), Qt::strong_ordering::less);
+    QT_TEST_ALL_COMPARISON_OPS(v.crbegin(), v.rend(), Qt::strong_ordering::less);
+    QT_TEST_ALL_COMPARISON_OPS(v.begin(), v.cend(), Qt::strong_ordering::less);
+    QT_TEST_ALL_COMPARISON_OPS(v.rbegin(), v.crend(), Qt::strong_ordering::less);
 
     // stl-style iterators
     idx = 0;
@@ -2629,6 +2643,10 @@ void tst_QList::iterators() const
 
     std::advance(it, 7);
     idx += 7;
+    QT_TEST_ALL_COMPARISON_OPS(it, v.end(), Qt::strong_ordering::less);
+    QT_TEST_ALL_COMPARISON_OPS(it, v.cend(), Qt::strong_ordering::less);
+    QT_TEST_ALL_COMPARISON_OPS(v.begin(), it, Qt::strong_ordering::less);
+    QT_TEST_ALL_COMPARISON_OPS(v.cbegin(), it, Qt::strong_ordering::less);
     QCOMPARE(*it, idx);
     // idx == 7
 
@@ -2765,8 +2783,19 @@ void tst_QList::constIterators() const
     QCOMPARE(constEmptyList.constBegin(), constEmptyList.cbegin());
     QCOMPARE(constEmptyList.constEnd(), constEmptyList.cend());
     QVERIFY(!constEmptyList.isDetached());
+    QT_TEST_ALL_COMPARISON_OPS(constEmptyList.begin(), constEmptyList.end(),
+                               Qt::strong_ordering::equal);
+    QT_TEST_ALL_COMPARISON_OPS(constEmptyList.rbegin(), constEmptyList.rend(),
+                               Qt::strong_ordering::equal);
 
     const QList<int> v { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
+    QCOMPARE_LT(v.begin(), v.end());
+    QT_TEST_ALL_COMPARISON_OPS(v.begin(), v.end(), Qt::strong_ordering::less);
+    QT_TEST_ALL_COMPARISON_OPS(v.rbegin(), v.rend(), Qt::strong_ordering::less);
+    QT_TEST_ALL_COMPARISON_OPS(v.cbegin(), v.end(), Qt::strong_ordering::less);
+    QT_TEST_ALL_COMPARISON_OPS(v.crbegin(), v.rend(), Qt::strong_ordering::less);
+    QT_TEST_ALL_COMPARISON_OPS(v.begin(), v.cend(), Qt::strong_ordering::less);
+    QT_TEST_ALL_COMPARISON_OPS(v.rbegin(), v.crend(), Qt::strong_ordering::less);
 
     // stl-style iterators
     qsizetype idx = 0;
@@ -2776,6 +2805,10 @@ void tst_QList::constIterators() const
 
     std::advance(it, 7);
     idx += 7;
+    QT_TEST_ALL_COMPARISON_OPS(it, v.end(), Qt::strong_ordering::less);
+    QT_TEST_ALL_COMPARISON_OPS(it, v.cend(), Qt::strong_ordering::less);
+    QT_TEST_ALL_COMPARISON_OPS(v.begin(), it, Qt::strong_ordering::less);
+    QT_TEST_ALL_COMPARISON_OPS(v.cbegin(), it, Qt::strong_ordering::less);
     QCOMPARE(*it, idx);
     // idx == 7