QDuplicateTracker: bring back appendTo() &&

This reverts commit c19695ab953c979f15bbc72c4f4a453e9a114cf6.

Just because QSet has limited API doesn't mean we can't provide this
in an efficient way for std::unordered_set :P

Added tests.

Pick-to: 6.2
Change-Id: I4f8f0e60c810acdc666cf34f929845227ed87f3b
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

2 files changed, 56 insertions, 8 deletions

diff --git a/src/corelib/tools/qduplicatetracker_p.h b/src/corelib/tools/qduplicatetracker_p.h
index 565d592ac2..8d64ee5371 100644
--- a/src/corelib/tools/qduplicatetracker_p.h
+++ b/src/corelib/tools/qduplicatetracker_p.h
@@ -105,6 +105,13 @@ class QDuplicateTracker {
 #endif
     Q_DISABLE_COPY_MOVE(QDuplicateTracker);
 public:
+    static constexpr inline bool uses_pmr =
+        #ifdef __cpp_lib_memory_resource
+            true
+        #else
+            false
+        #endif
+            ;
     QDuplicateTracker() = default;
     explicit QDuplicateTracker(qsizetype n)
 #ifdef __cpp_lib_memory_resource
@@ -125,11 +132,22 @@ public:
     }
 
     template <typename C>
-    void appendTo(C &c) const
+    void appendTo(C &c) const &
     {
         for (const auto &e : set)
             c.push_back(e);
     }
+
+    template <typename C>
+    void appendTo(C &c) &&
+    {
+        if constexpr (uses_pmr) {
+            while (!set.empty())
+                c.push_back(std::move(set.extract(set.begin()).value()));
+        } else {
+            return appendTo(c); // lvalue version
+        }
+    }
 };
 
 QT_END_NAMESPACE
diff --git a/tests/auto/corelib/tools/qduplicatetracker/tst_qduplicatetracker.cpp b/tests/auto/corelib/tools/qduplicatetracker/tst_qduplicatetracker.cpp
index 6462ef0dd7..12a4103060 100644
--- a/tests/auto/corelib/tools/qduplicatetracker/tst_qduplicatetracker.cpp
+++ b/tests/auto/corelib/tools/qduplicatetracker/tst_qduplicatetracker.cpp
@@ -94,9 +94,15 @@ void tst_QDuplicateTracker::appendTo()
 
     QVERIFY(!tracker.hasSeen(2));
     QList<int> c;
-    tracker.appendTo(c);
+    std::move(tracker).appendTo(c);
     std::sort(c.begin(), c.end());
     QCOMPARE(c, QList<int>({ 0, 1, 2 }));
+    if (QDuplicateTracker<int, 2>::uses_pmr) {
+        // the following is only true if we use the std container
+        QVERIFY(!tracker.hasSeen(0));
+        QVERIFY(!tracker.hasSeen(1));
+        QVERIFY(!tracker.hasSeen(2));
+    }
 }
 
 struct ConstructionCounted
@@ -172,12 +178,36 @@ void tst_QDuplicateTracker::appendTo_special()
     QVERIFY(!tracker.hasSeen(1));
     QVERIFY(!tracker.hasSeen(2));
     QVERIFY(!tracker.hasSeen(3));
-    QList<ConstructionCounted> a;
-    a.reserve(3);
-    tracker.appendTo(a);
-    for (const auto &counter : a) {
-        QCOMPARE(counter.moves, 1);
-        QCOMPARE(counter.copies, 1);
+
+    QVERIFY(tracker.hasSeen(1));
+    QVERIFY(tracker.hasSeen(2));
+    QVERIFY(tracker.hasSeen(3));
+    {
+        QList<ConstructionCounted> a;
+        a.reserve(3);
+        tracker.appendTo(a);
+        for (const auto &counter : a) {
+            QCOMPARE(counter.moves, 1);
+            QCOMPARE(counter.copies, 1);
+        }
+    }
+    QVERIFY(tracker.hasSeen(1));
+    QVERIFY(tracker.hasSeen(2));
+    QVERIFY(tracker.hasSeen(3));
+    {
+        QList<ConstructionCounted> a;
+        a.reserve(3);
+        std::move(tracker).appendTo(a);
+        if (QDuplicateTracker<ConstructionCounted>::uses_pmr) {
+            // the following is only true if we use the std container
+            for (const auto &counter : a) {
+                QCOMPARE(counter.moves, 2);
+                QCOMPARE(counter.copies, 0);
+            }
+            QVERIFY(!tracker.hasSeen(1));
+            QVERIFY(!tracker.hasSeen(2));
+            QVERIFY(!tracker.hasSeen(3));
+        }
     }
 }