From 09b77a8d07276e0b5e5fec596f957f8fc4a78869 Mon Sep 17 00:00:00 2001
From: Edward Welbourne <edward.welbourne@qt.io>
Date: Mon, 20 Jan 2025 15:40:04 +0100
Subject: [PATCH] Add a QDuplicateTracker<T>::contains()

When even some values I haven't seen may need to be left for later,
but values I have seen are definitely to be discarded, I need to know
if I've already processed them before doing the fiddly check for
whether to defer; but if I decide to defer, I haven't yet processed
and need the later check, to which I've deferred, to see the value as
still new, even though I did once ask about it before. So I need a way
to query without adding to the set.

Pick-to: 6.9 6.8 6.5
Change-Id: I712f1c400147210c149aeec6de1d15d2e095d6a9
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
---
 src/corelib/tools/qduplicatetracker_p.h         |  5 +++++
 .../qduplicatetracker/tst_qduplicatetracker.cpp | 17 ++++++++++++++++-
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/src/corelib/tools/qduplicatetracker_p.h b/src/corelib/tools/qduplicatetracker_p.h
index 7e47ab0272a..434285e4907 100644
--- a/src/corelib/tools/qduplicatetracker_p.h
+++ b/src/corelib/tools/qduplicatetracker_p.h
@@ -94,6 +94,11 @@ public:
     {
         return !set.insert(std::move(s)).second;
     }
+    // For when you want to know, but aren't *yet* sure you'll add it:
+    [[nodiscard]] bool contains(const T &s) const
+    {
+        return set.find(s) != set.end(); // TODO C++20: can use set.contains()
+    }
 
     template <typename C>
     void appendTo(C &c) const &
diff --git a/tests/auto/corelib/tools/qduplicatetracker/tst_qduplicatetracker.cpp b/tests/auto/corelib/tools/qduplicatetracker/tst_qduplicatetracker.cpp
index ad0b6abbc70..f370fcf6814 100644
--- a/tests/auto/corelib/tools/qduplicatetracker/tst_qduplicatetracker.cpp
+++ b/tests/auto/corelib/tools/qduplicatetracker/tst_qduplicatetracker.cpp
@@ -24,12 +24,17 @@ void tst_QDuplicateTracker::hasSeen()
 {
     {
         QDuplicateTracker<int, 2> tracker;
+        QVERIFY(!tracker.contains(0));
+        QVERIFY(!tracker.contains(0));
         QVERIFY(!tracker.hasSeen(0));
         QVERIFY(tracker.hasSeen(0));
+        QVERIFY(tracker.contains(0));
         QVERIFY(!tracker.hasSeen(1));
         QVERIFY(tracker.hasSeen(1));
         // past the prealloc amount
+        QVERIFY(!tracker.contains(2));
         QVERIFY(!tracker.hasSeen(2));
+        QVERIFY(tracker.contains(2));
         QVERIFY(tracker.hasSeen(2));
     }
 
@@ -41,12 +46,16 @@ void tst_QDuplicateTracker::hasSeen()
         QString string3("string3");
 
         // Move when seen
+        QVERIFY(!tracker.contains(string1));
         QVERIFY(!tracker.hasSeen(string1));
+        QVERIFY(tracker.contains(string1));
         QVERIFY(tracker.hasSeen(std::move(string1)));
 
         // Move when unseen
+        QVERIFY(!tracker.contains(string2));
         QVERIFY(!tracker.hasSeen(std::move(string2)));
         QVERIFY(tracker.hasSeen(string2_2));
+        QVERIFY(tracker.contains(string2_2));
 
         // Past the prealloc amount
         QVERIFY(!tracker.hasSeen(string3));
@@ -62,17 +71,19 @@ void tst_QDuplicateTracker::hasSeen()
 
         // Move when seen
         QVERIFY(!tracker.hasSeen(string1));
+        QVERIFY(tracker.contains(string1));
         QVERIFY(tracker.hasSeen(std::move(string1)));
 
         // Move when unseen
         QVERIFY(!tracker.hasSeen(std::move(string2)));
         QVERIFY(tracker.hasSeen(string2_2));
+        QVERIFY(tracker.contains(string2_2));
 
         // Past the prealloc amount
+        QVERIFY(!tracker.contains(string3));
         QVERIFY(!tracker.hasSeen(string3));
         QVERIFY(tracker.hasSeen(string3));
     }
-
 }
 
 void tst_QDuplicateTracker::clear()
@@ -80,14 +91,18 @@ void tst_QDuplicateTracker::clear()
     QDuplicateTracker<int, 2> tracker;
     QVERIFY(!tracker.hasSeen(0));
     QVERIFY(tracker.hasSeen(0));
+    QVERIFY(tracker.contains(0));
+    QVERIFY(!tracker.contains(1));
     QVERIFY(!tracker.hasSeen(1));
     QVERIFY(tracker.hasSeen(1));
 
     tracker.clear();
+    QVERIFY(!tracker.contains(0));
     QVERIFY(!tracker.hasSeen(0));
     QVERIFY(tracker.hasSeen(0));
     QVERIFY(!tracker.hasSeen(1));
     QVERIFY(tracker.hasSeen(1));
+    QVERIFY(tracker.contains(1));
 }
 
 void tst_QDuplicateTracker::appendTo()