From dc48e368fe6973d4fd6170735676aff9085c6105 Mon Sep 17 00:00:00 2001
From: Ivan Solovev <ivan.solovev@qt.io>
Date: Wed, 7 Jul 2021 14:51:36 +0200
Subject: [PATCH] QMultiHash::find - prevent detaching shared null

Do not detach when find(key, value) is called on an empty QMultiHash.

As a drive-by: fix return value for QMultiHash::remove() in case of
empty QMultiHash.

Task-number: QTBUG-91736
Change-Id: I1e32f359e7ee9ce8403dae79d02e0b88a20ec4a5
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
(cherry picked from commit 82499f81478032911d8f788aa28e8d780b31c973)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
---
 src/corelib/tools/qhash.h                    |  4 +++-
 tests/auto/corelib/tools/qhash/tst_qhash.cpp | 15 +++++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/src/corelib/tools/qhash.h b/src/corelib/tools/qhash.h
index 1a793e61636..bfa2da6dbd4 100644
--- a/src/corelib/tools/qhash.h
+++ b/src/corelib/tools/qhash.h
@@ -1782,7 +1782,7 @@ public:
     qsizetype remove(const Key &key, const T &value)
     {
         if (isEmpty()) // prevents detaching shared null
-            return false;
+            return 0;
         detach();
 
         auto it = d->find(key);
@@ -1844,6 +1844,8 @@ public:
 
     iterator find(const Key &key, const T &value)
     {
+        if (isEmpty())
+            return end();
         detach();
         auto it = constFind(key, value);
         return iterator(it.i, it.e);
diff --git a/tests/auto/corelib/tools/qhash/tst_qhash.cpp b/tests/auto/corelib/tools/qhash/tst_qhash.cpp
index 6ad7d15c771..375f9048c07 100644
--- a/tests/auto/corelib/tools/qhash/tst_qhash.cpp
+++ b/tests/auto/corelib/tools/qhash/tst_qhash.cpp
@@ -668,12 +668,17 @@ void tst_QHash::empty()
 //copied from tst_QMap
 void tst_QHash::find()
 {
+    const QHash<int, QString> constEmptyHash;
+    QVERIFY(constEmptyHash.find(1) == constEmptyHash.end());
+    QVERIFY(!constEmptyHash.isDetached());
+
     QHash<int, QString> map1;
     QString testString="Teststring %0";
     QString compareString;
     int i,count=0;
 
     QVERIFY(map1.find(1) == map1.end());
+    QVERIFY(!map1.isDetached());
 
     map1.insert(1,"Mensch");
     map1.insert(1,"Mayer");
@@ -682,6 +687,16 @@ void tst_QHash::find()
     QCOMPARE(map1.find(1).value(), QLatin1String("Mayer"));
     QCOMPARE(map1.find(2).value(), QLatin1String("Hej"));
 
+    const QMultiHash<int, QString> constEmptyMultiHash;
+    QVERIFY(constEmptyMultiHash.find(1) == constEmptyMultiHash.cend());
+    QVERIFY(constEmptyMultiHash.find(1, "value") == constEmptyMultiHash.cend());
+    QVERIFY(!constEmptyMultiHash.isDetached());
+
+    QMultiHash<int, QString> emptyMultiHash;
+    QVERIFY(emptyMultiHash.find(1) == emptyMultiHash.end());
+    QVERIFY(emptyMultiHash.find(1, "value") == emptyMultiHash.end());
+    QVERIFY(!emptyMultiHash.isDetached());
+
     QMultiHash<int, QString> multiMap(map1);
     for (i = 3; i < 10; ++i) {
         compareString = testString.arg(i);