From f5af4428c3ede16c742df7890bc5f5ebf8ed2535 Mon Sep 17 00:00:00 2001
From: David Faure <david.faure@kdab.com>
Date: Tue, 26 Jul 2016 10:07:57 +0200
Subject: [PATCH] QVector: fix crash on reserve(0)
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It crashed when d was equal to Data::unsharableEmpty().

Task-number: QTBUG-51758
Change-Id: If9f2a7d11892507135f4dc0aeef909f59b7478fc
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@theqtcompany.com>
---
 src/corelib/tools/qvector.h                   |  6 ++++-
 .../corelib/tools/qvector/tst_qvector.cpp     | 22 +++++++++++++++++++
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/src/corelib/tools/qvector.h b/src/corelib/tools/qvector.h
index 3154220634..eefab5905c 100644
--- a/src/corelib/tools/qvector.h
+++ b/src/corelib/tools/qvector.h
@@ -391,7 +391,11 @@ void QVector<T>::reserve(int asize)
 {
     if (asize > int(d->alloc))
         reallocData(d->size, asize);
-    if (isDetached())
+    if (isDetached()
+#if !defined(QT_NO_UNSHARABLE_CONTAINERS)
+            && d != Data::unsharableEmpty()
+#endif
+            )
         d->capacityReserved = 1;
     Q_ASSERT(capacity() >= asize);
 }
diff --git a/tests/auto/corelib/tools/qvector/tst_qvector.cpp b/tests/auto/corelib/tools/qvector/tst_qvector.cpp
index edcf4c72b6..7c90f05ea4 100644
--- a/tests/auto/corelib/tools/qvector/tst_qvector.cpp
+++ b/tests/auto/corelib/tools/qvector/tst_qvector.cpp
@@ -276,6 +276,7 @@ private slots:
     void testOperators() const;
 
     void reserve();
+    void reserveZero();
     void reallocAfterCopy_data();
     void reallocAfterCopy();
     void initializeListInt();
@@ -2369,13 +2370,34 @@ void tst_QVector::reserve()
     {
         QVector<Foo> a;
         a.resize(2);
+        QCOMPARE(fooCtor, 2);
         QVector<Foo> b(a);
         b.reserve(1);
         QCOMPARE(b.size(), a.size());
+        QCOMPARE(fooDtor, 0);
     }
     QCOMPARE(fooCtor, fooDtor);
 }
 
+// This is a regression test for QTBUG-51758
+void tst_QVector::reserveZero()
+{
+    QVector<int> vec;
+    vec.detach();
+    vec.reserve(0); // should not crash
+    QCOMPARE(vec.size(), 0);
+    QCOMPARE(vec.capacity(), 0);
+    vec.squeeze();
+    QCOMPARE(vec.size(), 0);
+    QCOMPARE(vec.capacity(), 0);
+    vec.reserve(-1);
+    QCOMPARE(vec.size(), 0);
+    QCOMPARE(vec.capacity(), 0);
+    vec.append(42);
+    QCOMPARE(vec.size(), 1);
+    QVERIFY(vec.capacity() >= 1);
+}
+
 // This is a regression test for QTBUG-11763, where memory would be reallocated
 // soon after copying a QVector.
 void tst_QVector::reallocAfterCopy_data()