Introduce QArrayData::detachCapacity

This follows QArrayData::detachFlags's lead. Given the (known) size for
a detached container, the function helps determine capacity, ensuring
the capacityReserved flag is respected.

This further helps aggregating behaviour on detach in QArrayData itself.

SimpleVector was previously using qMax(capacity(), newSize), but there's
no reason to pin the previous capacity value if reserve() wasn't
requested. It now uses detachCapacity().

Change-Id: Ide2d99ea7ecd2cd98ae4c1aa397b4475d09c8485
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

4 files changed, 21 insertions, 8 deletions

diff --git a/src/corelib/tools/qarraydata.h b/src/corelib/tools/qarraydata.h
index ae4cbc3081..78fbc9cf32 100644
--- a/src/corelib/tools/qarraydata.h
+++ b/src/corelib/tools/qarraydata.h
@@ -91,6 +91,13 @@ struct Q_CORE_EXPORT QArrayData
 
     Q_DECLARE_FLAGS(AllocationOptions, AllocationOption)
 
+    size_t detachCapacity(size_t newSize) const
+    {
+        if (capacityReserved && newSize < alloc)
+            return alloc;
+        return newSize;
+    }
+
     AllocationOptions detachFlags() const
     {
         AllocationOptions result;
diff --git a/src/corelib/tools/qarraydatapointer.h b/src/corelib/tools/qarraydatapointer.h
index f5ad53aa54..4eb90ac35e 100644
--- a/src/corelib/tools/qarraydatapointer.h
+++ b/src/corelib/tools/qarraydatapointer.h
@@ -171,7 +171,7 @@ public:
 private:
     Data *clone(QArrayData::AllocationOptions options) const Q_REQUIRED_RESULT
     {
-        QArrayDataPointer copy(Data::allocate(d->alloc ? d->alloc : d->size,
+        QArrayDataPointer copy(Data::allocate(d->detachCapacity(d->size),
                     options));
         if (d->size)
             copy->copyAppend(d->begin(), d->end());
diff --git a/tests/auto/corelib/tools/qarraydata/simplevector.h b/tests/auto/corelib/tools/qarraydata/simplevector.h
index 0cc7561b46..54c9fae589 100644
--- a/tests/auto/corelib/tools/qarraydata/simplevector.h
+++ b/tests/auto/corelib/tools/qarraydata/simplevector.h
@@ -184,7 +184,7 @@ public:
         if (d->ref.isShared()
                 || capacity() - size() < size_t(last - first)) {
             SimpleVector detached(Data::allocate(
-                        qMax(capacity(), size() + (last - first)),
+                        d->detachCapacity(size() + (last - first)),
                         d->detachFlags() | Data::Grow));
 
             detached.d->copyAppend(first, last);
@@ -205,7 +205,7 @@ public:
         if (d->ref.isShared()
                 || capacity() - size() < size_t(last - first)) {
             SimpleVector detached(Data::allocate(
-                        qMax(capacity(), size() + (last - first)),
+                        d->detachCapacity(size() + (last - first)),
                         d->detachFlags() | Data::Grow));
 
             if (d->size) {
@@ -245,7 +245,7 @@ public:
         if (d->ref.isShared()
                 || capacity() - size() < size_t(last - first)) {
             SimpleVector detached(Data::allocate(
-                        qMax(capacity(), size() + (last - first)),
+                        d->detachCapacity(size() + (last - first)),
                         d->detachFlags() | Data::Grow));
 
             if (position)
diff --git a/tests/auto/corelib/tools/qarraydata/tst_qarraydata.cpp b/tests/auto/corelib/tools/qarraydata/tst_qarraydata.cpp
index 6d3bbf046f..b3b8040b1c 100644
--- a/tests/auto/corelib/tools/qarraydata/tst_qarraydata.cpp
+++ b/tests/auto/corelib/tools/qarraydata/tst_qarraydata.cpp
@@ -1175,8 +1175,10 @@ void tst_QArrayData::setSharable_data()
 
     QArrayDataPointer<int> emptyReserved(QTypedArrayData<int>::allocate(5,
                 QArrayData::CapacityReserved));
-    QArrayDataPointer<int> nonEmpty(QTypedArrayData<int>::allocate(10,
+    QArrayDataPointer<int> nonEmpty(QTypedArrayData<int>::allocate(5,
                 QArrayData::Default));
+    QArrayDataPointer<int> nonEmptyExtraCapacity(
+            QTypedArrayData<int>::allocate(10, QArrayData::Default));
     QArrayDataPointer<int> nonEmptyReserved(QTypedArrayData<int>::allocate(15,
                 QArrayData::CapacityReserved));
     QArrayDataPointer<int> staticArray(
@@ -1185,13 +1187,15 @@ void tst_QArrayData::setSharable_data()
             QTypedArrayData<int>::fromRawData(staticArrayData.data, 10));
 
     nonEmpty->copyAppend(5, 1);
+    nonEmptyExtraCapacity->copyAppend(5, 1);
     nonEmptyReserved->copyAppend(7, 2);
 
     QTest::newRow("shared-null") << null << size_t(0) << size_t(0) << false << 0;
     QTest::newRow("shared-empty") << empty << size_t(0) << size_t(0) << false << 0;
     // unsharable-empty implicitly tested in shared-empty
     QTest::newRow("empty-reserved") << emptyReserved << size_t(0) << size_t(5) << true << 0;
-    QTest::newRow("non-empty") << nonEmpty << size_t(5) << size_t(10) << false << 1;
+    QTest::newRow("non-empty") << nonEmpty << size_t(5) << size_t(5) << false << 1;
+    QTest::newRow("non-empty-extra-capacity") << nonEmptyExtraCapacity << size_t(5) << size_t(10) << false << 1;
     QTest::newRow("non-empty-reserved") << nonEmptyReserved << size_t(7) << size_t(15) << true << 2;
     QTest::newRow("static-array") << staticArray << size_t(10) << size_t(0) << false << 3;
     QTest::newRow("raw-data") << rawData << size_t(10) << size_t(0) << false << 3;
@@ -1229,8 +1233,10 @@ void tst_QArrayData::setSharable()
     // Unshare, must detach
     array.setSharable(false);
 
-    // Immutability (alloc == 0) is lost on detach
-    if (capacity == 0 && size != 0)
+    // Immutability (alloc == 0) is lost on detach, as is additional capacity
+    // if capacityReserved flag is not set.
+    if ((capacity == 0 && size != 0)
+            || (!isCapacityReserved && capacity > size))
         capacity = size;
 
     QVERIFY(!array->ref.isShared());