Make sure that palette cache keys are unique

After 1d961491d817490da156769ddce6fce48a0bce4a, palettes are different
if they either have different brush data, or a different private. Two
privates can share data, but still must generate different cache keys.
The cacheKey has so far been composted of the serial number of the Data
struct, and a detach number that is incremented when we detach the
private.

This failed for two reasons:

- the implicit copy constructor of the Data class copied the serial
number, when it should have incremented it. Fix that by member-
initializing the serial number rather than doing it only in the default
constructor. The member initialization is also executed for the copy
constructor.

- the detach_no logic as it was implemented does not guarantee that two
copies of the same palette that share data, but have different resolve
masks (and thus different privates) have different detach_no values.
Use a static serial counter for that number as well.

Amend the test case to verfiy that cache keys, and the elements of the
cache keys, change when they are expected to.

Fixes: QTBUG-106984
Pick-to: 6.2 6.4
Change-Id: I84d7055ce8bfe0d42f1f8e9766f3f1ad610f4ec8
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

1 files changed, 16 insertions, 5 deletions

diff --git a/src/gui/kernel/qpalette.cpp b/src/gui/kernel/qpalette.cpp
index 33a885b510..081af38074 100644
--- a/src/gui/kernel/qpalette.cpp
+++ b/src/gui/kernel/qpalette.cpp
@@ -35,14 +35,25 @@ class QPalettePrivate
 public:
     class Data : public QSharedData {
     public:
-        Data() : ser_no(qt_palette_count++) { }
+        // Every instance of Data has to have a unique serial number, even
+        // if it gets created by copying another - we wouldn't create a copy
+        // in the first place if the serial number should be the same!
+        Data(const Data &other)
+            : QSharedData(other)
+        {
+            for (int grp = 0; grp < int(QPalette::NColorGroups); grp++) {
+                for (int role = 0; role < int(QPalette::NColorRoles); role++)
+                    br[grp][role] = other.br[grp][role];
+            }
+        }
+        Data() = default;
 
         QBrush br[QPalette::NColorGroups][QPalette::NColorRoles];
-        const int ser_no;
+        const int ser_no = qt_palette_count++;
     };
 
     QPalettePrivate(const QExplicitlySharedDataPointer<Data> &data)
-        : ref(1), detach_no(0), data(data)
+        : ref(1), data(data)
     { }
     QPalettePrivate()
         : QPalettePrivate(QExplicitlySharedDataPointer<Data>(new Data))
@@ -50,7 +61,8 @@ public:
 
     QAtomicInt ref;
     QPalette::ResolveMask resolveMask = {0};
-    int detach_no;
+    static inline int qt_palette_private_count = 0;
+    const int detach_no = ++qt_palette_private_count;
     QExplicitlySharedDataPointer<Data> data;
 };
 
@@ -853,7 +865,6 @@ void QPalette::detach()
             delete d;
         d = x;
     }
-    ++d->detach_no;
 }
 
 /*!