From 3e986578980f1c37e282ee15068fa250a763209d Mon Sep 17 00:00:00 2001
From: Marc Mutz <marc.mutz@qt.io>
Date: Tue, 20 May 2025 20:38:38 +0200
Subject: [PATCH] QPainter: make Private::d_ptrs a QVLA<unique_ptr>

This way, we remove the impedance mismatch between QPainter::d_ptr
(which already is a unique_ptr) and Private::d_ptrs, which still dealt
in raw pointers, simplifying the code.

Since we're now owning the objects in d_ptrs, add an assertion that
d_ptrs is empty on QPainter destruction.

Coverity-Id: 425479
Change-Id: I849e80752b4bc5a71aef8d47663c6ffc9fdca9f7
Reviewed-by: Matthias Rauter <matthias.rauter@qt.io>
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>
---
 src/gui/painting/qpainter.cpp | 13 +++++--------
 src/gui/painting/qpainter_p.h |  2 +-
 2 files changed, 6 insertions(+), 9 deletions(-)

diff --git a/src/gui/painting/qpainter.cpp b/src/gui/painting/qpainter.cpp
index 2982f05f2a3..b800952ae39 100644
--- a/src/gui/painting/qpainter.cpp
+++ b/src/gui/painting/qpainter.cpp
@@ -247,11 +247,7 @@ bool QPainterPrivate::attachPainterPrivate(QPainter *q, QPaintDevice *pdev)
     // the current d_ptr to the shared painter's d_ptr.
     sp->save();
     ++sp->d_ptr->refcount;
-    {
-        // ensure realloc happens before the unique_ptr::release():
-        auto &p = sp->d_ptr->d_ptrs.emplace_back();
-        p = q->d_ptr.release();
-    }
+    sp->d_ptr->d_ptrs.push_back(std::move(q->d_ptr));
     q->d_ptr.reset(sp->d_ptr.get());
 
     Q_ASSERT(q->d_ptr->state);
@@ -296,19 +292,19 @@ void QPainterPrivate::detachPainterPrivate(QPainter *q)
     Q_ASSERT(q);
 
     --refcount;
-    QPainterPrivate *original = d_ptrs.back();
+    auto original = std::move(d_ptrs.back());
     d_ptrs.pop_back();
     if (inDestructor) {
         inDestructor = false;
         if (original)
             original->inDestructor = true;
     } else if (!original) {
-        original = new QPainterPrivate(q);
+        original = std::make_unique<QPainterPrivate>(q);
     }
 
     q->restore();
     Q_UNUSED(q->d_ptr.release());
-    q->d_ptr.reset(original);
+    q->d_ptr = std::move(original);
 
     if (emulationEngine) {
         extended = emulationEngine->real_engine;
@@ -1488,6 +1484,7 @@ QPainter::~QPainter()
         Q_ASSERT(d_ptr->inDestructor);
         d_ptr->inDestructor = false;
         Q_ASSERT(d_ptr->refcount == 1);
+        Q_ASSERT(d_ptr->d_ptrs.empty());
     }
 }
 
diff --git a/src/gui/painting/qpainter_p.h b/src/gui/painting/qpainter_p.h
index 0ddd78fb2a4..dd4653a5788 100644
--- a/src/gui/painting/qpainter_p.h
+++ b/src/gui/painting/qpainter_p.h
@@ -166,7 +166,7 @@ public:
     // redirections within the same paintEvent(), which should be enough
     // in 99% of all cases). E.g: A renders B which renders C which renders D.
     static constexpr qsizetype NDPtrs = 4;
-    QVarLengthArray<QPainterPrivate*, NDPtrs> d_ptrs;
+    QVarLengthArray<std::unique_ptr<QPainterPrivate>, NDPtrs> d_ptrs;
 
     std::unique_ptr<QPainterState> state;
     template <typename T, std::size_t N = 8>