[analyzer] Suppress a leak false positive in Qt's QObject::connectImpl()

[NoQ]

Summary

A quick fix to address the false positive posted by Tiago Macarios in the mailing lists: http://lists.llvm.org/pipermail/cfe-dev/2016-December/051738.html

MallocChecker processes pointer escapes heuristically rather than regularly. Force it to treat the pointers passed to connectImpl() as escaping.

I dislike a few things about this patch - we're patching against implementation details and hardcoding names of private methods in an external library. I don't see a significantly better solution within the current approach though.

See also D27599 - a similar hack for another function.

[a.sidorin]

LGTM, thanks!

lib/StaticAnalyzer/Checkers/MallocChecker.cpp

2577 ↗

(On Diff #81239)

Sorry for disturbing you for code which is not yours but this line looks exactly like the line upper and seems to be a dead/useless code.

cfe/trunk/lib/StaticAnalyzer/Checkers/MallocChecker.cpp

if (FName == "postEvent" &&
     return true;
   }
 
   if (FName == "postEvent" &&
       FD->getQualifiedNameAsString() == "QCoreApplication::postEvent") {
     return true;
   }
 
+  if (FName == "connectImpl" &&
+      FD->getQualifiedNameAsString() == "QObject::connectImpl") {
+    return true;
+  }
+
   // Handle cases where we know a buffer's /address/ can escape.
   // Note that the above checks handle some special cases where we know that
   // even though the address escapes, it's still our responsibility to free the
   // buffer.
   if (Call->argumentsMayEscape())
     return true;
 
   // Otherwise, assume that the function does not free memory.

cfe/trunk/test/Analysis/Inputs/qt-simulator.h

 #pragma clang system_header
 
+namespace QtPrivate {
+struct QSlotObjectBase {};
+}
+
+namespace Qt {
+enum ConnectionType {};
+}
+
+struct QMetaObject {
+  struct Connection {};
+};
+
 struct QObject {
+  static QMetaObject::Connection connectImpl(const QObject *, void **,
+                                             const QObject *, void **,
+                                             QtPrivate::QSlotObjectBase *,
+                                             Qt::ConnectionType,
+                                             const int *, const QMetaObject *);
 };
 
 struct QEvent {
   enum Type { None };
   QEvent(Type) {}
 };
 
 struct QCoreApplication : public QObject {
   static void postEvent(QObject *receiver, QEvent *event);
   static QCoreApplication *instance();
 };
 
 struct QApplication : public QCoreApplication {};

cfe/trunk/test/Analysis/qt_malloc.cpp

-// RUN: %clang_cc1 -analyze -analyzer-checker=core,alpha.deadcode.UnreachableCode,alpha.core.CastSize,unix.Malloc,cplusplus -analyzer-store=region -verify %s
+// RUN: %clang_cc1 -std=c++11 -analyze -analyzer-checker=core,alpha.deadcode.UnreachableCode,alpha.core.CastSize,unix.Malloc,cplusplus -analyzer-store=region -verify %s
 // expected-no-diagnostics
 #include "Inputs/qt-simulator.h"
 
 void send(QObject *obj)
 {
   QEvent *e1 = new QEvent(QEvent::None);
   static_cast<QApplication *>(QCoreApplication::instance())->postEvent(obj, e1);
   QEvent *e2 = new QEvent(QEvent::None);
   QCoreApplication::instance()->postEvent(obj, e2);
   QEvent *e3 = new QEvent(QEvent::None);
   QCoreApplication::postEvent(obj, e3);
   QEvent *e4 = new QEvent(QEvent::None);
   QApplication::postEvent(obj, e4);
 }
+
+void connect(QObject *obj) {
+  obj->connectImpl(nullptr, nullptr, nullptr, nullptr,
+                   new QtPrivate::QSlotObjectBase(), (Qt::ConnectionType)0,
+                   nullptr, nullptr);
+}