QTest: fix bug dereferencing nullptr in toString<std::nullptr_t>()

Amends commit 0756cc1.

The generic instantiation of this function had a std::nullptr_t *
parameter, but callers had special code to pass a nullptr there because
we never needed a value of a nullptr (it's always a null pointer). For
example, in compare_ptr_helper():

        auto lhsFormatter = Internal::pointerToString<QObject>;
        auto rhsFormatter = Internal::genericToString<std::nullptr_t>;
        return compare_helper(t1 == nullptr, "Compared QObject pointers are not the same",
                              const_cast<const QObject *>(t1), nullptr,
                              lhsFormatter, rhsFormatter, actual, expected, file, line);

But in debug mode, some compilers did emit a load from this memory
location, causing a crash. So we just specialize this function to avoid
such.

We had a test for this... except it was never reached because the
earlier QCOMPARE() had already failed. For the test, this amends
commit ae02188.

Fixes: QTBUG-133330
Pick-to: 6.9 6.8
Change-Id: I2cd3bb475788431c6a0dfffd28e730e8b613e033
Reviewed-by: Christian Ehrlicher <ch.ehrlicher@gmx.de>
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>

src/testlib/qtestcase.h

@@ -384,6 +384,11 @@ namespace QTest
         return toString(static_cast<const char *>(arg));
     }
 
+    template <> inline const char *genericToString<std::nullptr_t>(const void *)
+    {
+        return QTest::toString(nullptr);
+    }
+
     template <typename T> const char *pointerToString(const void *arg)
     {
         using QTest::toString;

tests/auto/testlib/selftests/cmptest/tst_cmptest.cpp

@@ -282,10 +282,10 @@ void tst_Cmptest::compareQObjects()
     object1.setObjectName(QStringLiteral("object1"));
     QObject object2;
     object2.setObjectName(QStringLiteral("object2"));
-    QCOMPARE(&object1, &object1);
-    QCOMPARE(&object1, &object2);
-    QCOMPARE(&object1, nullptr);
-    QCOMPARE(nullptr, &object2);
+    [&] { QCOMPARE(&object1, &object1); }();
+    [&] { QCOMPARE(&object1, &object2); }();
+    [&] { QCOMPARE(&object1, nullptr); }();
+    [&] { QCOMPARE(nullptr, &object2); }();
 }
 
 void tst_Cmptest::compare_stringLiterals()

tests/auto/testlib/selftests/expected_cmptest.lightxml

@@ -172,6 +172,16 @@
     <Incident type="fail" file="qtbase/tests/auto/testlib/selftests/cmptest/tst_cmptest.cpp" line="0">
       <Description><![CDATA[Compared QObject pointers are not the same
    Actual   (&object1): QObject/"object1"
+   Expected (&object2): QObject/"object2"]]></Description>
+    </Incident>
+    <Incident type="fail" file="qtbase/tests/auto/testlib/selftests/cmptest/tst_cmptest.cpp" line="0">
+      <Description><![CDATA[Compared QObject pointers are not the same
+   Actual   (&object1): QObject/"object1"
+   Expected (nullptr) : "nullptr"]]></Description>
+    </Incident>
+    <Incident type="fail" file="qtbase/tests/auto/testlib/selftests/cmptest/tst_cmptest.cpp" line="0">
+      <Description><![CDATA[Compared QObject pointers are not the same
+   Actual   (nullptr) : "nullptr"
    Expected (&object2): QObject/"object2"]]></Description>
     </Incident>
     <Duration msecs="0"/>

tests/auto/testlib/selftests/expected_cmptest.tap

@@ -268,6 +268,30 @@ not ok 22 - compareQObjects()
   file: qtbase/tests/auto/testlib/selftests/cmptest/tst_cmptest.cpp
   line: 0
   ...
+not ok 22 - compareQObjects()
+  ---
+  type: QCOMPARE
+  message: Compared QObject pointers are not the same
+  wanted: "nullptr" (nullptr)
+  found: QObject/"object1" (&object1)
+  expected: "nullptr" (nullptr)
+  actual: QObject/"object1" (&object1)
+  at: tst_Cmptest::compareQObjects() (qtbase/tests/auto/testlib/selftests/cmptest/tst_cmptest.cpp:0)
+  file: qtbase/tests/auto/testlib/selftests/cmptest/tst_cmptest.cpp
+  line: 0
+  ...
+not ok 22 - compareQObjects()
+  ---
+  type: QCOMPARE
+  message: Compared QObject pointers are not the same
+  wanted: QObject/"object2" (&object2)
+  found: "nullptr" (nullptr)
+  expected: QObject/"object2" (&object2)
+  actual: "nullptr" (nullptr)
+  at: tst_Cmptest::compareQObjects() (qtbase/tests/auto/testlib/selftests/cmptest/tst_cmptest.cpp:0)
+  file: qtbase/tests/auto/testlib/selftests/cmptest/tst_cmptest.cpp
+  line: 0
+  ...
 ok 23 - compareQStringLists(empty lists)
 ok 24 - compareQStringLists(equal lists)
 not ok 25 - compareQStringLists(last item different)

tests/auto/testlib/selftests/expected_cmptest.teamcity

@@ -72,6 +72,10 @@
 ##teamcity[testStarted name='compareQObjects()' flowId='tst_Cmptest']
 ##teamcity[testFailed name='compareQObjects()' message='Failure! |[Loc: qtbase/tests/auto/testlib/selftests/cmptest/tst_cmptest.cpp(0)|]' details='Compared QObject pointers are not the same|n Actual (&object1): QObject/"object1"|n Expected (&object2): QObject/"object2"' flowId='tst_Cmptest']
 ##teamcity[testFinished name='compareQObjects()' flowId='tst_Cmptest']
+##teamcity[testFailed name='compareQObjects()' message='Failure! |[Loc: qtbase/tests/auto/testlib/selftests/cmptest/tst_cmptest.cpp(0)|]' details='Compared QObject pointers are not the same|n Actual (&object1): QObject/"object1"|n Expected (nullptr) : "nullptr"' flowId='tst_Cmptest']
+##teamcity[testFinished name='compareQObjects()' flowId='tst_Cmptest']
+##teamcity[testFailed name='compareQObjects()' message='Failure! |[Loc: qtbase/tests/auto/testlib/selftests/cmptest/tst_cmptest.cpp(0)|]' details='Compared QObject pointers are not the same|n Actual (nullptr) : "nullptr"|n Expected (&object2): QObject/"object2"' flowId='tst_Cmptest']
+##teamcity[testFinished name='compareQObjects()' flowId='tst_Cmptest']
 ##teamcity[testStarted name='compareQStringLists(empty lists)' flowId='tst_Cmptest']
 ##teamcity[testFinished name='compareQStringLists(empty lists)' flowId='tst_Cmptest']
 ##teamcity[testStarted name='compareQStringLists(equal lists)' flowId='tst_Cmptest']

tests/auto/testlib/selftests/expected_cmptest.txt

@@ -95,6 +95,14 @@ FAIL!  : tst_Cmptest::compareQObjects() Compared QObject pointers are not the sa
    Actual   (&object1): QObject/"object1"
    Expected (&object2): QObject/"object2"
    Loc: [qtbase/tests/auto/testlib/selftests/cmptest/tst_cmptest.cpp(0)]
+FAIL!  : tst_Cmptest::compareQObjects() Compared QObject pointers are not the same
+   Actual   (&object1): QObject/"object1"
+   Expected (nullptr) : "nullptr"
+   Loc: [qtbase/tests/auto/testlib/selftests/cmptest/tst_cmptest.cpp(0)]
+FAIL!  : tst_Cmptest::compareQObjects() Compared QObject pointers are not the same
+   Actual   (nullptr) : "nullptr"
+   Expected (&object2): QObject/"object2"
+   Loc: [qtbase/tests/auto/testlib/selftests/cmptest/tst_cmptest.cpp(0)]
 PASS   : tst_Cmptest::compareQStringLists(empty lists)
 PASS   : tst_Cmptest::compareQStringLists(equal lists)
 FAIL!  : tst_Cmptest::compareQStringLists(last item different) Compared lists differ at index 2.

tests/auto/testlib/selftests/expected_cmptest.xml

@@ -174,6 +174,16 @@
     <Incident type="fail" file="qtbase/tests/auto/testlib/selftests/cmptest/tst_cmptest.cpp" line="0">
       <Description><![CDATA[Compared QObject pointers are not the same
    Actual   (&object1): QObject/"object1"
+   Expected (&object2): QObject/"object2"]]></Description>
+    </Incident>
+    <Incident type="fail" file="qtbase/tests/auto/testlib/selftests/cmptest/tst_cmptest.cpp" line="0">
+      <Description><![CDATA[Compared QObject pointers are not the same
+   Actual   (&object1): QObject/"object1"
+   Expected (nullptr) : "nullptr"]]></Description>
+    </Incident>
+    <Incident type="fail" file="qtbase/tests/auto/testlib/selftests/cmptest/tst_cmptest.cpp" line="0">
+      <Description><![CDATA[Compared QObject pointers are not the same
+   Actual   (nullptr) : "nullptr"
    Expected (&object2): QObject/"object2"]]></Description>
     </Incident>
     <Duration msecs="0"/>