QString: fix an aliasing issue in remove(QString)

Even in Qt 5, remove() can be passed an alias to *this. In Qt 6, with
the advent of substring sharing, this will become even more
pronounced. Use the same fix as was already used in QString::insert().

Pick-to: 5.15
Change-Id: I1a0d3d99fd7dff6e727661646d2cbfdc94df2682
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

src/corelib/text/qstring.cpp

@@ -2883,7 +2883,15 @@ static void removeStringImpl(QString &s, const T &needle, Qt::CaseSensitivity cs
 */
 QString &QString::remove(const QString &str, Qt::CaseSensitivity cs)
 {
-    removeStringImpl(*this, str, cs);
+    const auto s = reinterpret_cast<const ushort *>(str.data());
+    const std::less<const ushort *> less;
+    if (!less(s, d.data()) && less(s, d.data() + d.size)) {
+        // Part of me - take a copy
+        const QVarLengthArray<ushort> copy(s, s + str.size());
+        removeStringImpl(*this, QStringView{copy.data(), copy.size()}, cs);
+    } else {
+        removeStringImpl(*this, qToStringViewIgnoringNull(str), cs);
+    }
     return *this;
 }
 

tests/auto/corelib/text/qstring/tst_qstring.cpp

@@ -388,6 +388,7 @@ private slots:
     void remove_string();
     void remove_regexp_data();
     void remove_regexp();
+    void remove_extra();
     void swap();
 
     void prepend_qstring()            { prepend_impl<QString>(); }
@@ -3028,6 +3029,15 @@ void tst_QString::remove_regexp()
     }
 }
 
+void tst_QString::remove_extra()
+{
+    {
+        QString s = "The quick brown fox jumps over the lazy dog. "
+                    "The lazy dog jumps over the quick brown fox.";
+        s.remove(s);
+    }
+}
+
 void tst_QString::toNum()
 {
 #if defined (Q_OS_WIN) && defined (Q_CC_MSVC)