QLatin1/String/View: don't decay the arg() arguments

This turns const char[] arrays into const char* pointers and
therefore prevents the implicit conversion of string literals
to QString in QT_RESTRICTED_CAST_FROM_ASCII.

Fix by avoiding the decay.

Also simplify the template magic.

Pick-to: 6.5 6.4 6.2 5.15
Change-Id: I88164a1866ac71b41d9cd1564f3a5e83d2d42aaa
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 5 insertions, 8 deletions

diff --git a/src/corelib/text/qstring.h b/src/corelib/text/qstring.h
index 62f0e078ee..883fc08d3c 100644
--- a/src/corelib/text/qstring.h
+++ b/src/corelib/text/qstring.h
@@ -538,14 +538,11 @@ public:
                 QChar fillChar = u' ') const;
 private:
     template <typename T>
-    struct is_convertible_to_view_or_qstring_helper
-        : std::integral_constant<bool,
-            std::is_convertible<T, QString>::value ||
-            std::is_convertible<T, QStringView>::value ||
-            std::is_convertible<T, QLatin1StringView>::value> {};
-    template <typename T>
-    struct is_convertible_to_view_or_qstring
-        : is_convertible_to_view_or_qstring_helper<typename std::decay<T>::type> {};
+    using is_convertible_to_view_or_qstring = std::disjunction<
+            std::is_convertible<T, QString>,
+            std::is_convertible<T, QStringView>,
+            std::is_convertible<T, QLatin1StringView>
+        >;
 public:
     template <typename...Args>
     [[nodiscard]]