QAnyStringView: support single wchar_t arguments also on UnixHEADdev

We support char32_t, so there's no reason to not support a
4-byte-wchar_t.

This also fixes a nasty asymmery between QString::arg(L'ä') (integral
output) and QL1SV::arg(L'ä') or QString::arg(L'ä', L'ä') (characters)

[ChangeLog][Important Behavior Changes][QtCore][QString] The unary
arg() function now treats wchar_t as a character (string-like; was:
integer), so u"%1".arg(L'ø') will now return "ø" and not '248". This
makes the function consistent with both QString multi-arg() and
QLatin1StringView::arg().

[ChangeLog][QtCore][QAnyStringView] Supports construction from a
single wchar_t on all platforms now (was: only on Windows).

Fixes: QTBUG-126054
Pick-to: 6.10
Change-Id: I21b7a9782f03d04686207db30d1b1c9d50bc8169
Reviewed-by: Thiago Macieira <[email protected]>

3 files changed, 12 insertions, 4 deletions

diff --git a/src/corelib/text/qanystringview.cpp b/src/corelib/text/qanystringview.cpp
index 717b53f06c2..7bf8a3fa1fd 100644
--- a/src/corelib/text/qanystringview.cpp
+++ b/src/corelib/text/qanystringview.cpp
@@ -138,6 +138,7 @@ QT_BEGIN_NAMESPACE
     \list
     \li \c QLatin1Char
     \li \c QChar::SpecialCharacter
+    \li \c wchar_t (where it's a 32-bit type, i.e. Unix) (since 6.10)
     \li \c char32_t
     \endlist
 
diff --git a/src/corelib/text/qanystringview.h b/src/corelib/text/qanystringview.h
index 4b89fa6edbf..079cf751af1 100644
--- a/src/corelib/text/qanystringview.h
+++ b/src/corelib/text/qanystringview.h
@@ -25,6 +25,11 @@ struct wrapped { using type = Result; };
 template <typename Tag, typename Result>
 using wrapped_t = typename wrapped<Tag, Result>::type;
 
+template <typename Char>
+struct is_compatible_utf32_char : std::false_type {};
+template <> struct is_compatible_utf32_char<char32_t> : std::true_type {};
+template <> struct is_compatible_utf32_char<wchar_t> : std::bool_constant<sizeof(wchar_t) == 4> {};
+
 } // namespace QtPrivate
 
 class QAnyStringView
@@ -60,6 +65,11 @@ private:
     };
 
     template <typename Char>
+    using if_compatible_utf32_char = std::enable_if_t<
+        QtPrivate::is_compatible_utf32_char<Char>::value
+    , bool>;
+
+    template <typename Char>
     using is_compatible_char = std::disjunction<
         QtPrivate::IsCompatibleCharType<Char>,
         QtPrivate::IsCompatibleChar8Type<Char>
@@ -220,7 +230,7 @@ public:
     constexpr QAnyStringView(Char ch, QCharContainer &&capacity = QCharContainer()) noexcept
         : QAnyStringView{&(capacity.ch = ch), 1} {}
     template <typename Char, typename Container = decltype(QChar::fromUcs4(U'x')),
-              std::enable_if_t<std::is_same_v<Char, char32_t>, bool> = true>
+              if_compatible_utf32_char<Char> = true>
     constexpr QAnyStringView(Char c, Container &&capacity = {}) noexcept
         : QAnyStringView(capacity = QChar::fromUcs4(c)) {}
 
diff --git a/src/corelib/text/qstring.h b/src/corelib/text/qstring.h
index 09cfbdfe94d..e4f06835bd1 100644
--- a/src/corelib/text/qstring.h
+++ b/src/corelib/text/qstring.h
@@ -66,9 +66,6 @@ template <> struct treat_as_integral_arg<unsigned short> : std::true_type {};
 template <> struct treat_as_integral_arg<  signed short> : std::true_type {};
 template <> struct treat_as_integral_arg<unsigned  char> : std::true_type {};
 template <> struct treat_as_integral_arg<  signed  char> : std::true_type {};
-// QTBUG-126054, keep until we can fix it for all platforms, not just Windows
-// (where wchar_t does convert to QAnyStringView):
-template <> struct treat_as_integral_arg<wchar_t> : std::true_type {};
 }
 
 // Qt 4.x compatibility