Long live Q{Any,Utf8}StringView!

We need to add these two classes at the same time, because
QAnyStringView makes all QUtf8StringView relational operators moot. We
might want to add some later, esp. for UTF-8/UTf-8 comparisons, to
avoid the pessimization that we can't early-out on size() mismatch in
QAnyStringView equality operators, but that's an optimization, not a
correctness issue, and can be fixed in a source-compatible way even
after Qt 6 is released.

To deal with the char8_t problem in C++20, make QUtf8StringView a
class template out of which two UTF-8 views can be instantiated: the
Qt 7 version, which depends on C++20 char8_t as value_type, and the Qt
6 version where value_type is a char. Use inline namespaces to map the
QUtf8StringView identifier to one or the other, depending on the C++
version used to compile the user code. The inline namespace names must
needs be a bit ugly, as their inline'ness depends on __cpp_char8_t. If
we simply used q_v1/q_v2 we'd be blocking these names for Qt inline
namespaces forever, because it's likely that inline'ness of other
users of inline namespaces in Qt depends on things other than
__cpp_char8_t. While inline'ness of namespaces is, theoretically
speaking, a compile-time-only property, at least Clang warns about
mixed use of inline on a given namespace, so we need to bite the
bullet here. This is also the reason for the QT_BEGIN_..._NAMESPACE
macros: GCC is ok with the first declaration making a namespace
inline, while Clang warns upon re-opening an inline namespace as a
non-inline one.

[ChangeLog][QtCore][QUtf8StringView] New class.

[ChangeLog][QtCore][QAnyStringView] New class.

Change-Id: Ia7179760fca0e0b67d52f5accb0a62e389b17913
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

1 files changed, 26 insertions, 1 deletions

diff --git a/src/corelib/text/qstringalgorithms.h b/src/corelib/text/qstringalgorithms.h
index 28c0760b61..c0619ca8e5 100644
--- a/src/corelib/text/qstringalgorithms.h
+++ b/src/corelib/text/qstringalgorithms.h
@@ -48,9 +48,27 @@
 
 QT_BEGIN_NAMESPACE
 
+#ifdef __cpp_char8_t
+# define QT_BEGIN_HAS_CHAR8_T_NAMESPACE inline namespace q_has_char8_t {
+# define QT_BEGIN_NO_CHAR8_T_NAMESPACE namespace q_no_char8_t {
+#else
+# define QT_BEGIN_HAS_CHAR8_T_NAMESPACE namespace q_has_char8_t {
+# define QT_BEGIN_NO_CHAR8_T_NAMESPACE inline namespace q_no_char8_t {
+#endif
+#define QT_END_HAS_CHAR8_T_NAMESPACE }
+#define QT_END_NO_CHAR8_T_NAMESPACE }
+
+// declare namespaces:
+QT_BEGIN_HAS_CHAR8_T_NAMESPACE
+QT_END_HAS_CHAR8_T_NAMESPACE
+QT_BEGIN_NO_CHAR8_T_NAMESPACE
+QT_END_NO_CHAR8_T_NAMESPACE
+
 class QByteArray;
 class QLatin1String;
 class QStringView;
+template <bool> class QBasicUtf8StringView;
+class QAnyStringView;
 class QChar;
 
 namespace QtPrivate {
@@ -60,10 +78,15 @@ Q_REQUIRED_RESULT Q_CORE_EXPORT Q_DECL_PURE_FUNCTION const char16_t *qustrchr(QS
 
 Q_REQUIRED_RESULT Q_CORE_EXPORT Q_DECL_PURE_FUNCTION int compareStrings(QStringView   lhs, QStringView   rhs, Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
 Q_REQUIRED_RESULT Q_CORE_EXPORT Q_DECL_PURE_FUNCTION int compareStrings(QStringView   lhs, QLatin1String rhs, Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
+Q_REQUIRED_RESULT Q_CORE_EXPORT Q_DECL_PURE_FUNCTION int compareStrings(QStringView   lhs, QBasicUtf8StringView<false> rhs, Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
 Q_REQUIRED_RESULT Q_CORE_EXPORT Q_DECL_PURE_FUNCTION int compareStrings(QLatin1String lhs, QStringView   rhs, Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
 Q_REQUIRED_RESULT Q_CORE_EXPORT Q_DECL_PURE_FUNCTION int compareStrings(QLatin1String lhs, QLatin1String rhs, Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
-Q_REQUIRED_RESULT Q_CORE_EXPORT Q_DECL_PURE_FUNCTION int compareStringsUtf8(const char *, qsizetype, QStringView rhs, Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
+Q_REQUIRED_RESULT Q_CORE_EXPORT Q_DECL_PURE_FUNCTION int compareStrings(QLatin1String lhs, QBasicUtf8StringView<false> rhs, Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
+Q_REQUIRED_RESULT Q_CORE_EXPORT Q_DECL_PURE_FUNCTION int compareStrings(QBasicUtf8StringView<false> lhs, QStringView   rhs, Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
+Q_REQUIRED_RESULT Q_CORE_EXPORT Q_DECL_PURE_FUNCTION int compareStrings(QBasicUtf8StringView<false> lhs, QLatin1String rhs, Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
+Q_REQUIRED_RESULT Q_CORE_EXPORT Q_DECL_PURE_FUNCTION int compareStrings(QBasicUtf8StringView<false> lhs, QBasicUtf8StringView<false> rhs, Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
 
+Q_DECL_DEPRECATED inline int compareStringsUtf8(const char *lhs, qsizetype lhss, QStringView rhs, Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
 
 Q_REQUIRED_RESULT Q_CORE_EXPORT Q_DECL_PURE_FUNCTION bool startsWith(QStringView   haystack, QStringView   needle, Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
 Q_REQUIRED_RESULT Q_CORE_EXPORT Q_DECL_PURE_FUNCTION bool startsWith(QStringView   haystack, QLatin1String needle, Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
@@ -91,6 +114,8 @@ Q_REQUIRED_RESULT Q_CORE_EXPORT Q_DECL_PURE_FUNCTION QLatin1String trimmed(QLati
 Q_REQUIRED_RESULT Q_CORE_EXPORT Q_DECL_PURE_FUNCTION qsizetype count(QStringView haystack, QChar needle, Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
 Q_REQUIRED_RESULT Q_CORE_EXPORT Q_DECL_PURE_FUNCTION qsizetype count(QStringView haystack, QStringView needle, Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
 
+Q_REQUIRED_RESULT Q_CORE_EXPORT QString convertToQString(QAnyStringView s);
+
 Q_REQUIRED_RESULT Q_CORE_EXPORT QByteArray convertToLatin1(QStringView str);
 Q_REQUIRED_RESULT Q_CORE_EXPORT QByteArray convertToUtf8(QStringView str);
 Q_REQUIRED_RESULT Q_CORE_EXPORT QByteArray convertToLocal8Bit(QStringView str);