QString: towards QStringView::arg() pt.3: Long live QStringView/QLatin1String::arg()

This version of arg(), unlike its QString counterpart, transparently accepts
views without conversion to QString, and is also extensible to further argument
types, say a future QFormattedNumber.

[ChangeLog][QtCore][QStringView/QLatin1String] Added arg(), taking arbitrarily
many strings.

Change-Id: If40ef3c445f63383e32573f3f515fdda84c7fe3a
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qstring.cpp

@@ -8754,19 +8754,23 @@ QString QString::arg(double a, int fieldWidth, char fmt, int prec, QChar fillCha
     return replaceArgEscapes(*this, d, fieldWidth, arg, locale_arg, fillChar);
 }
 
-static int getEscape(const QChar *uc, qsizetype *pos, qsizetype len, int maxNumber = 999)
+static inline ushort to_unicode(const QChar c) { return c.unicode(); }
+static inline ushort to_unicode(const char c) { return QLatin1Char{c}.unicode(); }
+
+template <typename Char>
+static int getEscape(const Char *uc, qsizetype *pos, qsizetype len, int maxNumber = 999)
 {
     int i = *pos;
     ++i;
     if (i < len && uc[i] == QLatin1Char('L'))
         ++i;
     if (i < len) {
-        int escape = uc[i].unicode() - '0';
+        int escape = to_unicode(uc[i]) - '0';
         if (uint(escape) >= 10U)
             return -1;
         ++i;
         while (i < len) {
-            int digit = uc[i].unicode() - '0';
+            int digit = to_unicode(uc[i]) - '0';
             if (uint(digit) >= 10U)
                 break;
             escape = (escape * 10) + digit;
@@ -8817,18 +8821,23 @@ static int getEscape(const QChar *uc, qsizetype *pos, qsizetype len, int maxNumb
 namespace {
 struct Part
 {
-    Q_DECL_CONSTEXPR Part() : string{}, number{0} {}
+    Part() = default; // for QVarLengthArray; do not use
     Q_DECL_CONSTEXPR Part(QStringView s, int num = -1)
-        : string{s}, number{num} {}
+        : tag{QtPrivate::ArgBase::U16}, number{num}, data{s.utf16()}, size{s.size()} {}
+    Q_DECL_CONSTEXPR Part(QLatin1String s, int num = -1)
+        : tag{QtPrivate::ArgBase::L1}, number{num}, data{s.data()}, size{s.size()} {}
 
-    QStringView string;
+    void reset(QStringView s) noexcept { *this = {s, number}; }
+    void reset(QLatin1String s) noexcept { *this = {s, number}; }
+
+    QtPrivate::ArgBase::Tag tag;
     int number;
+    const void *data;
+    qsizetype size;
 };
 } // unnamed namespace
 
-template <>
+Q_DECLARE_TYPEINFO(Part, Q_PRIMITIVE_TYPE);
-class QTypeInfo<Part> : public QTypeInfoMerger<Part, QStringView, int> {}; // Q_DECLARE_METATYPE
-
 
 namespace {
 
@@ -8837,7 +8846,8 @@ enum { ExpectedParts = 32 };
 typedef QVarLengthArray<Part, ExpectedParts> ParseResult;
 typedef QVarLengthArray<int, ExpectedParts/2> ArgIndexToPlaceholderMap;
 
-static ParseResult parseMultiArgFormatString(QStringView s)
+template <typename StringView>
+static ParseResult parseMultiArgFormatString(StringView s)
 {
     ParseResult result;
 
@@ -8884,16 +8894,29 @@ static ArgIndexToPlaceholderMap makeArgIndexToPlaceholderMap(const ParseResult &
     return result;
 }
 
-static qsizetype resolveStringRefsAndReturnTotalSize(ParseResult &parts, const ArgIndexToPlaceholderMap &argIndexToPlaceholderMap, const QString *args[])
+static qsizetype resolveStringRefsAndReturnTotalSize(ParseResult &parts, const ArgIndexToPlaceholderMap &argIndexToPlaceholderMap, const QtPrivate::ArgBase *args[])
 {
+    using namespace QtPrivate;
     qsizetype totalSize = 0;
     for (Part &part : parts) {
         if (part.number != -1) {
             const auto it = std::find(argIndexToPlaceholderMap.begin(), argIndexToPlaceholderMap.end(), part.number);
-            if (it != argIndexToPlaceholderMap.end())
+            if (it != argIndexToPlaceholderMap.end()) {
-                part.string = *args[it - argIndexToPlaceholderMap.begin()];
+                const auto &arg = *args[it - argIndexToPlaceholderMap.begin()];
+                switch (arg.tag) {
+                case ArgBase::L1:
+                    part.reset(static_cast<const QLatin1StringArg&>(arg).string);
+                    break;
+                case ArgBase::U8:
+                    Q_UNREACHABLE(); // waiting for QUtf8String...
+                    break;
+                case ArgBase::U16:
+                    part.reset(static_cast<const QStringViewArg&>(arg).string);
+                    break;
                 }
-        totalSize += part.string.size();
+            }
+        }
+        totalSize += part.size;
     }
     return totalSize;
 }
@@ -8901,18 +8924,35 @@ static qsizetype resolveStringRefsAndReturnTotalSize(ParseResult &parts, const A
 } // unnamed namespace
 
 QString QString::multiArg(int numArgs, const QString **args) const
+{
+    QVarLengthArray<QtPrivate::QStringViewArg, 9> sva;
+    sva.reserve(numArgs);
+    QVarLengthArray<const QtPrivate::ArgBase *, 9> pointers;
+    pointers.reserve(numArgs);
+    for (int i = 0; i < numArgs; ++i) {
+        sva.push_back(QtPrivate::qStringLikeToArg(*args[i]));
+        pointers.push_back(&sva.back());
+    }
+    return QtPrivate::argToQString(qToStringViewIgnoringNull(*this), static_cast<size_t>(numArgs), pointers.data());
+}
+
+Q_ALWAYS_INLINE QString to_string(QLatin1String s) noexcept { return s; }
+Q_ALWAYS_INLINE QString to_string(QStringView s) noexcept { return s.toString(); }
+
+template <typename StringView>
+static QString argToQStringImpl(StringView pattern, size_t numArgs, const QtPrivate::ArgBase **args)
 {
     // Step 1-2 above
-    ParseResult parts = parseMultiArgFormatString(qToStringViewIgnoringNull(*this));
+    ParseResult parts = parseMultiArgFormatString(pattern);
 
     // 3-4
     ArgIndexToPlaceholderMap argIndexToPlaceholderMap = makeArgIndexToPlaceholderMap(parts);
 
-    if (argIndexToPlaceholderMap.size() > numArgs) // 3a
+    if (static_cast<size_t>(argIndexToPlaceholderMap.size()) > numArgs) // 3a
-        argIndexToPlaceholderMap.resize(numArgs);
+        argIndexToPlaceholderMap.resize(int(numArgs));
-    else if (argIndexToPlaceholderMap.size() < numArgs) // 3b
+    else if (Q_UNLIKELY(static_cast<size_t>(argIndexToPlaceholderMap.size()) < numArgs)) // 3b
-        qWarning("QString::arg: %d argument(s) missing in %s",
+        qWarning("QString::arg: %d argument(s) missing in %ls",
-                 numArgs - argIndexToPlaceholderMap.size(), toLocal8Bit().data());
+                 int(numArgs - argIndexToPlaceholderMap.size()), qUtf16Printable(to_string(pattern)));
 
     // 5
     const qsizetype totalSize = resolveStringRefsAndReturnTotalSize(parts, argIndexToPlaceholderMap, args);
@@ -8922,15 +8962,37 @@ QString QString::multiArg(int numArgs, const QString **args) const
     auto out = const_cast<QChar*>(result.constData());
 
     for (Part part : parts) {
-        if (const qsizetype sz = part.string.size()) {
+        switch (part.tag) {
-            memcpy(out, part.string.data(), sz * sizeof(QChar));
+        case QtPrivate::ArgBase::L1:
-            out += sz;
+            if (part.size) {
+                qt_from_latin1(reinterpret_cast<ushort*>(out),
+                               reinterpret_cast<const char*>(part.data), part.size);
             }
+            break;
+        case QtPrivate::ArgBase::U8:
+            Q_UNREACHABLE(); // waiting for QUtf8String
+            break;
+        case QtPrivate::ArgBase::U16:
+            if (part.size)
+                memcpy(out, part.data, part.size * sizeof(QChar));
+            break;
+        }
+        out += part.size;
     }
 
     return result;
 }
 
+QString QtPrivate::argToQString(QStringView pattern, size_t n, const ArgBase **args)
+{
+    return argToQStringImpl(pattern, n, args);
+}
+
+QString QtPrivate::argToQString(QLatin1String pattern, size_t n, const ArgBase **args)
+{
+    return argToQStringImpl(pattern, n, args);
+}
+
 /*! \fn bool QString::isSimpleText() const
 
     \internal

src/corelib/tools/qstring.h

@@ -106,6 +106,9 @@ public:
     Q_DECL_CONSTEXPR bool isNull() const noexcept { return !data(); }
     Q_DECL_CONSTEXPR bool isEmpty() const noexcept { return !size(); }
 
+    template <typename...Args>
+    Q_REQUIRED_RESULT inline QString arg(Args &&...args) const;
+
     Q_DECL_CONSTEXPR QLatin1Char at(int i) const
     { return Q_ASSERT(i >= 0), Q_ASSERT(i < size()), QLatin1Char(m_data[i]); }
     Q_DECL_CONSTEXPR QLatin1Char operator[](int i) const { return at(i); }
@@ -1979,6 +1982,58 @@ inline const QString &asString(const QString &s)    { return s; }
 inline QString &&asString(QString &&s)              { return std::move(s); }
 }
 
+//
+// QStringView::arg() implementation
+//
+
+namespace QtPrivate {
+
+struct ArgBase {
+    enum Tag : uchar { L1, U8, U16 } tag;
+};
+
+struct QStringViewArg : ArgBase {
+    QStringView string;
+    QStringViewArg() = default;
+    Q_DECL_CONSTEXPR explicit QStringViewArg(QStringView v) noexcept : ArgBase{U16}, string{v} {}
+};
+
+struct QLatin1StringArg : ArgBase {
+    QLatin1String string;
+    QLatin1StringArg() = default;
+    Q_DECL_CONSTEXPR explicit QLatin1StringArg(QLatin1String v) noexcept : ArgBase{L1}, string{v} {}
+};
+
+Q_REQUIRED_RESULT Q_CORE_EXPORT QString argToQString(QStringView pattern, size_t n, const ArgBase **args);
+Q_REQUIRED_RESULT Q_CORE_EXPORT QString argToQString(QLatin1String pattern, size_t n, const ArgBase **args);
+
+template <typename StringView, typename...Args>
+Q_REQUIRED_RESULT Q_ALWAYS_INLINE QString argToQStringDispatch(StringView pattern, const Args &...args)
+{
+    const ArgBase *argBases[] = {&args..., /* avoid zero-sized array */ nullptr};
+    return QtPrivate::argToQString(pattern, sizeof...(Args), argBases);
+}
+
+Q_DECL_CONSTEXPR inline QStringViewArg   qStringLikeToArg(QStringView s) noexcept { return QStringViewArg{s}; }
+                 inline QStringViewArg   qStringLikeToArg(const QChar &c) noexcept { return QStringViewArg{QStringView{&c, 1}}; }
+Q_DECL_CONSTEXPR inline QLatin1StringArg qStringLikeToArg(QLatin1String s) noexcept { return QLatin1StringArg{s}; }
+
+} // namespace QtPrivate
+
+template <typename...Args>
+Q_ALWAYS_INLINE
+QString QStringView::arg(Args &&...args) const
+{
+    return QtPrivate::argToQStringDispatch(*this, QtPrivate::qStringLikeToArg(args)...);
+}
+
+template <typename...Args>
+Q_ALWAYS_INLINE
+QString QLatin1String::arg(Args &&...args) const
+{
+    return QtPrivate::argToQStringDispatch(*this, QtPrivate::qStringLikeToArg(args)...);
+}
+
 QT_END_NAMESPACE
 
 #if defined(QT_USE_FAST_OPERATOR_PLUS) || defined(QT_USE_QSTRINGBUILDER)

src/corelib/tools/qstringview.cpp

@@ -529,6 +529,24 @@ QT_BEGIN_NAMESPACE
     \sa operator[](), front(), back()
 */
 
+/*!
+    \fn QString QStringView::arg(Args &&...args) const
+    \fn QString QLatin1String::arg(Args &&...args) const
+    \since 5.14
+
+    Replaces occurrences of \c{%N} in this string with the corresponding
+    argument from \a args. The arguments are not positional: the first of
+    the \a args replaces the \c{%N} with the lowest \c{N} (all of them), the
+    second of the \a args the \c{%N} with the next-lowest \c{N} etc.
+
+    \c Args can consist of anything that implicitly converts to QStringView
+    or QLatin1String.
+
+    In addition, the following types are also supported: QChar, QLatin1Char.
+
+    \sa QString::arg()
+*/
+
 /*!
     \fn QChar QStringView::front() const
 

src/corelib/tools/qstringview.h

@@ -226,6 +226,9 @@ public:
     // QString API
     //
 
+    template <typename...Args>
+    Q_REQUIRED_RESULT inline QString arg(Args &&...args) const; // defined in qstring.h
+
     Q_REQUIRED_RESULT QByteArray toLatin1() const { return QtPrivate::convertToLatin1(*this); }
     Q_REQUIRED_RESULT QByteArray toUtf8() const { return QtPrivate::convertToUtf8(*this); }
     Q_REQUIRED_RESULT QByteArray toLocal8Bit() const { return QtPrivate::convertToLocal8Bit(*this); }

tests/auto/corelib/tools/qlatin1string/tst_qlatin1string.cpp

@@ -45,6 +45,7 @@ class tst_QLatin1String : public QObject
 
 private Q_SLOTS:
     void at();
+    void arg() const;
     void midLeftRight();
     void nullString();
     void emptyString();
@@ -63,6 +64,47 @@ void tst_QLatin1String::at()
     QCOMPARE(l1[l1.size() - 1], QLatin1Char('d'));
 }
 
+void tst_QLatin1String::arg() const
+{
+#define CHECK1(pattern, arg1, expected) \
+    do { \
+        auto p = QLatin1String(pattern); \
+        QCOMPARE(p.arg(QLatin1String(arg1)), expected); \
+        QCOMPARE(p.arg(QStringViewLiteral(arg1)), expected); \
+        QCOMPARE(p.arg(QStringLiteral(arg1)), expected); \
+        QCOMPARE(p.arg(QString(QLatin1String(arg1))), expected); \
+    } while (false) \
+    /*end*/
+#define CHECK2(pattern, arg1, arg2, expected) \
+    do { \
+        auto p = QLatin1String(pattern); \
+        QCOMPARE(p.arg(QLatin1String(arg1), QLatin1String(arg2)), expected); \
+        QCOMPARE(p.arg(QStringViewLiteral(arg1), QLatin1String(arg2)), expected); \
+        QCOMPARE(p.arg(QLatin1String(arg1), QStringViewLiteral(arg2)), expected); \
+        QCOMPARE(p.arg(QStringViewLiteral(arg1), QStringViewLiteral(arg2)), expected); \
+    } while (false) \
+    /*end*/
+
+    CHECK1("", "World", "");
+    CHECK1("%1", "World", "World");
+    CHECK1("!%1?", "World", "!World?");
+    CHECK1("%1%1", "World", "WorldWorld");
+    CHECK1("%1%2", "World", "World%2");
+    CHECK1("%2%1", "World", "%2World");
+
+    CHECK2("", "Hello", "World", "");
+    CHECK2("%1", "Hello", "World", "Hello");
+    CHECK2("!%1, %2?", "Hello", "World", "!Hello, World?");
+    CHECK2("%1%1", "Hello", "World", "HelloHello");
+    CHECK2("%1%2", "Hello", "World", "HelloWorld");
+    CHECK2("%2%1", "Hello", "World", "WorldHello");
+
+#undef CHECK2
+#undef CHECK1
+
+    QCOMPARE(QLatin1String(" %2 %2 %1 %3 ").arg(QLatin1Char('c'), QChar::CarriageReturn, u'C'), " \r \r c C ");
+}
+
 void tst_QLatin1String::midLeftRight()
 {
     const QLatin1String l1("Hello World");

tests/auto/corelib/tools/qstringview/tst_qstringview.cpp

@@ -134,6 +134,8 @@ private Q_SLOTS:
     void literals() const;
     void at() const;
 
+    void arg() const;
+
     void fromQString() const;
     void fromQStringRef() const;
 
@@ -425,6 +427,47 @@ void tst_QStringView::at() const
     QCOMPARE(sv.at(4), QChar('o')); QCOMPARE(sv[4], QChar('o'));
 }
 
+void tst_QStringView::arg() const
+{
+#define CHECK1(pattern, arg1, expected) \
+    do { \
+        auto p = QStringViewLiteral(pattern); \
+        QCOMPARE(p.arg(QLatin1String(arg1)), expected); \
+        QCOMPARE(p.arg(QStringViewLiteral(arg1)), expected); \
+        QCOMPARE(p.arg(QStringLiteral(arg1)), expected); \
+        QCOMPARE(p.arg(QString(QLatin1String(arg1))), expected); \
+    } while (false) \
+    /*end*/
+#define CHECK2(pattern, arg1, arg2, expected) \
+    do { \
+        auto p = QStringViewLiteral(pattern); \
+        QCOMPARE(p.arg(QLatin1String(arg1), QLatin1String(arg2)), expected); \
+        QCOMPARE(p.arg(QStringViewLiteral(arg1), QLatin1String(arg2)), expected); \
+        QCOMPARE(p.arg(QLatin1String(arg1), QStringViewLiteral(arg2)), expected); \
+        QCOMPARE(p.arg(QStringViewLiteral(arg1), QStringViewLiteral(arg2)), expected); \
+    } while (false) \
+    /*end*/
+
+    CHECK1("", "World", "");
+    CHECK1("%1", "World", "World");
+    CHECK1("!%1?", "World", "!World?");
+    CHECK1("%1%1", "World", "WorldWorld");
+    CHECK1("%1%2", "World", "World%2");
+    CHECK1("%2%1", "World", "%2World");
+
+    CHECK2("", "Hello", "World", "");
+    CHECK2("%1", "Hello", "World", "Hello");
+    CHECK2("!%1, %2?", "Hello", "World", "!Hello, World?");
+    CHECK2("%1%1", "Hello", "World", "HelloHello");
+    CHECK2("%1%2", "Hello", "World", "HelloWorld");
+    CHECK2("%2%1", "Hello", "World", "WorldHello");
+
+#undef CHECK2
+#undef CHECK1
+
+    QCOMPARE(QStringViewLiteral(" %2 %2 %1 %3 ").arg(QLatin1Char('c'), QChar::CarriageReturn, u'C'), " \r \r c C ");
+}
+
 void tst_QStringView::fromQString() const
 {
     QString null;