QLatin1String: add missing APIs for compatibility with Qt string views

As a drive-by, fixed misleading wording used in docs.

[ChangeLog][QtCore][Potentially Source-Incompatible Changes][QLatin1String]
Added QLatin1String(std::nullptr_t) constructor, which makes
QLatin1String(0) call ambiguous. To fix the ambiguity, nullptr
must be passed instead of 0.

Task-number: QTBUG-98433
Change-Id: I2b888aa23469343d78aa640dc39a6028b77165dd
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

3 files changed, 127 insertions, 28 deletions

diff --git a/src/corelib/text/qstring.cpp b/src/corelib/text/qstring.cpp
index f1ee16901b..ae5f57ce41 100644
--- a/src/corelib/text/qstring.cpp
+++ b/src/corelib/text/qstring.cpp
@@ -9108,6 +9108,14 @@ QString &QString::setRawData(const QChar *unicode, qsizetype size)
     \sa data(), isEmpty(), isNull(), {Distinction Between Null and Empty Strings}
 */
 
+/*! \fn QLatin1String::QLatin1String(std::nullptr_t)
+    \since 6.4
+
+    Constructs a QLatin1String object that stores a \nullptr.
+
+    \sa data(), isEmpty(), isNull(), {Distinction Between Null and Empty Strings}
+*/
+
 /*! \fn QLatin1String::QLatin1String(const char *str)
 
     Constructs a QLatin1String object that stores \a str.
@@ -9193,27 +9201,45 @@ QString &QString::setRawData(const QChar *unicode, qsizetype size)
 
 /*! \fn const char *QLatin1String::latin1() const
 
-    Returns the Latin-1 string stored in this object.
+    Returns the start of the Latin-1 string referenced by this object.
 */
 
 /*! \fn const char *QLatin1String::data() const
 
-    Returns the Latin-1 string stored in this object.
+    Returns the start of the Latin-1 string referenced by this object.
+*/
+
+/*! \fn const char *QLatin1String::constData() const
+    \since 6.4
+
+    Returns the start of the Latin-1 string referenced by this object.
+
+    This function is provided for compatibility with other Qt containers.
+
+    \sa data()
 */
 
 /*! \fn qsizetype QLatin1String::size() const
 
-    Returns the size of the Latin-1 string stored in this object.
+    Returns the size of the Latin-1 string referenced by this object.
 
     \note In version prior to Qt 6, this function returned \c{int},
     restricting the amount of data that could be held in a QLatin1String
     on 64-bit architectures.
 */
 
+/*! \fn qsizetype QLatin1String::length() const
+    \since 6.4
+
+    Same as size().
+
+    This function is provided for compatibility with other Qt containers.
+*/
+
 /*! \fn bool QLatin1String::isNull() const
     \since 5.10
 
-    Returns whether the Latin-1 string stored in this object is null
+    Returns whether the Latin-1 string referenced by this object is null
     (\c{data() == nullptr}) or not.
 
     \sa isEmpty(), data()
@@ -9222,12 +9248,23 @@ QString &QString::setRawData(const QChar *unicode, qsizetype size)
 /*! \fn bool QLatin1String::isEmpty() const
     \since 5.10
 
-    Returns whether the Latin-1 string stored in this object is empty
+    Returns whether the Latin-1 string referenced by this object is empty
     (\c{size() == 0}) or not.
 
     \sa isNull(), size()
 */
 
+/*! \fn bool QLatin1String::empty() const
+    \since 6.4
+
+    Returns whether the Latin-1 string referenced by this object is empty
+    (\c{size() == 0}) or not.
+
+    This function is provided for STL compatibility.
+
+    \sa isEmpty(), isNull(), size()
+*/
+
 /*! \fn QLatin1Char QLatin1String::at(qsizetype pos) const
     \since 5.8
 
@@ -9266,6 +9303,21 @@ QString &QString::setRawData(const QChar *unicode, qsizetype size)
 */
 
 /*!
+    \fn QLatin1Char QLatin1String::first() const
+    \since 6.4
+
+    Returns the first character in the string.
+    Same as \c{at(0)} or front().
+
+    This function is provided for compatibility with other Qt containers.
+
+    \warning Calling this function on an empty string constitutes
+    undefined behavior.
+
+    \sa last(), front(), back()
+*/
+
+/*!
     \fn QLatin1Char QLatin1String::back() const
     \since 5.10
 
@@ -9281,6 +9333,21 @@ QString &QString::setRawData(const QChar *unicode, qsizetype size)
 */
 
 /*!
+    \fn QLatin1Char QLatin1String::last() const
+    \since 6.4
+
+    Returns the last character in the string.
+    Same as \c{at(size() - 1)} or back().
+
+    This function is provided for compatibility with other Qt containers.
+
+    \warning Calling this function on an empty string constitutes
+    undefined behavior.
+
+    \sa first(), back(), front()
+*/
+
+/*!
     \fn int QLatin1String::compare(QStringView str, Qt::CaseSensitivity cs) const
     \fn int QLatin1String::compare(QLatin1String l1, Qt::CaseSensitivity cs) const
     \fn int QLatin1String::compare(QChar ch) const
@@ -9447,6 +9514,17 @@ QString &QString::setRawData(const QChar *unicode, qsizetype size)
 */
 
 /*!
+    \fn QLatin1String::const_iterator QLatin1String::constBegin() const
+    \since 6.4
+
+    Same as begin().
+
+    This function is provided for compatibility with other Qt containers.
+
+    \sa constEnd(), begin(), cbegin(), data()
+*/
+
+/*!
     \fn QLatin1String::const_iterator QLatin1String::end() const
     \since 5.10
 
@@ -9468,6 +9546,16 @@ QString &QString::setRawData(const QChar *unicode, qsizetype size)
     \sa cbegin(), end(), crend()
 */
 
+/*! \fn QLatin1String::const_iterator QLatin1String::constEnd() const
+    \since 6.4
+
+    Same as end().
+
+    This function is provided for compatibility with other Qt containers.
+
+    \sa constBegin(), end(), cend(), crend()
+*/
+
 /*!
     \fn QLatin1String::const_reverse_iterator QLatin1String::rbegin() const
     \since 5.10
diff --git a/src/corelib/text/qstring.h b/src/corelib/text/qstring.h
index 40e023be83..1c95b038c6 100644
--- a/src/corelib/text/qstring.h
+++ b/src/corelib/text/qstring.h
@@ -84,6 +84,7 @@ class QLatin1String
 {
 public:
     constexpr inline QLatin1String() noexcept : m_size(0), m_data(nullptr) {}
+    constexpr QLatin1String(std::nullptr_t) noexcept : QLatin1String() {}
     constexpr inline explicit QLatin1String(const char *s) noexcept : m_size(s ? qsizetype(strlen(s)) : 0), m_data(s) {}
     constexpr explicit QLatin1String(const char *f, const char *l)
         : QLatin1String(f, qsizetype(l - f)) {}
@@ -96,10 +97,20 @@ public:
     constexpr const char *latin1() const noexcept { return m_data; }
     constexpr qsizetype size() const noexcept { return m_size; }
     constexpr const char *data() const noexcept { return m_data; }
+    [[nodiscard]] constexpr const char *constData() const noexcept { return data(); }
+    [[nodiscard]] constexpr const char *constBegin() const noexcept { return begin(); }
+    [[nodiscard]] constexpr const char *constEnd() const noexcept { return end(); }
+
+    [[nodiscard]] constexpr QLatin1Char first() const { return front(); }
+    [[nodiscard]] constexpr QLatin1Char last() const { return back(); }
+
+    [[nodiscard]] constexpr qsizetype length() const noexcept { return size(); }
 
     constexpr bool isNull() const noexcept { return !data(); }
     constexpr bool isEmpty() const noexcept { return !size(); }
 
+    [[nodiscard]] constexpr bool empty() const noexcept { return size() == 0; }
+
     template <typename...Args>
     [[nodiscard]] inline QString arg(Args &&...args) const;
 
diff --git a/tests/auto/corelib/text/qstring/tst_qstring.cpp b/tests/auto/corelib/text/qstring/tst_qstring.cpp
index c295e96be4..52c0e07199 100644
--- a/tests/auto/corelib/text/qstring/tst_qstring.cpp
+++ b/tests/auto/corelib/text/qstring/tst_qstring.cpp
@@ -2670,7 +2670,7 @@ void tst_QString::insert_special_cases()
     QCOMPARE(a.insert(1, QLatin1String("ontr")), montreal);
     QCOMPARE(a.insert(4, ""), montreal);
     QCOMPARE(a.insert(3, QLatin1String("")), montreal);
-    QCOMPARE(a.insert(3, QLatin1String(0)), montreal);
+    QCOMPARE(a.insert(3, QLatin1String(nullptr)), montreal);
     QCOMPARE(a.insert(3, static_cast<const char *>(0)), montreal);
     QCOMPARE(a.insert(0, QLatin1String("a")), QLatin1String("aMontreal"));
 
@@ -4242,7 +4242,7 @@ void tst_QString::startsWith()
     QVERIFY( !a.startsWith(QLatin1String("C")) );
     QVERIFY( !a.startsWith(QLatin1String("ABCDEF")) );
     QVERIFY( a.startsWith(QLatin1String("")) );
-    QVERIFY( a.startsWith(QLatin1String(0)) );
+    QVERIFY( a.startsWith(QLatin1String(nullptr)) );
 
     QVERIFY( a.startsWith("A", Qt::CaseSensitive) );
     QVERIFY( a.startsWith("A", Qt::CaseInsensitive) );
@@ -4277,7 +4277,7 @@ void tst_QString::startsWith()
     QVERIFY( !a.startsWith(QLatin1String("c"), Qt::CaseInsensitive) );
     QVERIFY( !a.startsWith(QLatin1String("abcdef"), Qt::CaseInsensitive) );
     QVERIFY( a.startsWith(QLatin1String(""), Qt::CaseInsensitive) );
-    QVERIFY( a.startsWith(QLatin1String(0), Qt::CaseInsensitive) );
+    QVERIFY( a.startsWith(QLatin1String(nullptr), Qt::CaseInsensitive) );
     QVERIFY( a.startsWith('A', Qt::CaseSensitive) );
     QVERIFY( a.startsWith(QLatin1Char('A'), Qt::CaseSensitive) );
     QVERIFY( a.startsWith(QChar('A'), Qt::CaseSensitive) );
@@ -4298,7 +4298,7 @@ void tst_QString::startsWith()
     QVERIFY( !a.startsWith("ABC") );
 
     QVERIFY( a.startsWith(QLatin1String("")) );
-    QVERIFY( a.startsWith(QLatin1String(0)) );
+    QVERIFY( a.startsWith(QLatin1String(nullptr)) );
     QVERIFY( !a.startsWith(QLatin1String("ABC")) );
 
     QVERIFY( !a.startsWith(QLatin1Char(0)) );
@@ -4311,7 +4311,7 @@ void tst_QString::startsWith()
     QVERIFY( !a.startsWith("ABC") );
 
     QVERIFY( !a.startsWith(QLatin1String("")) );
-    QVERIFY( a.startsWith(QLatin1String(0)) );
+    QVERIFY( a.startsWith(QLatin1String(nullptr)) );
     QVERIFY( !a.startsWith(QLatin1String("ABC")) );
 
     QVERIFY( !a.startsWith(QLatin1Char(0)) );
@@ -4358,7 +4358,7 @@ void tst_QString::endsWith()
     QVERIFY( !a.endsWith(QLatin1String("C")) );
     QVERIFY( !a.endsWith(QLatin1String("ABCDEF")) );
     QVERIFY( a.endsWith(QLatin1String("")) );
-    QVERIFY( a.endsWith(QLatin1String(0)) );
+    QVERIFY( a.endsWith(QLatin1String(nullptr)) );
 
     QVERIFY( a.endsWith("B", Qt::CaseSensitive) );
     QVERIFY( a.endsWith("B", Qt::CaseInsensitive) );
@@ -4393,7 +4393,7 @@ void tst_QString::endsWith()
     QVERIFY( !a.endsWith(QLatin1String("c"), Qt::CaseInsensitive) );
     QVERIFY( !a.endsWith(QLatin1String("abcdef"), Qt::CaseInsensitive) );
     QVERIFY( a.endsWith(QLatin1String(""), Qt::CaseInsensitive) );
-    QVERIFY( a.endsWith(QLatin1String(0), Qt::CaseInsensitive) );
+    QVERIFY( a.endsWith(QLatin1String(nullptr), Qt::CaseInsensitive) );
     QVERIFY( a.endsWith('B', Qt::CaseSensitive) );
     QVERIFY( a.endsWith(QLatin1Char('B'), Qt::CaseSensitive) );
     QVERIFY( a.endsWith(QChar('B'), Qt::CaseSensitive) );
@@ -4407,7 +4407,7 @@ void tst_QString::endsWith()
     TEST_VIEW_ENDS_WITH(QLatin1String("C"), false);
     TEST_VIEW_ENDS_WITH(QLatin1String("ABCDEF"), false);
     TEST_VIEW_ENDS_WITH(QLatin1String(""), true);
-    TEST_VIEW_ENDS_WITH(QLatin1String(0), true);
+    TEST_VIEW_ENDS_WITH(QLatin1String(nullptr), true);
 #undef TEST_VIEW_ENDS_WITH
 
     a = "";
@@ -4419,7 +4419,7 @@ void tst_QString::endsWith()
     QVERIFY( !a.endsWith(QChar()) );
 
     QVERIFY( a.endsWith(QLatin1String("")) );
-    QVERIFY( a.endsWith(QLatin1String(0)) );
+    QVERIFY( a.endsWith(QLatin1String(nullptr)) );
     QVERIFY( !a.endsWith(QLatin1String("ABC")) );
 
     a = QString();
@@ -4428,7 +4428,7 @@ void tst_QString::endsWith()
     QVERIFY( !a.endsWith("ABC") );
 
     QVERIFY( !a.endsWith(QLatin1String("")) );
-    QVERIFY( a.endsWith(QLatin1String(0)) );
+    QVERIFY( a.endsWith(QLatin1String(nullptr)) );
     QVERIFY( !a.endsWith(QLatin1String("ABC")) );
 
     QVERIFY( !a.endsWith(QLatin1Char(0)) );
@@ -5736,8 +5736,8 @@ void tst_QString::operator_smaller()
     QVERIFY( foo > empty );
     QVERIFY( !(foo < empty) );
 
-    QVERIFY( !(null < QLatin1String(0)) );
-    QVERIFY( !(null > QLatin1String(0)) );
+    QVERIFY( !(null < QLatin1String(nullptr)) );
+    QVERIFY( !(null > QLatin1String(nullptr)) );
     QVERIFY( !(null < QLatin1String("")) );
     QVERIFY( !(null > QLatin1String("")) );
 
@@ -5746,28 +5746,28 @@ void tst_QString::operator_smaller()
     QVERIFY( !(empty < QLatin1String("")) );
     QVERIFY( !(empty > QLatin1String("")) );
 
-    QVERIFY( !(QLatin1String(0) < null) );
-    QVERIFY( !(QLatin1String(0) > null) );
+    QVERIFY( !(QLatin1String(nullptr) < null) );
+    QVERIFY( !(QLatin1String(nullptr) > null) );
     QVERIFY( !(QLatin1String("") < null) );
     QVERIFY( !(QLatin1String("") > null) );
 
-    QVERIFY( !(QLatin1String(0) < empty) );
-    QVERIFY( !(QLatin1String(0) > empty) );
+    QVERIFY( !(QLatin1String(nullptr) < empty) );
+    QVERIFY( !(QLatin1String(nullptr) > empty) );
     QVERIFY( !(QLatin1String("") < empty) );
     QVERIFY( !(QLatin1String("") > empty) );
 
-    QVERIFY( QLatin1String(0) < foo );
-    QVERIFY( !(QLatin1String(0) > foo) );
+    QVERIFY( QLatin1String(nullptr) < foo );
+    QVERIFY( !(QLatin1String(nullptr) > foo) );
     QVERIFY( QLatin1String("") < foo );
     QVERIFY( !(QLatin1String("") > foo) );
 
-    QVERIFY( foo > QLatin1String(0) );
-    QVERIFY( !(foo < QLatin1String(0)) );
+    QVERIFY( foo > QLatin1String(nullptr) );
+    QVERIFY( !(foo < QLatin1String(nullptr)) );
     QVERIFY( foo > QLatin1String("") );
     QVERIFY( !(foo < QLatin1String("")) );
 
-    QVERIFY( QLatin1String(0) == empty);
-    QVERIFY( QLatin1String(0) == null);
+    QVERIFY( QLatin1String(nullptr) == empty);
+    QVERIFY( QLatin1String(nullptr) == null);
     QVERIFY( QLatin1String("") == empty);
     QVERIFY( QLatin1String("") == null);
 
@@ -7580,7 +7580,7 @@ void tst_QString::assignQLatin1String()
     QVERIFY(empty.isEmpty());
     QVERIFY(!empty.isNull());
 
-    QString null = QLatin1String(0);
+    QString null = QLatin1String(nullptr);
     QVERIFY(null.isEmpty());
     QVERIFY(null.isNull());