Introduce QT_NO_QSNPRINTF and mark QtCore as qsnprintf-free

... except, of course, the implementation file, which therefore has to
be excluded from PCH'ed builds.

Remove qvsnprintf.cpp from libbootstrap, as it's no longer needed
after porting all five uses of qsnprintf() in QtCore to C++11's
std::snprintf(), which even Windows implements with std behavior.

The reason we're removing the function is that std::snprintf() is the
better alternative: qsnprintf() just introduces even more platform
variance than any implementation-defined behavior of C or C++
snprintf().

To wit:

- On Windows, the return value is sometimes "wrong"
  (cf. Windows-specific qsnprintf() tests in tst_qbytearray.cpp)

- On WASM and at least some Android configurations, it is incorrectly
  implmented using the QString::asprintf().toLocal8Bit() work-around,
  even though both platforms have a working snprintf().
  QString::asprintf() is implemented in Qt itself, so has some
  differences:

  - the `a` format for hex floats is not supported

  - %ls expects char16_t*, not wchar_t* (these are, in general, not
     the same width)

We will deprecate these functions in 6.9, but before we do, we need to
get the Qt code in order, and that's where this macro comes in.

[ChangeLog][QtCore] Added the QT_NO_QSNPRINTF macro to disable
qsnprintf() and qvsnprintf(), which will also be deprecated in 6.9.
See the documentation for details why we take this step.

Task-number: QTBUG-127110
Pick-to: 6.8
Change-Id: I4e1c1f213bcfd615f83387f5f51e77fa1ff2062e
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/corelib/CMakeLists.txt

@@ -335,6 +335,7 @@ qt_internal_add_module(Core
         QT_NO_CONTEXTLESS_CONNECT
         QT_NO_FOREACH
         QT_NO_QPAIR
+        QT_NO_QSNPRINTF
         QT_NO_USING_NAMESPACE
         QT_TYPESAFE_FLAGS
         QT_USE_NODISCARD_FILE_OPEN

src/corelib/global/qglobal.cpp

@@ -361,6 +361,7 @@ bool QInternal::activateCallbacks(Callback cb, void **parameters)
     \row \li 6.7.0 \li Overloads of QObject::connect that do not take a context object (see \l{QT_NO_CONTEXTLESS_CONNECT})
     \row \li 6.8.0 \li The qAsConst() function (see \l{QT_NO_QASCONST})
     \row \li 6.8.0 \li File-related I/O classes have their \c{open()} functions marked \c{[[nodiscard]]} (see \l{QT_USE_NODISCARD_FILE_OPEN})
+    \row\li  6.9.0 \li The qsnprintf() and qvnprintf() functions (see \l{QT_NO_QSNPRINTF}).
     \endtable
 
     Moreover, individual APIs may also get disabled as part of the

src/corelib/global/qtconfigmacros.h

@@ -205,6 +205,10 @@ namespace QT_NAMESPACE {}
 #    define QT_USE_NODISCARD_FILE_OPEN
 #  endif
 #endif // 6.8.0
+
+#if QT_ENABLE_STRICT_MODE_UP_TO >= QT_VERSION_CHECK(6, 9, 0)
+#  define QT_NO_QSNPRINTF
+#endif // 6.9.0
 #endif // QT_ENABLE_STRICT_MODE_UP_TO
 
 #endif /* QTCONFIGMACROS_H */

src/corelib/io/qdebug.cpp

@@ -11,6 +11,7 @@
 
 #include <array>
 #include <q20chrono.h>
+#include <cstdio>
 
 QT_BEGIN_NAMESPACE
 
@@ -406,9 +407,9 @@ static QByteArray timeUnit(qint64 num, qint64 den)
     };
     auto appendNumber = [&](qint64 value) {
         if (value >= 10'000 && (value % 1000) == 0)
-            len += qsnprintf(buf + len, sizeof(buf) - len, "%.6g", double(value));  // "1e+06"
+            len += std::snprintf(buf + len, sizeof(buf) - len, "%.6g", double(value));  // "1e+06"
         else
-            len += qsnprintf(buf + len, sizeof(buf) - len, "%lld", value);
+            len += std::snprintf(buf + len, sizeof(buf) - len, "%lld", value);
     };
     appendChar('[');
     appendNumber(num);

src/corelib/io/qfilesystemengine_win.cpp

@@ -37,6 +37,8 @@
 #define SECURITY_WIN32
 #include <security.h>
 
+#include <cstdio>
+
 #include <QtCore/private/qfunctions_win_p.h>
 
 #ifndef SPI_GETPLATFORMTYPE
@@ -1010,10 +1012,10 @@ static inline QByteArray fileId(HANDLE handle)
     BY_HANDLE_FILE_INFORMATION info;
     if (GetFileInformationByHandle(handle, &info)) {
         char buffer[sizeof "01234567:0123456701234567"];
-        qsnprintf(buffer, sizeof(buffer), "%lx:%08lx%08lx",
-                  info.dwVolumeSerialNumber,
-                  info.nFileIndexHigh,
-                  info.nFileIndexLow);
+        std::snprintf(buffer, sizeof(buffer), "%lx:%08lx%08lx",
+                      info.dwVolumeSerialNumber,
+                      info.nFileIndexHigh,
+                      info.nFileIndexLow);
         return buffer;
     }
     return QByteArray();

src/corelib/kernel/qeventdispatcher_unix.cpp

@@ -14,6 +14,8 @@
 #include <private/qcoreapplication_p.h>
 #include <private/qcore_unix_p.h>
 
+#include <cstdio>
+
 #include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -87,7 +89,7 @@ bool QThreadPipe::init()
 #if defined(Q_OS_WASM)
     // do nothing.
 #elif defined(Q_OS_VXWORKS)
-    qsnprintf(name, sizeof(name), "/pipe/qt_%08x", int(taskIdSelf()));
+    std::snprintf(name, sizeof(name), "/pipe/qt_%08x", int(taskIdSelf()));
 
     // make sure there is no pipe with this name
     pipeDevDelete(name, true);

src/corelib/text/qbytearrayalgorithms.h

@@ -138,11 +138,13 @@ Q_CORE_EXPORT int qstricmp(const char *, const char *);
 Q_CORE_EXPORT int qstrnicmp(const char *, const char *, size_t len);
 Q_CORE_EXPORT int qstrnicmp(const char *, qsizetype, const char *, qsizetype = -1);
 
+#ifndef QT_NO_QSNPRINTF // use std::(v)snprintf() from <cstdio> instead
 // implemented in qvsnprintf.cpp
 Q_CORE_EXPORT int qvsnprintf(char *str, size_t n, const char *fmt, va_list ap)
     Q_ATTRIBUTE_FORMAT_PRINTF(3, 0);
 Q_CORE_EXPORT int qsnprintf(char *str, size_t n, const char *fmt, ...)
     Q_ATTRIBUTE_FORMAT_PRINTF(3, 4);
+#endif // QT_NO_QSNPRINTF
 
 // qChecksum: Internet checksum
 Q_CORE_EXPORT quint16 qChecksum(QByteArrayView data, Qt::ChecksumType standard = Qt::ChecksumIso3309);

src/corelib/text/qlocale_tools.cpp

@@ -10,6 +10,8 @@
 #include <private/qtools_p.h>
 #include <private/qnumeric_p.h>
 
+#include <cstdio>
+
 #include <ctype.h>
 #include <errno.h>
 #include <float.h>
@@ -324,7 +326,8 @@ QSimpleParsedNumber<double> qt_asciiToDouble(const char *num, qsizetype numLen,
     constexpr auto maxDigitsForULongLong = 1 + std::numeric_limits<unsigned long long>::digits10;
     // need to ensure that we don't read more than numLen of input:
     char fmt[1 + maxDigitsForULongLong + 4 + 1];
-    qsnprintf(fmt, sizeof fmt, "%s%llu%s", "%", static_cast<unsigned long long>(numLen), "lf%n");
+    std::snprintf(fmt, sizeof fmt, "%s%llu%s",
+                  "%", static_cast<unsigned long long>(numLen), "lf%n");
 
     if (qDoubleSscanf(num, QT_CLOCALE, fmt, &d, &processed) < 1)
         processed = 0;

src/corelib/text/qvsnprintf.cpp

@@ -10,9 +10,22 @@
 
 QT_BEGIN_NAMESPACE
 
+/*!
+    \macro QT_NO_QSNPRINTF
+    \since 6.8
+    \relates QByteArray
+
+    Defining this macro removes the availability of the qsnprintf() and
+    qvsnprintf() functions. See the functions' documentation for why you may
+    want to disable them.
+
+    \sa qsnprintf(), qvsnprintf().
+*/
+
 #if !defined(QT_VSNPRINTF) || defined(Q_QDOC)
 
 /*!
+    \fn int qvsnprintf(char *str, size_t n, const char *fmt, va_list ap)
     \relates QByteArray
 
     \obsolete
@@ -40,6 +53,7 @@ QT_BEGIN_NAMESPACE
     \sa qsnprintf(), QString::asprintf()
 */
 
+Q_CORE_EXPORT // QT_NO_QSNPRINTF is in effect
 int qvsnprintf(char *str, size_t n, const char *fmt, va_list ap)
 {
     if (!str || !fmt)
@@ -62,6 +76,7 @@ QT_BEGIN_INCLUDE_NAMESPACE
 #include <stdio.h>
 QT_END_INCLUDE_NAMESPACE
 
+Q_CORE_EXPORT // QT_NO_QSNPRINTF is in effect
 int qvsnprintf(char *str, size_t n, const char *fmt, va_list ap)
 {
     return QT_VSNPRINTF(str, n, fmt, ap);
@@ -70,6 +85,7 @@ int qvsnprintf(char *str, size_t n, const char *fmt, va_list ap)
 #endif
 
 /*!
+    \fn int qsnprintf(char *str, size_t n, const char *fmt, ...)
     \target bytearray-qsnprintf
     \relates QByteArray
 
@@ -89,6 +105,7 @@ int qvsnprintf(char *str, size_t n, const char *fmt, va_list ap)
     \sa qvsnprintf(), QString::asprintf()
 */
 
+Q_CORE_EXPORT // QT_NO_QSNPRINTF is in effect
 int qsnprintf(char *str, size_t n, const char *fmt, ...)
 {
     va_list ap;

src/tools/bootstrap/CMakeLists.txt

@@ -61,7 +61,6 @@ qt_internal_extend_target(Bootstrap
         ../../corelib/text/qstringbuilder.cpp
         ../../corelib/text/qstringconverter.cpp
         ../../corelib/text/qstringlist.cpp
-        ../../corelib/text/qvsnprintf.cpp
         ../../corelib/time/qcalendar.cpp
         ../../corelib/time/qdatetime.cpp
         ../../corelib/time/qgregoriancalendar.cpp