Android: Fix logging of the category

87d8ee755bfdef8e72a122789c2e3ed382881a12 changed the logging behavior
on Android to use the category as tag. But it was missed that
`formatLogMessage` only fills the fields given in the messagePattern.
Our default messagePattern includes the category but on Android it
is never filled since this change.

So we change the default messagePattern on Android to omit the category
and only use the category as tag when the category is not given in the
messagePattern.

Pick-to: 6.5
Task-number: QTBUG-94708
Change-Id: I80f65d0f7f8c0ca9c2fff2dcd63d4599848b6e2b
Reviewed-by: Assam Boudjelthia <assam.boudjelthia@qt.io>
(cherry picked from commit 709bc29a1d2abf40bf3f1c067fe3b96b6e0c09d0)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/doc/src/external-resources.qdoc

@@ -181,3 +181,13 @@
     \externalpage https://developer.android.com/develop/connectivity/bluetooth/bt-permissions
     \title Android Bluetooth Permissions
 */
+
+/*!
+    \externalpage https://developer.android.com/reference/android/util/Log
+    \title Android: Log
+*/
+
+/*!
+    \externalpage https://developer.android.com/ndk/reference/group/logging#__android_log_print
+    \title Android: log_print
+*/

src/corelib/global/qlogging.cpp

@@ -1130,7 +1130,11 @@ static const char ifFatalTokenC[] = "%{if-fatal}";
 static const char endifTokenC[] = "%{endif}";
 static const char emptyTokenC[] = "";
 
+#ifdef Q_OS_ANDROID
+static const char defaultPattern[] = "%{message}";
+#else
 static const char defaultPattern[] = "%{if-category}%{category}: %{endif}%{message}";
+#endif
 
 struct QMessagePattern
 {
@@ -1158,6 +1162,18 @@ struct QMessagePattern
 
     bool fromEnvironment;
     static QBasicMutex mutex;
+
+#ifdef Q_OS_ANDROID
+    bool containsToken(const char *token) const
+    {
+        for (int i = 0; tokens[i]; ++i) {
+            if (tokens[i] == token)
+                return true;
+        }
+
+        return false;
+    }
+#endif
 };
 #ifdef QLOGGING_HAVE_BACKTRACE
 Q_DECLARE_TYPEINFO(QMessagePattern::BacktraceParams, Q_RELOCATABLE_TYPE);
@@ -1619,10 +1635,7 @@ static QString formatLogMessage(QtMsgType type, const QMessageLogContext &contex
         } else if (token == messageTokenC) {
             message.append(str);
         } else if (token == categoryTokenC) {
-#ifndef Q_OS_ANDROID
-            // Don't add the category to the message on Android
             message.append(QLatin1StringView(context.category));
-#endif
         } else if (token == typeTokenC) {
             switch (type) {
             case QtDebugMsg:   message.append("debug"_L1); break;
@@ -1878,11 +1891,12 @@ static bool android_default_message_handler(QtMsgType type,
         break;
     };
 
+    QMessagePattern *pattern = qMessagePattern();
+    const QString tag = (pattern && pattern->containsToken(categoryTokenC))
         // If application name is a tag ensure it has no spaces
-    // If a category is defined, use it as an Android logging tag
-    __android_log_print(priority, isDefaultCategory(context.category) ?
-                        qPrintable(QCoreApplication::applicationName().replace(u' ', u'_')) : context.category,
-                        "%s\n", qPrintable(formattedMessage));
+        ? QCoreApplication::applicationName().replace(u' ', u'_')
+        : QString::fromUtf8(context.category);
+    __android_log_print(priority, qPrintable(tag), "%s\n", qPrintable(formattedMessage));
 
     return true; // Prevent further output to stderr
 }
@@ -2299,6 +2313,11 @@ void qErrnoWarning(int code, const char *msg, ...)
 
     The default \a pattern is \c{%{if-category}%{category}: %{endif}%{message}}.
 
+    \note On Android, the default \a pattern is \c{%{message}} because the category is used as
+    \l{Android: log_print}{tag} since Android logcat has has a dedicated field for the logging
+    categories, see \l{Android: Log}{Android Logging}. If a custom \a pattern including the
+    category is used, QCoreApplication::applicationName() is used as \l{Android: log_print}{tag}.
+
     The \a pattern can also be changed at runtime by setting the QT_MESSAGE_PATTERN
     environment variable; if both \l qSetMessagePattern() is called and QT_MESSAGE_PATTERN is
     set, the environment variable takes precedence.

tests/auto/corelib/global/qlogging/tst_qlogging.cpp

@@ -955,11 +955,7 @@ void tst_qmessagehandler::formatLogMessage_data()
             << format << "[F] msg"
             << QtFatalMsg << BA("") << 0 << BA("func") << QByteArray() << "msg";
     QTest::newRow("if_cat")
-#ifndef Q_OS_ANDROID
             << format << "[F] cat: msg"
-#else
-            << format << "[F] : msg"
-#endif
             << QtFatalMsg << BA("") << 0 << BA("func") << BA("cat") << "msg";
 }