Update the detection of when to log to stderr

On Windows, the detection changes only by inserting the use of the
environment variable before the existing tests and removing the check on
stderr.

This commit adds logic similar to Windows's: if the application has a
controlling TTY, we'll use stderr. Otherwise, we'll use the system log.
This is technically a change in behavior: previously, we would always
use the system log, unless the environment variable told us not to.

In practice, the behavior doesn't really change: Android and BlackBerry
and systemd-spawned applications are launched with no controlling TTY,
so logging will go to their logging systems.

[ChangeLog][Important behavior changes][Logging (including qDebug and
qWarning)] Log output will now go to the system log (if support for it
was compiled into Qt) if the application has no controlling terminal or
console window. Set QT_LOGGING_TO_CONSOLE to 1 to force logging to go to
stderr.

Task-number: QTCREATORBUG-12564
Change-Id: I043c5c4f47c15f26d4f4a5cf43df466ea38cdbc7
Reviewed-by: Kai Koehne <kai.koehne@digia.com>

1 files changed, 57 insertions, 47 deletions

diff --git a/src/corelib/global/qlogging.cpp b/src/corelib/global/qlogging.cpp
index 323c86f511..575f484dd3 100644
--- a/src/corelib/global/qlogging.cpp
+++ b/src/corelib/global/qlogging.cpp
@@ -2,6 +2,7 @@
 **
 ** Copyright (C) 2014 Digia Plc and/or its subsidiary(-ies).
 ** Copyright (C) 2014 Olivier Goffart <ogoffart@woboq.com>
+** Copyright (C) 2014 Intel Corporation.
 ** Contact: http://www.qt-project.org/legal
 **
 ** This file is part of the QtCore module of the Qt Toolkit.
@@ -46,6 +47,7 @@
 #include "qcoreapplication.h"
 #include "qthread.h"
 #include "private/qloggingregistry_p.h"
+#include "private/qcoreapplication_p.h"
 #endif
 #ifdef Q_OS_WIN
 #include <qt_windows.h>
@@ -62,7 +64,12 @@
 # define SD_JOURNAL_SUPPRESS_LOCATION
 # include <systemd/sd-journal.h>
 # include <syslog.h>
+#endif
+#ifdef Q_OS_UNIX
+# include <sys/types.h>
+# include <sys/stat.h>
 # include <unistd.h>
+# include "private/qcore_unix_p.h"
 #endif
 
 #if !defined QT_NO_REGULAREXPRESSION && !defined(QT_BOOTSTRAPPED)
@@ -109,32 +116,54 @@ static bool isFatal(QtMsgType msgType)
     return false;
 }
 
-#ifdef Q_OS_WIN
-
-// Do we have stderr for QDebug? - Either there is a console or we are running
-// with redirected stderr.
-#  if !defined(Q_OS_WINCE) && !defined(Q_OS_WINRT)
-static inline bool hasStdErr()
+static bool willLogToConsole()
 {
-    if (GetConsoleWindow())
+#if defined(Q_OS_WINCE) || defined(Q_OS_WINRT)
+    // these systems have no stderr, so always log to the system log
+    return false;
+#elif defined(QT_BOOTSTRAPPED)
+    return true;
+#else
+    // rules to determine if we'll log preferably to the console:
+    //  1) if QT_LOGGING_TO_CONSOLE is set, it determines behavior:
+    //    - if it's set to 0, we will not log to console
+    //    - if it's set to 1, we will log to console
+    //  2) otherwise, we will log to console if we have a console window (Windows)
+    //     or a controlling TTY (Unix). This is done even if stderr was redirected
+    //     to the blackhole device (NUL or /dev/null).
+
+    bool ok = true;
+    uint envcontrol = qgetenv("QT_LOGGING_TO_CONSOLE").toUInt(&ok);
+    if (ok)
+        return envcontrol;
+
+#  ifdef Q_OS_WIN
+    return GetConsoleWindow();
+#  elif defined(Q_OS_UNIX)
+    // if /dev/tty exists, we can only open it if we have a controlling TTY
+    int devtty = qt_safe_open("/dev/tty", O_RDONLY);
+    if (devtty == -1 && (errno == ENOENT || errno == EPERM)) {
+        // no /dev/tty, fall back to isatty on stderr
+        return isatty(STDERR_FILENO);
+    } else if (devtty != -1) {
+        // there is a /dev/tty and we could open it: we have a controlling TTY
+        qt_safe_close(devtty);
         return true;
-    STARTUPINFO info;
-    GetStartupInfo(&info);
-    return (info.dwFlags & STARTF_USESTDHANDLES) && info.hStdError
-        && info.hStdError != INVALID_HANDLE_VALUE;
-}
-#  endif // !Q_OS_WINCE && !Q_OS_WINRT
+    }
 
-Q_CORE_EXPORT bool qWinLogToStderr()
-{
-#  if !defined(Q_OS_WINCE) && !defined(Q_OS_WINRT)
-    static const bool result = hasStdErr();
-    return result;
-#  else
+    // no controlling TTY
     return false;
+#  else
+#    error "Not Unix and not Windows?"
 #  endif
+#endif
+}
+
+Q_CORE_EXPORT bool qt_logging_to_console()
+{
+    static const bool logToConsole = willLogToConsole();
+    return logToConsole;
 }
-#endif // Q_OS_WIN
 
 /*!
     \class QMessageLogContext
@@ -977,7 +1006,7 @@ void QMessagePattern::setPattern(const QString &pattern)
         OutputDebugString(reinterpret_cast<const wchar_t*>(error.utf16()));
         if (0)
 #elif defined(Q_OS_WIN) && defined(QT_BUILD_CORE_LIB)
-        if (!qWinLogToStderr()) {
+        if (!qt_logging_to_console()) {
             OutputDebugString(reinterpret_cast<const wchar_t*>(error.utf16()));
         } else
 #endif
@@ -1269,44 +1298,25 @@ static void qDefaultMessageHandler(QtMsgType type, const QMessageLogContext &con
 {
     QString logMessage = qFormatLogMessage(type, context, buf);
 
-#if defined(Q_OS_WIN) && defined(QT_BUILD_CORE_LIB)
-    if (!qWinLogToStderr()) {
+    if (!qt_logging_to_console()) {
+#if defined(Q_OS_WIN)
         OutputDebugString(reinterpret_cast<const wchar_t *>(logMessage.utf16()));
         return;
-    }
-#endif // Q_OS_WIN
-
-    static const bool logToConsole = qEnvironmentVariableIsSet("QT_LOGGING_TO_CONSOLE");
-#if defined(QT_USE_SLOG2)
-    if (!logToConsole) {
+#elif defined(QT_USE_SLOG2)
         slog2_default_handler(type, logMessage.toLocal8Bit().constData());
-    } else {
-        fprintf(stderr, "%s", logMessage.toLocal8Bit().constData());
-        fflush(stderr);
-    }
+        return;
 #elif defined(QT_USE_JOURNALD) && !defined(QT_BOOTSTRAPPED)
-    // We support environment variables for Qt Creator use, or more complicated cases
-    // like subprocesses.
-    if (!logToConsole) {
         // remove trailing \n, systemd appears to want them newline-less
         logMessage.chop(1);
         systemd_default_message_handler(type, context, logMessage);
-    } else {
-        fprintf(stderr, "%s", logMessage.toLocal8Bit().constData());
-        fflush(stderr);
-    }
+        return;
 #elif defined(Q_OS_ANDROID)
-    if (!logToConsole) {
         android_default_message_handler(type, context, logMessage);
-    } else {
-        fprintf(stderr, "%s", logMessage.toLocal8Bit().constData());
-        fflush(stderr);
+        return;
+#endif
     }
-#else
     fprintf(stderr, "%s", logMessage.toLocal8Bit().constData());
     fflush(stderr);
-#endif
-    Q_UNUSED(logToConsole);
 }
 
 /*!