add QProcess::Forwarded{Output,Error}Channel

Change-Id: Ifc5ed20c38f3228ef25c28681f296d0456b61abe
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>

4 files changed, 36 insertions, 6 deletions

diff --git a/src/corelib/io/qprocess.cpp b/src/corelib/io/qprocess.cpp
index d473281acc..27a8bce3fe 100644
--- a/src/corelib/io/qprocess.cpp
+++ b/src/corelib/io/qprocess.cpp
@@ -533,7 +533,11 @@ void QProcessPrivate::Channel::clear()
     MergedChannels before starting the process to activative
     this feature. You also have the option of forwarding the output of
     the running process to the calling, main process, by passing
-    ForwardedChannels as the argument.
+    ForwardedChannels as the argument. It is also possible to forward
+    only one of the output channels - typically one would use
+    ForwardedErrorChannel, but ForwardedOutputChannel also exists.
+    Note that using channel forwarding is typically a bad idea in GUI
+    applications - you should present errors graphically instead.
 
     Certain processes need special environment settings in order to
     operate. You can set environment variables for your process by
@@ -625,6 +629,17 @@ void QProcessPrivate::Channel::clear()
     writes to its standard output and standard error will be written
     to the standard output and standard error of the main process.
 
+    \value ForwardedErrorChannel QProcess manages the standard output
+    of the running process, but forwards its standard error onto the
+    main process. This reflects the typical use of command line tools
+    as filters, where the standard output is redirected to another
+    process or a file, while standard error is printed to the console
+    for diagnostic purposes.
+    (This value was introduced in Qt 5.2.)
+
+    \value ForwardedOutputChannel Complementary to ForwardedErrorChannel.
+    (This value was introduced in Qt 5.2.)
+
     \note Windows intentionally suppresses output from GUI-only
     applications to inherited consoles.
     This does \e not apply to output redirected to files or pipes.
diff --git a/src/corelib/io/qprocess.h b/src/corelib/io/qprocess.h
index 2919788e34..0984d501fd 100644
--- a/src/corelib/io/qprocess.h
+++ b/src/corelib/io/qprocess.h
@@ -124,7 +124,9 @@ public:
     enum ProcessChannelMode {
         SeparateChannels,
         MergedChannels,
-        ForwardedChannels
+        ForwardedChannels,
+        ForwardedOutputChannel,
+        ForwardedErrorChannel
     };
     enum ExitStatus {
         NormalExit,
diff --git a/src/corelib/io/qprocess_unix.cpp b/src/corelib/io/qprocess_unix.cpp
index bc0ae5a382..0e0ead5897 100644
--- a/src/corelib/io/qprocess_unix.cpp
+++ b/src/corelib/io/qprocess_unix.cpp
@@ -813,6 +813,16 @@ pid_t QProcessPrivate::spawnChild(const char *workingDir, char **argv, char **en
         fd_map[1] = QT_FILENO(stdout);
         fd_map[2] = QT_FILENO(stderr);
         break;
+    case QProcess::ForwardedOutputChannel:
+        fd_map[0] = stdinChannel.pipe[0];
+        fd_map[1] = QT_FILENO(stdout);
+        fd_map[2] = stderrChannel.pipe[1];
+        break;
+    case QProcess::ForwardedErrorChannel:
+        fd_map[0] = stdinChannel.pipe[0];
+        fd_map[1] = stdoutChannel.pipe[1];
+        fd_map[2] = QT_FILENO(stderr);
+        break;
     case QProcess::MergedChannels:
         fd_map[0] = stdinChannel.pipe[0];
         fd_map[1] = stdoutChannel.pipe[1];
@@ -850,12 +860,13 @@ void QProcessPrivate::execChild(const char *workingDir, char **path, char **argv
 
     // copy the stdout and stderr if asked to
     if (processChannelMode != QProcess::ForwardedChannels) {
-        qt_safe_dup2(stdoutChannel.pipe[1], fileno(stdout), 0);
+        if (processChannelMode != QProcess::ForwardedOutputChannel)
+            qt_safe_dup2(stdoutChannel.pipe[1], fileno(stdout), 0);
 
         // merge stdout and stderr if asked to
         if (processChannelMode == QProcess::MergedChannels) {
             qt_safe_dup2(fileno(stdout), fileno(stderr), 0);
-        } else {
+        } else if (processChannelMode != QProcess::ForwardedErrorChannel) {
             qt_safe_dup2(stderrChannel.pipe[1], fileno(stderr), 0);
         }
     }
diff --git a/src/corelib/io/qprocess_win.cpp b/src/corelib/io/qprocess_win.cpp
index 880cbf659d..f545386f56 100644
--- a/src/corelib/io/qprocess_win.cpp
+++ b/src/corelib/io/qprocess_win.cpp
@@ -160,7 +160,8 @@ bool QProcessPrivate::createChannel(Channel &channel)
         } else {
             QWindowsPipeReader *pipeReader = 0;
             if (&channel == &stdoutChannel) {
-                if (processChannelMode != QProcess::ForwardedChannels) {
+                if (processChannelMode != QProcess::ForwardedChannels
+                        && processChannelMode != QProcess::ForwardedOutputChannel) {
                     if (!stdoutReader) {
                         stdoutReader = new QWindowsPipeReader(q);
                         q->connect(stdoutReader, SIGNAL(readyRead()), SLOT(_q_canReadStandardOutput()));
@@ -170,7 +171,8 @@ bool QProcessPrivate::createChannel(Channel &channel)
                     duplicateStdWriteChannel(channel.pipe, STD_OUTPUT_HANDLE);
                 }
             } else /* if (&channel == &stderrChannel) */ {
-                if (processChannelMode != QProcess::ForwardedChannels) {
+                if (processChannelMode != QProcess::ForwardedChannels
+                        && processChannelMode != QProcess::ForwardedErrorChannel) {
                     if (!stderrReader) {
                         stderrReader = new QWindowsPipeReader(q);
                         q->connect(stderrReader, SIGNAL(readyRead()), SLOT(_q_canReadStandardError()));