Process: Introduce DetachedChannelMode enum

The default impl of Process::startDetached() forwards
process channels. Make it optional by providing an additional
argument of DetachedChannelMode type for Process::startDetached().

Change-Id: I6cb55377c21dfedacd53117756894d07e354e0fe
Reviewed-by: hjk <hjk@qt.io>

src/libs/utils/processenums.h

@@ -41,6 +41,11 @@ enum class Channel {
     Error
 };
 
+enum class DetachedChannelMode {
+    Forward,
+    Discard
+};
+
 enum class TextChannelMode {
                 // Keep | Emit | Emit
                 //  raw | text | content

src/libs/utils/qtcprocess.cpp

@@ -1317,12 +1317,18 @@ void Process::closeWriteChannel()
     d->sendControlSignal(ControlSignal::CloseWriteChannel);
 }
 
-bool Process::startDetached(const CommandLine &cmd, const FilePath &workingDirectory, qint64 *pid)
+bool Process::startDetached(const CommandLine &cmd, const FilePath &workingDirectory,
+                            DetachedChannelMode channelMode, qint64 *pid)
 {
-    return QProcess::startDetached(cmd.executable().toUserOutput(),
-                                   cmd.splitArguments(),
-                                   workingDirectory.toUserOutput(),
-                                   pid);
+    QProcess process;
+    process.setProgram(cmd.executable().toUserOutput());
+    process.setArguments(cmd.splitArguments());
+    process.setWorkingDirectory(workingDirectory.toUserOutput());
+    if (channelMode == DetachedChannelMode::Discard) {
+        process.setStandardOutputFile(QProcess::nullDevice());
+        process.setStandardErrorFile(QProcess::nullDevice());
+    }
+    return process.startDetached(pid);
 }
 
 void Process::setLowPriority()

src/libs/utils/qtcprocess.h

@@ -137,6 +137,7 @@ public:
     // Some of them could be aggregated in another public utils class.
 
     static bool startDetached(const CommandLine &cmd, const FilePath &workingDirectory = {},
+                              DetachedChannelMode channelMode = DetachedChannelMode::Forward,
                               qint64 *pid = nullptr);
 
     // Starts the command and waits for finish.