QProcess::startDetached/Unix: move up the chdir() and remove qWarning

That qWarning cannot be in the child process (we don't know if a user
logger is fork-no-exec-safe) and the failure to chdir() should be
reported as a failure in QProcess::startDetached() instead.

Change-Id: Ic90d8429a0eb4837971dfffd1664e7577c81610b
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Reviewed-by: David Llewellyn-Jones <david.llewellyn-jones@jolla.com>
(cherry picked from commit 31bb141aed52549fae52f2156ac66bd2647cad16)

src/corelib/io/qprocess_unix.cpp

@@ -916,18 +916,18 @@ bool QProcessPrivate::startDetached(qint64 *pid)
         qt_safe_close(startedPipe[0]);
         qt_safe_close(pidPipe[0]);
 
-        pid_t doubleForkPid = fork();
+        pid_t doubleForkPid = 0;
+        if (!encodedWorkingDirectory.isEmpty())
+            doubleForkPid = QT_CHDIR(encodedWorkingDirectory.constData());
+
+        if (doubleForkPid == 0)
+            doubleForkPid = fork();
         if (doubleForkPid == 0) {
             qt_safe_close(pidPipe[1]);
 
             // Render channels configuration.
             commitChannels();
 
-            if (!encodedWorkingDirectory.isEmpty()) {
-                if (QT_CHDIR(encodedWorkingDirectory.constData()) == -1)
-                    qWarning("QProcessPrivate::startDetached: failed to chdir to %s", encodedWorkingDirectory.constData());
-            }
-
             char **argv = new char *[arguments.size() + 2];
             for (int i = 0; i < arguments.size(); ++i)
                 argv[i + 1] = ::strdup(QFile::encodeName(arguments.at(i)).constData());

tests/auto/corelib/io/qprocess/tst_qprocess.cpp

@@ -118,6 +118,7 @@ private slots:
     void discardUnwantedOutput();
     void setWorkingDirectory();
     void setNonExistentWorkingDirectory();
+    void detachedSetNonExistentWorkingDirectory();
 
     void exitStatus_data();
     void exitStatus();
@@ -2266,6 +2267,20 @@ void tst_QProcess::setNonExistentWorkingDirectory()
 #endif
 }
 
+void tst_QProcess::detachedSetNonExistentWorkingDirectory()
+{
+    QProcess process;
+    process.setWorkingDirectory("this/directory/should/not/exist/for/sure");
+
+    // use absolute path because on Windows, the executable is relative to the parent's CWD
+    // while on Unix with fork it's relative to the child's (with posix_spawn, it could be either).
+    process.setProgram(QFileInfo("testSetWorkingDirectory/testSetWorkingDirectory").absoluteFilePath());
+
+    qint64 pid = -1;
+    QVERIFY(!process.startDetached(&pid));
+    QCOMPARE(pid, -1);
+}
+
 void tst_QProcess::startFinishStartFinish()
 {
     QProcess process;