--- a/mercurial/posix.py	Sat Apr 07 20:50:38 2018 +0900
+++ b/mercurial/posix.py	Sat Apr 07 21:09:21 2018 +0900
@@ -469,9 +469,6 @@
 def quotecommand(cmd):
     return cmd
 
-def popen(command, mode='r'):
-    return os.popen(command, mode)
-
 def testpid(pid):
     '''return False if pid dead, True if running or not sure'''
     if pycompat.sysplatform == 'OpenVMS':

--- a/mercurial/utils/procutil.py	Sat Apr 07 20:50:38 2018 +0900
+++ b/mercurial/utils/procutil.py	Sat Apr 07 21:09:21 2018 +0900
@@ -58,7 +58,6 @@
 getuser = platform.getuser
 getpid = os.getpid
 hidewindow = platform.hidewindow
-popen = platform.popen
 quotecommand = platform.quotecommand
 readpipe = platform.readpipe
 setbinary = platform.setbinary
@@ -80,6 +79,49 @@
 
 closefds = pycompat.isposix
 
+class _pfile(object):
+    """File-like wrapper for a stream opened by subprocess.Popen()"""
+
+    def __init__(self, proc, fp):
+        self._proc = proc
+        self._fp = fp
+
+    def close(self):
+        # unlike os.popen(), this returns an integer in subprocess coding
+        self._fp.close()
+        return self._proc.wait()
+
+    def __iter__(self):
+        return iter(self._fp)
+
+    def __getattr__(self, attr):
+        return getattr(self._fp, attr)
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_value, exc_tb):
+        self.close()
+
+def popen(cmd, mode='rb', bufsize=-1):
+    if mode == 'rb':
+        return _popenreader(cmd, bufsize)
+    elif mode == 'wb':
+        return _popenwriter(cmd, bufsize)
+    raise error.ProgrammingError('unsupported mode: %r' % mode)
+
+def _popenreader(cmd, bufsize):
+    p = subprocess.Popen(quotecommand(cmd), shell=True, bufsize=bufsize,
+                         close_fds=closefds,
+                         stdout=subprocess.PIPE)
+    return _pfile(p, p.stdout)
+
+def _popenwriter(cmd, bufsize):
+    p = subprocess.Popen(quotecommand(cmd), shell=True, bufsize=bufsize,
+                         close_fds=closefds,
+                         stdin=subprocess.PIPE)
+    return _pfile(p, p.stdin)
+
 def popen2(cmd, env=None, newlines=False):
     # Setting bufsize to -1 lets the system decide the buffer size.
     # The default for bufsize is 0, meaning unbuffered. This leads to

--- a/mercurial/windows.py	Sat Apr 07 20:50:38 2018 +0900
+++ b/mercurial/windows.py	Sat Apr 07 21:09:21 2018 +0900
@@ -311,13 +311,6 @@
         return '"' + cmd + '"'
     return cmd
 
-def popen(command, mode='r'):
-    # Work around "popen spawned process may not write to stdout
-    # under windows"
-    # http://bugs.python.org/issue1366
-    command += " 2> %s" % pycompat.bytestr(os.devnull)
-    return os.popen(quotecommand(command), mode)
-
 def explainexit(code):
     return _("exited with status %d") % code, code
 

--- a/tests/test-patch.t	Sat Apr 07 20:50:38 2018 +0900
+++ b/tests/test-patch.t	Sat Apr 07 21:09:21 2018 +0900
@@ -89,4 +89,12 @@
   # User lines looks like this - but it _is_ just a comment
   
   
+
+Error exit (issue4746)
+
+  $ hg import ../c/p --config ui.patch='sh -c "exit 1"'
+  applying ../c/p
+  abort: patch command failed: exited with status 1
+  [255]
+
   $ cd ..