[PATCH V3] posix: update os.popen with subprocess (issue4746)

[Rishabh Madan]

# HG changeset patch
# User Rishabh Madan <rishabhmadan96 at gmail.com>
# Date 1488572534 -19800
#      Sat Mar 04 01:52:14 2017 +0530
# Node ID 96bd01e81f0c8402392daa9f41cac72e31cbdc32
# Parent  71f692f1f678d86ffb4f95a3621aacfdaeb96b05
posix: update os.popen with subprocess (issue4746)

While importing a patch, we use a patch tool, say 'patch --merge', and the
patch doesn't merge cleanly, 'patch --merge' will return with exit status 1,
but 'hg import' displays 'abort: patch command failed: exited with status 256'.
This patch replaces the deprecated os.popen with subprocess.Popen with
conditional statements for 'r', 'rb' and 'w' mode and raise ValueError otherwise.

diff -r 71f692f1f678 -r 96bd01e81f0c mercurial/posix.py
--- a/mercurial/posix.py	Wed Mar 01 20:22:04 2017 +0100
+++ b/mercurial/posix.py	Sat Mar 04 01:52:14 2017 +0530
@@ -16,6 +16,7 @@
 import re
 import select
 import stat
+import subprocess
 import sys
 import tempfile
 import unicodedata
@@ -419,7 +420,14 @@
     return cmd
 
 def popen(command, mode='r'):
-    return os.popen(command, mode)
+    if 'r' in mode:
+        return subprocess.Popen(command, shell=True,
+            stdout=subprocess.PIPE).stdout
+    elif mode == 'w':
+        return subprocess.Popen(command, shell=True,
+            stdin=subprocess.PIPE).stdin
+    else:
+        raise ValueError
 
 def testpid(pid):
     '''return False if pid dead, True if running or not sure'''