From 22e8227fef18350d3441e52dd2a2677ff6bf33ba Mon Sep 17 00:00:00 2001
From: Luis Martinez de Bartolome <lasote@gmail.com>
Date: Mon, 29 Jul 2019 12:02:14 +0200
Subject: [PATCH 1/2] Print stderr

---
 conans/client/tools/oss.py | 13 +++++++++----
 conans/errors.py           | 10 ++++++++++
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/conans/client/tools/oss.py b/conans/client/tools/oss.py
index a0217c29709..41406408271 100644
--- a/conans/client/tools/oss.py
+++ b/conans/client/tools/oss.py
@@ -4,11 +4,13 @@
 import subprocess
 import sys
 import tempfile
-from subprocess import CalledProcessError, PIPE
+from subprocess import PIPE
+
 import six
+
 from conans.client.tools.env import environment_append
 from conans.client.tools.files import load, which
-from conans.errors import ConanException
+from conans.errors import ConanException, CalledProcessErrorWithStderr
 from conans.model.version import Version
 from conans.util.fallbacks import default_output
 
@@ -489,17 +491,20 @@ def get_gnu_triplet(os_, arch, compiler=None):
 def check_output(cmd, folder=None, return_code=False, stderr=None):
     tmp_file = tempfile.mktemp()
     try:
+        # We don't want stderr to print warnings that will mess the pristine outputs
         stderr = stderr or PIPE
         cmd = cmd if isinstance(cmd, six.string_types) else subprocess.list2cmdline(cmd)
         process = subprocess.Popen("{} > {}".format(cmd, tmp_file), shell=True,
                                    stderr=stderr, cwd=folder)
-        process.communicate()
+
+        _, stderr = process.communicate()
 
         if return_code:
             return process.returncode
 
         if process.returncode:
-            raise CalledProcessError(process.returncode, cmd)
+            # Only in case of error, we print also the stderr to know what happened
+            raise CalledProcessErrorWithStderr(process.returncode, cmd, stderr=stderr)
 
         output = load(tmp_file)
         return output
diff --git a/conans/errors.py b/conans/errors.py
index f7ae1e68ed6..7f52254fbcd 100644
--- a/conans/errors.py
+++ b/conans/errors.py
@@ -9,8 +9,18 @@
 
 """
 from contextlib import contextmanager
+from subprocess import CalledProcessError
 
 from conans.util.env_reader import get_env
+from conans.util.files import decode_text
+
+
+class CalledProcessErrorWithStderr(CalledProcessError):
+    def __str__(self):
+        ret = super(CalledProcessErrorWithStderr, self).__str__()
+        if self.stderr:
+            ret += "\n" + decode_text(self.stderr)
+        return ret
 
 
 @contextmanager

From 8db5fb40f60ed4d83a74ac1c41d750bdd828b2b8 Mon Sep 17 00:00:00 2001
From: Luis Martinez de Bartolome <lasote@gmail.com>
Date: Mon, 29 Jul 2019 12:21:31 +0200
Subject: [PATCH 2/2] Use output, stderr is not py27

---
 conans/client/tools/oss.py | 2 +-
 conans/errors.py           | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/conans/client/tools/oss.py b/conans/client/tools/oss.py
index 41406408271..aa84a7bcc77 100644
--- a/conans/client/tools/oss.py
+++ b/conans/client/tools/oss.py
@@ -504,7 +504,7 @@ def check_output(cmd, folder=None, return_code=False, stderr=None):
 
         if process.returncode:
             # Only in case of error, we print also the stderr to know what happened
-            raise CalledProcessErrorWithStderr(process.returncode, cmd, stderr=stderr)
+            raise CalledProcessErrorWithStderr(process.returncode, cmd, output=stderr)
 
         output = load(tmp_file)
         return output
diff --git a/conans/errors.py b/conans/errors.py
index 7f52254fbcd..994842b5e40 100644
--- a/conans/errors.py
+++ b/conans/errors.py
@@ -18,8 +18,8 @@
 class CalledProcessErrorWithStderr(CalledProcessError):
     def __str__(self):
         ret = super(CalledProcessErrorWithStderr, self).__str__()
-        if self.stderr:
-            ret += "\n" + decode_text(self.stderr)
+        if self.output:
+            ret += "\n" + decode_text(self.output)
         return ret