subprocess2: Fix CalledProcessError str() method on Python 3.

stdout and stderr are bytes in Python 3 and must be decoded before
printing the exception.

Bug: 1060409
Change-Id: Ib855f6104919734b7505aa5e978ebe394a1e9db6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2097595
Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>

subprocess2.py

@@ -48,7 +48,11 @@ class CalledProcessError(subprocess.CalledProcessError):
         ' '.join(self.cmd), self.returncode)
     if self.cwd:
       out += ' in ' + self.cwd
-    return '\n'.join(filter(None, (out, self.stdout, self.stderr)))
+    if self.stdout:
+      out += '\n' + self.stdout.decode('utf-8', 'ignore')
+    if self.stderr:
+      out += '\n' + self.stderr.decode('utf-8', 'ignore')
+    return out
 
 
 class CygwinRebaseError(CalledProcessError):

tests/subprocess2_test.py

@@ -142,6 +142,15 @@ class SmokeTests(unittest.TestCase):
       with self.assertRaises(ValueError):
         subp.check_output(TEST_COMMAND, stdout=subp.PIPE)
 
+  def test_print_exception(self):
+    cmd = TEST_COMMAND + ['--fail', '--stdout']
+    with self.assertRaises(subprocess2.CalledProcessError) as e:
+      subprocess2.check_output(cmd)
+    exception_str = str(e.exception)
+    self.assertIn(' '.join(cmd), exception_str)
+    self.assertIn(str(e.exception.returncode), exception_str)
+    self.assertIn(e.exception.stdout.decode('utf-8', 'ignore'), exception_str)
+
   @_run_test()
   def test_check_output_throw_stdout(self, c, cmd, un, subp):
     with self.assertRaises(subp.CalledProcessError) as e: