management commands' OutputWrapper adds newline wrapped inside style

[Markus Holtermann]

According to the ​docs the self.stdout.write() adds a newline (or explicitly defined ending) add the end of the message, if it's not already there. However, if the output is wrapped in some kind of style the message, including the ending, is wrapped.

Instead of

'\x1b[31;1mHello, world!\x1b[0m\n'

one gets

'\x1b[31;1mHello, world!\n\x1b[0m'

The issue came up while investigating ​https://github.com/django/django/pull/3153#issuecomment-68471839

A potential patch would be:

django/core/management/base.py

@@ -107 +107 @@
         return getattr(self._out, name)
 
     def write(self, msg, style_func=None, ending=None):
-        ending = self.ending if ending is None else ending
-        if ending and not msg.endswith(ending):
-            msg += ending
         style_func = style_func or self.style_func
-        self._out.write(force_str(style_func(msg)))
+        ending = self.ending if ending is None else ending
+        if ending and msg.endswith(ending):
+            msg = msg[:-len(ending)]
+        msg = force_str(style_func(msg)) + ending
+        self._out.write(msg)

[Tim Graham]

Let's focus our efforts on #21429 instead. We can merge ​PR 3823 to fix the particular problem.