color: move 'write-err' logic to the core ui class

This is similar to what we needed for 'write', we move the logic from the
extension to the core class. Beside the dispatch to 'win32print', we just apply
label to the argument.

hgext/color.py

@@ -297,19 +297,7 b' def _modesetup(ui, coloropt):'
     return None
 
 class colorui(uimod.ui):
-
-    def write_err(self, *args, **opts):
-        if self._colormode is None:
-            return super(colorui, self).write_err(*args, **opts)
-
-        label = opts.get('label', '')
-        if self._bufferstates and self._bufferstates[-1][0]:
-            return self.write(*args, **opts)
-        if self._colormode == 'win32':
-            color.win32print(super(colorui, self).write_err, *args, **opts)
-        else:
-            return super(colorui, self).write_err(
-                *[self.label(a, label) for a in args], **opts)
+    pass
 
 def uisetup(ui):
     if ui.plain():

mercurial/ui.py

@@ -823,8 +823,17 b' class ui(object):'
     def write_err(self, *args, **opts):
         self._progclear()
         if self._bufferstates and self._bufferstates[-1][0]:
-            return self.write(*args, **opts)
-        self._write_err(*args, **opts)
+            self.write(*args, **opts)
+        elif self._colormode == 'win32':
+            # windows color printing is its own can of crab, defer to
+            # the color module and that is it.
+            color.win32print(self._write_err, *args, **opts)
+        else:
+            msgs = args
+            if self._colormode is not None:
+                label = opts.get('label', '')
+                msgs = [self.label(a, label) for a in args]
+            self._write_err(*msgs, **opts)
 
     def _write_err(self, *msgs, **opts):
         try: