color: extract the label code into its own function

We extract the logic into a function. This will allow us to move the logic into
the core 'color' module and later call it directly from core.

hgext/color.py

@@ -331,16 +331,17 class colorui(uimod.ui):
     def label(self, msg, label):
         if self._colormode is None:
             return super(colorui, self).label(msg, label)
+        return colorlabel(self, msg, label)
 
-        if self._colormode == 'debug':
+def colorlabel(ui, msg, label):
+    """add color control code according to the mode"""
+    if ui._colormode == 'debug':
             if label and msg:
                 if msg[-1] == '\n':
-                    return "[%s|%s]\n" % (label, msg[:-1])
+                msg = "[%s|%s]\n" % (label, msg[:-1])
                 else:
-                    return "[%s|%s]" % (label, msg)
-            else:
-                return msg
-
+                msg = "[%s|%s]" % (label, msg)
+    elif ui._colormode is not None:
         effects = []
         for l in label.split():
             s = color._styles.get(l, '')
@@ -350,7 +351,7 class colorui(uimod.ui):
                 effects.append(l)
         effects = ' '.join(effects)
         if effects:
-            return '\n'.join([color._render_effects(line, effects)
+            msg = '\n'.join([color._render_effects(line, effects)
                               for line in msg.split('\n')])
         return msg