[commands] Add support for rgb function in ColourConverter

This also adds support for 3 digit hex.

Fixes #6374

discord/ext/commands/converter.py

@@ -449,24 +449,71 @@ class ColourConverter(Converter):
     - ``0x<hex>``
     - ``#<hex>``
     - ``0x#<hex>``
+    - ``rgb(<number>, <number>, <number>)``
     - Any of the ``classmethod`` in :class:`Colour`
 
         - The ``_`` in the name can be optionally replaced with spaces.
 
+    Like CSS, ``<number>`` can be either 0-255 or 0-100% and ``<hex>`` can be
+    either a 6 digit hex number or a 3 digit hex shortcut (e.g. #fff).
+
     .. versionchanged:: 1.5
          Raise :exc:`.BadColourArgument` instead of generic :exc:`.BadArgument`
-    """
-    async def convert(self, ctx, argument):
-        arg = argument.replace('0x', '').lower()
 
-        if arg[0] == '#':
-            arg = arg[1:]
+    .. versionchanged:: 1.7
+        Added support for ``rgb`` function and 3-digit hex shortcuts
+    """
+
+    RGB_REGEX = re.compile(r'rgb\s*\((?P<r>[0-9]{1,3}%?)\s*,\s*(?P<g>[0-9]{1,3}%?)\s*,\s*(?P<b>[0-9]{1,3}%?)\s*\)')
+
+    def parse_hex_number(self, argument):
+        arg = ''.join(i * 2 for i in argument) if len(argument) == 3 else argument
         try:
             value = int(arg, base=16)
             if not (0 <= value <= 0xFFFFFF):
-                raise BadColourArgument(arg)
-            return discord.Colour(value=value)
+                raise BadColourArgument(argument)
         except ValueError:
+            raise BadColourArgument(argument)
+        else:
+            return discord.Color(value=value)
+
+    def parse_rgb_number(self, argument, number):
+        if number[-1] == '%':
+            value = int(number[:-1])
+            if not (0 <= value <= 100):
+                raise BadColourArgument(argument)
+            return round(255 * (value / 100))
+
+        value = int(number)
+        if not (0 <= value <= 255):
+            raise BadColourArgument(argument)
+        return value
+
+    def parse_rgb(self, argument, *, regex=RGB_REGEX):
+        match = regex.match(argument)
+        if match is None:
+            raise BadColourArgument(argument)
+
+        red = self.parse_rgb_number(argument, match.group('r'))
+        green = self.parse_rgb_number(argument, match.group('g'))
+        blue = self.parse_rgb_number(argument, match.group('b'))
+        return discord.Color.from_rgb(red, green, blue)
+
+    async def convert(self, ctx, argument):
+        if argument[0] == '#':
+            return self.parse_hex_number(argument[1:])
+
+        if argument[0:2] == '0x':
+            rest = argument[2:]
+            # Legacy backwards compatible syntax
+            if rest.startswith('#'):
+                return self.parse_hex_number(rest[1:])
+            return self.parse_hex_number(rest)
+
+        arg = argument.lower()
+        if arg[0:3] == 'rgb':
+            return self.parse_rgb(arg)
+
         arg = arg.replace(' ', '_')
         method = getattr(discord.Colour, arg, None)
         if arg.startswith('from_') or method is None or not inspect.ismethod(method):