Add support for spoiler attachments.

discord/file.py

@@ -48,11 +48,13 @@ class File:
         The filename to display when uploading to Discord.
         If this is not given then it defaults to ``fp.name`` or if ``fp`` is
         a string then the ``filename`` will default to the string given.
+    spoiler: :class:`bool`
+        Whether the attachment is a spoiler.
     """
 
     __slots__ = ('fp', 'filename', '_true_fp')
 
-    def __init__(self, fp, filename=None):
+    def __init__(self, fp, filename=None, *, spoiler=False):
         self.fp = fp
         self._true_fp = None
 
@@ -64,6 +66,9 @@ class File:
         else:
             self.filename = filename
 
+        if spoiler and not self.filename.startswith('SPOILER_'):
+            self.filename = 'SPOILER_' + self.filename
+
     def open_file(self):
         fp = self.fp
         if isinstance(fp, str):

discord/message.py

@@ -71,6 +71,10 @@ class Attachment:
         self.proxy_url = data.get('proxy_url')
         self._http = state.http
 
+    def is_spoiler(self):
+        """:class:`bool`: Whether this attachment contains a spoiler."""
+        return self.filename.startswith('SPOILER_')
+
     async def save(self, fp, *, seek_begin=True):
         """|coro|