[Modlog] userinfo stops breaking with high numbers of roles on a user (#2971)

* Fixes it, I guess

* changelog

* reluctant handling of what the people want here

* mypy would have prevented this one

changelog.d/mod/2910.bugfix.rst

@@ -0,0 +1 @@
+userinfo doesn't break with absurd numbers of roles.

redbot/cogs/mod/names.py

@@ -125,15 +125,46 @@ class ModInfo(MixinMeta):
             activity = _("Watching {}").format(user.activity.name)
 
         if roles:
-            roles = ", ".join([x.mention for x in roles])
+
+            role_str = ", ".join([x.mention for x in roles])
+            # 400 BAD REQUEST (error code: 50035): Invalid Form Body
+            # In embed.fields.2.value: Must be 1024 or fewer in length.
+            if len(role_str) > 1024:
+                # Alternative string building time.
+                # This is not the most optimal, but if you're hitting this, you are losing more time
+                # to every single check running on users than the occasional user info invoke
+                # We don't start by building this way, since the number of times we hit this should be
+                # infintesimally small compared to when we don't across all uses of Red.
+                continuation_string = _(
+                    "and {numeric_number} more roles not displayed due to embed limits."
+                )
+                available_length = 1024 - len(continuation_string)  # do not attempt to tweak, i18n
+
+                role_chunks = []
+                remaining_roles = 0
+
+                for r in roles:
+                    chunk = f"{r.mention}, "
+                    chunk_size = len(chunk)
+
+                    if chunk_size < available_length:
+                        available_length -= chunk_size
+                        role_chunks.append(chunk)
                     else:
-            roles = None
+                        remaining_roles += 1
+
+                role_chunks.append(continuation_string.format(numeric_number=remaining_roles))
+
+                role_str = "".join(role_chunks)
+
+        else:
+            role_str = None
 
         data = discord.Embed(description=activity, colour=user.colour)
         data.add_field(name=_("Joined Discord on"), value=created_on)
         data.add_field(name=_("Joined this server on"), value=joined_on)
-        if roles is not None:
+        if role_str is not None:
-            data.add_field(name=_("Roles"), value=roles, inline=False)
+            data.add_field(name=_("Roles"), value=role_str, inline=False)
         if names:
             # May need sanitizing later, but mentions do not ping in embeds currently
             val = filter_invites(", ".join(names))