Make EditRole::icon and EditRole::unicode_emoji nullable in addit…

…ion to undefined (serenity-rs#2539)

All `EditRole` fields are skipped when they are `None`. This does not work for `EditRole::icon` and `EditRole::unicode_emoji` because the field being `undefined` is different from the field being `null` at the API: if the field is `undefined` it will be kept unchanged, and if it is `null` it will be cleared.

With a double `Option` it is possible to distinguish `undefined` from `null` from a set value. This is the [canonical](serde-rs/serde#984 (comment)) solution using serde (the example shows de-serialization but it works the same in reverse).

Then, `None` is "keep field unchanged", `Some(None)` is "clear this field" and `Some(Some(value)` is "set this field to this value"

# Breaking changes

- `EditRole::unicode_emoji()` takes a `Option<String>` instead of `impl Into<String>`.
- `EditRole::icon()` takes a `Option<&CreateAttachment>` instead of `&CreateAttachment`

src/builder/edit_role.rs

@@ -56,9 +56,10 @@ pub struct EditRole<'a> {
  #[serde(skip_serializing_if = "Option::is_none")]
  hoist: Option<bool>,
  #[serde(skip_serializing_if = "Option::is_none")]
- icon: Option<String>,
+ icon: Option<Option<String>>,
  #[serde(skip_serializing_if = "Option::is_none")]
- unicode_emoji: Option<String>,
+ unicode_emoji: Option<Option<String>>,
+
  #[serde(skip_serializing_if = "Option::is_none")]
  mentionable: Option<bool>,
 
@@ -83,7 +84,7 @@ impl<'a> EditRole<'a> {
  permissions: Some(role.permissions.bits()),
  position: Some(role.position),
  colour: Some(role.colour),
- unicode_emoji: role.unicode_emoji.clone(),
+ unicode_emoji: role.unicode_emoji.as_ref().map(|v| Some(v.clone())),
  audit_log_reason: None,
  // TODO: Do we want to download role.icon?
  icon: None,
@@ -129,16 +130,16 @@ impl<'a> EditRole<'a> {
  }
 
  /// Set the role icon to a unicode emoji.
- pub fn unicode_emoji(mut self, unicode_emoji: impl Into<String>) -> Self {
- self.unicode_emoji = Some(unicode_emoji.into());
- self.icon = None;
+ pub fn unicode_emoji(mut self, unicode_emoji: Option<String>) -> Self {
+ self.unicode_emoji = Some(unicode_emoji);
+ self.icon = Some(None);
  self
  }
 
  /// Set the role icon to a custom image.
- pub fn icon(mut self, icon: &CreateAttachment) -> Self {
- self.icon = Some(icon.to_base64());
- self.unicode_emoji = None;
+ pub fn icon(mut self, icon: Option<&CreateAttachment>) -> Self {
+ self.icon = Some(icon.map(CreateAttachment::to_base64));
+ self.unicode_emoji = Some(None);
  self
  }