common: Add support for translatable text content.

According to MSC3554

crates/ruma-common/Cargo.toml

@@ -39,6 +39,7 @@ unstable-msc3488 = ["unstable-msc1767"]
 unstable-msc3551 = ["unstable-msc1767"]
 unstable-msc3552 = ["unstable-msc1767", "unstable-msc3551"]
 unstable-msc3553 = ["unstable-msc3552"]
+unstable-msc3554 = ["unstable-msc1767"]
 
 [dependencies]
 base64 = "0.13.0"

crates/ruma-common/src/events/message.rs

@@ -100,6 +100,12 @@ impl MessageContent {
     }
 }
 
+impl From<Vec<Text>> for MessageContent {
+    fn from(variants: Vec<Text>) -> Self {
+        Self(variants)
+    }
+}
+
 /// Text message content.
 #[derive(Clone, Debug, Serialize, Deserialize)]
 #[cfg_attr(not(feature = "unstable-exhaustive-types"), non_exhaustive)]
@@ -110,17 +116,34 @@ pub struct Text {
 
     /// The text content.
     pub body: String,
+
+    /// The language of the text.
+    ///
+    /// This must be a valid language code according to [BCP 47](https://www.rfc-editor.org/rfc/bcp/bcp47.txt).
+    #[cfg(feature = "unstable-msc3554")]
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub lang: Option<String>,
 }
 
 impl Text {
     /// Creates a new plain text message body.
     pub fn plain(body: impl Into<String>) -> Self {
-        Self { mimetype: "text/plain".to_owned(), body: body.into() }
+        Self {
+            mimetype: "text/plain".to_owned(),
+            body: body.into(),
+            #[cfg(feature = "unstable-msc3554")]
+            lang: None,
+        }
     }
 
     /// Creates a new HTML-formatted message body.
     pub fn html(body: impl Into<String>) -> Self {
-        Self { mimetype: "text/html".to_owned(), body: body.into() }
+        Self {
+            mimetype: "text/html".to_owned(),
+            body: body.into(),
+            #[cfg(feature = "unstable-msc3554")]
+            lang: None,
+        }
     }
 
     /// Creates a new HTML-formatted message body by parsing the Markdown in `body`.

crates/ruma-common/tests/events/message.rs

@@ -354,3 +354,45 @@ fn emote_event_deserialization() {
             && unsigned.is_empty()
     );
 }
+
+#[test]
+#[cfg(feature = "unstable-msc3554")]
+fn lang_serialization() {
+    use ruma_common::events::message::{MessageContent, Text};
+
+    let content = MessageContent::from(vec![
+        assign!(Text::plain("Bonjour le monde !"), { lang: Some("fr".into()) }),
+        assign!(Text::plain("Hallo Welt!"), { lang: Some("de".into()) }),
+        assign!(Text::plain("Hello World!"), { lang: Some("en".into()) }),
+    ]);
+
+    assert_eq!(
+        to_json_value(&content).unwrap(),
+        json!({
+            "org.matrix.msc1767.message": [
+                { "body": "Bonjour le monde !", "mimetype": "text/plain", "lang": "fr"},
+                { "body": "Hallo Welt!", "mimetype": "text/plain", "lang": "de"},
+                { "body": "Hello World!", "mimetype": "text/plain", "lang": "en"},
+            ]
+        })
+    );
+}
+
+#[test]
+#[cfg(feature = "unstable-msc3554")]
+fn lang_deserialization() {
+    use ruma_common::events::message::MessageContent;
+
+    let json_data = json!({
+        "org.matrix.msc1767.message": [
+            { "body": "Bonjour le monde !", "mimetype": "text/plain", "lang": "fr"},
+            { "body": "Hallo Welt!", "mimetype": "text/plain", "lang": "de"},
+            { "body": "Hello World!", "mimetype": "text/plain", "lang": "en"},
+        ]
+    });
+
+    let content = from_json_value::<MessageContent>(json_data).unwrap();
+    assert_eq!(content.variants()[0].lang.as_deref(), Some("fr"));
+    assert_eq!(content.variants()[1].lang.as_deref(), Some("de"));
+    assert_eq!(content.variants()[2].lang.as_deref(), Some("en"));
+}

crates/ruma/Cargo.toml

@@ -129,6 +129,7 @@ unstable-msc3488 = [
 unstable-msc3551 = ["ruma-common/unstable-msc3551"]
 unstable-msc3552 = ["ruma-common/unstable-msc3552"]
 unstable-msc3553 = ["ruma-common/unstable-msc3553"]
+unstable-msc3554 = ["ruma-common/unstable-msc3554"]
 unstable-msc3618 = ["ruma-federation-api/unstable-msc3618"]
 unstable-msc3723 = ["ruma-federation-api/unstable-msc3723"]
 
@@ -147,6 +148,7 @@ __ci = [
     "unstable-msc3551",
     "unstable-msc3552",
     "unstable-msc3553",
+    "unstable-msc3554",
     "unstable-msc3618",
     "unstable-msc3723",
     "ruma-state-res/__ci",