events: Improve room::message markdown constructors

Only return an html message if some markdown formatting was detected.

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

@@ -427,13 +427,13 @@ impl EmoteMessageEventContent {
     }
 
     /// A convenience constructor to create a markdown emote.
+    ///
+    /// Returns an html emote message if some markdown formatting was detected, otherwise returns a
+    /// plain-text emote.
     #[cfg(feature = "markdown")]
     #[cfg_attr(docsrs, doc(cfg(feature = "markdown")))]
-    pub fn markdown(body: impl Into<String>) -> Self {
-        let body = body.into();
-        let mut html_body = String::new();
-        pulldown_cmark::html::push_html(&mut html_body, pulldown_cmark::Parser::new(&body));
-        Self::html(body, html_body)
+    pub fn markdown(body: impl AsRef<str> + Into<String>) -> Self {
+        Self { formatted: FormattedBody::markdown(&body), ..Self::plain(body) }
     }
 }
 
@@ -629,6 +629,16 @@ impl NoticeMessageEventContent {
     pub fn html(body: impl Into<String>, html_body: impl Into<String>) -> Self {
         Self { formatted: Some(FormattedBody::html(html_body)), ..Self::plain(body) }
     }
+
+    /// A convenience constructor to create a markdown notice.
+    ///
+    /// Returns an html notice if some markdown formatting was detected, otherwise returns a plain
+    /// text notice.
+    #[cfg(feature = "markdown")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "markdown")))]
+    pub fn markdown(body: impl AsRef<str> + Into<String>) -> Self {
+        Self { formatted: FormattedBody::markdown(&body), ..Self::plain(body) }
+    }
 }
 
 /// The payload for a server notice message.
@@ -725,6 +735,24 @@ impl FormattedBody {
     pub fn html(body: impl Into<String>) -> Self {
         Self { format: MessageFormat::Html, body: body.into() }
     }
+
+    /// Creates a new HTML-formatted message body by parsing the markdown in `body`.
+    ///
+    /// Returns `None` if no markdown formatting was found.
+    #[cfg(feature = "markdown")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "markdown")))]
+    pub fn markdown(body: impl AsRef<str>) -> Option<Self> {
+        let body = body.as_ref();
+        let mut html_body = String::new();
+
+        pulldown_cmark::html::push_html(&mut html_body, pulldown_cmark::Parser::new(body));
+
+        if html_body == format!("<p>{}</p>\n", body) {
+            None
+        } else {
+            Some(Self::html(html_body))
+        }
+    }
 }
 
 /// The payload for a text message.
@@ -752,13 +780,13 @@ impl TextMessageEventContent {
     }
 
     /// A convenience constructor to create a markdown message.
+    ///
+    /// Returns an html message if some markdown formatting was detected, otherwise returns a plain
+    /// text message.
     #[cfg(feature = "markdown")]
     #[cfg_attr(docsrs, doc(cfg(feature = "markdown")))]
-    pub fn markdown(body: impl Into<String>) -> Self {
-        let body = body.into();
-        let mut html_body = String::new();
-        pulldown_cmark::html::push_html(&mut html_body, pulldown_cmark::Parser::new(&body));
-        Self::html(body, html_body)
+    pub fn markdown(body: impl AsRef<str> + Into<String>) -> Self {
+        Self { formatted: FormattedBody::markdown(&body), ..Self::plain(body) }
     }
 
     /// A convenience constructor to create a plain text message.

crates/ruma-events/tests/room_message.rs

@@ -155,6 +155,50 @@ fn plain_text_content_serialization() {
     );
 }
 
+#[test]
+#[cfg(feature = "markdown")]
+fn markdown_content_serialization() {
+    let formatted_message = MessageEventContent::new(MessageType::Text(
+        TextMessageEventContent::markdown("Testing **bold** and _italic_!"),
+    ));
+
+    assert_eq!(
+        to_json_value(&formatted_message).unwrap(),
+        json!({
+            "body": "Testing **bold** and _italic_!",
+            "formatted_body": "<p>Testing <strong>bold</strong> and <em>italic</em>!</p>\n",
+            "format": "org.matrix.custom.html",
+            "msgtype": "m.text"
+        })
+    );
+
+    let plain_message_simple = MessageEventContent::new(MessageType::Text(
+        TextMessageEventContent::markdown("Testing a simple phrase…"),
+    ));
+
+    assert_eq!(
+        to_json_value(&plain_message_simple).unwrap(),
+        json!({
+            "body": "Testing a simple phrase…",
+            "msgtype": "m.text"
+        })
+    );
+
+    let plain_message_paragraphs = MessageEventContent::new(MessageType::Text(
+        TextMessageEventContent::markdown("Testing\n\nSeveral\n\nParagraphs."),
+    ));
+
+    assert_eq!(
+        to_json_value(&plain_message_paragraphs).unwrap(),
+        json!({
+            "body": "Testing\n\nSeveral\n\nParagraphs.",
+            "formatted_body": "<p>Testing</p>\n<p>Several</p>\n<p>Paragraphs.</p>\n",
+            "format": "org.matrix.custom.html",
+            "msgtype": "m.text"
+        })
+    );
+}
+
 #[test]
 fn relates_to_content_serialization() {
     let message_event_content =