events: Remove p tag around inline markdown

As recommended by the spec.

crates/ruma-events/CHANGELOG.md

@@ -10,6 +10,8 @@ Bug fixes:
 - `Restricted` no longer fails to deserialize when the `allow` field is missing
 - Markdown text constructors now also detect markdown syntax like backslash
   escapes and entity references to decide if the text should be sent as HTML.
+- Markdown text with only inline syntax generates HTML that is not wrapped
+  inside a `<p>` element anymore, as recommended by the spec.
 
 Improvements:
 

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

@@ -915,46 +915,97 @@ pub(crate) fn parse_markdown(text: &str) -> Option<String> {
         return None;
     }
 
+    // If the markdown contains only inline tags, i.e. if there is only one paragraph, remove the
+    // wrapping paragraph, as instructed by the spec.
+    let first_event_is_paragraph_start =
+        parser_events.first().is_some_and(|event| matches!(event, Event::Start(Tag::Paragraph)));
+    let last_event_is_paragraph_end =
+        parser_events.last().is_some_and(|event| matches!(event, Event::End(TagEnd::Paragraph)));
+    let mut has_several_blocks = true;
+
+    if first_event_is_paragraph_start && last_event_is_paragraph_end {
+        has_several_blocks = parser_events.iter().skip(1).any(|event| {
+            if let Event::Start(tag) = event {
+                is_block_tag(tag)
+            } else {
+                false
+            }
+        });
+    }
+
+    let mut events_iter = parser_events.into_iter();
+    if !has_several_blocks {
+        events_iter.next();
+        events_iter.next_back();
+    }
+
     let mut html_body = String::new();
-    pulldown_cmark::html::push_html(&mut html_body, parser_events.into_iter());
+    pulldown_cmark::html::push_html(&mut html_body, events_iter);
 
     Some(html_body)
 }
 
+/// Whether the given tag is a block HTML element.
+#[cfg(feature = "markdown")]
+fn is_block_tag(tag: &pulldown_cmark::Tag<'_>) -> bool {
+    use pulldown_cmark::Tag;
+
+    matches!(
+        tag,
+        Tag::Paragraph
+            | Tag::Heading { .. }
+            | Tag::BlockQuote(_)
+            | Tag::CodeBlock(_)
+            | Tag::HtmlBlock
+            | Tag::List(_)
+            | Tag::FootnoteDefinition(_)
+            | Tag::Table(_)
+    )
+}
+
 #[cfg(all(test, feature = "markdown"))]
 mod tests {
-    use assert_matches2::assert_matches;
-
     use super::parse_markdown;
 
     #[test]
     fn detect_markdown() {
         // Simple single-line text.
         let text = "Hello world.";
-        assert_matches!(parse_markdown(text), None);
+        assert_eq!(parse_markdown(text), None);
 
         // Simple double-line text.
         let text = "Hello\nworld.";
-        assert_matches!(parse_markdown(text), None);
+        assert_eq!(parse_markdown(text), None);
 
         // With new paragraph.
         let text = "Hello\n\nworld.";
-        assert_matches!(parse_markdown(text), Some(_));
+        assert_eq!(parse_markdown(text).as_deref(), Some("<p>Hello</p>\n<p>world.</p>\n"));
+
+        // With heading and paragraph.
+        let text = "## Hello\n\nworld.";
+        assert_eq!(parse_markdown(text).as_deref(), Some("<h2>Hello</h2>\n<p>world.</p>\n"));
+
+        // With paragraph and code block.
+        let text = "Hello\n\n```\nworld.\n```";
+        assert_eq!(
+            parse_markdown(text).as_deref(),
+            Some("<p>Hello</p>\n<pre><code>world.\n</code></pre>\n")
+        );
 
         // With tagged element.
         let text = "Hello **world**.";
-        assert_matches!(parse_markdown(text), Some(_));
+        assert_eq!(parse_markdown(text).as_deref(), Some("Hello <strong>world</strong>."));
 
         // With backslash escapes.
         let text = r#"Hello \<world\>."#;
-        assert_matches!(parse_markdown(text), Some(_));
+        assert_eq!(parse_markdown(text).as_deref(), Some("Hello &lt;world&gt;."));
 
         // With entity reference.
         let text = r#"Hello &lt;world&gt;."#;
-        assert_matches!(parse_markdown(text), Some(_));
+        assert_eq!(parse_markdown(text).as_deref(), Some("Hello &lt;world&gt;."));
 
         // With numeric reference.
         let text = "Hello w&#8853;rld.";
-        assert_matches!(parse_markdown(text), Some(_));
+        assert_eq!(parse_markdown(text).as_deref(), Some("Hello w⊕rld."));
     }
 }

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

@@ -82,7 +82,7 @@ fn markdown_content_serialization() {
             "org.matrix.msc1767.text": [
                 {
                     "mimetype": "text/html",
-                    "body": "<p>Testing <strong>bold</strong> and <em>italic</em>!</p>\n",
+                    "body": "Testing <strong>bold</strong> and <em>italic</em>!",
                 },
                 {
                     "body": "Testing **bold** and _italic_!",

crates/ruma-events/tests/it/room_message.rs

@@ -117,7 +117,7 @@ fn text_msgtype_markdown_serialization() {
         to_json_value(&formatted_message).unwrap(),
         json!({
             "body": text,
-            "formatted_body": "<p>Testing <strong>bold</strong> and <em>italic</em>!</p>\n",
+            "formatted_body": "Testing <strong>bold</strong> and <em>italic</em>!",
             "format": "org.matrix.custom.html",
             "msgtype": "m.text"
         })
@@ -198,16 +198,20 @@ fn markdown_detection() {
     assert_matches!(formatted_body, None);
 
     // Multiple paragraphs trigger markdown
-    let formatted_body = FormattedBody::markdown("A message\nwith\n\nmultiple\n\nparagraphs");
+    let formatted_body =
-    formatted_body.unwrap();
+        FormattedBody::markdown("A message\nwith\n\nmultiple\n\nparagraphs").unwrap();
+    assert_eq!(
+        formatted_body.body,
+        "<p>A message<br />\nwith</p>\n<p>multiple</p>\n<p>paragraphs</p>\n"
+    );
 
     // "Less than" symbol triggers markdown.
-    let formatted_body = FormattedBody::markdown("A message with & HTML < entities");
+    let formatted_body = FormattedBody::markdown("A message with & HTML < entities").unwrap();
-    assert_matches!(formatted_body, Some(_));
+    assert_eq!(formatted_body.body, "A message with &amp; HTML &lt; entities");
 
     // HTML triggers markdown.
-    let formatted_body = FormattedBody::markdown("<span>An HTML message</span>");
+    let formatted_body = FormattedBody::markdown("<span>An HTML message</span>").unwrap();
-    formatted_body.unwrap();
+    assert_eq!(formatted_body.body, "<span>An HTML message</span>");
 }
 
 #[test]
@@ -232,7 +236,7 @@ fn markdown_options() {
 
     // Strikethrough
     let formatted_body = FormattedBody::markdown("A message with a ~~strike~~");
-    assert_eq!(formatted_body.unwrap().body, "<p>A message with a <del>strike</del></p>\n");
+    assert_eq!(formatted_body.unwrap().body, "A message with a <del>strike</del>");
 }
 
 #[test]