huskies: merge 579_bug_matrix_bot_messages_render_markdown_headings_without_line_breaks_or_formatting

server/src/chat/util.rs

@@ -223,12 +223,24 @@ pub fn normalize_line_breaks(text: &str) -> String {
 
         let prev_line = lines[i - 1];
 
-        // Insert a blank separator when both the current and previous lines
-        // are non-empty prose (not inside a code fence, not structured Markdown).
+        // ATX headings (lines starting with one or more `#` characters) always
+        // need a blank line before and after them so that Matrix clients render
+        // the heading with visual separation.  Without a blank line, a single
+        // newline between a heading and adjacent text is swallowed by many
+        // Matrix clients (including Element X), joining the heading text and
+        // the following content on the same line without any heading formatting.
+        let is_cur_heading = line.trim_start().starts_with('#');
+        let is_prev_heading = prev_line.trim_start().starts_with('#');
+
+        // Insert a blank separator when:
+        //   1. Both lines are non-empty prose (standard prose-to-prose rule).
+        //   2. The current line is an ATX heading (adds blank line *before* it).
+        //   3. The previous line was an ATX heading (adds blank line *after* it).
         let should_double = !line.is_empty()
             && !prev_line.is_empty()
-            && !is_structured_line(line)
-            && !is_structured_line(prev_line);
+            && ((!is_structured_line(line) && !is_structured_line(prev_line))
+                || is_cur_heading
+                || is_prev_heading);
 
         if should_double {
             result.push("");
@@ -599,10 +611,42 @@ mod tests {
     }
 
     #[test]
-    fn normalize_heading_single_newline_preserved() {
+    fn normalize_heading_followed_by_prose_gets_blank_line() {
+        // A blank line must be inserted after a heading so Matrix clients render
+        // the heading with visual separation from the following paragraph.
         let input = "# My Heading\nSome text below.";
         let output = normalize_line_breaks(input);
-        assert_eq!(output, "# My Heading\nSome text below.");
+        assert_eq!(output, "# My Heading\n\nSome text below.");
+    }
+
+    #[test]
+    fn normalize_prose_before_heading_gets_blank_line() {
+        // A blank line must be inserted before a heading when prose precedes it.
+        let input = "Some intro text.\n## Section";
+        let output = normalize_line_breaks(input);
+        assert_eq!(output, "Some intro text.\n\n## Section");
+    }
+
+    #[test]
+    fn normalize_heading_surrounded_by_prose_gets_blank_lines_both_sides() {
+        let input = "Intro.\n## Heading\nContent.";
+        let output = normalize_line_breaks(input);
+        assert_eq!(output, "Intro.\n\n## Heading\n\nContent.");
+    }
+
+    #[test]
+    fn normalize_consecutive_headings_separated_by_blank_lines() {
+        let input = "## Section 1\n## Section 2";
+        let output = normalize_line_breaks(input);
+        assert_eq!(output, "## Section 1\n\n## Section 2");
+    }
+
+    #[test]
+    fn normalize_heading_already_separated_by_blank_line_unchanged() {
+        // When there is already a blank line, no extra blank is inserted.
+        let input = "# Heading\n\nContent.";
+        let output = normalize_line_breaks(input);
+        assert_eq!(output, "# Heading\n\nContent.");
     }
 
     #[test]