diff --git a/xtask/src/codegen.rs b/xtask/src/codegen.rs
index b4907f4b2b0..2e8fd34943e 100644
--- a/xtask/src/codegen.rs
+++ b/xtask/src/codegen.rs
@@ -61,8 +61,24 @@ fn extract_comment_blocks(text: &str) -> Vec<Vec<String>> {
     do_extract_comment_blocks(text, false)
 }
 
-fn extract_comment_blocks_with_empty_lines(text: &str) -> Vec<Vec<String>> {
-    do_extract_comment_blocks(text, true)
+fn extract_comment_blocks_with_empty_lines(tag: &str, text: &str) -> Vec<CommentBlock> {
+    assert!(tag.starts_with(char::is_uppercase));
+    let tag = format!("{}:", tag);
+    let mut res = Vec::new();
+    for mut block in do_extract_comment_blocks(text, true) {
+        let first = block.remove(0);
+        if first.starts_with(&tag) {
+            let id = first[tag.len()..].trim().to_string();
+            let block = CommentBlock { id, contents: block };
+            res.push(block);
+        }
+    }
+    res
+}
+
+struct CommentBlock {
+    id: String,
+    contents: Vec<String>,
 }
 
 fn do_extract_comment_blocks(text: &str, allow_blocks_with_empty_lines: bool) -> Vec<Vec<String>> {
diff --git a/xtask/src/codegen/gen_assists_docs.rs b/xtask/src/codegen/gen_assists_docs.rs
index 20dcde82068..6ebeb8aea4e 100644
--- a/xtask/src/codegen/gen_assists_docs.rs
+++ b/xtask/src/codegen/gen_assists_docs.rs
@@ -33,22 +33,18 @@ impl Assist {
 
         fn collect_file(acc: &mut Vec<Assist>, path: &Path) -> Result<()> {
             let text = fs::read_to_string(path)?;
-            let comment_blocks = extract_comment_blocks_with_empty_lines(&text);
+            let comment_blocks = extract_comment_blocks_with_empty_lines("Assist", &text);
 
             for block in comment_blocks {
                 // FIXME: doesn't support blank lines yet, need to tweak
                 // `extract_comment_blocks` for that.
-                let mut lines = block.iter();
-                let first_line = lines.next().unwrap();
-                if !first_line.starts_with("Assist: ") {
-                    continue;
-                }
-                let id = first_line["Assist: ".len()..].to_string();
+                let id = block.id;
                 assert!(
                     id.chars().all(|it| it.is_ascii_lowercase() || it == '_'),
                     "invalid assist id: {:?}",
                     id
                 );
+                let mut lines = block.contents.iter();
 
                 let doc = take_until(lines.by_ref(), "```").trim().to_string();
                 assert!(