Add argument-comment Dylint runner (#14651)

tools/argument-comment-lint/src/comment_parser.rs

@@ -0,0 +1,63 @@
+pub fn parse_argument_comment(text: &str) -> Option<&str> {
+    let trimmed = text.trim_end();
+    let comment_start = trimmed.rfind("/*")?;
+    let comment = &trimmed[comment_start..];
+    let name = comment.strip_prefix("/*")?.strip_suffix("*/")?;
+    is_identifier(name).then_some(name)
+}
+
+pub fn parse_argument_comment_prefix(text: &str) -> Option<&str> {
+    let trimmed = text.trim_start();
+    let comment = trimmed.strip_prefix("/*")?;
+    let (name, _) = comment.split_once("*/")?;
+    is_identifier(name).then_some(name)
+}
+
+fn is_identifier(text: &str) -> bool {
+    let mut chars = text.chars();
+    let Some(first) = chars.next() else {
+        return false;
+    };
+    if !(first == '_' || first.is_ascii_alphabetic()) {
+        return false;
+    }
+    chars.all(|ch| ch == '_' || ch.is_ascii_alphanumeric())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::parse_argument_comment;
+    use super::parse_argument_comment_prefix;
+
+    #[test]
+    fn parses_trailing_comment() {
+        assert_eq!(parse_argument_comment("(/*base_url*/ "), Some("base_url"));
+        assert_eq!(
+            parse_argument_comment(", /*timeout_ms*/ "),
+            Some("timeout_ms")
+        );
+        assert_eq!(
+            parse_argument_comment(".method::<u8>(/*base_url*/ "),
+            Some("base_url")
+        );
+    }
+
+    #[test]
+    fn rejects_non_matching_shapes() {
+        assert_eq!(parse_argument_comment("(\n"), None);
+        assert_eq!(parse_argument_comment("(/* base_url*/ "), None);
+        assert_eq!(parse_argument_comment("(/*base_url */ "), None);
+        assert_eq!(parse_argument_comment("(/*base_url=*/ "), None);
+        assert_eq!(parse_argument_comment("(/*1base_url*/ "), None);
+        assert_eq!(parse_argument_comment_prefix("/*env=*/ None"), None);
+    }
+
+    #[test]
+    fn parses_prefix_comment() {
+        assert_eq!(parse_argument_comment_prefix("/*env*/ None"), Some("env"));
+        assert_eq!(
+            parse_argument_comment_prefix("\n    /*retry_count*/ 3"),
+            Some("retry_count")
+        );
+    }
+}