Parse ellipsis operator and emit a customized error message

crates/metaslang/cst/src/query/parser.rs

@@ -112,7 +112,7 @@ pub(super) fn parse_matcher_alt_sequence<T: KindTypes>(
 pub(super) fn parse_sequence_item<T: KindTypes>(
     i: &str,
 ) -> IResult<&str, ASTNode<T>, VerboseError<&str>> {
-    alt((anchor::<T>, parse_quantified_matcher::<T>)).parse(i)
+    alt((ellipsis_token, anchor::<T>, parse_quantified_matcher::<T>)).parse(i)
 }
 
 pub(super) fn parse_quantified_matcher<T: KindTypes>(
@@ -335,3 +335,30 @@ fn anchor<T: KindTypes>(i: &str) -> IResult<&str, ASTNode<T>, VerboseError<&str>
         .map(|_| ASTNode::Anchor)
         .parse(i)
 }
+
+fn recognize_as_failure<I: Clone, O1, O2, E: nom::error::ParseError<I>, F>(
+    mut parser: F,
+) -> impl FnMut(I) -> IResult<I, O2, E>
+where
+    F: nom::Parser<I, O1, E>,
+{
+    use nom::error::{make_error, ErrorKind};
+    use nom::Err::Failure;
+    move |input: I| {
+        let i = input.clone();
+        match parser.parse(i) {
+            Ok((_, _)) => Err(Failure(make_error(input, ErrorKind::Fail))),
+            Err(e) => Err(e),
+        }
+    }
+}
+
+fn ellipsis_token<O>(i: &str) -> IResult<&str, O, VerboseError<&str>> {
+    use nom::bytes::complete::tag;
+    use nom::error::context;
+    context(
+        "deprecated ellipsis operator",
+        recognize_as_failure(terminated(tag("..."), multispace0)),
+    )
+    .parse(i)
+}

crates/testlang/outputs/cargo/tests/src/query/parser_tests.rs

@@ -64,7 +64,10 @@ fn test_fails_parsing_ellipsis() {
     let result = Query::parse(r#"[_ ...]"#);
     match result {
         Ok(_) => panic!("Expected parse failure"),
-        Err(e) => assert_eq!(e.message, "Parse error:\nNoneOf at: ..]\n"),
+        Err(e) => assert_eq!(
+            e.message,
+            "Parse error:\nFail at: ...]\nin section 'deprecated ellipsis operator', at: ...]\n"
+        ),
     }
 }