fix(query): forbid an anchor at the end of a group

A `.` at the end of a group, such as `((comment)+ @c .)`, was silently dropped
during compilation. Reject rather than dropping.

crates/cli/src/tests/query_test.rs

@@ -256,6 +256,51 @@ fn test_query_errors_on_invalid_syntax() {
     });
 }
 
+#[test]
+fn test_query_errors_on_anchor_at_group_edge() {
+    allocations::record(|| {
+        let language = get_language("javascript");
+
+        // Anchors between siblings, or at the first/last position of a *node*
+        // pattern, are valid.
+        assert!(Query::new(&language, "((_) . (_))").is_ok());
+        assert!(Query::new(&language, "(program (_) (_) .)").is_ok());
+        assert!(Query::new(&language, "(program (_)* @x . (_))").is_ok());
+
+        // A `.` at the edge of a *group* is rejected. A group is not a node, so it
+        // has no last child to anchor, and there is no sibling within the group to
+        // anchor to.
+        assert_eq!(
+            Query::new(&language, "((_) .)").unwrap_err(),
+            QueryError {
+                row: 0,
+                offset: 5,
+                column: 5,
+                kind: QueryErrorKind::Syntax,
+                message: [
+                    "((_) .)", //
+                    "     ^"
+                ]
+                .join("\n")
+            }
+        );
+        assert_eq!(
+            Query::new(&language, "(program ((_)+ .)? (_))").unwrap_err(),
+            QueryError {
+                row: 0,
+                offset: 15,
+                column: 15,
+                kind: QueryErrorKind::Syntax,
+                message: [
+                    "(program ((_)+ .)? (_))", //
+                    "               ^"
+                ]
+                .join("\n")
+            }
+        );
+    });
+}
+
 #[test]
 fn test_query_errors_on_invalid_symbols() {
     allocations::record(|| {

lib/src/query.c

@@ -2485,9 +2485,17 @@ static TSQueryError ts_query__parse_pattern(
       CaptureQuantifiers child_capture_quantifiers = capture_quantifiers_new();
       for (;;) {
         if (stream->next == '.') {
+          const char *anchor_start = stream->input;
           child_is_immediate = true;
           stream_advance(stream);
           stream_skip_whitespace(stream);
+          // A `.` at a group's end has no sibling to anchor, and a group is not a
+          // node, so there is no last child to anchor against.
+          if (stream->next == ')') {
+            stream_reset(stream, anchor_start);
+            capture_quantifiers_delete(&child_capture_quantifiers);
+            return TSQueryErrorSyntax;
+          }
         }
         TSQueryError e = ts_query__parse_pattern(
           self,