fix: allow line_format in metric queries (#12)

Author: everpcpc

src/logql/mod.rs

@@ -879,6 +879,15 @@ mod tests {
         assert!(err.contains("drop"), "unexpected error: {}", err);
     }
 
+    #[test]
+    fn metric_drop_labels_ignore_line_format() {
+        let expr = LogqlParser
+            .parse("{job=\"api\"} | line_format \"{{.message}}\"")
+            .unwrap();
+        let drops = expr.pipeline.metric_drop_labels().unwrap();
+        assert!(drops.is_empty());
+    }
+
     #[test]
     fn duration_literal_with_multiple_segments() {
         let value = DurationValue::parse_literal("1h30m15s").unwrap();

src/logql/pipeline.rs

@@ -36,6 +36,9 @@ impl Pipeline {
         for stage in &self.stages {
             match stage {
                 PipelineStage::Drop(stage) => labels.extend(stage.targets.iter().cloned()),
+                PipelineStage::LineFormat(_) => {
+                    continue;
+                }
                 _ => {
                     return Err(
                         "metric queries only support `drop` stages inside the selector pipeline"