implement check for missing filters in pipeline

src/syntax/check.rs

@@ -14,6 +14,12 @@ pub fn check(
         errs.push(SyntaxError::MissingStreamer(vec![(file_id, e_span)]));
     }
 
+    if let Err(mut err_locs) = check_missing_filters(&syntax) {
+        errs.push(SyntaxError::MissingFilter(
+            err_locs.into_iter().map(|loc| (file_id, loc)).collect(),
+        ))
+    }
+
     if errs.is_empty() {
         Ok(syntax)
     } else {
@@ -32,3 +38,29 @@ fn check_missing_streamer(syntax: &Vec<PipelineElement>) -> Result<(), logos::Sp
         Ok(())
     }
 }
+
+fn check_missing_filters(syntax: &Vec<PipelineElement>) -> Result<(), Vec<logos::Span>> {
+    let mut missing_filter_locs = Vec::new();
+
+    for i in 0..syntax.len() {
+        if let (
+            Some(PipelineElement {
+                kind: PipelineElementKind::Pipe,
+                ref span,
+            }),
+            Some(PipelineElement {
+                kind: PipelineElementKind::Pipe,
+                span: ref span1,
+            }),
+        ) = (syntax.get(i), syntax.get(i + 1))
+        {
+            missing_filter_locs.push(span.start..span1.end)
+        }
+    }
+
+    if missing_filter_locs.is_empty() {
+        Ok(())
+    } else {
+        Err(missing_filter_locs)
+    }
+}