feat: add MetricsQL range functions (#6)

Author: milindsrivastava1997

src/parser/function.rs

@@ -247,7 +247,23 @@ lazy_static! {
             ValueType::Vector,
             false
         ),
+        // MetricsQL extension.
+        function!(
+            "distinct_over_time",
+            vec![ValueType::Matrix],
+            0,
+            ValueType::Vector,
+            false
+        ),
         function!("end", vec![], 0, ValueType::Scalar, true),
+        // MetricsQL extension.
+        function!(
+            "entropy_over_time",
+            vec![ValueType::Matrix],
+            0,
+            ValueType::Vector,
+            false
+        ),
         function!("exp", vec![ValueType::Vector], 0, ValueType::Vector, false),
         function!(
             "first_over_time",
@@ -668,13 +684,20 @@ mod tests {
         let rate = get_function("rate").unwrap();
         assert_eq!(rate.variadic, 0);
         assert!(!rate.experimental);
-
         for func_name in ["max_of", "min_of"] {
             let func = get_function(func_name).unwrap();
             assert_eq!(func.arg_types, vec![ValueType::Scalar, ValueType::Scalar]);
             assert_eq!(func.variadic, 0);
             assert_eq!(func.return_type, ValueType::Scalar);
             assert!(func.experimental);
         }
+
+        for func_name in ["distinct_over_time", "entropy_over_time"] {
+            let func = get_function(func_name).unwrap();
+            assert_eq!(func.arg_types, vec![ValueType::Matrix]);
+            assert_eq!(func.variadic, 0);
+            assert_eq!(func.return_type, ValueType::Vector);
+            assert!(!func.experimental);
+        }
     }
 }

src/parser/parse.rs

@@ -1345,6 +1345,30 @@ mod tests {
                     Expr::new_call(get_function("rate").unwrap(), FunctionArgs::new_args(ex))
                 })
             }),
+            ("distinct_over_time(some_metric[5m])", {
+                Expr::new_matrix_selector(
+                    Expr::from(VectorSelector::from("some_metric")),
+                    duration::MINUTE_DURATION * 5,
+                )
+                .and_then(|ex| {
+                    Expr::new_call(
+                        get_function("distinct_over_time").unwrap(),
+                        FunctionArgs::new_args(ex),
+                    )
+                })
+            }),
+            ("entropy_over_time(some_metric[5m])", {
+                Expr::new_matrix_selector(
+                    Expr::from(VectorSelector::from("some_metric")),
+                    duration::MINUTE_DURATION * 5,
+                )
+                .and_then(|ex| {
+                    Expr::new_call(
+                        get_function("entropy_over_time").unwrap(),
+                        FunctionArgs::new_args(ex),
+                    )
+                })
+            }),
             ("round(some_metric)", {
                 let ex = Expr::from(VectorSelector::from("some_metric"));
                 Expr::new_call(get_function("round").unwrap(), FunctionArgs::new_args(ex))