Disallow derivative call with non-duration 2nd arg

Previously, calling derivative with a non-duration second argument was
allowed during parsing but would panic during execution due to a failed
type conversion. This change ensures the second argument is a duration
literal.

influxql/ast.go

@@ -1667,11 +1667,7 @@ func (s *SelectStatement) validateAggregates(tr targetRequirement) error {
 					return err
 				}
 				switch expr.Name {
-				case "derivative", "non_negative_derivative":
-					if min, max, got := 1, 2, len(expr.Args); got > max || got < min {
-						return fmt.Errorf("invalid number of arguments for %s, expected at least %d but no more than %d, got %d", expr.Name, min, max, got)
-					}
-				case "elapsed":
+				case "derivative", "non_negative_derivative", "elapsed":
 					if min, max, got := 1, 2, len(expr.Args); got > max || got < min {
 						return fmt.Errorf("invalid number of arguments for %s, expected at least %d but no more than %d, got %d", expr.Name, min, max, got)
 					}
@@ -1679,7 +1675,7 @@ func (s *SelectStatement) validateAggregates(tr targetRequirement) error {
 					if len(expr.Args) == 2 {
 						// Second must be a duration .e.g (1h)
 						if _, ok := expr.Args[1].(*DurationLiteral); !ok {
-							return errors.New("elapsed requires a duration argument")
+							return fmt.Errorf("second argument to %s must be a duration, got %T", expr.Name, expr.Args[1])
 						}
 					}
 				case "difference", "cumulative_sum":

influxql/ast_test.go

@@ -1313,6 +1313,29 @@ func TestSources_HasSystemSource(t *testing.T) {
 	}
 }
 
+// Parse statements that might appear valid but should return an error.
+// If allowed to execute, at least some of these statements would result in a panic.
+func TestParse_Errors(t *testing.T) {
+	for _, tt := range []struct {
+		tmpl string
+		good string
+		bad  string
+	}{
+		// Second argument to derivative must be duration
+		{tmpl: `SELECT derivative(f, %s) FROM m`, good: "1h", bad: "true"},
+	} {
+		good := fmt.Sprintf(tt.tmpl, tt.good)
+		if _, err := influxql.ParseStatement(good); err != nil {
+			t.Fatalf("statement %q should have parsed correctly but returned error: %s", good, err)
+		}
+
+		bad := fmt.Sprintf(tt.tmpl, tt.bad)
+		if _, err := influxql.ParseStatement(bad); err == nil {
+			t.Fatalf("statement %q should have resulted in a parse error but did not", bad)
+		}
+	}
+}
+
 // Valuer represents a simple wrapper around a map to implement the influxql.Valuer interface.
 type Valuer map[string]interface{}