Add type check on topk/bottomk parameter.

promql/parse.go

@@ -1049,6 +1049,9 @@ func (p *parser) checkType(node Node) (typ model.ValueType) {
 			p.errorf("aggregation operator expected in aggregation expression but got %q", n.Op)
 		}
 		p.expectType(n.Expr, model.ValVector, "aggregation expression")
+		if n.Op == itemTopK || n.Op == itemBottomK {
+			p.expectType(n.Param, model.ValScalar, "aggregation parameter")
+		}
 
 	case *BinaryExpr:
 		lt := p.checkType(n.LHS)

promql/parse_test.go

@@ -1253,6 +1253,10 @@ var testExpr = []struct {
 		input:  `topk(some_metric)`,
 		fail:   true,
 		errMsg: "parse error at char 17: unexpected \")\" in aggregation, expected \",\"",
+	}, {
+		input:  `topk(some_metric, other_metric)`,
+		fail:   true,
+		errMsg: "parse error at char 32: expected type scalar in aggregation parameter, got vector",
 	},
 	// Test function calls.
 	{