fix PQL, Rows and Group By problems

make sure that args which are Uints are positive and return an error if not.

improve group by error messages if field for Rows query is invalid

executor.go

@@ -2763,7 +2763,10 @@ func newGroupByIterator(rowIDs []RowIDs, children []*pql.Call, filter *Row, inde
 	for i, call := range children {
 		fieldName, ok := call.Args["field"].(string)
 		if !ok {
-			return nil, errors.Errorf("%s call must have 'field' argument", call.Name)
+			return nil, errors.Errorf("%s call must have 'field' argument with valid (string) field name. Got %v of type %[2]T", call.Name, call.Args["field"])
+		}
+		if holder.Field(index, fieldName) == nil {
+			return nil, ErrFieldNotFound
 		}
 		gbi.fields[i].Field = fieldName
 		// Fetch fragment.

executor_test.go

@@ -2672,10 +2672,9 @@ func TestExecutor_Execute_Rows(t *testing.T) {
 	if !reflect.DeepEqual(rows, pilosa.RowIdentifiers{Rows: []uint64{11, 12}}) {
 		t.Fatalf("unexpected rows: %+v", rows)
 	}
-
 }
 
-func TestExecutor_Execute_Rows_Error(t *testing.T) {
+func TestExecutor_Execute_Query_Error(t *testing.T) {
 	c := test.MustRunCluster(t, 3)
 	defer c.Close()
 	c.CreateField(t, "i", pilosa.IndexOptions{}, "general")
@@ -2688,6 +2687,30 @@ func TestExecutor_Execute_Rows_Error(t *testing.T) {
 			query: "GroupBy(Rows())",
 			error: "Rows call must have 'field' argument",
 		},
+		{
+			query: "GroupBy(Rows(field=true))",
+			error: "Rows call must have 'field' argument",
+		},
+		{
+			query: "GroupBy(Rows(field=\"true\"))",
+			error: "field not found",
+		},
+		{
+			query: "GroupBy(Rows(field=1))",
+			error: "Rows call must have 'field' argument",
+		},
+		{
+			query: "GroupBy(Rows(field))",
+			error: "parse error",
+		},
+		{
+			query: "GroupBy(Rows(field=general, limit=-1))",
+			error: "must be positive, but got",
+		},
+		{
+			query: "GroupBy(Rows(field=general), limit=-1)",
+			error: "must be positive, but got",
+		},
 	}
 
 	for i, test := range tests {

pql/ast.go

@@ -291,6 +291,9 @@ func (c *Call) UintArg(key string) (uint64, bool, error) {
 	}
 	switch tval := val.(type) {
 	case int64:
+		if tval < 0 {
+			return 0, true, fmt.Errorf("value for '%s' must be positive, but got %v", key, tval)
+		}
 		return uint64(tval), true, nil
 	case uint64:
 		return tval, true, nil