Fix compiler fold optimization of "integer divide by zero"

Author: antonmedv

expr_test.go

@@ -1142,6 +1142,17 @@ func TestIssue_nested_closures(t *testing.T) {
 	require.True(t, output.(bool))
 }
 
+func TestIssue138(t *testing.T) {
+	env := map[string]interface{}{}
+
+	_, err := expr.Compile(`1 / (1 - 1)`, expr.Env(env))
+	require.Error(t, err)
+	require.Equal(t, "integer divide by zero (1:3)\n | 1 / (1 - 1)\n | ..^", err.Error())
+
+	_, err = expr.Compile(`1 % 0`, expr.Env(env))
+	require.Error(t, err)
+}
+
 //
 // Mock types
 //

optimizer/fold.go

@@ -5,10 +5,12 @@ import (
 	"reflect"
 
 	. "github.com/antonmedv/expr/ast"
+	"github.com/antonmedv/expr/file"
 )
 
 type fold struct {
 	applied bool
+	err     *file.Error
 }
 
 func (*fold) Enter(*Node) {}
@@ -65,12 +67,26 @@ func (fold *fold) Exit(node *Node) {
 		case "/":
 			if a, ok := n.Left.(*IntegerNode); ok {
 				if b, ok := n.Right.(*IntegerNode); ok {
+					if b.Value == 0 {
+						fold.err = &file.Error{
+							Location: (*node).Location(),
+							Message:  "integer divide by zero",
+						}
+						return
+					}
 					patchWithType(&IntegerNode{Value: a.Value / b.Value}, a.Type())
 				}
 			}
 		case "%":
 			if a, ok := n.Left.(*IntegerNode); ok {
 				if b, ok := n.Right.(*IntegerNode); ok {
+					if b.Value == 0 {
+						fold.err = &file.Error{
+							Location: (*node).Location(),
+							Message:  "integer divide by zero",
+						}
+						return
+					}
 					patch(&IntegerNode{Value: a.Value % b.Value})
 				}
 			}

optimizer/optimizer.go

@@ -10,6 +10,9 @@ func Optimize(node *Node, config *conf.Config) error {
 	for limit := 1000; limit >= 0; limit-- {
 		fold := &fold{}
 		Walk(node, fold)
+		if fold.err != nil {
+			return fold.err
+		}
 		if !fold.applied {
 			break
 		}