Fix panic in checker

Author: antonmedv

checker/checker.go

@@ -475,7 +475,7 @@ func (v *visitor) MemberNode(node *ast.MemberNode) (reflect.Type, info) {
 func (v *visitor) SliceNode(node *ast.SliceNode) (reflect.Type, info) {
 	t, _ := v.visit(node.Node)
 
-	switch t.Kind() {
+	switch kind(t) {
 	case reflect.Interface:
 		// ok
 	case reflect.String, reflect.Array, reflect.Slice:
@@ -532,7 +532,7 @@ func (v *visitor) CallNode(node *ast.CallNode) (reflect.Type, info) {
 			fn.NumOut() == 1 &&
 			fn.Out(0).Kind() == reflect.Interface {
 			rest := fn.In(fn.NumIn() - 1) // function has only one param for functions and two for methods
-			if rest.Kind() == reflect.Slice && rest.Elem().Kind() == reflect.Interface {
+			if kind(rest) == reflect.Slice && rest.Elem().Kind() == reflect.Interface {
 				node.Fast = true
 			}
 		}
@@ -666,7 +666,7 @@ func (v *visitor) checkBuiltinGet(node *ast.BuiltinNode) (reflect.Type, info) {
 
 	t, _ := v.visit(val)
 
-	switch t.Kind() {
+	switch kind(t) {
 	case reflect.Interface:
 		return anyType, info{}
 	case reflect.Slice, reflect.Array:
@@ -791,7 +791,7 @@ func (v *visitor) checkArguments(name string, fn reflect.Type, method bool, argu
 			continue
 		}
 
-		if !t.AssignableTo(in) && t.Kind() != reflect.Interface {
+		if !t.AssignableTo(in) && kind(t) != reflect.Interface {
 			return anyType, &file.Error{
 				Location: arg.Location(),
 				Message:  fmt.Sprintf("cannot use %v as argument (type %v) to call %v ", t, in, name),

checker/types.go

@@ -223,6 +223,13 @@ func deref(t reflect.Type) reflect.Type {
 	return t
 }
 
+func kind(t reflect.Type) reflect.Kind {
+	if t == nil {
+		return reflect.Invalid
+	}
+	return t.Kind()
+}
+
 func isIntegerOrArithmeticOperation(node ast.Node) bool {
 	switch n := node.(type) {
 	case *ast.IntegerNode:

compiler/compiler_test.go

@@ -5,6 +5,7 @@ import (
 	"testing"
 
 	"github.com/antonmedv/expr"
+	"github.com/antonmedv/expr/test/playground"
 	"github.com/antonmedv/expr/vm"
 	"github.com/antonmedv/expr/vm/runtime"
 	"github.com/stretchr/testify/assert"
@@ -278,3 +279,15 @@ func TestCompile(t *testing.T) {
 		assert.Equal(t, test.program.Disassemble(), program.Disassemble(), test.input)
 	}
 }
+
+func TestCompile_panic(t *testing.T) {
+	tests := []string{
+		`(TotalPosts.Profile[Authors > TotalPosts == get(nil, TotalLikes)] > Authors) ^ (TotalLikes / (Posts?.PublishDate[TotalPosts] < Posts))`,
+	}
+	for _, test := range tests {
+		t.Run(test, func(t *testing.T) {
+			_, err := expr.Compile(test, expr.Env(playground.Blog{}))
+			require.Error(t, err)
+		})
+	}
+}