Fix nil key check in map (#351)

Author: antonmedv

checker/checker.go

@@ -417,7 +417,7 @@ func (v *visitor) MemberNode(node *ast.MemberNode) (reflect.Type, info) {
 		return anyType, info{}
 
 	case reflect.Map:
-		if !prop.AssignableTo(base.Key()) && !isAny(prop) {
+		if prop != nil && !prop.AssignableTo(base.Key()) && !isAny(prop) {
 			return v.error(node.Property, "cannot use %v to get an element from %v", prop, base)
 		}
 		t, c := deref(base.Elem())

expr_test.go

@@ -1772,6 +1772,45 @@ func TestRun_NilCoalescingOperator(t *testing.T) {
 	})
 }
 
+func TestEval_nil_in_maps(t *testing.T) {
+	env := map[string]interface{}{
+		"m":     map[interface{}]interface{}{nil: "bar"},
+		"empty": map[interface{}]interface{}{},
+	}
+	t.Run("nil key exists", func(t *testing.T) {
+		p, err := expr.Compile(`m[nil]`, expr.Env(env))
+		assert.NoError(t, err)
+
+		out, err := expr.Run(p, env)
+		assert.NoError(t, err)
+		assert.Equal(t, "bar", out)
+	})
+	t.Run("no nil key", func(t *testing.T) {
+		p, err := expr.Compile(`empty[nil]`, expr.Env(env))
+		assert.NoError(t, err)
+
+		out, err := expr.Run(p, env)
+		assert.NoError(t, err)
+		assert.Equal(t, nil, out)
+	})
+	t.Run("nil in m", func(t *testing.T) {
+		p, err := expr.Compile(`nil in m`, expr.Env(env))
+		assert.NoError(t, err)
+
+		out, err := expr.Run(p, env)
+		assert.NoError(t, err)
+		assert.Equal(t, true, out)
+	})
+	t.Run("nil in empty", func(t *testing.T) {
+		p, err := expr.Compile(`nil in empty`, expr.Env(env))
+		assert.NoError(t, err)
+
+		out, err := expr.Run(p, env)
+		assert.NoError(t, err)
+		assert.Equal(t, false, out)
+	})
+}
+
 // Mock types
 
 type mockEnv struct {

vm/runtime/runtime.go

@@ -48,7 +48,12 @@ func Fetch(from, i interface{}) interface{} {
 		}
 
 	case reflect.Map:
-		value := v.MapIndex(reflect.ValueOf(i))
+		var value reflect.Value
+		if i == nil {
+			value = v.MapIndex(reflect.Zero(v.Type().Key()))
+		} else {
+			value = v.MapIndex(reflect.ValueOf(i))
+		}
 		if value.IsValid() {
 			return value.Interface()
 		} else {
@@ -221,11 +226,16 @@ func In(needle interface{}, array interface{}) bool {
 		return false
 
 	case reflect.Map:
-		n := reflect.ValueOf(needle)
-		if !n.IsValid() {
-			panic(fmt.Sprintf("cannot use %T as index to %T", needle, array))
+		var value reflect.Value
+		if needle == nil {
+			value = v.MapIndex(reflect.Zero(v.Type().Key()))
+		} else {
+			n := reflect.ValueOf(needle)
+			if !n.IsValid() {
+				panic(fmt.Sprintf("cannot use %T as index to %T", needle, array))
+			}
+			value = v.MapIndex(n)
 		}
-		value := v.MapIndex(n)
 		if value.IsValid() {
 			return true
 		}