fix(gnovm): allow private struct fields to be set

Go reflect doesn't allow to set unexported struct fields.
We use `unsafe` to override this limitation.

Fixes #1155 and #3812

gnovm/pkg/gnolang/gonative.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"math"
 	"reflect"
+	"unsafe"
 
 	"github.com/gnolang/gno/gnovm/pkg/gnolang/internal/softfloat"
 )
@@ -1133,7 +1134,12 @@ func gno2GoValue(tv *TypedValue, rv reflect.Value) (ret reflect.Value) {
 			if ftv.IsUndefined() {
 				continue
 			}
-			gno2GoValue(ftv, rv.Field(i))
+			fv := rv.Field(i)
+			if !fv.CanSet() {
+				// Normally private fields can not bet set via reflect. Override this limitation.
+				fv = reflect.NewAt(fv.Type(), unsafe.Pointer(fv.UnsafeAddr())).Elem()
+			}
+			gno2GoValue(ftv, fv)
 		}
 	case *MapType:
 		// If uninitialized map, return zero value.

gnovm/tests/files/struct59.gno

@@ -0,0 +1,15 @@
+package main
+
+import "fmt"
+
+type X struct {
+	v string
+}
+
+func main() {
+	x := X{v: "a"}
+	fmt.Printf("test %#v\n", x)
+}
+
+// Output:
+// test struct { v string }{v:"a"}