core: handle NativeJsError.stack as before since it's "special"

Its v8::Object::get returns None sometimes (not undefined), which isn't expected.

Might be able to handle this better in the future, but for now it's better to panic than to swallow the value

core/error.rs

@@ -158,7 +158,8 @@ fn get_property<'a>(
 struct NativeJsError {
  name: Option<String>,
  message: Option<String>,
- stack: Option<String>,
+ // Warning! .stack is special so handled by itself
+ // stack: Option<String>,
 }
 
 impl JsError {
@@ -181,12 +182,8 @@ impl JsError {
  let exception: v8::Local<v8::Object> =
  exception.clone().try_into().unwrap();
 
- // Decode native JS error, internally this should access error.stack
- // ensuring that prepareStackTrace() has been called.
- // Which in turn should populate error.__callSiteEvals.
  let e: NativeJsError =
  serde_v8::from_v8(scope, exception.into()).unwrap();
-
  // Get the message by formatting error.name and error.message.
  let name = e.name.unwrap_or_else(|| "Error".to_string());
  let message_prop = e.message.unwrap_or_else(|| "".to_string());
@@ -200,18 +197,25 @@ impl JsError {
  "Uncaught".to_string()
  };
 
+ // Access error.stack to ensure that prepareStackTrace() has been called.
+ // This should populate error.__callSiteEvals.
+ let stack = get_property(scope, exception, "stack");
+ let stack: Option<v8::Local<v8::String>> =
+ stack.and_then(|s| s.try_into().ok());
+ let stack = stack.map(|s| s.to_rust_string_lossy(scope));
+
  // Read an array of structured frames from error.__callSiteEvals.
  let frames_v8 = get_property(scope, exception, "__callSiteEvals");
  // Ignore non-array values
  let frames_v8: Option<v8::Local<v8::Array>> =
- frames_v8.and_then(|a| a.try_into().ok());
+  frames_v8.and_then(|a| a.try_into().ok());
 
- // Convert them into Vec<JSStack>
+ // Convert them into Vec<JsStackFrame>
  let frames: Vec<JsStackFrame> = match frames_v8 {
  Some(frames_v8) => serde_v8::from_v8(scope, frames_v8.into()).unwrap(),
  None => vec![],
  };
- (message, frames, e.stack)
+ (message, frames, stack)
  } else {
  // The exception is not a JS Error object.
  // Get the message given by V8::Exception::create_message(), and provide