Output cause on JS runtime errors

[petamoriken]

Since Deno 1.13.0, Error Cause Proposal is supported, so the Error object can hold inner errors. However, their contents are usually not displayed and I need to explicitly access the cause property.

function bar() {
  throw new Error("bar");
}

function foo() {
  try {
    bar();
  } catch (e) {
    throw new Error("foo", { cause: e });
  }
}

foo();

I think it should also show inner errors, just like Firefox does.

[bartlomieju]

Showing Error.cause when inspecting in console landed in v1.16 (https://deno.com/blog/v1.16#errorcause-is-now-displayed-in-the-console), we should add the same feature for errors that were returned by the runtime. It will require to modify deno_core and cli to also account for cause property in errors.

Most likely these functions need to be updated:

deno/core/error.rs

Lines 173 to 200 in 1947f89

	pub fn from_v8_exception(
	scope: &mut v8::HandleScope,
	exception: v8::Local<v8::Value>,
	) -> Self {
	// Create a new HandleScope because we're creating a lot of new local
	// handles below.
	let scope = &mut v8::HandleScope::new(scope);
	let msg = v8::Exception::create_message(scope, exception);
	let (message, frames, stack) = if is_instance_of_error(scope, exception) {
	// The exception is a JS Error object.
	let exception: v8::Local<v8::Object> = exception.try_into().unwrap();
	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());
	let message = if !name.is_empty() && !message_prop.is_empty() {
	format!("Uncaught {}: {}", name, message_prop)
	} else if !name.is_empty() {
	format!("Uncaught {}", name)
	} else if !message_prop.is_empty() {
	format!("Uncaught {}", message_prop)
	} else {
	"Uncaught".to_string()
	};

deno/cli/fmt_errors.rs

Lines 245 to 280 in 1947f89

	impl fmt::Display for PrettyJsError {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
	let mut frames = self.0.frames.clone();
	// When the stack frame array is empty, but the source location given by
	// (script_resource_name, line_number, start_column + 1) exists, this is
	// likely a syntax error. For the sake of formatting we treat it like it was
	// given as a single stack frame.
	if frames.is_empty()
	&& self.0.script_resource_name.is_some()
	&& self.0.line_number.is_some()
	&& self.0.start_column.is_some()
	{
	frames = vec![JsStackFrame::from_location(
	self.0.script_resource_name.clone(),
	self.0.line_number,
	self.0.start_column.map(|n| n + 1),
	)];
	}
	write!(
	f,
	"{}",
	&format_stack(
	true,
	&self.0.message,
	self.0.source_line.as_deref(),
	self.0.start_column,
	self.0.end_column,
	&frames,
	0
	)
	)?;
	Ok(())
	}
	}