[compat] when using dynamic import in Node compat mode and module is not found, err.code needs to be set to 'ERR_MODULE_NOT_FOUND'

[kt3k]

In Node.js, it's common to check err.code to detect the kind of errors:

if (err.code === 'ERR_MODULE_NOT_FOUND') {
  // do something
}

std/node simulates these error codes in API layer (ref: https://github.com/denoland/deno_std/blob/0b31c1647649f9b6aa53432370daab4483803e77/node/_errors.ts#L289-L304 )

But in the case of dynamic import, the above shim can't be used. So err.code needs to be set to ERR_MODULE_NOT_FOUND directly in CLI runtime when --compat flag is specified.

This feature is used in mocha when looking up the test files (ref: https://github.com/mochajs/mocha/blob/97b84708afb42e552cb906a54f9f2aa2e6a98ba4/lib/nodejs/esm-utils.js#L47-L56 )

related: #12577

[bartlomieju]

I'm a bit at loss how to tackle this problem right now...

Module loading is done by deno_core and any additional fields on the error instance would need to be created there, but deno_core is completely agnostic of compat layer.

Moreover we need to decide how are we going to handle this situation in wider context - ie. in runtime Deno APIs (ref #12591).

[kt3k]

TypeError for dynamic import rejection seems created here (hard-coded to type_error)

deno/core/runtime.rs

Lines 1145 to 1152 in e06515c

	let exception = err
	.downcast_ref::<ErrWithV8Handle>()
	.map(|err| err.get_handle(scope))
	.unwrap_or_else(|| {
	let message = err.to_string();
	let message = v8::String::new(scope, &message).unwrap();
	v8::Exception::type_error(scope, message)
	});

But that err comes from cli/proc_state.rs

deno/cli/proc_state.rs

Lines 528 to 531 in e06515c

	return Err(custom_error(
	"NotFound",
	format!("Cannot load module \"{}\".", specifier),
	));

and it has class_name at the creation, but that class_name is not used in core/runtime.rs. I guess we can use that class name and swap the error constructor in core/runtime.rs

(pseudo code)

let value = execute_script(get_custom_error_class(err).unwrap());
let err = value.to_object(scope).call_as_constructor(1, err_message);
resolver.reject(scope, err).unwrap();