fix: double invalidate bug

[sinasab]

Currently, if a query gets invalidated while its state is Loading(Some(value)), it loses the value. This can be annoying in cases where the query is invalidated multiple times within a short timespan, or for long-running queries.

We can fix this by nooping set_loading calls for queries that are already loading, which is what this change adds.

Manually verified this behavior locally via dx serve --example queries 🫡

[marc2332]

But how is the value lost if there is this:

let result = mem::replace(self, Self::Pending).into();
// this:
if let Some(v) = result {
    *self = Self::Loading(Some(v))
}

to consider:

impl<T, E> From<MutationResult<T, E>> for Option<T> {
    fn from(result: MutationResult<T, E>) -> Self {
        match result {
            MutationResult::Ok(v) => Some(v),
            MutationResult::Err(_) => None,
            MutationResult::Loading(v) => v,
            MutationResult::Pending => None,
        }
    }
}

If the value was already Loading it would be assigned as loading again, not sure why would that not be the case, do you? 🤔

[sinasab]

Cleaned up fix looks good, thanks for taking a look 😁