Add datetime value parser

[bim9262]

Resolves #1708 (well will)

I added a new parsers for the current time.

Issues to resolve
* icon doesn't work
* Instead of parsing the format each iteration it seems that a StrftimeItems could be used, but the lifetimes eluded me so far.

[MaxVerevkin]

Instead of parsing the format each iteration it seems that a StrftimeItems could be used, but the lifetimes eluded me so far.

Ah, self referential structs... AFAIK there are a few approaches: use some library that will do some magic, leak the string to get static lifetime, write a wrapper type (like StrftimeItemsOwned) with a bit of unsafe which will "leak" (Box::into_raw) string on creation and will free to on drop (Box::from_raw). I'm okay with either the first or third option.

[MaxVerevkin]

I think this is correct, as long as it is in its own module: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=ffad275ea8783f05068a850ac351195c

[bim9262]

@MaxVerevkin, why does it matter if it's in its own module?

[MaxVerevkin]

why does it matter if it's in its own module?

This way it can be proven that no code accidentally leaks static reference, because public API would only provide access to borrowed items.

Actually, never mind. Any chrono::format::Item can be made 'static:

fn make_static_item(item: Item<'_>) -> Item<'static> {
    match item {
        Item::Literal(str) => Item::OwnedLiteral(str.into()),
        // And so on
    }
}

fn parse(str: &str) -> Vec<Item<'static>> {
    StrftimeItems::new(str).map(make_static_item).collect()
}

[MaxVerevkin]

Actually, never mind. Any chrono::format::Item can be made 'static:

I even think this could be upstreamed to chrono

[bim9262]

Thanks @MaxVerevkin for your help getting the static item stuff worked out!! I added docs the the formatting page as well.

[bim9262]

This should be tagged as breaking (removal of the locale option and addition of the new datetime formatter)

[bim9262]

Updates to the parser still to come...
Done :)

[bim9262]

Hopefully that does it 🤞!