Wishlist: Blocked on upstream changes

[jonasbb]

• MSRV Rust 1.64:
  • Use workspace.package and workspace.dependencies. The main advantage is sharing the metadata between the related packages. The slightly simpler dependency management is a bonus.
• feature(adt_const_params)

  • Add extra layers for serializing/deserializing. Serialize struct with additional root element #340 (comment)

     #![feature(adt_const_params)]
     
     #[derive(Copy, Clone, Debug, Default)]
     pub struct Layer<const FIELD: &'static str, T: ?Sized>(T);
     
     impl<const FIELD: &'static str, T, U> SerializeAs<T> for Layer<FIELD, U>
     where
         U: SerializeAs<T>,
         T: ?Sized,
         U: ?Sized,
     {
         fn serialize_as<S>(source: &T, serializer: S) -> Result<S::Ok, S::Error> where S: Serializer {
             use serde::ser::SerializeStruct;
     
             let mut ser_struct = serializer.serialize_struct("Layer", 1)?;
             ser_struct.serialize_field(FIELD, &ser::SerializeAsWrap::<T, U>::new(source))?;
             ser_struct.end()
         }
     }
     
     // Can be used like this
     #[serde_as]
     #[derive(Serialize)]
     struct Data {
         i: i32,
         #[serde_as(as = r#"Layer<"extra", Layer<"foobar", Layer<"really_another_one", DisplayFromStr>>>"#)]
         b: bool,
     }
     
     // or like
     serde_json::to_string(&Layer::<"root">(&data))

    https://github.com/dtolnay/monostate contains a solution to encode &str into a static type without requiring adt_const_params. It doesn't quite fit the above use case, since the value is not accessible as a &'static str. But Layer could be implemented if it uses serialize_map.

  • Add a macro-free version of with_prefix!.

  • Get rid of the special key name requirement for `KeyValueMap
    

    serde_with/serde_with/src/key_value_map.rs

    Lines 210 to 215 in 725d177

    	// TODO Replace this with a const generic string once adt_const_params is stable.
    	// This will allow something like this.
    	// The `"id"` part is the field name, which gets converted to/from the map key.
    	// #[serde_as(as = r#"KeyValueMap<"id", _>"#)]
    	// Vec<SimpleStruct>,
    	static MAP_KEY_IDENTIFIER: &str = "$key$";

• feature(array_try_from_fn) Tracking issue for try_array_from_fn rust-lang/rust#89379
  • Replace the unsafe implementation of array_from_iterator with something from std.
    Provide a means of turning iterators into fixed-size arrays rust-lang/rust#81615
    

    serde_with/serde_with/src/utils.rs

    Lines 119 to 174 in b50b611

    	/// Collect an array of a fixed size from an iterator.
    	///
    	/// # Safety
    	/// The code follow exactly the pattern of initializing an array element-by-element from the standard library.
    	/// <https://doc.rust-lang.org/nightly/std/mem/union.MaybeUninit.html#initializing-an-array-element-by-element>
    	pub(crate) fn array_from_iterator<I, T, E, const N: usize>(
    	mut iter: I,
    	expected: &dyn Expected,
    	) -> Result<[T; N], E>
    	where
    	I: Iterator<Item = Result<T, E>>,
    	E: DeError,
    	{
    	use core::mem::MaybeUninit;
    	fn drop_array_elems<T, const N: usize>(num: usize, mut arr: [MaybeUninit<T>; N]) {
    	arr[..num].iter_mut().for_each(|elem| {
    	// TODO This would be better with assume_init_drop nightly function
    	// https://github.com/rust-lang/rust/issues/63567
    	unsafe { core::ptr::drop_in_place(elem.as_mut_ptr()) };
    	});
    	}
    	// Create an uninitialized array of `MaybeUninit`. The `assume_init` is
    	// safe because the type we are claiming to have initialized here is a
    	// bunch of `MaybeUninit`s, which do not require initialization.
    	//
    	// TODO could be simplified with nightly maybe_uninit_uninit_array feature
    	// https://doc.rust-lang.org/nightly/std/mem/union.MaybeUninit.html#method.uninit_array
    	let mut arr: [MaybeUninit<T>; N] = unsafe { MaybeUninit::uninit().assume_init() };
    	// Dropping a `MaybeUninit` does nothing. Thus using raw pointer
    	// assignment instead of `ptr::write` does not cause the old
    	// uninitialized value to be dropped. Also if there is a panic during
    	// this loop, we have a memory leak, but there is no memory safety
    	// issue.
    	for (idx, elem) in arr[..].iter_mut().enumerate() {
    	*elem = match iter.next() {
    	Some(Ok(value)) => MaybeUninit::new(value),
    	Some(Err(err)) => {
    	drop_array_elems(idx, arr);
    	return Err(err);
    	}
    	None => {
    	drop_array_elems(idx, arr);
    	return Err(DeError::invalid_length(idx, expected));
    	}
    	};
    	}
    	// Everything is initialized. Transmute the array to the
    	// initialized type.
    	// A normal transmute is not possible because of:
    	// https://github.com/rust-lang/rust/issues/61956
    	Ok(unsafe { core::mem::transmute_copy::<_, [T; N]>(&arr) })
    	}

• Use workspace lints with separate overrides per crate: Packages overriding inherited lints in Cargo.toml + adding lints rust-lang/cargo#13157