serde-detach 0.0.1

//! Nudges Serde to deserialise into fully owned (`'static`) instances where this is possible.
//!
//! This is primarily useful when you have a structure that can *optionally* borrow the input (Think [`Cow<str>`] or [`Cow<[u8]>`].), but a deserialiser that requires [`DeserializeOwned`] (which unfortunately seems to be common).
//!
//! Deserialising borrow-only types (like plain references) naturally leads to a runtime error with this method.
//!
//! # Example
//!
//! Given:
//!
//! ```rust no_run
//! use {
//!     serde_detach::detach,
//!     serde_object::Object,
//!     serde_taml::de::from_str,
//! };
//!
//! let input = "key: \"value\"".to_string();
//! ```
//!
//! This does not compile, since [`Object`] tries to borrow from the input:
//! ```rust compile_fail startline=8
//! # use {serde_detach::detach, serde_object::Object, serde_taml::de::from_str};
//! # let input = "key: \"value\"".to_string();
//! let object: Object<'static> = from_str(&input, &mut ())?;
//! //          ---------------            ^^^^^^ borrowed value does not live long enough
//! //          |
//! //          type annotation requires that `input` is borrowed for `'static`
//! # Ok::<_, serde_taml::de::Error>(())
//! ```
//!
//! This works:
//! ```rust startline=8
//! # use {serde_detach::detach, serde_object::Object, serde_taml::de::from_str};
//! # let input = "key: \"value\"".to_string();
//! let object: Object<'static> = from_str(&input, &mut ()).map(detach)?;
//! # Ok::<_, serde_taml::de::Error>(())
//! ```

use serde::{de, serde_if_integer128};
use std::marker::PhantomData;
use wyz::Pipe as _;

/// Gently nudges the compiler into deserialising as [`Detach<T>`] and unwraps it.
pub fn detach<T>(detach: Detach<T>) -> T {
	detach.0
}

/// A [`de::DeserializeOwned`] wrapper around any [`de::Deserialize<'de>`].
#[derive(Debug)]
pub struct Detach<T>(T);

impl<'de, T: de::Deserialize<'static>> de::Deserialize<'de> for Detach<T> {
	fn deserialize<D>(
		deserializer: D,
	) -> std::result::Result<Self, <D as serde::de::Deserializer<'de>>::Error>
	where
		D: de::Deserializer<'de>,
	{
		T::deserialize(Deserializer::new(deserializer)).map(Detach)
	}

	fn deserialize_in_place<D>(deserializer: D, place: &mut Self) -> Result<(), D::Error>
	where
		D: serde::Deserializer<'de>,
	{
		T::deserialize_in_place(Deserializer::new(deserializer), &mut place.0)
	}
}

/// A [`de::Deserializer<'static>`] wrapper around any [`de::Deserializer<'de>`].
#[derive(Debug)]
pub struct Deserializer<'de, D: de::Deserializer<'de>>(D, PhantomData<&'de ()>);
impl<'de, D: de::Deserializer<'de>> Deserializer<'de, D> {
	pub fn new(deserializer: D) -> Self {
		Self(deserializer, PhantomData)
	}
	pub fn inner(&self) -> &D {
		&self.0
	}
	pub fn inner_mut(&mut self) -> &mut D {
		&mut self.0
	}
	pub fn into_inner(self) -> D {
		self.0
	}
}

macro_rules! deserialize {
    ($($deserialize_:ident$(($($param:ident: $param_type:ty),*$(,)?))?),*$(,)?) => {
        $(
            fn $deserialize_<V>(self, $($($param: $param_type, )*)?visitor: V) -> Result<V::Value, Self::Error>
            where
                V: de::Visitor<'static>
            {
                self.0 .$deserialize_($($($param, )?)*Visitor(visitor))
            }
        )*
    };
}

impl<'de, D: de::Deserializer<'de>> de::Deserializer<'static> for Deserializer<'de, D> {
	type Error = D::Error;

	deserialize! {
		deserialize_any,
		deserialize_bool,

		deserialize_i8,
		deserialize_i16,
		deserialize_i32,
		deserialize_i64,

		deserialize_u8,
		deserialize_u16,
		deserialize_u32,
		deserialize_u64,

		deserialize_f32,
		deserialize_f64,

		deserialize_char,

		deserialize_str,
		deserialize_string,

		deserialize_bytes,
		deserialize_byte_buf,

		deserialize_option,
		deserialize_unit,
		deserialize_unit_struct(name: &'static str),
		deserialize_newtype_struct(name: &'static str),
		deserialize_seq,
		deserialize_tuple(len: usize),
		deserialize_tuple_struct(name: &'static str, len: usize),
		deserialize_map,
		deserialize_struct(name: &'static str, fields: &'static [&'static str]),
		deserialize_enum(name: &'static str, variants: &'static [&'static str]),
		deserialize_identifier,
		deserialize_ignored_any,
	}

	serde_if_integer128!(deserialize! {
		deserialize_i128,
		deserialize_u128,
	});

	fn is_human_readable(&self) -> bool {
		self.0.is_human_readable()
	}
}

struct Visitor<V: de::Visitor<'static>>(V);

macro_rules! visit {
    ($($visit_:ident(
        $($ty:ty
            $( | $($expr:expr);+$(;)?)?
        )?
        ) $(/ ::$Error:ident where T: $t_path:path)?),*$(,)?) => {
        $(
            fn $visit_<T>(self$(, v: $ty)?) -> Result<Self::Value, T$(::$Error)?>
            where
                T: $($t_path, T::Error: )?de::Error,
            {
                self.0 .$visit_($({let _: $ty; v$($(.pipe($expr))+)?})?)
            }
        )*
    };
}

impl<'de, V: de::Visitor<'static>> de::Visitor<'de> for Visitor<V> {
	type Value = V::Value;

	fn expecting(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
		self.0.expecting(formatter)
	}

	visit! {
		visit_bool(bool),

		visit_i8(i8),
		visit_i16(i16),
		visit_i32(i32),
		visit_i64(i64),

		visit_u8(u8),
		visit_u16(u16),
		visit_u32(u32),
		visit_u64(u64),

		visit_f32(f32),
		visit_f64(f64),

		visit_char(char),

		visit_str(&str),
		// visit_borrowed_str not implemented! Default implementation forwards to visit_str ✨
		visit_string(String),

		visit_bytes(&[u8]),
		// visit_borrowed_bytes's default implementation forwards to visit_bytes.
		visit_byte_buf(Vec<u8>),

		visit_none(),
		visit_some(T | Deserializer::new) / ::Error where T: de::Deserializer<'de>,

		visit_unit(),
		visit_newtype_struct(T | Deserializer::new) / ::Error where T: de::Deserializer<'de>,
		visit_seq(T | SeqAccess::new) / ::Error where T: de::SeqAccess<'de>,
		visit_map(T | MapAccess::new) / ::Error where T: de::MapAccess<'de>,
		visit_enum(T | EnumAccess::new) / ::Error where T: de::EnumAccess<'de>,
	}

	serde_if_integer128!(visit! {
		visit_i128(i128),
		visit_u128(u128),
	});
}

struct SeqAccess<'de, A: de::SeqAccess<'de>>(A, PhantomData<&'de ()>);
impl<'de, A: de::SeqAccess<'de>> SeqAccess<'de, A> {
	fn new(access: A) -> Self {
		Self(access, PhantomData)
	}
}
impl<'de, A: de::SeqAccess<'de>> de::SeqAccess<'static> for SeqAccess<'de, A> {
	type Error = A::Error;
	fn next_element_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, Self::Error>
	where
		T: de::DeserializeSeed<'static>,
	{
		self.0.next_element_seed(Seed(seed))
	}
	fn size_hint(&self) -> Option<usize> {
		self.0.size_hint()
	}
}

struct MapAccess<'de, A: de::MapAccess<'de>>(A, PhantomData<&'de ()>);
impl<'de, A: de::MapAccess<'de>> MapAccess<'de, A> {
	fn new(access: A) -> Self {
		Self(access, PhantomData)
	}
}
impl<'de, A: de::MapAccess<'de>> de::MapAccess<'static> for MapAccess<'de, A> {
	type Error = A::Error;
	fn next_key_seed<K>(&mut self, seed: K) -> Result<Option<K::Value>, Self::Error>
	where
		K: de::DeserializeSeed<'static>,
	{
		self.0.next_key_seed(Seed(seed))
	}
	fn next_value_seed<V>(&mut self, seed: V) -> Result<V::Value, Self::Error>
	where
		V: de::DeserializeSeed<'static>,
	{
		self.0.next_value_seed(Seed(seed))
	}
	#[allow(clippy::type_complexity)]
	fn next_entry_seed<K, V>(
		&mut self,
		kseed: K,
		vseed: V,
	) -> Result<Option<(K::Value, V::Value)>, Self::Error>
	where
		K: de::DeserializeSeed<'static>,
		V: de::DeserializeSeed<'static>,
	{
		self.0.next_entry_seed(Seed(kseed), Seed(vseed))
	}
	fn size_hint(&self) -> Option<usize> {
		self.0.size_hint()
	}
}

struct EnumAccess<'de, A: de::EnumAccess<'de>>(A, PhantomData<&'de ()>);
impl<'de, A: de::EnumAccess<'de>> EnumAccess<'de, A> {
	fn new(access: A) -> Self {
		Self(access, PhantomData)
	}
}
impl<'de, A: de::EnumAccess<'de>> de::EnumAccess<'static> for EnumAccess<'de, A> {
	type Error = A::Error;
	type Variant = VariantAccess<'de, A::Variant>;
	fn variant_seed<V>(self, seed: V) -> Result<(V::Value, Self::Variant), Self::Error>
	where
		V: de::DeserializeSeed<'static>,
	{
		self.0
			.variant_seed(Seed(seed))
			.map(|(value, variant)| (value, VariantAccess::new(variant)))
	}
}

struct VariantAccess<'de, A: de::VariantAccess<'de>>(A, PhantomData<&'de ()>);
impl<'de, A: de::VariantAccess<'de>> VariantAccess<'de, A> {
	fn new(access: A) -> Self {
		Self(access, PhantomData)
	}
}
impl<'de, A: de::VariantAccess<'de>> de::VariantAccess<'static> for VariantAccess<'de, A> {
	type Error = A::Error;
	fn unit_variant(self) -> Result<(), Self::Error> {
		self.0.unit_variant()
	}
	fn newtype_variant_seed<T>(self, seed: T) -> Result<T::Value, Self::Error>
	where
		T: de::DeserializeSeed<'static>,
	{
		self.0.newtype_variant_seed(Seed(seed))
	}
	fn tuple_variant<V>(self, len: usize, visitor: V) -> Result<V::Value, Self::Error>
	where
		V: de::Visitor<'static>,
	{
		self.0.tuple_variant(len, Visitor(visitor))
	}
	fn struct_variant<V>(
		self,
		fields: &'static [&'static str],
		visitor: V,
	) -> Result<V::Value, Self::Error>
	where
		V: de::Visitor<'static>,
	{
		self.0.struct_variant(fields, Visitor(visitor))
	}
}

struct Seed<S: de::DeserializeSeed<'static>>(S);
impl<'de, S: de::DeserializeSeed<'static>> de::DeserializeSeed<'de> for Seed<S> {
	type Value = S::Value;
	fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
	where
		D: serde::Deserializer<'de>,
	{
		self.0.deserialize(Deserializer::new(deserializer))
	}
}