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33: Remove pin_project! macro and add #[pinned_drop] attribute r=taiki-e a=taiki-e This removes `pin_project!` block and adds `#[pinned_drop]` attribute as proc-macro-attribute. If you want a custom `Drop` implementation, you need to pass the `PinnedDrop` argument to `pin_project` attribute instead of defining items in `pin_project!` block. In the previous implementation, `#[pinned_drop]` implemented `Drop` directly, but this PR changes it to implement this via a private unsafe trait method. Also, this renames `pin_projectable` to `pin_project`. cc #21, #26 Related: #18 (comment) ### Examples Before: ```rust use std::fmt::Debug; use pin_project::{pin_project, pin_projectable}; use std::pin::Pin; pin_project! { #[pin_projectable] pub struct Foo<T: Debug, U: Debug> { #[pin] pinned_field: T, unpin_field: U } #[pinned_drop] fn my_drop_fn<T: Debug, U: Debug>(foo: Pin<&mut Foo<T, U>>) { let foo = foo.project(); println!("Dropping pinned field: {:?}", foo.pinned_field); println!("Dropping unpin field: {:?}", foo.unpin_field); } } ``` After: ```rust use std::fmt::Debug; use pin_project::{pin_project, pinned_drop}; use std::pin::Pin; #[pin_project(PinnedDrop)] pub struct Foo<T: Debug, U: Debug> { #[pin] pinned_field: T, unpin_field: U } #[pinned_drop] fn my_drop_fn<T: Debug, U: Debug>(foo: Pin<&mut Foo<T, U>>) { let foo = foo.project(); println!("Dropping pinned field: {:?}", foo.pinned_field); println!("Dropping unpin field: {:?}", foo.unpin_field); } ``` ### TODO - [x] Update docs Co-authored-by: Taiki Endo <te316e89@gmail.com>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,254 @@ | ||
| use proc_macro2::{Ident, Span, TokenStream}; | ||
| use quote::{quote, quote_spanned}; | ||
| use syn::{ | ||
| parse::{Parse, ParseStream}, | ||
| Fields, FieldsNamed, FieldsUnnamed, Generics, Index, Item, ItemStruct, Meta, NestedMeta, | ||
| Result, Type, | ||
| }; | ||
|
|
||
| use crate::utils::{crate_path, Nothing}; | ||
|
|
||
| mod enums; | ||
| mod structs; | ||
|
|
||
| /// The annotation for pinned type. | ||
| const PIN: &str = "pin"; | ||
|
|
||
| pub(super) fn attribute(args: TokenStream, input: TokenStream) -> TokenStream { | ||
| parse(args, input).unwrap_or_else(|e| e.to_compile_error()) | ||
| } | ||
|
|
||
| #[derive(Clone, Copy)] | ||
| struct Args { | ||
| pinned_drop: Option<Span>, | ||
| unsafe_unpin: Option<Span>, | ||
| } | ||
|
|
||
| impl Args { | ||
| fn impl_drop(self, generics: &Generics) -> ImplDrop<'_> { | ||
| ImplDrop::new(generics, self.pinned_drop) | ||
| } | ||
|
|
||
| fn impl_unpin(self, generics: &Generics) -> ImplUnpin { | ||
| ImplUnpin::new(generics, self.unsafe_unpin) | ||
| } | ||
| } | ||
|
|
||
| impl Parse for Args { | ||
| fn parse(input: ParseStream<'_>) -> Result<Self> { | ||
| let mut pinned_drop = None; | ||
| let mut unsafe_unpin = None; | ||
| while !input.is_empty() { | ||
| let i = input.parse::<Ident>()?; | ||
| match &*i.to_string() { | ||
| "PinnedDrop" => pinned_drop = Some(i.span()), | ||
| "unsafe_Unpin" => unsafe_unpin = Some(i.span()), | ||
| _ => return Err(error!(i, "an invalid argument was passed")), | ||
| } | ||
| } | ||
| Ok(Self { pinned_drop, unsafe_unpin }) | ||
| } | ||
| } | ||
|
|
||
| fn parse(args: TokenStream, input: TokenStream) -> Result<TokenStream> { | ||
| let args = syn::parse2(args)?; | ||
| match syn::parse2(input)? { | ||
| Item::Struct(item) => { | ||
| let packed_check = ensure_not_packed(&item)?; | ||
| let mut res = structs::parse(args, item)?; | ||
| res.extend(packed_check); | ||
| Ok(res) | ||
| } | ||
| Item::Enum(item) => { | ||
| // We don't need to check for '#[repr(packed)]', | ||
| // since it does not apply to enums | ||
| enums::parse(args, item) | ||
| } | ||
| item => Err(error!(item, "may only be used on structs or enums")), | ||
| } | ||
| } | ||
|
|
||
| fn ensure_not_packed(item: &ItemStruct) -> Result<TokenStream> { | ||
| for meta in item.attrs.iter().filter_map(|attr| attr.parse_meta().ok()) { | ||
| if let Meta::List(l) = meta { | ||
| if l.ident == "repr" { | ||
| for repr in l.nested.iter() { | ||
| if let NestedMeta::Meta(Meta::Word(w)) = repr { | ||
| if w == "packed" { | ||
| return Err(error!( | ||
| w, | ||
| "pin_project may not be used on #[repr(packed)] types" | ||
| )); | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| // Workaround for https://github.com/taiki-e/pin-project/issues/32 | ||
| // Through the tricky use of proc macros, it's possible to bypass | ||
| // the above check for the 'repr' attribute. | ||
| // To ensure that it's impossible to use pin projections on a #[repr(packed)][ | ||
| // struct, we generate code like this: | ||
| // | ||
| // #[deny(safe_packed_borrows)] | ||
| // fn enforce_not_packed_for_MyStruct(val: MyStruct) { | ||
| // let _field1 = &val.field1; | ||
| // let _field2 = &val.field2; | ||
| // ... | ||
| // let _fieldn = &val.fieldn; | ||
| // } | ||
| // | ||
| // Taking a reference to a packed field is unsafe, amd appplying | ||
| // #[deny(safe_packed_borrows)] makes sure that doing this without | ||
| // an 'unsafe' block (which we deliberately do not generate) | ||
| // is a hard error. | ||
| // | ||
| // If the struct ends up having #[repr(packed)] applied somehow, | ||
| // this will generate an (unfriendly) error message. Under all reasonable | ||
| // circumstances, we'll detect the #[repr(packed)] attribute, and generate | ||
| // a much nicer error above. | ||
| // | ||
| // There is one exception: If the type of a struct field has a alignemtn of 1 | ||
| // (e.g. u8), it is always safe to take a reference to it, even if the struct | ||
| // is #[repr(packed)]. If the struct is composed entirely of types of alignent 1, | ||
| // our generated method will not trigger an error if the struct is #[repr(packed)] | ||
| // | ||
| // Fortunately, this should have no observable consequence - #[repr(packed)] | ||
| // is essentially a no-op on such a type. Nevertheless, we include a test | ||
| // to ensure that the compiler doesn't ever try to copy the fields on | ||
| // such a struct when trying to drop it - which is reason we prevent | ||
| // #[repr(packed)] in the first place | ||
| let mut field_refs = vec![]; | ||
| match &item.fields { | ||
| Fields::Named(FieldsNamed { named, .. }) => { | ||
| for field in named.iter() { | ||
| let ident = field.ident.as_ref().unwrap(); | ||
| field_refs.push(quote!(&val.#ident;)); | ||
| } | ||
| } | ||
| Fields::Unnamed(FieldsUnnamed { unnamed, .. }) => { | ||
| for (i, _) in unnamed.iter().enumerate() { | ||
| let index = Index::from(i); | ||
| field_refs.push(quote!(&val.#index;)); | ||
| } | ||
| } | ||
| Fields::Unit => {} | ||
| } | ||
|
|
||
| let (impl_generics, ty_generics, where_clause) = item.generics.split_for_impl(); | ||
|
|
||
| let struct_name = &item.ident; | ||
| let method_name = Ident::new( | ||
| &("__pin_project_assert_not_repr_packed_".to_string() + &item.ident.to_string()), | ||
| Span::call_site(), | ||
| ); | ||
| let test_fn = quote! { | ||
| #[deny(safe_packed_borrows)] | ||
| fn #method_name #impl_generics (val: #struct_name #ty_generics) #where_clause { | ||
| #(#field_refs)* | ||
| } | ||
| }; | ||
| Ok(test_fn) | ||
| } | ||
|
|
||
| /// Makes the generics of projected type from the reference of the original generics. | ||
| fn proj_generics(generics: &Generics) -> Generics { | ||
| let mut generics = generics.clone(); | ||
| generics.params.insert(0, syn::parse_quote!('__a)); | ||
| generics | ||
| } | ||
|
|
||
| // ================================================================================================= | ||
| // Drop implementation | ||
|
|
||
| struct ImplDrop<'a> { | ||
| generics: &'a Generics, | ||
| pinned_drop: Option<Span>, | ||
| } | ||
|
|
||
| impl<'a> ImplDrop<'a> { | ||
| fn new(generics: &'a Generics, pinned_drop: Option<Span>) -> Self { | ||
| Self { generics, pinned_drop } | ||
| } | ||
|
|
||
| fn build(self, ident: &Ident) -> TokenStream { | ||
| let (impl_generics, ty_generics, where_clause) = self.generics.split_for_impl(); | ||
|
|
||
| if let Some(pinned_drop) = self.pinned_drop { | ||
| let crate_path = crate_path(); | ||
| let call = quote_spanned! { pinned_drop => | ||
| ::#crate_path::__private::UnsafePinnedDrop::pinned_drop(pinned_self) | ||
| }; | ||
|
|
||
| quote! { | ||
| impl #impl_generics ::core::ops::Drop for #ident #ty_generics #where_clause { | ||
| fn drop(&mut self) { | ||
| // Safety - we're in 'drop', so we know that 'self' will | ||
| // never move again | ||
| let pinned_self = unsafe { ::core::pin::Pin::new_unchecked(self) }; | ||
| // We call `pinned_drop` only once. Since `UnsafePinnedDrop::pinned_drop` | ||
| // is an unsafe function and a private API, it is never called again in safe | ||
| // code *unless the user uses a maliciously crafted macro*. | ||
| unsafe { | ||
| #call; | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } else { | ||
| quote! { | ||
| impl #impl_generics ::core::ops::Drop for #ident #ty_generics #where_clause { | ||
| fn drop(&mut self) { | ||
| // Do nothing. The precense of this Drop | ||
| // impl ensures that the user can't provide one of their own | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| // ================================================================================================= | ||
| // conditional Unpin implementation | ||
|
|
||
| struct ImplUnpin { | ||
| generics: Generics, | ||
| unsafe_unpin: bool, | ||
| } | ||
|
|
||
| impl ImplUnpin { | ||
| fn new(generics: &Generics, unsafe_unpin: Option<Span>) -> Self { | ||
| let mut generics = generics.clone(); | ||
| if let Some(unsafe_unpin) = unsafe_unpin { | ||
| let crate_path = crate_path(); | ||
| generics.make_where_clause().predicates.push( | ||
| syn::parse2(quote_spanned! { unsafe_unpin => | ||
| ::#crate_path::__private::Wrapper<Self>: ::#crate_path::UnsafeUnpin | ||
| }) | ||
| .unwrap(), | ||
| ); | ||
| } | ||
|
|
||
| Self { generics, unsafe_unpin: unsafe_unpin.is_some() } | ||
| } | ||
|
|
||
| fn push(&mut self, ty: &Type) { | ||
| // We only add bounds for automatically generated impls | ||
| if !self.unsafe_unpin { | ||
| self.generics | ||
| .make_where_clause() | ||
| .predicates | ||
| .push(syn::parse_quote!(#ty: ::core::marker::Unpin)); | ||
| } | ||
| } | ||
|
|
||
| /// Creates `Unpin` implementation. | ||
| fn build(self, ident: &Ident) -> TokenStream { | ||
| let (impl_generics, ty_generics, where_clause) = self.generics.split_for_impl(); | ||
| quote! { | ||
| impl #impl_generics ::core::marker::Unpin for #ident #ty_generics #where_clause {} | ||
| } | ||
| } | ||
| } |
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