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Diffstat (limited to 'vendor/ref-cast-impl/src/lib.rs')
| -rw-r--r-- | vendor/ref-cast-impl/src/lib.rs | 540 |
1 files changed, 540 insertions, 0 deletions
diff --git a/vendor/ref-cast-impl/src/lib.rs b/vendor/ref-cast-impl/src/lib.rs new file mode 100644 index 00000000..96da08a0 --- /dev/null +++ b/vendor/ref-cast-impl/src/lib.rs @@ -0,0 +1,540 @@ +#![allow( + clippy::blocks_in_conditions, + clippy::needless_pass_by_value, + clippy::if_not_else +)] + +extern crate proc_macro; + +use proc_macro::TokenStream; +use proc_macro2::{Ident, Span, TokenStream as TokenStream2, TokenTree}; +use quote::{quote, quote_spanned}; +use syn::parse::{Nothing, ParseStream, Parser}; +use syn::punctuated::Punctuated; +use syn::{ + parenthesized, parse_macro_input, token, Abi, Attribute, Data, DeriveInput, Error, Expr, Field, + Generics, Path, Result, Token, Type, Visibility, +}; + +/// Derive the `RefCast` trait. +/// +/// See the [crate-level documentation](./index.html) for usage examples! +/// +/// # Attributes +/// +/// Use the `#[trivial]` attribute to mark any zero-sized fields that are *not* +/// the one that references are going to be converted from. +/// +/// ``` +/// use ref_cast::RefCast; +/// use std::marker::PhantomData; +/// +/// #[derive(RefCast)] +/// #[repr(transparent)] +/// pub struct Generic<T, U> { +/// raw: Vec<U>, +/// #[trivial] +/// aux: Variance<T, U>, +/// } +/// +/// type Variance<T, U> = PhantomData<fn(T) -> U>; +/// ``` +/// +/// Fields with a type named `PhantomData` or `PhantomPinned` are automatically +/// recognized and do not need to be marked with this attribute. +/// +/// ``` +/// use ref_cast::RefCast; +/// use std::marker::{PhantomData, PhantomPinned}; +/// +/// #[derive(RefCast)] // generates a conversion from &[u8] to &Bytes<'_> +/// #[repr(transparent)] +/// pub struct Bytes<'arena> { +/// lifetime: PhantomData<&'arena ()>, +/// pin: PhantomPinned, +/// bytes: [u8], +/// } +/// ``` +#[proc_macro_derive(RefCast, attributes(trivial))] +pub fn derive_ref_cast(input: TokenStream) -> TokenStream { + let input = parse_macro_input!(input as DeriveInput); + expand_ref_cast(&input) + .unwrap_or_else(Error::into_compile_error) + .into() +} + +/// Derive that makes the `ref_cast_custom` attribute able to generate +/// freestanding reference casting functions for a type. +/// +/// Please refer to the documentation of +/// [`#[ref_cast_custom]`][macro@ref_cast_custom] where these two macros are +/// documented together. +#[proc_macro_derive(RefCastCustom, attributes(trivial))] +pub fn derive_ref_cast_custom(input: TokenStream) -> TokenStream { + let input = parse_macro_input!(input as DeriveInput); + expand_ref_cast_custom(&input) + .unwrap_or_else(Error::into_compile_error) + .into() +} + +/// Create a function for a RefCast-style reference cast. Call site gets control +/// of the visibility, function name, argument name, `const`ness, unsafety, and +/// documentation. +/// +/// The `derive(RefCast)` macro produces a trait impl, which means the function +/// names are predefined, and public if your type is public, and not callable in +/// `const` (at least today on stable Rust). As an alternative to that, +/// `derive(RefCastCustom)` exposes greater flexibility so that instead of a +/// trait impl, the casting functions can be made associated functions or free +/// functions, can be named what you want, documented, `const` or `unsafe` if +/// you want, and have your exact choice of visibility. +/// +/// ```rust +/// use ref_cast::{ref_cast_custom, RefCastCustom}; +/// +/// #[derive(RefCastCustom)] // does not generate any public API by itself +/// #[repr(transparent)] +/// pub struct Frame([u8]); +/// +/// impl Frame { +/// #[ref_cast_custom] // requires derive(RefCastCustom) on the return type +/// pub(crate) const fn new(bytes: &[u8]) -> &Self; +/// +/// #[ref_cast_custom] +/// pub(crate) fn new_mut(bytes: &mut [u8]) -> &mut Self; +/// } +/// +/// // example use of the const fn +/// const FRAME: &Frame = Frame::new(b"..."); +/// ``` +/// +/// The above shows associated functions, but you might alternatively want to +/// generate free functions: +/// +/// ```rust +/// # use ref_cast::{ref_cast_custom, RefCastCustom}; +/// # +/// # #[derive(RefCastCustom)] +/// # #[repr(transparent)] +/// # pub struct Frame([u8]); +/// # +/// impl Frame { +/// pub fn new<T: AsRef<[u8]>>(bytes: &T) -> &Self { +/// #[ref_cast_custom] +/// fn ref_cast(bytes: &[u8]) -> &Frame; +/// +/// ref_cast(bytes.as_ref()) +/// } +/// } +/// ``` +#[proc_macro_attribute] +pub fn ref_cast_custom(args: TokenStream, input: TokenStream) -> TokenStream { + let input = TokenStream2::from(input); + let expanded = match (|input: ParseStream| { + let attrs = input.call(Attribute::parse_outer)?; + let vis: Visibility = input.parse()?; + let constness: Option<Token![const]> = input.parse()?; + let asyncness: Option<Token![async]> = input.parse()?; + let unsafety: Option<Token![unsafe]> = input.parse()?; + let abi: Option<Abi> = input.parse()?; + let fn_token: Token![fn] = input.parse()?; + let ident: Ident = input.parse()?; + let mut generics: Generics = input.parse()?; + + let content; + let paren_token = parenthesized!(content in input); + let arg: Ident = content.parse()?; + let colon_token: Token![:] = content.parse()?; + let from_type: Type = content.parse()?; + let _trailing_comma: Option<Token![,]> = content.parse()?; + if !content.is_empty() { + let rest: TokenStream2 = content.parse()?; + return Err(Error::new_spanned( + rest, + "ref_cast_custom function is required to have a single argument", + )); + } + + let arrow_token: Token![->] = input.parse()?; + let to_type: Type = input.parse()?; + generics.where_clause = input.parse()?; + let semi_token: Token![;] = input.parse()?; + + let _: Nothing = syn::parse::<Nothing>(args)?; + + Ok(Function { + attrs, + vis, + constness, + asyncness, + unsafety, + abi, + fn_token, + ident, + generics, + paren_token, + arg, + colon_token, + from_type, + arrow_token, + to_type, + semi_token, + }) + }) + .parse2(input.clone()) + { + Ok(function) => expand_function_body(function), + Err(parse_error) => { + let compile_error = parse_error.to_compile_error(); + quote!(#compile_error #input) + } + }; + TokenStream::from(expanded) +} + +struct Function { + attrs: Vec<Attribute>, + vis: Visibility, + constness: Option<Token![const]>, + asyncness: Option<Token![async]>, + unsafety: Option<Token![unsafe]>, + abi: Option<Abi>, + fn_token: Token![fn], + ident: Ident, + generics: Generics, + paren_token: token::Paren, + arg: Ident, + colon_token: Token![:], + from_type: Type, + arrow_token: Token![->], + to_type: Type, + semi_token: Token![;], +} + +fn expand_ref_cast(input: &DeriveInput) -> Result<TokenStream2> { + check_repr(input)?; + + let name = &input.ident; + let name_str = name.to_string(); + let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl(); + + let fields = fields(input)?; + let from = only_field_ty(fields)?; + let trivial = trivial_fields(fields)?; + + let assert_trivial_fields = if !trivial.is_empty() { + Some(quote! { + if false { + #( + ::ref_cast::__private::assert_trivial::<#trivial>(); + )* + } + }) + } else { + None + }; + + Ok(quote! { + impl #impl_generics ::ref_cast::RefCast for #name #ty_generics #where_clause { + type From = #from; + + #[inline] + fn ref_cast(_from: &Self::From) -> &Self { + #assert_trivial_fields + #[cfg(debug_assertions)] + { + #[allow(unused_imports)] + use ::ref_cast::__private::LayoutUnsized; + ::ref_cast::__private::assert_layout::<Self, Self::From>( + #name_str, + ::ref_cast::__private::Layout::<Self>::SIZE, + ::ref_cast::__private::Layout::<Self::From>::SIZE, + ::ref_cast::__private::Layout::<Self>::ALIGN, + ::ref_cast::__private::Layout::<Self::From>::ALIGN, + ); + } + unsafe { + &*(_from as *const Self::From as *const Self) + } + } + + #[inline] + fn ref_cast_mut(_from: &mut Self::From) -> &mut Self { + #[cfg(debug_assertions)] + { + #[allow(unused_imports)] + use ::ref_cast::__private::LayoutUnsized; + ::ref_cast::__private::assert_layout::<Self, Self::From>( + #name_str, + ::ref_cast::__private::Layout::<Self>::SIZE, + ::ref_cast::__private::Layout::<Self::From>::SIZE, + ::ref_cast::__private::Layout::<Self>::ALIGN, + ::ref_cast::__private::Layout::<Self::From>::ALIGN, + ); + } + unsafe { + &mut *(_from as *mut Self::From as *mut Self) + } + } + } + }) +} + +fn expand_ref_cast_custom(input: &DeriveInput) -> Result<TokenStream2> { + check_repr(input)?; + + let vis = &input.vis; + let name = &input.ident; + let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl(); + + let fields = fields(input)?; + let from = only_field_ty(fields)?; + let trivial = trivial_fields(fields)?; + + let assert_trivial_fields = if !trivial.is_empty() { + Some(quote! { + fn __static_assert() { + if false { + #( + ::ref_cast::__private::assert_trivial::<#trivial>(); + )* + } + } + }) + } else { + None + }; + + Ok(quote! { + const _: () = { + #[non_exhaustive] + #vis struct RefCastCurrentCrate {} + + unsafe impl #impl_generics ::ref_cast::__private::RefCastCustom<#from> for #name #ty_generics #where_clause { + type CurrentCrate = RefCastCurrentCrate; + #assert_trivial_fields + } + }; + }) +} + +fn expand_function_body(function: Function) -> TokenStream2 { + let Function { + attrs, + vis, + constness, + asyncness, + unsafety, + abi, + fn_token, + ident, + generics, + paren_token, + arg, + colon_token, + from_type, + arrow_token, + to_type, + semi_token, + } = function; + + let args = quote_spanned! {paren_token.span=> + (#arg #colon_token #from_type) + }; + + let allow_unused_unsafe = if unsafety.is_some() { + Some(quote!(#[allow(unused_unsafe)])) + } else { + None + }; + + let mut inline_attr = Some(quote!(#[inline])); + for attr in &attrs { + if attr.path().is_ident("inline") { + inline_attr = None; + break; + } + } + + // Apply a macro-generated span to the "unsafe" token for the unsafe block. + // This is instead of reusing the caller's function signature's #unsafety + // across both the generated function signature and generated unsafe block, + // and instead of using `semi_token.span` like for the rest of the generated + // code below, both of which would cause `forbid(unsafe_code)` located in + // the caller to reject the expanded code. + let macro_generated_unsafe = quote!(unsafe); + + quote_spanned! {semi_token.span=> + #(#attrs)* + #inline_attr + #vis #constness #asyncness #unsafety #abi + #fn_token #ident #generics #args #arrow_token #to_type { + // check lifetime + let _ = || { + ::ref_cast::__private::ref_cast_custom::<#from_type, #to_type>(#arg); + }; + + // check same crate + let _ = ::ref_cast::__private::CurrentCrate::<#from_type, #to_type> {}; + + #allow_unused_unsafe // in case they are building with deny(unsafe_op_in_unsafe_fn) + #[allow(clippy::transmute_ptr_to_ptr)] + #macro_generated_unsafe { + ::ref_cast::__private::transmute::<#from_type, #to_type>(#arg) + } + } + } +} + +fn check_repr(input: &DeriveInput) -> Result<()> { + let mut has_repr = false; + let mut errors = None; + let mut push_error = |error| match &mut errors { + Some(errors) => Error::combine(errors, error), + None => errors = Some(error), + }; + + for attr in &input.attrs { + if attr.path().is_ident("repr") { + if let Err(error) = attr.parse_args_with(|input: ParseStream| { + while !input.is_empty() { + let path = input.call(Path::parse_mod_style)?; + if path.is_ident("transparent") || path.is_ident("C") { + has_repr = true; + } else if path.is_ident("packed") { + // ignore + } else { + let meta_item_span = if input.peek(token::Paren) { + let group: TokenTree = input.parse()?; + quote!(#path #group) + } else if input.peek(Token![=]) { + let eq_token: Token![=] = input.parse()?; + let value: Expr = input.parse()?; + quote!(#path #eq_token #value) + } else { + quote!(#path) + }; + let msg = if path.is_ident("align") { + "aligned repr on struct that implements RefCast is not supported" + } else { + "unrecognized repr on struct that implements RefCast" + }; + push_error(Error::new_spanned(meta_item_span, msg)); + } + if !input.is_empty() { + input.parse::<Token![,]>()?; + } + } + Ok(()) + }) { + push_error(error); + } + } + } + + if !has_repr { + let mut requires_repr = Error::new( + Span::call_site(), + "RefCast trait requires #[repr(transparent)]", + ); + if let Some(errors) = errors { + requires_repr.combine(errors); + } + errors = Some(requires_repr); + } + + match errors { + None => Ok(()), + Some(errors) => Err(errors), + } +} + +type Fields = Punctuated<Field, Token![,]>; + +fn fields(input: &DeriveInput) -> Result<&Fields> { + use syn::Fields; + + match &input.data { + Data::Struct(data) => match &data.fields { + Fields::Named(fields) => Ok(&fields.named), + Fields::Unnamed(fields) => Ok(&fields.unnamed), + Fields::Unit => Err(Error::new( + Span::call_site(), + "RefCast does not support unit structs", + )), + }, + Data::Enum(_) => Err(Error::new( + Span::call_site(), + "RefCast does not support enums", + )), + Data::Union(_) => Err(Error::new( + Span::call_site(), + "RefCast does not support unions", + )), + } +} + +fn only_field_ty(fields: &Fields) -> Result<&Type> { + let is_trivial = decide_trivial(fields)?; + let mut only_field = None; + + for field in fields { + if !is_trivial(field)? { + if only_field.take().is_some() { + break; + } + only_field = Some(&field.ty); + } + } + + only_field.ok_or_else(|| { + Error::new( + Span::call_site(), + "RefCast requires a struct with a single field", + ) + }) +} + +fn trivial_fields(fields: &Fields) -> Result<Vec<&Type>> { + let is_trivial = decide_trivial(fields)?; + let mut trivial = Vec::new(); + + for field in fields { + if is_trivial(field)? { + trivial.push(&field.ty); + } + } + + Ok(trivial) +} + +fn decide_trivial(fields: &Fields) -> Result<fn(&Field) -> Result<bool>> { + for field in fields { + if is_explicit_trivial(field)? { + return Ok(is_explicit_trivial); + } + } + Ok(is_implicit_trivial) +} + +#[allow(clippy::unnecessary_wraps)] // match signature of is_explicit_trivial +fn is_implicit_trivial(field: &Field) -> Result<bool> { + match &field.ty { + Type::Tuple(ty) => Ok(ty.elems.is_empty()), + Type::Path(ty) => { + let ident = &ty.path.segments.last().unwrap().ident; + Ok(ident == "PhantomData" || ident == "PhantomPinned") + } + _ => Ok(false), + } +} + +fn is_explicit_trivial(field: &Field) -> Result<bool> { + for attr in &field.attrs { + if attr.path().is_ident("trivial") { + attr.meta.require_path_only()?; + return Ok(true); + } + } + Ok(false) +} |