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der_derive: add proc macro for deriving
ValueOrd (#206)
Support for deriving `ValueOrd` on structs, which is used by the `SetOf*` types to determine ordering.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,144 @@ | ||
| //! Support for deriving the `ValueOrd` trait on enums and structs. | ||
| //! | ||
| //! This trait is used in conjunction with ASN.1 `SET OF` types to determine | ||
| //! the lexicographical order of their DER encodings. | ||
|
|
||
| // TODO(tarcieri): enum support | ||
|
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||
| use crate::{FieldAttrs, TypeAttrs}; | ||
| use proc_macro2::TokenStream; | ||
| use proc_macro_error::abort; | ||
| use quote::quote; | ||
| use syn::{DeriveInput, Field, Ident, Lifetime, Variant}; | ||
|
|
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| /// Derive the `Enumerated` trait for an enum. | ||
| pub(crate) struct DeriveValueOrd { | ||
| /// Name of the enum. | ||
| ident: Ident, | ||
|
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| /// Lifetime of the struct. | ||
| lifetime: Option<Lifetime>, | ||
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| /// Fields of structs or enum variants. | ||
| fields: Vec<ValueField>, | ||
| } | ||
|
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| impl DeriveValueOrd { | ||
| /// Parse [`DeriveInput`]. | ||
| pub fn new(input: DeriveInput) -> Self { | ||
| let ident = input.ident; | ||
| let type_attrs = TypeAttrs::parse(&input.attrs); | ||
|
|
||
| // TODO(tarcieri): properly handle multiple lifetimes | ||
| let lifetime = input | ||
| .generics | ||
| .lifetimes() | ||
| .next() | ||
| .map(|lt| lt.lifetime.clone()); | ||
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|
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| let fields = match input.data { | ||
| syn::Data::Enum(data) => data | ||
| .variants | ||
| .into_iter() | ||
| .map(|variant| ValueField::new_enum(variant, &type_attrs)) | ||
| .collect(), | ||
| syn::Data::Struct(data) => data | ||
| .fields | ||
| .into_iter() | ||
| .map(|field| ValueField::new_struct(field, &type_attrs)) | ||
| .collect(), | ||
| _ => abort!( | ||
| ident, | ||
| "can't derive `ValueOrd` on this type: \ | ||
| only `enum` and `struct` types are allowed", | ||
| ), | ||
| }; | ||
|
|
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| Self { | ||
| ident, | ||
| lifetime, | ||
| fields, | ||
| } | ||
| } | ||
|
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| /// Lower the derived output into a [`TokenStream`]. | ||
| pub fn to_tokens(&self) -> TokenStream { | ||
| let ident = &self.ident; | ||
|
|
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| // Lifetime parameters | ||
| // TODO(tarcieri): support multiple lifetimes | ||
| let lt_params = self | ||
| .lifetime | ||
| .as_ref() | ||
| .map(|lt| vec![lt.clone()]) | ||
| .unwrap_or_default(); | ||
|
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| let mut body = Vec::new(); | ||
|
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| for field in &self.fields { | ||
| body.push(field.to_tokens()); | ||
| } | ||
|
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| quote! { | ||
| impl<#(#lt_params)*> ::der::ValueOrd for #ident<#(#lt_params)*> { | ||
| fn value_cmp(&self, other: &Self) -> ::der::Result<::core::cmp::Ordering> { | ||
| #[allow(unused_imports)] | ||
| use ::der::DerOrd; | ||
|
|
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| #(#body)* | ||
|
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| Ok(::core::cmp::Ordering::Equal) | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
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| struct ValueField { | ||
| /// Name of the field | ||
| ident: Ident, | ||
|
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| /// Field-level attributes. | ||
| attrs: FieldAttrs, | ||
| } | ||
|
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| impl ValueField { | ||
| /// Create from an `enum` variant. | ||
| fn new_enum(variant: Variant, _: &TypeAttrs) -> Self { | ||
| abort!( | ||
| variant, | ||
| "deriving `ValueOrd` only presently supported for structs" | ||
| ); | ||
| } | ||
|
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| /// Create from a `struct` field. | ||
| fn new_struct(field: Field, type_attrs: &TypeAttrs) -> Self { | ||
| let ident = field | ||
| .ident | ||
| .as_ref() | ||
| .cloned() | ||
| .unwrap_or_else(|| abort!(&field, "tuple structs are not supported")); | ||
|
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| let attrs = FieldAttrs::parse(&field.attrs, type_attrs); | ||
| Self { ident, attrs } | ||
| } | ||
|
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| /// Lower to [`TokenStream`]. | ||
| fn to_tokens(&self) -> TokenStream { | ||
| let ident = &self.ident; | ||
| let mut binding1 = quote!(self.#ident); | ||
| let mut binding2 = quote!(other.#ident); | ||
|
|
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| if let Some(ty) = &self.attrs.asn1_type { | ||
| binding1 = ty.encoder(&binding1); | ||
| binding2 = ty.encoder(&binding2); | ||
| } | ||
|
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| quote! { | ||
| match #binding1.der_cmp(&#binding2)? { | ||
| ::core::cmp::Ordering::Equal => (), | ||
| other => return Ok(other), | ||
| } | ||
| } | ||
| } | ||
| } |
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