src/connectivity/lib/net-types/src/macros.rs - fuchsia - Git at Google

 // Copyright 2022 The Fuchsia Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 use assert_matches::assert_matches;
 use proc_macro::TokenStream;
 use proc_macro2::{TokenStream as TokenStream2, TokenTree};
 use quote::{quote, ToTokens as _};
 use syn::{
     parse_quote, punctuated::Punctuated, spanned::Spanned, AngleBracketedGenericArguments,
     GenericArgument, GenericParam, Generics, Ident, Type, TypeParam, TypeParamBound, TypePath,
 };

 /// Implements a derive macro for [`net_types::ip::GenericOverIp`].
 /// Requires that #[derive(GenericOverIp)] invocations explicitly specify
 /// which type parameter is the generic-over-ip one with the
 /// `#[generic_over_ip]` attribute, rather than inferring it from the bounds
 /// on the struct generics.
 ///
 /// Consider the following example:
 ///
 /// ```
 ///  #[derive(GenericOverIp)]
 ///  #[generic_over_ip(<ARGUMENTS EXPLAINED BELOW>)]
 ///  struct Foo<T>(T);
 /// ```
 ///
 /// `#[generic_over_ip(T, Ip)]` specifies that the GenericOverIp impl
 /// should be written treating `T` as an `Ip` implementor (either `Ipv4` or
 /// `Ipv6`).
 ///
 /// `#[generic_over_ip(T, IpAddress)]` specifies that `T` is an `IpAddress`
 /// implementor (`Ipv4Addr` or `Ipv6Addr`).
 ///
 /// `#[generic_over_ip(T, GenericOverIp)]` specifies that `T` implements
 /// `GenericOverIp<I>` for all `I: Ip`. (Notably, we'd like to use this case
 /// for the Ip and IpAddress cases above, but we cannot due to issues
 /// with conflicting blanket impls.)
 ///
 /// `#[generic_over_ip()]` specifies that `Foo` is IP-invariant.
 #[proc_macro_derive(GenericOverIp, attributes(generic_over_ip))]
 pub fn derive_generic_over_ip(input: TokenStream) -> TokenStream {
     let ast = syn::parse(input).unwrap();

     impl_derive_generic_over_ip(&ast).into()
 }

 fn impl_derive_generic_over_ip(ast: &syn::DeriveInput) -> TokenStream2 {
     let (impl_generics, type_generics, where_clause) = ast.generics.split_for_impl();
     if where_clause.is_some() {
         return quote! {
             compile_error!("deriving GenericOverIp for types with 'where' clauses is unsupported")
         }
         .into();
     }

     let name = &ast.ident;

     let specified_generic_over_ip = match find_generic_over_ip_attr(ast) {
         Ok(param) => param,
         Err(e) => return e.into_compile_error().into(),
     };

     let extra_bounds = match &specified_generic_over_ip {
         None => Vec::new(),
         Some((ident, _)) => match collect_bounds(ident, ast.generics.type_params()) {
             Some(bounds) => bounds,
             None => {
                 return syn::Error::new(
                     ast.generics.span(),
                     format!(
                         "found no type parameter named {ident:?} as specified in \
                             the generic_over_ip attribute"
                     ),
                 )
                 .into_compile_error()
                 .into();
             }
         },
     };

     // Drop the first and last tokens, which should be '<' and '>', and the
     // trailing comma if there is one.
     let mut impl_generics = impl_generics.into_token_stream().into_iter();

     let expect_trailing_angle_bracket = impl_generics.next().is_some_and(|first| {
         assert_matches!(first, TokenTree::Punct(p) if p.as_char() == '<');
         true
     });
     let mut impl_generics: Vec<_> = impl_generics.collect();
     if expect_trailing_angle_bracket {
         assert_matches!(impl_generics.pop(), Some(TokenTree::Punct(p)) if p.as_char() == '>');
     }

     // Add a trailing comma if `impl_generics` is non-empty and doesn't have one.
     match impl_generics.last() {
         Some(TokenTree::Punct(p)) if p.as_char() == ',' => {}
         None => {}
         Some(_) => {
             impl_generics.push(parse_quote! { , });
         }
     }

     let impl_generics = impl_generics.into_iter().collect::<TokenStream2>();

     match specified_generic_over_ip.clone() {
         Some((ident, param_type)) => {
             // Emit an impl that substitutes the identified type parameter
             // to produce the new GenericOverIp::Type.
             let generic_ip_name: Ident = parse_quote!(IpType);
             let extra_bounds_target: TypePath = match param_type {
                 IpGenericParamType::IpVersion => parse_quote!(#generic_ip_name),
                 IpGenericParamType::IpAddress => parse_quote!(#generic_ip_name::Addr),
                 IpGenericParamType::GenericOverIp => parse_quote! {
                     <#ident as GenericOverIp<IpType>>::Type
                 },
             };

             let bound_if_generic_over_ip = match param_type {
                 IpGenericParamType::IpVersion | IpGenericParamType::IpAddress => None,
                 IpGenericParamType::GenericOverIp => Some(quote! {
                     #ident: GenericOverIp<IpType>,
                 }),
             };

             let generic_bounds = with_type_param_replaced(
                 &ast.generics,
                 &ident,
                 parse_quote! {
                     #extra_bounds_target
                 },
             );

             quote! {
                 impl <#impl_generics #generic_ip_name: Ip>
                 GenericOverIp<IpType> for #name #type_generics
                 where #bound_if_generic_over_ip #extra_bounds_target: #(#extra_bounds)+*, {
                     type Type = #name #generic_bounds;
                 }
             }
         }
         None => {
             // The type is IP-invariant so `GenericOverIp::Type` is always Self.`
             quote! {
                 impl <#impl_generics IpType: Ip> GenericOverIp<IpType> for #name #type_generics {
                     type Type = Self;
                 }
             }
         }
     }
 }

 #[derive(Debug, Clone)]
 enum IpGenericParamType {
     IpVersion,
     IpAddress,
     GenericOverIp,
 }

 fn find_generic_over_ip_attr(
     ast: &syn::DeriveInput,
 ) -> Result<Option<(Ident, IpGenericParamType)>, syn::Error> {
     let mut attrs = ast
         .attrs
         .iter()
         .filter(|attr| attr.path.get_ident().map(|i| i == "generic_over_ip").unwrap_or(false));
     let attr = attrs.next().ok_or_else(|| {
         syn::Error::new(
             ast.ident.span(),
             "derive(GenericOverIp) cannot be used without the generic_over_ip attribute",
         )
     })?;
     match attrs.next() {
         None => {}
         Some(attr) => {
             return Err(syn::Error::new(
                 attr.span(),
                 "derive(GenericOverIp) cannot be used with multiple generic_over_ip attributes",
             ))
         }
     }

     let meta = attr.parse_meta().map_err(|e| {
         syn::Error::new(attr.span(), format!("generic_over_ip attr did not parse as Meta: {e:?}"))
     })?;

     let list = match meta {
         syn::Meta::Path(_) | syn::Meta::NameValue(_) => {
             return Err(syn::Error::new(
                 meta.span(),
                 "generic_over_ip must be passed at most one\
                 type parameter identifier",
             ));
         }
         syn::Meta::List(list) => list,
     };

     if list.nested.is_empty() {
         return Ok(None);
     } else if list.nested.len() != 2 {
         return Err(syn::Error::new(
             list.span(),
             "generic_over_ip must be either be passed no \
                          arguments, or one type parameter identifier and its \
                          trait bound (Ip, IpAddress, or GenericOverIp)",
         ));
     }

     let mut iter = list.nested.into_iter();
     let (ident, bound) = (iter.next().unwrap(), iter.next().unwrap());

     let ident = match ident {
         syn::NestedMeta::Meta(meta) => match meta {
             syn::Meta::Path(path) => match path.get_ident() {
                 None => Err(syn::Error::new(
                     path.span(),
                     "generic_over_ip must be passed a parameter identifier",
                 )),
                 Some(ident) => Ok(ident.clone()),
             },
             syn::Meta::List(_) | syn::Meta::NameValue(_) => Err(syn::Error::new(
                 meta.span(),
                 "generic_over_ip must be passed at most one \
                              type parameter identifier, not a list or name-value pair",
             )),
         },
         syn::NestedMeta::Lit(lit) => Err(syn::Error::new(
             lit.span(),
             "generic_over_ip must be passed at most one \
                         type parameter identifier, not a literal",
         )),
     }?;

     let bound_error_message = "the bound passed to generic_over_ip \
                                              must be Ip, IpAddress, or GenericOverIp";

     let bound = match bound {
         syn::NestedMeta::Meta(meta) => match meta {
             syn::Meta::Path(path) => match path.get_ident() {
                 None => Err(syn::Error::new(path.span(), bound_error_message)),
                 Some(ident) => Ok(ident.clone()),
             },
             syn::Meta::List(_) | syn::Meta::NameValue(_) => {
                 Err(syn::Error::new(meta.span(), bound_error_message))
             }
         },
         syn::NestedMeta::Lit(lit) => Err(syn::Error::new(lit.span(), bound_error_message)),
     }?;

     let bound = match bound.to_string().as_str() {
         "Ip" => IpGenericParamType::IpVersion,
         "IpAddress" => IpGenericParamType::IpAddress,
         "GenericOverIp" => IpGenericParamType::GenericOverIp,
         _ => return Err(syn::Error::new(bound.span(), bound_error_message)),
     };

     Ok(Some((ident, bound)))
 }

 fn collect_bounds<'a>(
     ident: &'a Ident,
     mut generics: impl Iterator<Item = &'a TypeParam>,
 ) -> Option<Vec<&'a TypeParamBound>> {
     generics.find_map(|t| if &t.ident == ident { Some(t.bounds.iter().collect()) } else { None })
 }

 fn with_type_param_replaced(
     generics: &Generics,
     to_find: &Ident,
     replacement: TypePath,
 ) -> Option<AngleBracketedGenericArguments> {
     let args: Punctuated<_, _> = generics
         .params
         .iter()
         .map(|g| match g {
             GenericParam::Const(c) => GenericArgument::Const(parse_quote!(#c.ident)),
             GenericParam::Lifetime(l) => GenericArgument::Lifetime(l.lifetime.clone()),
             GenericParam::Type(t) => {
                 if &t.ident == to_find {
                     GenericArgument::Type(Type::Path(replacement.clone()))
                 } else {
                     GenericArgument::Type(Type::Path(TypePath {
                         path: t.ident.clone().into(),
                         qself: None,
                     }))
                 }
             }
         })
         .collect();
     (args.len() != 0).then(|| AngleBracketedGenericArguments {
         args,
         colon2_token: None,
         lt_token: Default::default(),
         gt_token: Default::default(),
     })
 }
	// Copyright 2022 The Fuchsia Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	use assert_matches::assert_matches;
	use proc_macro::TokenStream;
	use proc_macro2::{TokenStream as TokenStream2, TokenTree};
	use quote::{quote, ToTokens as _};
	use syn::{
	parse_quote, punctuated::Punctuated, spanned::Spanned, AngleBracketedGenericArguments,
	GenericArgument, GenericParam, Generics, Ident, Type, TypeParam, TypeParamBound, TypePath,
	};

	/// Implements a derive macro for [`net_types::ip::GenericOverIp`].
	/// Requires that #[derive(GenericOverIp)] invocations explicitly specify
	/// which type parameter is the generic-over-ip one with the
	/// `#[generic_over_ip]` attribute, rather than inferring it from the bounds
	/// on the struct generics.
	///
	/// Consider the following example:
	///
	/// ```
	/// #[derive(GenericOverIp)]
	/// #[generic_over_ip(<ARGUMENTS EXPLAINED BELOW>)]
	/// struct Foo<T>(T);
	/// ```
	///
	/// `#[generic_over_ip(T, Ip)]` specifies that the GenericOverIp impl
	/// should be written treating `T` as an `Ip` implementor (either `Ipv4` or
	/// `Ipv6`).
	///
	/// `#[generic_over_ip(T, IpAddress)]` specifies that `T` is an `IpAddress`
	/// implementor (`Ipv4Addr` or `Ipv6Addr`).
	///
	/// `#[generic_over_ip(T, GenericOverIp)]` specifies that `T` implements
	/// `GenericOverIp<I>` for all `I: Ip`. (Notably, we'd like to use this case
	/// for the Ip and IpAddress cases above, but we cannot due to issues
	/// with conflicting blanket impls.)
	///
	/// `#[generic_over_ip()]` specifies that `Foo` is IP-invariant.
	#[proc_macro_derive(GenericOverIp, attributes(generic_over_ip))]
	pub fn derive_generic_over_ip(input: TokenStream) -> TokenStream {
	let ast = syn::parse(input).unwrap();

	impl_derive_generic_over_ip(&ast).into()
	}

	fn impl_derive_generic_over_ip(ast: &syn::DeriveInput) -> TokenStream2 {
	let (impl_generics, type_generics, where_clause) = ast.generics.split_for_impl();
	if where_clause.is_some() {
	return quote! {
	compile_error!("deriving GenericOverIp for types with 'where' clauses is unsupported")
	}
	.into();
	}

	let name = &ast.ident;

	let specified_generic_over_ip = match find_generic_over_ip_attr(ast) {
	Ok(param) => param,
	Err(e) => return e.into_compile_error().into(),
	};

	let extra_bounds = match &specified_generic_over_ip {
	None => Vec::new(),
	Some((ident, _)) => match collect_bounds(ident, ast.generics.type_params()) {
	Some(bounds) => bounds,
	None => {
	return syn::Error::new(
	ast.generics.span(),
	format!(
	"found no type parameter named {ident:?} as specified in \
	the generic_over_ip attribute"
	),
	)
	.into_compile_error()
	.into();
	}
	},
	};

	// Drop the first and last tokens, which should be '<' and '>', and the
	// trailing comma if there is one.
	let mut impl_generics = impl_generics.into_token_stream().into_iter();

	let expect_trailing_angle_bracket = impl_generics.next().is_some_and(\|first\| {
	assert_matches!(first, TokenTree::Punct(p) if p.as_char() == '<');
	true
	});
	let mut impl_generics: Vec<_> = impl_generics.collect();
	if expect_trailing_angle_bracket {
	assert_matches!(impl_generics.pop(), Some(TokenTree::Punct(p)) if p.as_char() == '>');
	}

	// Add a trailing comma if `impl_generics` is non-empty and doesn't have one.
	match impl_generics.last() {
	Some(TokenTree::Punct(p)) if p.as_char() == ',' => {}
	None => {}
	Some(_) => {
	impl_generics.push(parse_quote! { , });
	}
	}

	let impl_generics = impl_generics.into_iter().collect::<TokenStream2>();

	match specified_generic_over_ip.clone() {
	Some((ident, param_type)) => {
	// Emit an impl that substitutes the identified type parameter
	// to produce the new GenericOverIp::Type.
	let generic_ip_name: Ident = parse_quote!(IpType);
	let extra_bounds_target: TypePath = match param_type {
	IpGenericParamType::IpVersion => parse_quote!(#generic_ip_name),
	IpGenericParamType::IpAddress => parse_quote!(#generic_ip_name::Addr),
	IpGenericParamType::GenericOverIp => parse_quote! {
	<#ident as GenericOverIp<IpType>>::Type
	},
	};

	let bound_if_generic_over_ip = match param_type {
	IpGenericParamType::IpVersion \| IpGenericParamType::IpAddress => None,
	IpGenericParamType::GenericOverIp => Some(quote! {
	#ident: GenericOverIp<IpType>,
	}),
	};

	let generic_bounds = with_type_param_replaced(
	&ast.generics,
	&ident,
	parse_quote! {
	#extra_bounds_target
	},
	);

	quote! {
	impl <#impl_generics #generic_ip_name: Ip>
	GenericOverIp<IpType> for #name #type_generics
	where #bound_if_generic_over_ip #extra_bounds_target: #(#extra_bounds)+*, {
	type Type = #name #generic_bounds;
	}
	}
	}
	None => {
	// The type is IP-invariant so `GenericOverIp::Type` is always Self.`
	quote! {
	impl <#impl_generics IpType: Ip> GenericOverIp<IpType> for #name #type_generics {
	type Type = Self;
	}
	}
	}
	}
	}

	#[derive(Debug, Clone)]
	enum IpGenericParamType {
	IpVersion,
	IpAddress,
	GenericOverIp,
	}

	fn find_generic_over_ip_attr(
	ast: &syn::DeriveInput,
	) -> Result<Option<(Ident, IpGenericParamType)>, syn::Error> {
	let mut attrs = ast
	.attrs
	.iter()
	.filter(\|attr\| attr.path.get_ident().map(\|i\| i == "generic_over_ip").unwrap_or(false));
	let attr = attrs.next().ok_or_else(\|\| {
	syn::Error::new(
	ast.ident.span(),
	"derive(GenericOverIp) cannot be used without the generic_over_ip attribute",
	)
	})?;
	match attrs.next() {
	None => {}
	Some(attr) => {
	return Err(syn::Error::new(
	attr.span(),
	"derive(GenericOverIp) cannot be used with multiple generic_over_ip attributes",
	))
	}
	}

	let meta = attr.parse_meta().map_err(\|e\| {
	syn::Error::new(attr.span(), format!("generic_over_ip attr did not parse as Meta: {e:?}"))
	})?;

	let list = match meta {
	syn::Meta::Path(_) \| syn::Meta::NameValue(_) => {
	return Err(syn::Error::new(
	meta.span(),
	"generic_over_ip must be passed at most one\
	type parameter identifier",
	));
	}
	syn::Meta::List(list) => list,
	};

	if list.nested.is_empty() {
	return Ok(None);
	} else if list.nested.len() != 2 {
	return Err(syn::Error::new(
	list.span(),
	"generic_over_ip must be either be passed no \
	arguments, or one type parameter identifier and its \
	trait bound (Ip, IpAddress, or GenericOverIp)",
	));
	}

	let mut iter = list.nested.into_iter();
	let (ident, bound) = (iter.next().unwrap(), iter.next().unwrap());

	let ident = match ident {
	syn::NestedMeta::Meta(meta) => match meta {
	syn::Meta::Path(path) => match path.get_ident() {
	None => Err(syn::Error::new(
	path.span(),
	"generic_over_ip must be passed a parameter identifier",
	)),
	Some(ident) => Ok(ident.clone()),
	},
	syn::Meta::List(_) \| syn::Meta::NameValue(_) => Err(syn::Error::new(
	meta.span(),
	"generic_over_ip must be passed at most one \
	type parameter identifier, not a list or name-value pair",
	)),
	},
	syn::NestedMeta::Lit(lit) => Err(syn::Error::new(
	lit.span(),
	"generic_over_ip must be passed at most one \
	type parameter identifier, not a literal",
	)),
	}?;

	let bound_error_message = "the bound passed to generic_over_ip \
	must be Ip, IpAddress, or GenericOverIp";

	let bound = match bound {
	syn::NestedMeta::Meta(meta) => match meta {
	syn::Meta::Path(path) => match path.get_ident() {
	None => Err(syn::Error::new(path.span(), bound_error_message)),
	Some(ident) => Ok(ident.clone()),
	},
	syn::Meta::List(_) \| syn::Meta::NameValue(_) => {
	Err(syn::Error::new(meta.span(), bound_error_message))
	}
	},
	syn::NestedMeta::Lit(lit) => Err(syn::Error::new(lit.span(), bound_error_message)),
	}?;

	let bound = match bound.to_string().as_str() {
	"Ip" => IpGenericParamType::IpVersion,
	"IpAddress" => IpGenericParamType::IpAddress,
	"GenericOverIp" => IpGenericParamType::GenericOverIp,
	_ => return Err(syn::Error::new(bound.span(), bound_error_message)),
	};

	Ok(Some((ident, bound)))
	}

	fn collect_bounds<'a>(
	ident: &'a Ident,
	mut generics: impl Iterator<Item = &'a TypeParam>,
	) -> Option<Vec<&'a TypeParamBound>> {
	generics.find_map(\|t\| if &t.ident == ident { Some(t.bounds.iter().collect()) } else { None })
	}

	fn with_type_param_replaced(
	generics: &Generics,
	to_find: &Ident,
	replacement: TypePath,
	) -> Option<AngleBracketedGenericArguments> {
	let args: Punctuated<_, _> = generics
	.params
	.iter()
	.map(\|g\| match g {
	GenericParam::Const(c) => GenericArgument::Const(parse_quote!(#c.ident)),
	GenericParam::Lifetime(l) => GenericArgument::Lifetime(l.lifetime.clone()),
	GenericParam::Type(t) => {
	if &t.ident == to_find {
	GenericArgument::Type(Type::Path(replacement.clone()))
	} else {
	GenericArgument::Type(Type::Path(TypePath {
	path: t.ident.clone().into(),
	qself: None,
	}))
	}
	}
	})
	.collect();
	(args.len() != 0).then(\|\| AngleBracketedGenericArguments {
	args,
	colon2_token: None,
	lt_token: Default::default(),
	gt_token: Default::default(),
	})
	}