diff options
Diffstat (limited to 'third_party/rust/serde_derive/src/pretend.rs')
| -rw-r--r-- | third_party/rust/serde_derive/src/pretend.rs | 185 |
1 files changed, 185 insertions, 0 deletions
diff --git a/third_party/rust/serde_derive/src/pretend.rs b/third_party/rust/serde_derive/src/pretend.rs new file mode 100644 index 0000000000..2c9e779368 --- /dev/null +++ b/third_party/rust/serde_derive/src/pretend.rs @@ -0,0 +1,185 @@ +use crate::internals::ast::{Container, Data, Field, Style, Variant}; +use proc_macro2::TokenStream; +use quote::{format_ident, quote}; + +// Suppress dead_code warnings that would otherwise appear when using a remote +// derive. Other than this pretend code, a struct annotated with remote derive +// never has its fields referenced and an enum annotated with remote derive +// never has its variants constructed. +// +// warning: field is never used: `i` +// --> src/main.rs:4:20 +// | +// 4 | struct StructDef { i: i32 } +// | ^^^^^^ +// +// warning: variant is never constructed: `V` +// --> src/main.rs:8:16 +// | +// 8 | enum EnumDef { V } +// | ^ +// +pub fn pretend_used(cont: &Container, is_packed: bool) -> TokenStream { + let pretend_fields = pretend_fields_used(cont, is_packed); + let pretend_variants = pretend_variants_used(cont); + + quote! { + #pretend_fields + #pretend_variants + } +} + +// For structs with named fields, expands to: +// +// match None::<&T> { +// Some(T { a: __v0, b: __v1 }) => {} +// _ => {} +// } +// +// For packed structs on sufficiently new rustc, expands to: +// +// match None::<&T> { +// Some(__v @ T { a: _, b: _ }) => { +// let _ = addr_of!(__v.a); +// let _ = addr_of!(__v.b); +// } +// _ => {} +// } +// +// For packed structs on older rustc, we assume Sized and !Drop, and expand to: +// +// match None::<T> { +// Some(T { a: __v0, b: __v1 }) => {} +// _ => {} +// } +// +// For enums, expands to the following but only including struct variants: +// +// match None::<&T> { +// Some(T::A { a: __v0 }) => {} +// Some(T::B { b: __v0 }) => {} +// _ => {} +// } +// +fn pretend_fields_used(cont: &Container, is_packed: bool) -> TokenStream { + match &cont.data { + Data::Enum(variants) => pretend_fields_used_enum(cont, variants), + Data::Struct(Style::Struct | Style::Tuple | Style::Newtype, fields) => { + if is_packed { + pretend_fields_used_struct_packed(cont, fields) + } else { + pretend_fields_used_struct(cont, fields) + } + } + Data::Struct(Style::Unit, _) => quote!(), + } +} + +fn pretend_fields_used_struct(cont: &Container, fields: &[Field]) -> TokenStream { + let type_ident = &cont.ident; + let (_, ty_generics, _) = cont.generics.split_for_impl(); + + let members = fields.iter().map(|field| &field.member); + let placeholders = (0usize..).map(|i| format_ident!("__v{}", i)); + + quote! { + match _serde::__private::None::<&#type_ident #ty_generics> { + _serde::__private::Some(#type_ident { #(#members: #placeholders),* }) => {} + _ => {} + } + } +} + +fn pretend_fields_used_struct_packed(cont: &Container, fields: &[Field]) -> TokenStream { + let type_ident = &cont.ident; + let (_, ty_generics, _) = cont.generics.split_for_impl(); + + let members = fields.iter().map(|field| &field.member).collect::<Vec<_>>(); + + quote! { + match _serde::__private::None::<&#type_ident #ty_generics> { + _serde::__private::Some(__v @ #type_ident { #(#members: _),* }) => { + #( + let _ = _serde::__private::ptr::addr_of!(__v.#members); + )* + } + _ => {} + } + } +} + +fn pretend_fields_used_enum(cont: &Container, variants: &[Variant]) -> TokenStream { + let type_ident = &cont.ident; + let (_, ty_generics, _) = cont.generics.split_for_impl(); + + let patterns = variants + .iter() + .filter_map(|variant| match variant.style { + Style::Struct | Style::Tuple | Style::Newtype => { + let variant_ident = &variant.ident; + let members = variant.fields.iter().map(|field| &field.member); + let placeholders = (0usize..).map(|i| format_ident!("__v{}", i)); + Some(quote!(#type_ident::#variant_ident { #(#members: #placeholders),* })) + } + Style::Unit => None, + }) + .collect::<Vec<_>>(); + + quote! { + match _serde::__private::None::<&#type_ident #ty_generics> { + #( + _serde::__private::Some(#patterns) => {} + )* + _ => {} + } + } +} + +// Expands to one of these per enum variant: +// +// match None { +// Some((__v0, __v1,)) => { +// let _ = E::V { a: __v0, b: __v1 }; +// } +// _ => {} +// } +// +fn pretend_variants_used(cont: &Container) -> TokenStream { + let variants = match &cont.data { + Data::Enum(variants) => variants, + Data::Struct(_, _) => { + return quote!(); + } + }; + + let type_ident = &cont.ident; + let (_, ty_generics, _) = cont.generics.split_for_impl(); + let turbofish = ty_generics.as_turbofish(); + + let cases = variants.iter().map(|variant| { + let variant_ident = &variant.ident; + let placeholders = &(0..variant.fields.len()) + .map(|i| format_ident!("__v{}", i)) + .collect::<Vec<_>>(); + + let pat = match variant.style { + Style::Struct => { + let members = variant.fields.iter().map(|field| &field.member); + quote!({ #(#members: #placeholders),* }) + } + Style::Tuple | Style::Newtype => quote!(( #(#placeholders),* )), + Style::Unit => quote!(), + }; + + quote! { + match _serde::__private::None { + _serde::__private::Some((#(#placeholders,)*)) => { + let _ = #type_ident::#variant_ident #turbofish #pat; + } + _ => {} + } + } + }); + + quote!(#(#cases)*) +} |