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Support Default Field Values, backwards compatibly #1955

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Support Default Field Values, backwards compatibly #1955

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17 changes: 9 additions & 8 deletions examples/heapsize/heapsize_derive/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,13 +2,14 @@ use proc_macro2::TokenStream;
use quote::{quote, quote_spanned};
use syn::spanned::Spanned;
use syn::{
parse_macro_input, parse_quote, Data, DeriveInput, Fields, GenericParam, Generics, Index,
parse_macro_input, parse_quote, DataWithDefault, DeriveInputWithDefault, FieldsWithDefault,
GenericParam, Generics, Index,
};

#[proc_macro_derive(HeapSize)]
pub fn derive_heap_size(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
// Parse the input tokens into a syntax tree.
let input = parse_macro_input!(input as DeriveInput);
let input = parse_macro_input!(input as DeriveInputWithDefault);

// Used in the quasi-quotation below as `#name`.
let name = input.ident;
Expand Down Expand Up @@ -44,11 +45,11 @@ fn add_trait_bounds(mut generics: Generics) -> Generics {
}

// Generate an expression to sum up the heap size of each field.
fn heap_size_sum(data: &Data) -> TokenStream {
fn heap_size_sum(data: &DataWithDefault) -> TokenStream {
match *data {
Data::Struct(ref data) => {
DataWithDefault::Struct(ref data) => {
match data.fields {
Fields::Named(ref fields) => {
FieldsWithDefault::Named(ref fields) => {
// Expands to an expression like
//
// 0 + self.x.heap_size() + self.y.heap_size() + self.z.heap_size()
Expand All @@ -71,7 +72,7 @@ fn heap_size_sum(data: &Data) -> TokenStream {
0 #(+ #recurse)*
}
}
Fields::Unnamed(ref fields) => {
FieldsWithDefault::Unnamed(ref fields) => {
// Expands to an expression like
//
// 0 + self.0.heap_size() + self.1.heap_size() + self.2.heap_size()
Expand All @@ -85,12 +86,12 @@ fn heap_size_sum(data: &Data) -> TokenStream {
0 #(+ #recurse)*
}
}
Fields::Unit => {
FieldsWithDefault::Unit => {
// Unit structs cannot own more than 0 bytes of heap memory.
quote!(0)
}
}
}
Data::Enum(_) | Data::Union(_) => unimplemented!(),
DataWithDefault::Enum(_) | DataWithDefault::Union(_) => unimplemented!(),
}
}
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