Skip to content

serde_derive: replace .fold(sum + expr) with sum_tokens #3042

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
dishmaker wants to merge 2 commits into
base: master
Choose a base branch
from
Open

serde_derive: replace .fold(sum + expr) with sum_tokens #3042

Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
89b4256
serde_derive: add fn sum_tokens
dishmaker Feb 16, 2026
1cc8999
serde_derive: use sum_tokens in all `let len =` calculations
dishmaker Feb 16, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
49 changes: 30 additions & 19 deletions serde_derive/src/ser.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -272,8 +272,9 @@ fn serialize_tuple_struct(

let let_mut = mut_if(serialized_fields.peek().is_some());

let len = serialized_fields
.map(|(i, field)| match field.attrs.skip_serializing_if() {
let len = sum_tokens(
quote!(0),
serialized_fields.map(|(i, field)| match field.attrs.skip_serializing_if() {
None => quote!(1),
Some(path) => {
let index = syn::Index {
Expand All @@ -283,8 +284,8 @@ fn serialize_tuple_struct(
let field_expr = get_member(params, field, &Member::Unnamed(index));
quote!(if #path(#field_expr) { 0 } else { 1 })
}
})
.fold(quote!(0), |sum, expr| quote!(#sum + #expr));
}),
);

quote_block! {
let #let_mut __serde_state = _serde::Serializer::serialize_tuple_struct(__serializer, #type_name, #len)?;
Expand All @@ -293,6 +294,16 @@ fn serialize_tuple_struct(
}
}

/// `quote!(#init + #item + ...)`
fn sum_tokens(init: TokenStream, iter: impl Iterator<Item = TokenStream>) -> TokenStream {
let mut tokens = init;
for item in iter {
tokens.extend(quote!( + ));
tokens.extend(item);
}
tokens
}

fn serialize_struct(params: &Parameters, fields: &[Field], cattrs: &attr::Container) -> Fragment {
assert!(
fields.len() as u64 <= u64::from(u32::MAX),
Expand Down Expand Up @@ -345,18 +356,16 @@ fn serialize_struct_as_struct(

let let_mut = mut_if(serialized_fields.peek().is_some() || tag_field_exists);

let len = serialized_fields
.map(|field| match field.attrs.skip_serializing_if() {
let len = sum_tokens(
quote!(#tag_field_exists as usize),
serialized_fields.map(|field| match field.attrs.skip_serializing_if() {
None => quote!(1),
Some(path) => {
let field_expr = get_member(params, field, &field.member);
quote!(if #path(#field_expr) { 0 } else { 1 })
}
})
.fold(
quote!(#tag_field_exists as usize),
|sum, expr| quote!(#sum + #expr),
);
}),
);

quote_block! {
let #let_mut __serde_state = _serde::Serializer::serialize_struct(__serializer, #type_name, #len)?;
Expand Down Expand Up @@ -830,15 +839,16 @@ fn serialize_tuple_variant(

let let_mut = mut_if(serialized_fields.peek().is_some());

let len = serialized_fields
.map(|(i, field)| match field.attrs.skip_serializing_if() {
let len = sum_tokens(
quote!(0),
serialized_fields.map(|(i, field)| match field.attrs.skip_serializing_if() {
None => quote!(1),
Some(path) => {
let field_expr = field_i(i);
quote!(if #path(#field_expr) { 0 } else { 1 })
}
})
.fold(quote!(0), |sum, expr| quote!(#sum + #expr));
}),
);

match context {
TupleVariant::ExternallyTagged {
Expand Down Expand Up @@ -907,16 +917,17 @@ fn serialize_struct_variant(

let let_mut = mut_if(serialized_fields.peek().is_some());

let len = serialized_fields
.map(|field| {
let len = sum_tokens(
quote!(0),
serialized_fields.map(|field| {
let member = &field.member;

match field.attrs.skip_serializing_if() {
Some(path) => quote!(if #path(#member) { 0 } else { 1 }),
None => quote!(1),
}
})
.fold(quote!(0), |sum, expr| quote!(#sum + #expr));
}),
);

match context {
StructVariant::ExternallyTagged {
Expand Down