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feat(derive): Support RFC 3681 default field values #6220

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86b1c8b
refactor(derive): Use WithDefault syn types
agraven Jan 11, 2026
d102cfe
feat(derive): Support RFC 3681 default field values
agraven Jan 11, 2026
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42 changes: 26 additions & 16 deletions Cargo.lock
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2 changes: 1 addition & 1 deletion clap_derive/Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -30,7 +30,7 @@ proc-macro = true
bench = false

[dependencies]
syn = { version = "2.0.8", features = ["full"] }
syn = { git = "https://github.com/DJMcNab/syn.git", branch = "with-default-fields", features = ["full"] }
quote = "1.0.9"
proc-macro2 = "1.0.69"
heck = "0.5.0"
Expand Down
33 changes: 18 additions & 15 deletions clap_derive/src/derives/args.rs
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Expand Up @@ -14,34 +14,35 @@

use proc_macro2::{Ident, Span, TokenStream};
use quote::{format_ident, quote, quote_spanned};
use syn::{punctuated::Punctuated, spanned::Spanned, token::Comma, Generics};
use syn::{
punctuated::Punctuated, spanned::Spanned, token::Comma, Data, DataStruct, DeriveInput, Field,
Fields, FieldsNamed, Generics,
DataStructWithDefault, DataWithDefault, DeriveInputWithDefault, FieldWithDefault,
FieldsNamedWithDefault, FieldsWithDefault,
};

use crate::item::{Item, Kind, Name};
use crate::utils::{inner_type, sub_type, Sp, Ty};

pub(crate) fn derive_args(input: &DeriveInput) -> Result<TokenStream, syn::Error> {
pub(crate) fn derive_args(input: &DeriveInputWithDefault) -> Result<TokenStream, syn::Error> {
let ident = &input.ident;

match input.data {
Data::Struct(DataStruct {
fields: Fields::Named(ref fields),
DataWithDefault::Struct(DataStructWithDefault {
fields: FieldsWithDefault::Named(ref fields),
..
}) => {
let name = Name::Derived(ident.clone());
let item = Item::from_args_struct(input, name)?;
let fields = collect_args_fields(&item, fields)?;
gen_for_struct(&item, ident, &input.generics, &fields)
}
Data::Struct(DataStruct {
fields: Fields::Unit,
DataWithDefault::Struct(DataStructWithDefault {
fields: FieldsWithDefault::Unit,
..
}) => {
let name = Name::Derived(ident.clone());
let item = Item::from_args_struct(input, name)?;
let fields = Punctuated::<Field, Comma>::new();
let fields = Punctuated::<FieldWithDefault, Comma>::new();
let fields = fields
.iter()
.map(|field| {
Expand All @@ -59,7 +60,7 @@ pub(crate) fn gen_for_struct(
item: &Item,
item_name: &Ident,
generics: &Generics,
fields: &[(&Field, Item)],
fields: &[(&FieldWithDefault, Item)],
) -> Result<TokenStream, syn::Error> {
if !matches!(&*item.kind(), Kind::Command(_)) {
abort! { item.kind().span(),
Expand Down Expand Up @@ -167,7 +168,7 @@ pub(crate) fn gen_for_struct(
/// Generate a block of code to add arguments/subcommands corresponding to
/// the `fields` to an cmd.
pub(crate) fn gen_augment(
fields: &[(&Field, Item)],
fields: &[(&FieldWithDefault, Item)],
app_var: &Ident,
parent_item: &Item,
override_required: bool,
Expand Down Expand Up @@ -440,7 +441,9 @@ pub(crate) fn gen_augment(
}})
}

pub(crate) fn gen_constructor(fields: &[(&Field, Item)]) -> Result<TokenStream, syn::Error> {
pub(crate) fn gen_constructor(
fields: &[(&FieldWithDefault, Item)],
) -> Result<TokenStream, syn::Error> {
let fields = fields.iter().map(|(field, item)| {
let field_name = field.ident.as_ref().unwrap();
let kind = item.kind();
Expand Down Expand Up @@ -552,7 +555,7 @@ pub(crate) fn gen_constructor(fields: &[(&Field, Item)]) -> Result<TokenStream,
}

pub(crate) fn gen_updater(
fields: &[(&Field, Item)],
fields: &[(&FieldWithDefault, Item)],
use_self: bool,
) -> Result<TokenStream, syn::Error> {
let mut genned_fields = Vec::new();
Expand Down Expand Up @@ -661,7 +664,7 @@ fn gen_parsers(
item: &Item,
ty: &Sp<Ty>,
field_name: &Ident,
field: &Field,
field: &FieldWithDefault,
update: Option<&TokenStream>,
) -> Result<TokenStream, syn::Error> {
let span = ty.span();
Expand Down Expand Up @@ -776,8 +779,8 @@ pub(crate) fn raw_deprecated() -> TokenStream {

pub(crate) fn collect_args_fields<'a>(
item: &'a Item,
fields: &'a FieldsNamed,
) -> Result<Vec<(&'a Field, Item)>, syn::Error> {
fields: &'a FieldsNamedWithDefault,
) -> Result<Vec<(&'a FieldWithDefault, Item)>, syn::Error> {
fields
.named
.iter()
Expand Down
30 changes: 16 additions & 14 deletions clap_derive/src/derives/parser.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -14,39 +14,41 @@

use proc_macro2::TokenStream;
use quote::quote;
use syn::DataStructWithDefault;
use syn::DataWithDefault;
use syn::DeriveInputWithDefault;
use syn::FieldWithDefault;
use syn::FieldsWithDefault;
use syn::Ident;
use syn::Variant;
use syn::{
self, punctuated::Punctuated, token::Comma, Data, DataStruct, DeriveInput, Field, Fields,
Generics,
};
use syn::VariantWithDefault;
use syn::{self, punctuated::Punctuated, token::Comma, Generics};

use crate::derives::args::collect_args_fields;
use crate::derives::{args, into_app, subcommand};
use crate::item::Item;
use crate::item::Name;

pub(crate) fn derive_parser(input: &DeriveInput) -> Result<TokenStream, syn::Error> {
pub(crate) fn derive_parser(input: &DeriveInputWithDefault) -> Result<TokenStream, syn::Error> {
let ident = &input.ident;
let pkg_name = std::env::var("CARGO_PKG_NAME").ok().unwrap_or_default();

match input.data {
Data::Struct(DataStruct {
fields: Fields::Named(ref fields),
DataWithDefault::Struct(DataStructWithDefault {
fields: FieldsWithDefault::Named(ref fields),
..
}) => {
let name = Name::Assigned(quote!(#pkg_name));
let item = Item::from_args_struct(input, name)?;
let fields = collect_args_fields(&item, fields)?;
gen_for_struct(&item, ident, &input.generics, &fields)
}
Data::Struct(DataStruct {
fields: Fields::Unit,
DataWithDefault::Struct(DataStructWithDefault {
fields: FieldsWithDefault::Unit,
..
}) => {
let name = Name::Assigned(quote!(#pkg_name));
let item = Item::from_args_struct(input, name)?;
let fields = Punctuated::<Field, Comma>::new();
let fields = Punctuated::<FieldWithDefault, Comma>::new();
let fields = fields
.iter()
.map(|field| {
Expand All @@ -56,7 +58,7 @@ pub(crate) fn derive_parser(input: &DeriveInput) -> Result<TokenStream, syn::Err
.collect::<Result<Vec<_>, syn::Error>>()?;
gen_for_struct(&item, ident, &input.generics, &fields)
}
Data::Enum(ref e) => {
DataWithDefault::Enum(ref e) => {
let name = Name::Assigned(quote!(#pkg_name));
let item = Item::from_subcommand_enum(input, name)?;
let variants = e
Expand All @@ -78,7 +80,7 @@ fn gen_for_struct(
item: &Item,
item_name: &Ident,
generics: &Generics,
fields: &[(&Field, Item)],
fields: &[(&FieldWithDefault, Item)],
) -> Result<TokenStream, syn::Error> {
let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();

Expand All @@ -102,7 +104,7 @@ fn gen_for_enum(
item: &Item,
item_name: &Ident,
generics: &Generics,
variants: &[(&Variant, Item)],
variants: &[(&VariantWithDefault, Item)],
) -> Result<TokenStream, syn::Error> {
let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();

Expand Down
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