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Specify default field value for field with type that uses generic parameters with defaults #73

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6 changes: 4 additions & 2 deletions Cargo.toml
Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,8 @@ categories = ["rust-patterns"]
proc-macro = true

[dependencies]
syn = { version = "1", features = ["full", "extra-traits"] }
quote = "1"
either = "1"
proc-macro2 = "1"
quote = "1"
regex = "1"
syn = { version = "1", features = ["full", "extra-traits"] }
36 changes: 36 additions & 0 deletions examples/default_generics.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,36 @@
use typed_builder::TypedBuilder;

#[derive(TypedBuilder)]
pub struct Props<'a, OnInput: FnOnce(usize) -> usize = Box<dyn FnOnce(usize) -> usize>> {
#[builder(default, setter(into))]
pub class: Option<&'a str>,
pub label: &'a str,
#[builder(setter(into))]
pub on_input: Option<OnInput>,
}

#[derive(TypedBuilder)]
struct Foo<T = usize> {
#[builder(default = 12)]
x: T,
}

#[allow(dead_code)]
#[derive(TypedBuilder)]
struct Bar<T, U = usize, V = usize> {
t: T,
#[builder(default = 12)]
u: U,
v: (T, U, V),
}

fn main() {
let props = Props::builder().label("label").on_input(|x: usize| x).build();
assert_eq!(props.class, None);
assert_eq!(props.label, "label");
assert_eq!((props.on_input.unwrap())(123), 123);

assert_eq!(Foo::builder().build().x, 12);

assert_eq!(Bar::builder().t("test").v(("t", 0, 3.14f64)).build().v.0, "t");
}
70 changes: 66 additions & 4 deletions src/field_info.rs
Original file line number Diff line number Diff line change
@@ -1,9 +1,13 @@
use either::Either::*;
use proc_macro2::{Span, TokenStream};
use quote::quote;
use std::collections::HashSet;
use syn::parse::Error;
use syn::spanned::Spanned;

use crate::util::{expr_to_single_string, ident_to_type, path_to_single_string, strip_raw_ident_prefix};
use crate::util::{
empty_type, expr_to_single_string, ident_to_type, path_to_single_string, strip_raw_ident_prefix, GenericDefault,
};

#[derive(Debug)]
pub struct FieldInfo<'a> {
Expand All @@ -12,19 +16,61 @@ pub struct FieldInfo<'a> {
pub generic_ident: syn::Ident,
pub ty: &'a syn::Type,
pub builder_attr: FieldBuilderAttr,
pub default_ty: Option<(syn::Type, syn::Expr)>,
pub used_default_generic_idents: HashSet<syn::Ident>,
}

impl<'a> FieldInfo<'a> {
pub fn new(ordinal: usize, field: &syn::Field, field_defaults: FieldBuilderAttr) -> Result<FieldInfo, Error> {
pub fn new(
ordinal: usize,
field: &'a syn::Field,
field_defaults: FieldBuilderAttr,
generic_defaults: &[GenericDefault],
) -> Result<Self, Error> {
if let Some(ref name) = field.ident {
FieldInfo {
let mut field_info = FieldInfo {
ordinal,
name,
generic_ident: syn::Ident::new(&format!("__{}", strip_raw_ident_prefix(name.to_string())), Span::call_site()),
ty: &field.ty,
builder_attr: field_defaults.with(&field.attrs)?,
default_ty: None,
used_default_generic_idents: HashSet::default(),
}
.post_process()
.post_process()?;

let mut ty_includes_params_without_defaults = false;
let mut ty_includes_params_with_defaults = false;
let ty = &field.ty;
let mut ty_str = format!("{}", quote! { #ty });
for (generic_param, regular_expression, default_type) in generic_defaults.iter() {
if regular_expression.is_match(&ty_str) {
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Are you doing this to determine if the type depends on the generic parameter? I'd prefer doing this with https://docs.rs/syn/latest/syn/visit/index.html

match default_type.as_ref() {
Some(default_type) => {
ty_includes_params_with_defaults = true;
ty_str = regular_expression.replace(&ty_str, default_type).into();
match generic_param {
Left(type_param) => field_info.used_default_generic_idents.insert(type_param.ident.clone()),
Right(const_param) => field_info.used_default_generic_idents.insert(const_param.ident.clone()),
};
}
None => {
ty_includes_params_without_defaults = true;
}
}
}
}
if !ty_includes_params_without_defaults && ty_includes_params_with_defaults {
if let Some(default_expr) = field_info.builder_attr.default.as_ref() {
use std::str::FromStr;
field_info.default_ty = Some((
syn::parse(TokenStream::from_str(&format!("({ty_str},)"))?.into())?,
syn::parse(quote! { (#default_expr,) }.into())?,
));
}
}

Ok(field_info)
} else {
Err(Error::new(field.span(), "Nameless field in struct"))
}
Expand Down Expand Up @@ -94,6 +140,22 @@ impl<'a> FieldInfo<'a> {
}
Ok(self)
}

pub fn default_type(&self) -> syn::Type {
if let Some((ty, _)) = self.default_ty.as_ref() {
ty.clone()
} else {
empty_type()
}
}

pub fn default_expr(&self) -> syn::Expr {
if let Some((_, expr)) = self.default_ty.as_ref() {
expr.clone()
} else {
syn::parse(quote!(()).into()).unwrap()
}
}
}

#[derive(Debug, Default, Clone)]
Expand Down
2 changes: 1 addition & 1 deletion src/lib.rs
Original file line number Diff line number Diff line change
Expand Up @@ -179,7 +179,7 @@ fn impl_my_derive(ast: &syn::DeriveInput) -> Result<TokenStream, Error> {
let fields = quote!(#(#fields)*).into_iter();
let required_fields = struct_info
.included_fields()
.filter(|f| f.builder_attr.default.is_none())
.filter(|f| f.builder_attr.default.is_none() && f.default_ty.is_none())
.map(|f| struct_info.required_field_impl(f))
.collect::<Vec<_>>();
let build_method = struct_info.build_method_impl();
Expand Down
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