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fix(nearest-derive): add Flat bounds to unbounded type params in emit impl #32

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Merged
uael merged 2 commits into from
Mar 9, 2026
Merged

fix(nearest-derive): add Flat bounds to unbounded type params in emit impl #32

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d5cd94b
fix(nearest-derive): add Flat bounds to unbounded type params in emit…
uael Mar 9, 2026
5a19b14
style: format imports in emit derive
uael Mar 9, 2026
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31 changes: 25 additions & 6 deletions nearest-derive/src/emit.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,10 @@ use syn::{Data, DataEnum, DataStruct, DeriveInput, Fields, Variant};

use crate::{
attrs::{parse_field_attrs, parse_variant_attrs},
util::{capitalize, has_flat_bound, opt_where_clause, to_snake_case},
util::{
capitalize, combine_where, flat_bounded_param_names, has_flat_bound, opt_where_clause,
to_snake_case,
},
};

// ---------------------------------------------------------------------------
Expand Down Expand Up @@ -176,10 +179,25 @@ fn builder_generics(
// Structs
// ---------------------------------------------------------------------------

/// Generate a where clause that adds `Flat` bounds to unbounded type parameters.
fn outer_where_clause(generics: &syn::Generics) -> TokenStream {
let already_bounded = flat_bounded_param_names(generics);
let preds: Vec<_> = generics
.type_params()
.filter(|tp| !already_bounded.contains(&tp.ident.to_string()))
.map(|tp| {
let ident = &tp.ident;
quote! { #ident: ::nearest::Flat }
})
.collect();
combine_where(generics.where_clause.as_ref(), &preds)
}

fn gen_emit_struct(input: &DeriveInput, data: &DataStruct) -> TokenStream {
let name = &input.ident;
let vis = &input.vis;
let (impl_generics, ty_generics, input_where) = input.generics.split_for_impl();
let (impl_generics, ty_generics, _) = input.generics.split_for_impl();
let outer_where = outer_where_clause(&input.generics);

match &data.fields {
Fields::Named(named) => {
Expand Down Expand Up @@ -234,7 +252,7 @@ fn gen_emit_struct(input: &DeriveInput, data: &DataStruct) -> TokenStream {
};

quote! {
impl #impl_generics #name #ty_generics #input_where {
impl #impl_generics #name #ty_generics #outer_where {
#vis fn make #fn_make_generics (#(#fn_params),*) -> impl ::nearest::Emit<Self> {
struct __Builder #bsg {
#bpf
Expand Down Expand Up @@ -308,7 +326,7 @@ fn gen_emit_struct(input: &DeriveInput, data: &DataStruct) -> TokenStream {
};

quote! {
impl #impl_generics #name #ty_generics #input_where {
impl #impl_generics #name #ty_generics #outer_where {
#vis fn make #fn_make_generics (#(#fn_params),*) -> impl ::nearest::Emit<Self> {
struct __Builder #bsg {
#bpf
Expand Down Expand Up @@ -340,7 +358,8 @@ fn gen_emit_struct(input: &DeriveInput, data: &DataStruct) -> TokenStream {
fn gen_emit_enum(input: &DeriveInput, data: &DataEnum) -> TokenStream {
let name = &input.ident;
let vis = &input.vis;
let (impl_generics, ty_generics, input_where) = input.generics.split_for_impl();
let (impl_generics, ty_generics, _) = input.generics.split_for_impl();
let outer_where = outer_where_clause(&input.generics);

let methods: Vec<_> = data
.variants
Expand All @@ -350,7 +369,7 @@ fn gen_emit_enum(input: &DeriveInput, data: &DataEnum) -> TokenStream {
.collect();

quote! {
impl #impl_generics #name #ty_generics #input_where {
impl #impl_generics #name #ty_generics #outer_where {
#(#methods)*
}
}
Expand Down