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use syn::{DeriveInput, Fields, FieldsNamed};
use crate::DeriveInputStructExt;
const ERR_MUST_BE_UNIT_OR_NAMED: &str =
"Macro must be used on either a unit struct or a struct with named fields.\n\
This derive does not work on tuple structs.";
pub trait FieldsNamedAppend {
fn append_named(&mut self, fields_named: FieldsNamed);
}
impl FieldsNamedAppend for DeriveInput {
fn append_named(&mut self, fields_named: FieldsNamed) {
self.fields_mut().append_named(fields_named);
self.data_struct_mut().semi_token = None;
}
}
impl FieldsNamedAppend for Fields {
fn append_named(&mut self, fields_named: FieldsNamed) {
match self {
Fields::Named(self_fields_named) => self_fields_named.append_named(fields_named),
Fields::Unit => *self = Fields::from(fields_named),
Fields::Unnamed(_) => panic!(ERR_MUST_BE_UNIT_OR_NAMED),
}
}
}
impl FieldsNamedAppend for FieldsNamed {
fn append_named(&mut self, fields_named: FieldsNamed) {
self.named.extend(fields_named.named);
}
}
#[cfg(test)]
mod tests {
use pretty_assertions::assert_eq;
use syn::{parse_quote, DeriveInput, Fields, FieldsNamed};
use super::FieldsNamedAppend;
#[test]
fn append_fields_named_to_fields_named() {
let mut fields: FieldsNamed = parse_quote!({ a: u32, b: i32 });
let fields_additional: FieldsNamed = parse_quote!({ c: i64, d: usize });
let fields_expected: FieldsNamed = parse_quote!({ a: u32, b: i32, c: i64, d: usize });
fields.append_named(fields_additional);
assert_eq!(fields_expected, fields);
}
#[test]
fn append_fields_named_to_fields_unit() {
let mut fields = Fields::Unit;
let fields_additional: FieldsNamed = parse_quote!({ c: i64, d: usize });
let fields_expected: Fields = Fields::Named(parse_quote!({ c: i64, d: usize }));
fields.append_named(fields_additional);
assert_eq!(fields_expected, fields);
}
#[test]
#[should_panic(
expected = "Macro must be used on either a unit struct or a struct with named fields.\n\
This derive does not work on tuple structs."
)]
fn append_fields_named_to_fields_unnamed_panics() {
let mut fields: Fields = Fields::Unnamed(parse_quote!((u32, i32)));
let fields_additional: FieldsNamed = parse_quote!({ c: i64, d: usize });
fields.append_named(fields_additional);
}
#[test]
fn append_fields_named_to_struct_named() {
let mut ast: DeriveInput = parse_quote! {
struct StructNamed { a: u32, b: i32 }
};
let fields_additional: FieldsNamed = parse_quote!({ c: i64, d: usize });
ast.append_named(fields_additional);
let ast_expected: DeriveInput = parse_quote! {
struct StructNamed { a: u32, b: i32, c: i64, d: usize }
};
assert_eq!(ast_expected, ast);
}
#[test]
fn append_fields_named_to_struct_unit() {
let mut ast: DeriveInput = parse_quote! {
struct StructUnit;
};
let fields_additional: FieldsNamed = parse_quote!({ c: i64, d: usize });
ast.append_named(fields_additional);
let ast_expected: DeriveInput = parse_quote! {
struct StructUnit { c: i64, d: usize }
};
assert_eq!(ast_expected, ast);
}
}