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|
use quote::ToTokens;
use syn::parse::Parse;
use syn::punctuated::Punctuated;
use syn::token::Paren;
use syn::{parenthesized, parse_str, Ident, Token, TraitBound, Type};
/// A function trait. `dyn Fn(u32) -> String`
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct FnTrait
{
pub dyn_token: Token![dyn],
pub trait_ident: Ident,
pub paren_token: Paren,
pub inputs: Punctuated<Type, Token![,]>,
pub r_arrow_token: Token![->],
pub output: Type,
pub trait_bounds: Punctuated<TraitBound, Token![+]>,
}
impl FnTrait
{
pub fn add_trait_bound(&mut self, trait_bound: TraitBound)
{
self.trait_bounds.push(trait_bound);
}
}
impl Parse for FnTrait
{
fn parse(input: syn::parse::ParseStream) -> syn::Result<Self>
{
let dyn_token = input.parse::<Token![dyn]>()?;
let trait_ident = input.parse::<Ident>()?;
if trait_ident.to_string().as_str() != "Fn" {
return Err(syn::Error::new(trait_ident.span(), "Expected 'Fn'"));
}
let content;
let paren_token = parenthesized!(content in input);
let inputs = content.parse_terminated(Type::parse)?;
let r_arrow_token = input.parse::<Token![->]>()?;
let output = input.parse::<Type>()?;
Ok(Self {
dyn_token,
trait_ident,
paren_token,
inputs,
r_arrow_token,
output,
trait_bounds: Punctuated::new(),
})
}
}
impl ToTokens for FnTrait
{
fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream)
{
self.dyn_token.to_tokens(tokens);
self.trait_ident.to_tokens(tokens);
self.paren_token.surround(tokens, |tokens_inner| {
self.inputs.to_tokens(tokens_inner);
});
self.r_arrow_token.to_tokens(tokens);
self.output.to_tokens(tokens);
if !self.trait_bounds.is_empty() {
let plus: Token![+] = parse_str("+").unwrap();
plus.to_tokens(tokens);
self.trait_bounds.to_tokens(tokens);
}
}
}
#[cfg(test)]
mod tests
{
use std::error::Error;
use quote::{format_ident, quote};
use syn::token::{Dyn, RArrow};
use syn::{parse2, PathSegment};
use super::*;
use crate::test_utils;
#[test]
fn can_parse_fn_trait() -> Result<(), Box<dyn Error>>
{
assert_eq!(
parse2::<FnTrait>(quote! {
dyn Fn(String, u32) -> Handle
})?,
FnTrait {
dyn_token: Dyn::default(),
trait_ident: format_ident!("Fn"),
paren_token: Paren::default(),
inputs: Punctuated::from_iter(vec![
test_utils::create_type(test_utils::create_path(&[
PathSegment::from(format_ident!("String"))
])),
test_utils::create_type(test_utils::create_path(&[
PathSegment::from(format_ident!("u32"))
]))
]),
r_arrow_token: RArrow::default(),
output: test_utils::create_type(test_utils::create_path(&[
PathSegment::from(format_ident!("Handle"))
])),
trait_bounds: Punctuated::new()
}
);
assert!(parse2::<FnTrait>(quote! {
Fn(u32) -> Handle
})
.is_err());
Ok(())
}
#[test]
fn can_parse_fn_trait_to_tokens()
{
assert_eq!(
FnTrait {
dyn_token: Dyn::default(),
trait_ident: format_ident!("Fn"),
paren_token: Paren::default(),
inputs: Punctuated::from_iter(vec![
test_utils::create_type(test_utils::create_path(&[
PathSegment::from(format_ident!("Bread"))
])),
test_utils::create_type(test_utils::create_path(&[
PathSegment::from(format_ident!("Cheese"))
])),
test_utils::create_type(test_utils::create_path(&[
PathSegment::from(format_ident!("Tomatoes"))
]))
]),
r_arrow_token: RArrow::default(),
output: test_utils::create_type(test_utils::create_path(&[
PathSegment::from(format_ident!("Taco"))
])),
trait_bounds: Punctuated::new()
}
.into_token_stream()
.to_string(),
"dyn Fn (Bread , Cheese , Tomatoes) -> Taco".to_string()
);
}
}
|
