impl-trait-for-tuples 0.2.3

//! Implementation of the full-automatic tuple trait implementation.
//!
//! The full-automatic implementation uses the trait definition to generate the implementations for
//! tuples. This has some limitations, as no support for associated types, consts, return values or
//! functions with a default implementation.

use crate::utils::add_tuple_element_generics;

use proc_macro2::{Span, TokenStream};

use std::iter::repeat;

use syn::{
    parse_quote,
    spanned::Spanned,
    visit::{self, Visit},
    Error, FnArg, Generics, Ident, Index, ItemTrait, Pat, Result, ReturnType, Signature, TraitItem,
    TraitItemFn, Type,
};

use quote::quote;

/// Generate the full-automatic tuple implementations for a given trait definition and the given tuples.
pub fn full_automatic_impl(
    definition: ItemTrait,
    tuple_elements: Vec<Ident>,
    min: Option<usize>,
) -> Result<TokenStream> {
    check_trait_declaration(&definition)?;

    let impls = (min.unwrap_or(0)..=tuple_elements.len())
        .map(|i| generate_tuple_impl(&definition, &tuple_elements[0..i]));

    Ok(quote!(
        #definition
        #( #impls )*
    ))
}

fn check_trait_declaration(trait_decl: &ItemTrait) -> Result<()> {
    let mut visitor = CheckTraitDeclaration { errors: Vec::new() };
    visit::visit_item_trait(&mut visitor, trait_decl);

    match visitor.errors.pop() {
        Some(init) => Err(visitor.errors.into_iter().fold(init, |mut old, new| {
            old.combine(new);
            old
        })),
        None => Ok(()),
    }
}

/// Checks that the given trait declaration corresponds to the expected format.
struct CheckTraitDeclaration {
    /// Stores all errors that are found.
    errors: Vec<Error>,
}

impl CheckTraitDeclaration {
    fn add_error<T: Spanned>(&mut self, span: &T) {
        self.errors.push(Error::new(span.span(), CHECK_ERROR_MSG));
    }
}

const CHECK_ERROR_MSG: &str = "Not supported by full-automatic tuple implementation. \
     Use semi-automatic tuple implementation for more control of the implementation.";

impl<'ast> Visit<'ast> for CheckTraitDeclaration {
    fn visit_trait_item(&mut self, ti: &'ast TraitItem) {
        match ti {
            TraitItem::Fn(f) => visit::visit_trait_item_fn(self, f),
            _ => self.add_error(ti),
        }
    }

    fn visit_return_type(&mut self, rt: &'ast ReturnType) {
        match rt {
            ReturnType::Default => {}
            ReturnType::Type(_, ty) => match **ty {
                Type::Tuple(ref tuple) if tuple.elems.is_empty() => {}
                _ => self.add_error(rt),
            },
        }
    }
}

fn generate_tuple_impl(definition: &ItemTrait, tuple_elements: &[Ident]) -> TokenStream {
    let name = &definition.ident;
    let unsafety = &definition.unsafety;
    let generics = generate_generics(definition, tuple_elements);
    let ty_generics = definition.generics.split_for_impl().1;
    let (impl_generics, _, where_clause) = generics.split_for_impl();
    let fns = definition.items.iter().filter_map(|i| match i {
        TraitItem::Fn(f) => Some(generate_delegate_method(f, tuple_elements)),
        _ => None,
    });

    quote!(
        #[allow(unused)]
        #unsafety impl #impl_generics #name #ty_generics for ( #( #tuple_elements, )* ) #where_clause {
            #( #fns )*
        }
    )
}

/// Collects all non-reference argument types.
struct CollectNonReferenceArgTypes {
    result: Vec<Type>,
}

impl<'ast> Visit<'ast> for CollectNonReferenceArgTypes {
    fn visit_receiver(&mut self, _: &'ast syn::Receiver) {
        // Do nothing: explicitly ignore any receiver type.
    }
    fn visit_type(&mut self, ty: &'ast Type) {
        if !is_reference_type(ty) {
            self.result.push(ty.clone());
        }
    }
}

fn generate_generics(definition: &ItemTrait, tuple_elements: &[Ident]) -> Generics {
    let mut generics = definition.generics.clone();
    let name = &definition.ident;
    let ty_generics = definition.generics.split_for_impl().1;

    // Make sure that all non-reference types implement `Clone`.
    let mut visitor = CollectNonReferenceArgTypes { result: Vec::new() };
    definition
        .items
        .iter()
        .for_each(|item| visit::visit_trait_item(&mut visitor, item));
    visitor.result.dedup();
    {
        let where_clause = generics.make_where_clause();
        visitor
            .result
            .into_iter()
            .for_each(|ty| where_clause.predicates.push(parse_quote!(#ty: Clone)));
    }

    add_tuple_element_generics(
        tuple_elements,
        Some(quote!(#name #ty_generics)),
        &mut generics,
    );

    generics
}

fn generate_delegate_method(method: &TraitItemFn, tuple_elements: &[Ident]) -> TokenStream {
    let name = repeat(&method.sig.ident);
    let self_arg = method
        .sig
        .inputs
        .first()
        .map(|a| match a {
            FnArg::Receiver(_) => true,
            _ => false,
        })
        .unwrap_or(false);
    let (sig, arg_names, arg_clones) = update_signature_and_extract_arg_infos(method.sig.clone());
    let arg_names_per_tuple = repeat(&arg_names);
    let arg_clones_per_tuple = repeat(&arg_clones);
    let tuple_access = tuple_elements.iter().enumerate().map(|(i, te)| {
        if self_arg {
            let index = Index::from(i);
            quote!(self.#index.)
        } else {
            quote!(#te::)
        }
    });

    let mut res = method.clone();
    res.sig = sig;
    res.semi_token = None;
    res.default = Some(parse_quote!(
        { #( #tuple_access #name ( #( #arg_names_per_tuple #arg_clones_per_tuple ),* ); )* }
    ));

    quote!( #res )
}

/// Update `Signature` by replacing all wild card argument names with unique identifiers, collect all
/// argument names and if we need to clone an argument.
fn update_signature_and_extract_arg_infos(
    mut sig: Signature,
) -> (Signature, Vec<Ident>, Vec<TokenStream>) {
    let mut unique_id = 0;
    let mut arg_clone = Vec::new();
    let mut push_arg_clone = |is_ref: bool| {
        if is_ref {
            arg_clone.push(quote!())
        } else {
            arg_clone.push(quote!(.clone()))
        }
    };

    let arg_names = sig
        .inputs
        .iter_mut()
        .filter_map(|a| match a {
            FnArg::Typed(ref mut arg) => match &mut *arg.pat {
                Pat::Ident(p) => {
                    push_arg_clone(is_reference_type(&arg.ty));
                    Some(p.ident.clone())
                }
                Pat::Wild(_) => {
                    push_arg_clone(is_reference_type(&arg.ty));
                    let ident = Ident::new(
                        &format!("tuple_element_unique_ident_{}", unique_id),
                        Span::call_site(),
                    );
                    unique_id += 1;
                    let ident2 = ident.clone();

                    arg.pat = parse_quote!(#ident);
                    Some(ident2)
                }
                _ => None,
            },
            _ => None,
        })
        .collect::<Vec<_>>();

    (sig, arg_names, arg_clone)
}

fn is_reference_type(ty: &Type) -> bool {
    match ty {
        Type::Reference(_) => true,
        _ => false,
    }
}