codegen/src/fold.rs

use crate::file;
use quote::quote;
use syn_codegen as types;

const FOLD_SRC: &str = "../src/gen/fold.rs";

mod codegen {
    use inflections::Inflect;
    use proc_macro2::{Span, TokenStream};
    use quote::{quote, TokenStreamExt};
    use syn::*;
    use syn_codegen as types;

    #[derive(Default)]
    pub struct State {
        pub fold_trait: TokenStream,
        pub fold_impl: TokenStream,
    }

    fn under_name(name: &str) -> Ident {
        Ident::new(&name.to_snake_case(), Span::call_site())
    }

    fn simple_visit(item: &str, name: &TokenStream) -> TokenStream {
        let ident = under_name(item);

        let method = Ident::new(&format!("fold_{}", ident), Span::call_site());
        quote! {
            _visitor.#method(#name)
        }
    }

    fn box_visit(
        elem: &types::Type,
        features: &types::Features,
        defs: &types::Definitions,
        name: &TokenStream,
    ) -> Option<TokenStream> {
        let res = visit(elem, features, defs, &quote!(*#name))?;
        Some(quote! {
            Box::new(#res)
        })
    }

    fn vec_visit(
        elem: &types::Type,
        features: &types::Features,
        defs: &types::Definitions,
        name: &TokenStream,
    ) -> Option<TokenStream> {
        let operand = quote!(it);
        let val = visit(elem, features, defs, &operand)?;
        Some(quote! {
            FoldHelper::lift(#name, |it| { #val })
        })
    }

    fn punctuated_visit(
        elem: &types::Type,
        features: &types::Features,
        defs: &types::Definitions,
        name: &TokenStream,
    ) -> Option<TokenStream> {
        let operand = quote!(it);
        let val = visit(elem, features, defs, &operand)?;
        Some(quote! {
            FoldHelper::lift(#name, |it| { #val })
        })
    }

    fn option_visit(
        elem: &types::Type,
        features: &types::Features,
        defs: &types::Definitions,
        name: &TokenStream,
    ) -> Option<TokenStream> {
        let it = quote!(it);
        let val = visit(elem, features, defs, &it)?;
        Some(quote! {
            (#name).map(|it| { #val })
        })
    }

    fn tuple_visit(
        elems: &[types::Type],
        features: &types::Features,
        defs: &types::Definitions,
        name: &TokenStream,
    ) -> Option<TokenStream> {
        if elems.is_empty() {
            return None;
        }

        let mut code = TokenStream::new();
        for (i, elem) in elems.iter().enumerate() {
            let i = Index::from(i);
            let it = quote!((#name).#i);
            let val = visit(elem, features, defs, &it).unwrap_or(it);
            code.append_all(val);
            code.append_all(quote!(,));
        }
        Some(quote! {
            (#code)
        })
    }

    fn token_punct_visit(repr: &str, name: &TokenStream) -> TokenStream {
        let ty: TokenStream = syn::parse_str(&format!("Token![{}]", repr)).unwrap();
        quote! {
            #ty(tokens_helper(_visitor, &#name.spans))
        }
    }

    fn token_keyword_visit(repr: &str, name: &TokenStream) -> TokenStream {
        let ty: TokenStream = syn::parse_str(&format!("Token![{}]", repr)).unwrap();
        quote! {
            #ty(tokens_helper(_visitor, &#name.span))
        }
    }

    fn token_group_visit(ty: &str, name: &TokenStream) -> TokenStream {
        let ty = Ident::new(ty, Span::call_site());
        quote! {
            #ty(tokens_helper(_visitor, &#name.span))
        }
    }

    fn visit(
        ty: &types::Type,
        features: &types::Features,
        defs: &types::Definitions,
        name: &TokenStream,
    ) -> Option<TokenStream> {
        match ty {
            types::Type::Box(t) => box_visit(&*t, features, defs, name),
            types::Type::Vec(t) => vec_visit(&*t, features, defs, name),
            types::Type::Punctuated(p) => punctuated_visit(&p.element, features, defs, name),
            types::Type::Option(t) => option_visit(&*t, features, defs, name),
            types::Type::Tuple(t) => tuple_visit(t, features, defs, name),
            types::Type::Token(t) => {
                let repr = &defs.tokens[t];
                let is_keyword = repr.chars().next().unwrap().is_alphabetic();
                if is_keyword {
                    Some(token_keyword_visit(repr, name))
                } else {
                    Some(token_punct_visit(repr, name))
                }
            }
            types::Type::Group(t) => Some(token_group_visit(&t[..], name)),
            types::Type::Syn(t) => {
                fn requires_full(features: &types::Features) -> bool {
                    features.any.contains("full") && features.any.len() == 1
                }

                let res = simple_visit(t, name);

                let target = defs.types.iter().find(|ty| ty.ident == *t).unwrap();

                Some(
                    if requires_full(&target.features) && !requires_full(features) {
                        quote! {
                            full!(#res)
                        }
                    } else {
                        res
                    },
                )
            }
            types::Type::Ext(t) if super::TERMINAL_TYPES.contains(&&t[..]) => {
                Some(simple_visit(t, name))
            }
            types::Type::Ext(_) | types::Type::Std(_) => None,
        }
    }

    fn visit_features(features: &types::Features) -> TokenStream {
        let features = &features.any;
        match features.len() {
            0 => quote!(),
            1 => quote!(#[cfg(feature = #(#features)*)]),
            _ => quote!(#[cfg(any(#(feature = #features),*))]),
        }
    }

    pub fn generate(state: &mut State, s: &types::Node, defs: &types::Definitions) {
        let features = visit_features(&s.features);
        let under_name = under_name(&s.ident);
        let ty = Ident::new(&s.ident, Span::call_site());
        let fold_fn = Ident::new(&format!("fold_{}", under_name), Span::call_site());

        let mut fold_impl = TokenStream::new();

        match &s.data {
            types::Data::Enum(variants) => {
                let mut fold_variants = TokenStream::new();

                for (variant, fields) in variants {
                    let variant_ident = Ident::new(variant, Span::call_site());

                    if fields.is_empty() {
                        fold_variants.append_all(quote! {
                            #ty::#variant_ident => {
                                #ty::#variant_ident
                            }
                        });
                    } else {
                        let mut bind_fold_fields = TokenStream::new();
                        let mut fold_fields = TokenStream::new();

                        for (idx, ty) in fields.iter().enumerate() {
                            let name = format!("_binding_{}", idx);
                            let binding = Ident::new(&name, Span::call_site());

                            bind_fold_fields.append_all(quote! {
                                #binding,
                            });

                            let owned_binding = quote!(#binding);

                            fold_fields.append_all(
                                visit(ty, &s.features, defs, &owned_binding)
                                    .unwrap_or(owned_binding),
                            );

                            fold_fields.append_all(quote!(,));
                        }

                        fold_variants.append_all(quote! {
                            #ty::#variant_ident(#bind_fold_fields) => {
                                #ty::#variant_ident(
                                    #fold_fields
                                )
                            }
                        });
                    }
                }

                fold_impl.append_all(quote! {
                    match _i {
                        #fold_variants
                    }
                });
            }
            types::Data::Struct(fields) => {
                let mut fold_fields = TokenStream::new();

                for (field, ty) in fields {
                    let id = Ident::new(&field, Span::call_site());
                    let ref_toks = quote!(_i.#id);
                    let fold = visit(&ty, &s.features, defs, &ref_toks).unwrap_or(ref_toks);

                    fold_fields.append_all(quote! {
                        #id: #fold,
                    });
                }

                if !fields.is_empty() {
                    fold_impl.append_all(quote! {
                        #ty {
                            #fold_fields
                        }
                    })
                } else {
                    if ty == "Ident" {
                        fold_impl.append_all(quote! {
                            let mut _i = _i;
                            let span = _visitor.fold_span(_i.span());
                            _i.set_span(span);
                        });
                    }
                    fold_impl.append_all(quote! {
                        _i
                    });
                }
            }
            types::Data::Private => {
                if ty == "Ident" {
                    fold_impl.append_all(quote! {
                        let mut _i = _i;
                        let span = _visitor.fold_span(_i.span());
                        _i.set_span(span);
                    });
                }
                fold_impl.append_all(quote! {
                    _i
                });
            }
        }

        let include_fold_impl = match &s.data {
            types::Data::Private => super::TERMINAL_TYPES.contains(&s.ident.as_str()),
            types::Data::Struct(_) | types::Data::Enum(_) => true,
        };

        state.fold_trait.append_all(quote! {
            #features
            fn #fold_fn(&mut self, i: #ty) -> #ty {
                #fold_fn(self, i)
            }
        });

        if include_fold_impl {
            state.fold_impl.append_all(quote! {
                #features
                pub fn #fold_fn<V: Fold + ?Sized>(
                    _visitor: &mut V, _i: #ty
                ) -> #ty {
                    #fold_impl
                }
            });
        }
    }
}

const TERMINAL_TYPES: &[&str] = &["Span", "Ident"];

pub fn generate(defs: &types::Definitions) {
    let mut state = codegen::State::default();
    for s in &defs.types {
        codegen::generate(&mut state, s, defs);
    }
    for tt in TERMINAL_TYPES {
        let s = types::Node {
            ident: tt.to_string(),
            features: types::Features::default(),
            data: types::Data::Private,
        };
        codegen::generate(&mut state, &s, defs);
    }

    let full_macro = quote! {
        #[cfg(feature = "full")]
        macro_rules! full {
            ($e:expr) => {
                $e
            };
        }

        #[cfg(all(feature = "derive", not(feature = "full")))]
        macro_rules! full {
            ($e:expr) => {
                unreachable!()
            };
        }
    };

    let fold_trait = state.fold_trait;
    let fold_impl = state.fold_impl;
    file::write(
        FOLD_SRC,
        quote! {
            // Unreachable code is generated sometimes without the full feature.
            #![allow(unreachable_code)]

            use *;
            #[cfg(any(feature = "full", feature = "derive"))]
            use token::{Brace, Bracket, Paren, Group};
            use proc_macro2::Span;
            #[cfg(any(feature = "full", feature = "derive"))]
            use gen::helper::fold::*;

            #full_macro

            /// Syntax tree traversal to transform the nodes of an owned syntax tree.
            ///
            /// See the [module documentation] for details.
            ///
            /// [module documentation]: index.html
            ///
            /// *This trait is available if Syn is built with the `"fold"` feature.*
            pub trait Fold {
                #fold_trait
            }

            #[cfg(any(feature = "full", feature = "derive"))]
            macro_rules! fold_span_only {
                ($f:ident : $t:ident) => {
                    pub fn $f<V: Fold + ?Sized>(_visitor: &mut V, mut _i: $t) -> $t {
                        let span = _visitor.fold_span(_i.span());
                        _i.set_span(span);
                        _i
                    }
                }
            }

            #[cfg(any(feature = "full", feature = "derive"))]
            fold_span_only!(fold_lit_byte: LitByte);
            #[cfg(any(feature = "full", feature = "derive"))]
            fold_span_only!(fold_lit_byte_str: LitByteStr);
            #[cfg(any(feature = "full", feature = "derive"))]
            fold_span_only!(fold_lit_char: LitChar);
            #[cfg(any(feature = "full", feature = "derive"))]
            fold_span_only!(fold_lit_float: LitFloat);
            #[cfg(any(feature = "full", feature = "derive"))]
            fold_span_only!(fold_lit_int: LitInt);
            #[cfg(any(feature = "full", feature = "derive"))]
            fold_span_only!(fold_lit_str: LitStr);

            #fold_impl
        },
    );
}