third_party_rust_cxx/syntax/parse.rs

use crate::syntax::{
    attrs, error, Api, Atom, Doc, ExternFn, ExternType, Receiver, Ref, Struct, Ty1, Type, Var,
};
use proc_macro2::Ident;
use quote::quote;
use syn::{
    Abi, Error, Fields, FnArg, ForeignItem, ForeignItemFn, ForeignItemType, GenericArgument, Item,
    ItemForeignMod, ItemStruct, Pat, PathArguments, Result, ReturnType, Type as RustType,
};

#[derive(Copy, Clone)]
enum Lang {
    Cxx,
    Rust,
}

pub fn parse_items(items: Vec<Item>) -> Result<Vec<Api>> {
    let mut apis = Vec::new();
    for item in items {
        match item {
            Item::Struct(item) => {
                let strct = parse_struct(item)?;
                apis.push(strct);
            }
            Item::ForeignMod(foreign_mod) => {
                let functions = parse_foreign_mod(foreign_mod)?;
                apis.extend(functions);
            }
            Item::Use(item) => return Err(Error::new_spanned(item, error::USE_NOT_ALLOWED)),
            _ => return Err(Error::new_spanned(item, "unsupported item")),
        }
    }
    Ok(apis)
}

fn parse_struct(item: ItemStruct) -> Result<Api> {
    let generics = &item.generics;
    if !generics.params.is_empty() || generics.where_clause.is_some() {
        let struct_token = item.struct_token;
        let ident = &item.ident;
        let where_clause = &generics.where_clause;
        let span = quote!(#struct_token #ident #generics #where_clause);
        return Err(Error::new_spanned(
            span,
            "struct with generic parameters is not supported yet",
        ));
    }

    let mut doc = Doc::new();
    let mut derives = Vec::new();
    attrs::parse(&item.attrs, &mut doc, Some(&mut derives))?;
    check_reserved_name(&item.ident)?;
    match item.fields {
        Fields::Named(fields) => Ok(Api::Struct(Struct {
            doc,
            derives,
            struct_token: item.struct_token,
            ident: item.ident,
            fields: fields
                .named
                .into_iter()
                .map(|field| {
                    Ok(Var {
                        ident: field.ident.unwrap(),
                        ty: parse_type(&field.ty)?,
                    })
                })
                .collect::<Result<_>>()?,
        })),
        Fields::Unit => Err(Error::new_spanned(item, "unit structs are not supported")),
        Fields::Unnamed(_) => Err(Error::new_spanned(item, "tuple structs are not supported")),
    }
}

fn parse_foreign_mod(foreign_mod: ItemForeignMod) -> Result<Vec<Api>> {
    let lang = parse_lang(foreign_mod.abi)?;
    let api_type = match lang {
        Lang::Cxx => Api::CxxType,
        Lang::Rust => Api::RustType,
    };
    let api_function = match lang {
        Lang::Cxx => Api::CxxFunction,
        Lang::Rust => Api::RustFunction,
    };

    let mut items = Vec::new();
    for foreign in &foreign_mod.items {
        match foreign {
            ForeignItem::Type(foreign) => {
                check_reserved_name(&foreign.ident)?;
                let ety = parse_extern_type(foreign)?;
                items.push(api_type(ety));
            }
            ForeignItem::Fn(foreign) => {
                let efn = parse_extern_fn(foreign)?;
                items.push(api_function(efn));
            }
            ForeignItem::Macro(foreign) if foreign.mac.path.is_ident("include") => {
                let include = foreign.mac.parse_body()?;
                items.push(Api::Include(include));
            }
            _ => return Err(Error::new_spanned(foreign, "unsupported foreign item")),
        }
    }
    Ok(items)
}

fn parse_lang(abi: Abi) -> Result<Lang> {
    let name = match &abi.name {
        Some(name) => name,
        None => {
            return Err(Error::new_spanned(
                abi,
                "ABI name is required, extern \"C\" or extern \"Rust\"",
            ));
        }
    };
    match name.value().as_str() {
        "C" => Ok(Lang::Cxx),
        "Rust" => Ok(Lang::Rust),
        _ => Err(Error::new_spanned(abi, "unrecognized ABI")),
    }
}

fn parse_extern_type(foreign_type: &ForeignItemType) -> Result<ExternType> {
    let doc = attrs::parse_doc(&foreign_type.attrs)?;
    let type_token = foreign_type.type_token;
    let ident = foreign_type.ident.clone();
    Ok(ExternType {
        doc,
        type_token,
        ident,
    })
}

fn parse_extern_fn(foreign_fn: &ForeignItemFn) -> Result<ExternFn> {
    let generics = &foreign_fn.sig.generics;
    if !generics.params.is_empty() || generics.where_clause.is_some() {
        return Err(Error::new_spanned(
            foreign_fn,
            "extern function with generic parameters is not supported yet",
        ));
    }
    if let Some(variadic) = &foreign_fn.sig.variadic {
        return Err(Error::new_spanned(
            variadic,
            "variadic function is not supported yet",
        ));
    }

    let mut receiver = None;
    let mut args = Vec::new();
    for arg in &foreign_fn.sig.inputs {
        match arg {
            FnArg::Receiver(receiver) => {
                return Err(Error::new_spanned(receiver, "unsupported signature"))
            }
            FnArg::Typed(arg) => {
                let ident = match arg.pat.as_ref() {
                    Pat::Ident(pat) => pat.ident.clone(),
                    _ => return Err(Error::new_spanned(arg, "unsupported signature")),
                };
                let ty = parse_type(&arg.ty)?;
                if ident != "self" {
                    args.push(Var { ident, ty });
                    continue;
                }
                if let Type::Ref(reference) = ty {
                    if let Type::Ident(ident) = reference.inner {
                        receiver = Some(Receiver {
                            mutability: reference.mutability,
                            ident,
                        });
                        continue;
                    }
                }
                return Err(Error::new_spanned(arg, "unsupported method receiver"));
            }
        }
    }
    let ret = match &foreign_fn.sig.output {
        ReturnType::Default => None,
        ReturnType::Type(_, ty) => Some(parse_type(ty)?),
    };
    let doc = attrs::parse_doc(&foreign_fn.attrs)?;
    let fn_token = foreign_fn.sig.fn_token;
    let ident = foreign_fn.sig.ident.clone();
    let semi_token = foreign_fn.semi_token;
    Ok(ExternFn {
        doc,
        fn_token,
        ident,
        receiver,
        args,
        ret,
        semi_token,
    })
}

fn parse_type(ty: &RustType) -> Result<Type> {
    match &ty {
        RustType::Reference(ty) => {
            let inner = parse_type(&ty.elem)?;
            let which = match &inner {
                Type::Ident(ident) if ident == "str" => {
                    if ty.mutability.is_some() {
                        return Err(Error::new_spanned(ty, "unsupported type"));
                    } else {
                        Type::Str
                    }
                }
                _ => Type::Ref,
            };
            return Ok(which(Box::new(Ref {
                ampersand: ty.and_token,
                mutability: ty.mutability,
                inner,
            })));
        }
        RustType::Path(ty) => {
            let path = &ty.path;
            if ty.qself.is_none() && path.leading_colon.is_none() && path.segments.len() == 1 {
                let segment = &path.segments[0];
                let ident = segment.ident.clone();
                match &segment.arguments {
                    PathArguments::None => return Ok(Type::Ident(ident)),
                    PathArguments::AngleBracketed(generic) => {
                        if ident == "UniquePtr" && generic.args.len() == 1 {
                            if let GenericArgument::Type(arg) = &generic.args[0] {
                                let inner = parse_type(arg)?;
                                return Ok(Type::UniquePtr(Box::new(Ty1 {
                                    name: ident,
                                    langle: generic.lt_token,
                                    inner,
                                    rangle: generic.gt_token,
                                })));
                            }
                        } else if ident == "Box" && generic.args.len() == 1 {
                            if let GenericArgument::Type(arg) = &generic.args[0] {
                                let inner = parse_type(arg)?;
                                return Ok(Type::RustBox(Box::new(Ty1 {
                                    name: ident,
                                    langle: generic.lt_token,
                                    inner,
                                    rangle: generic.gt_token,
                                })));
                            }
                        }
                    }
                    PathArguments::Parenthesized(_) => {}
                }
            }
        }
        _ => {}
    }
    Err(Error::new_spanned(ty, "unsupported type"))
}

fn check_reserved_name(ident: &Ident) -> Result<()> {
    if ident == "Box" || ident == "UniquePtr" || Atom::from(ident).is_some() {
        Err(Error::new(ident.span(), "reserved name"))
    } else {
        Ok(())
    }
}