实现proc宏时的循环包依赖项

我尝试实现一个proc_宏 Dump ,类似于塞尔维亚人 Serialize .

为此,我有一个板条箱 foo 它包含我的“原始”结构( P1 和 P2 在这种情况下),应该只能转储。

接下来我有一个 foo_derive 包含程序宏本身的板条箱。

因为我想支持多种格式,所以我有第三个板条箱 foo_dump 它包含了 转储 (例如,可以转储此结构)和 Dumper (这是后端应该实现的功能)。 一直往前走到这一点。

当我现在想编译它时,我得到了这个错误:

$ cargo build
error: cyclic package dependency: package `foo v0.1.0 (/tmp/tmp.u34pI5J6qd/example/foo)` depends on itself. Cycle:
package `foo v0.1.0 (/tmp/tmp.u34pI5J6qd/example/foo)`
    ... which is depended on by `foo_dump v0.1.0 (/tmp/tmp.u34pI5J6qd/example/foo_dump)`
    ... which is depended on by `foo_derive v0.1.0 (/tmp/tmp.u34pI5J6qd/example/foo_derive)`

我不知道正确的方法是什么,如何在这个板条箱中使用依赖项。我现在的是:

这当然是不可能的。

我错过了什么?我必须做什么才能打破依赖关系循环?

( mcve@github )

/CAMGL

[workspace]
members = [ 
    "foo",
    "foo_derive",
    "foo_dump",
]

/oo/cGOG.ToMl

[package]
name = "foo"
version = "0.1.0"
edition = "2018"

[dependencies]
foo_derive = { path = "../foo_derive" }

/Fo/SRC/LIB

use foo_derive::Dump;

struct P1;
struct P2;

#[derive(Dump)]
struct Bar {
    primitive_one: P1,
    primitive_two: P2,
}

/foo_dump/cargo.toml

[package]
name = "foo_dump"
version = "0.1.0"
edition = "2018"

[dependencies]
foo = { path = "../foo" }

/foo_转储/src/lib.rs

use foo::{P1, P2};

pub trait Dumper {
    fn dump_p1(&mut self, value: &P1);
    fn dump_p2(&mut self, value: &P2);
}

pub trait Dump {
    fn dump<D: Dumper>(&self, d: D);
}

impl Dump for P1 {
    fn dump<D: Dumper>(&self, d: D) {
        d.dump_p1(self);
    }
}

impl Dump for P2 {
    fn dump<D: Dumper>(&self, d: D) {
        d.dump_p2(self);
    }
}

/foo_derive/cargo.toml

[package]
name = "foo_derive"
version = "0.1.0"
edition = "2018"

[lib]
proc-macro = true

[dependencies]
syn = "*"
quote = "*"
foo_dump = { path = "../foo_dump" }

/foo_-derive/src/lib.rs

extern crate proc_macro;

use quote::quote;
use proc_macro::TokenStream;
use syn::DeriveInput;

#[proc_macro_derive(Dump)]
pub fn derive_dump(input: TokenStream) -> TokenStream {
    let input = syn::parse_macro_input!(input as DeriveInput);
    let name = &input.ident;

    quote!(
        impl foo_dump::Dump for #name {
            fn dump<D: foo_dump::Dumper>(&self, d: D) {
                unimplemented!()
            }
        }
    ).into()
}