我尝试实现一个 proc_macro
为此,我有一个包含我的“基本”结构体(在这种情况下是
接下来,我有一个包含过程宏本身的 crate
因为我想支持多种格式,所以我有第三个 crate
直到这一点都非常简单。
当我现在想要编译它时,我得到了这个错误:
翻译为:
Dump
,类似于 serdes 的 Serialize
。为此,我有一个包含我的“基本”结构体(在这种情况下是
P1
和 P2
)的 crate foo
,这些结构体应该只能被转储。接下来,我有一个包含过程宏本身的 crate
foo_derive
。因为我想支持多种格式,所以我有第三个 crate
foo_dump
,其中包含 Dump
的 trait 定义(例如,可以转储此结构体)和 Dumper
(这是后端应该实现的内容)。直到这一点都非常简单。
当我现在想要编译它时,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)`
我不知道在这个crate中使用依赖的正确方式是什么。目前我的做法是:
而这显然是不可能的。
我错过了什么?我必须怎样打破依赖循环?
翻译为:
({{链接1: mcve@github}})
/Cargo.toml
[workspace]
members = [
"foo",
"foo_derive",
"foo_dump",
]
/foo/Cargo.toml
[package]
name = "foo"
version = "0.1.0"
edition = "2018"
[dependencies]
foo_derive = { path = "../foo_derive" }
/foo/src/lib.rs
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_dump/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()
}