rust - 在其他proc宏内调用proc宏

Question

我有一个小型的复制项目，无法编译。该项目可以在这里下载:https://github.com/Jasperav/proc_macro_collision。错误是:

error[E0659]: `proc_macro_call` is ambiguous (macro-expanded name vs less macro-expanded name from outer scope during import/macro resolution)

我在项目中有3个库和1个可执行文件:

Lib 1-解析器-解析proc宏调用

Lib 2-proc_two-将文字字符串作为proc宏调用

返回

库3-proc_one-将宏转发到proc_two(尽管它对proc_two没有依赖性)。这就像proc_two也是proc宏。

proc_one的相关代码:

#[proc_macro_hack]
pub fn one(input: TokenStream) -> TokenStream {
    let parse = parse_macro_input!(input as Parser);
    let r = parse.lit;

    let x = quote! {
        two!(#r) // This is the problem I guess...
    };

    x.into()
}

可执行文件:调用proc_one(产生编译错误)。

相关代码:

use proc_macro_hack::proc_macro_hack;
extern crate proc_one;
extern crate proc_two;

#[proc_macro_hack]
use proc_one::one;
#[proc_macro_hack]
use proc_two::two;

fn main() {
    let hi: &'static str = one!("hi");

    assert_eq!("hi", hi);
}

我不明白为什么可执行文件中的调用是模棱两可的，lib 2和3不相互依赖。这是完整的错误:

error[E0659]: `proc_macro_call` is ambiguous (macro-expanded name vs less macro-expanded name from outer scope during import/macro resolution)
  --> src\main.rs:10:1
   |
10 | #[proc_macro_hack]
   | ^^^^^^^^^^^^^^^^^^ ambiguous name
...
14 |     let hi: &'static str = one!("hi");
   |                            ---------- in this macro invocation
   |
note: `proc_macro_call` could refer to the macro defined here
  --> src\main.rs:11:15
   |
11 | use proc_two::two;
   |               ^^^
...
14 |     let hi: &'static str = one!("hi");
   |                            ---------- in this macro invocation
note: `proc_macro_call` could also refer to the macro defined here
  --> src\main.rs:9:15
   |
9  | use proc_one::one;
   |               ^^^
...
14 |     let hi: &'static str = one!("hi");
   |                            ---------- in this macro invocation
   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

Answer 1

根据proc_macro_hack documentation 不支持嵌套调用:

By default, nested invocations are not supported i.e. the code emitted by a proc-macro-hack macro invocation cannot contain recursive calls to the same proc-macro-hack macro nor calls to any other proc-macro-hack macros. Use proc-macro-nested if you require support for nested invocations.

因此，您标记的代码才是真正的问题:

let x = quote! {
    two!(#r) // This is the problem
};

建议您查看 proc-macro-nested“如果您需要对嵌套调用的支持”。