在其他 proc 宏中调用 proc 宏

Question

我有一个无法编译的小型复制项目。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：

库 1 - 解析器 - 解析 proc 宏调用
Lib 2 - proc_two - returns 作为 proc 宏调用的文字字符串
Lib 3 - proc_one - 将宏转发到 proc_two（尽管它不依赖于 proc_two）。这就像 proc_two 也是一个 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（给出编译错误）。

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不明确，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.

因此您标记的代码是真正的问题：

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

还有一个建议可以看看proc-macro-nested"if you require support for nested invocations"。

在其他 proc 宏中调用 proc 宏

Call proc macro inside other proc macro

rust

rust-proc-macros