rust - 为什么 Serde 不能为仅包含 &Path 的结构派生反序列化？

Question

我尝试为包含对 Path 的引用的结构派生 serde::Deserialize。这会产生一条错误消息，如果您将 &'a Path 替换为 &'a str 则不会出现该错误消息。是什么导致了 #[derive(Deserialize)] 的不同行为？

Playground

#!/bin/cargo script
//! ```cargo
//! [dependencies]
//! serde_derive="1.0"
//! serde="1.0"
//! ```

extern crate serde_derive;

use serde_derive::*;

#[derive(Deserialize)]
struct A<'a> {
    a: &'a std::path::Path,
    //a: &'a str,
}

fn main() {}

error[E0495]: cannot infer an appropriate lifetime for lifetime parameter `'de` due to conflicting requirements
 --> src/main.rs:7:5
  |
7 |     a: &'a std::path::Path,
  |     ^
  |
note: first, the lifetime cannot outlive the lifetime 'de as defined on the impl at 5:10...
 --> src/main.rs:5:10
  |
5 | #[derive(Deserialize)]
  |          ^^^^^^^^^^^
  = note: ...so that the types are compatible:
          expected _IMPL_DESERIALIZE_FOR_A::_serde::de::SeqAccess<'_>
             found _IMPL_DESERIALIZE_FOR_A::_serde::de::SeqAccess<'de>
note: but, the lifetime must be valid for the lifetime 'a as defined on the impl at 6:10...
 --> src/main.rs:6:10
  |
6 | struct A<'a> {
  |          ^^
  = note: ...so that the types are compatible:
          expected _IMPL_DESERIALIZE_FOR_A::_serde::Deserialize<'_>
             found _IMPL_DESERIALIZE_FOR_A::_serde::Deserialize<'_>

error[E0495]: cannot infer an appropriate lifetime for lifetime parameter `'de` due to conflicting requirements
 --> src/main.rs:7:5
  |
7 |     a: &'a std::path::Path,
  |     ^
  |
note: first, the lifetime cannot outlive the lifetime 'de as defined on the impl at 5:10...
 --> src/main.rs:5:10
  |
5 | #[derive(Deserialize)]
  |          ^^^^^^^^^^^
  = note: ...so that the types are compatible:
          expected _IMPL_DESERIALIZE_FOR_A::_serde::de::MapAccess<'_>
             found _IMPL_DESERIALIZE_FOR_A::_serde::de::MapAccess<'de>
note: but, the lifetime must be valid for the lifetime 'a as defined on the impl at 6:10...
 --> src/main.rs:6:10
  |
6 | struct A<'a> {
  |          ^^
  = note: ...so that the types are compatible:
          expected _IMPL_DESERIALIZE_FOR_A::_serde::Deserialize<'_>
             found _IMPL_DESERIALIZE_FOR_A::_serde::Deserialize<'_>

奇怪的是，如果结构包含两个字段 _a: &'a Path 和 _b: &'a str 代码编译......在这一点上我认为这是bug .

Answer 1

向字段添加属性:#[serde(borrow)]。这将向 serde 表明它应该借用该值。您必须为除 &str 和 &[u8] 之外的每个借用提供此属性。

来源:https://serde.rs/lifetimes.html#borrowing-data-in-a-derived-impl