I tried to derive serde::Deserialize
for a struct containing a reference to a Path
. This yielded an error message which doesn't occur if you replace &'a Path
with &'a str
. What causes the different behaviours of #[derive(Deserialize)]
?
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<'_>
Strangely enough, the code compiles if the struct contains both fields _a: &'a Path
and _b: &'a str
... At this point I think this is a bug.
Add an attribute to the field: #[serde(borrow)]
. That will indicate to serde that it should be borrowing the value. You must provide this attribute for every borrow except for &str
and &[u8]
.
Source: https://serde.rs/lifetimes.html#borrowing-data-in-a-derived-impl
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