rspec/rules/S7460/rust/rule.adoc

== Why is this an issue?

Serde is a popular framework in the Rust ecosystem for serializing and deserializing data. It provides a flexible and efficient way to convert Rust data structures into various formats (e.g., JSON, YAML) and vice versa.

One of the core components of Serde is the `Visitor` trait, which allows custom deserialization logic by visiting each element of the data structure. According to Serde's link:https://docs.rs/serde/latest/serde/de/trait.Visitor.html#method.visit_str[documentation], any implementation of the `Visitor` trait that implements the `visit_string` method must also implement the `visit_str` method. Failing to do so can lead to unexpected behavior.

This rule ensures that implementations of the `Visitor` trait adhere to this requirement, promoting correctness and preventing subtle bugs in deserialization logic.

=== Code examples

==== Noncompliant code example

[source,rust,diff-id=1,diff-type=noncompliant]
----
struct A;

impl<'de> serde::de::Visitor<'de> for A {
    type Value = ();

    fn expecting(&self, _: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
      unimplemented!()
    }

    fn visit_string<E>(self, _v: String) -> Result<Self::Value, E>
    where
        E: serde::de::Error,
    {
      unimplemented!()
    }
}
----

==== Compliant solution

[source,rust,diff-id=1,diff-type=compliant]
----
impl<'de> serde::de::Visitor<'de> for A {
    type Value = ();

    fn expecting(&self, _: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
        unimplemented!()
    }

    fn visit_str<E>(self, _v: &str) -> Result<Self::Value, E>
    where
        E: serde::de::Error,
    {
        unimplemented!()
    }

    fn visit_string<E>(self, _v: String) -> Result<Self::Value, E>
    where
        E: serde::de::Error,
    {
        unimplemented!()
    }
}
----

== Resources
=== Documentation

* Clippy Lints - https://rust-lang.github.io/rust-clippy/master/index.html#serde_api_misuse