serde_json ignores a renamed Struct name when throwing an error.

[GeeWee]

When renaming a Struct via Serde, I would expect that this name would also be used in error messages.

I am unsure if this is serde or serde_json behaviour, as I was not able to find the cursory code in either repository, but please feel free to move or tell me to go somewhere else.

See this reproduction case for what happens vs what I expect to happen:

    use serde::{Deserialize, Serialize};
    use serde_json::json;

    #[test]
    fn repro_case() {
        #[derive(Deserialize, Debug)]
        struct Foo {
            bar: Bar,
        }

        #[derive(Deserialize, Debug)]
        #[serde(rename = "AnotherName!")]
        struct Bar {
            qux: String,
        }

        let res = serde_json::from_value::<Foo>(json!({
            "bar": "not_a_struct"
        }))
        .unwrap_err();

        // Passes
        assert_eq!(
            res.to_string(),
            "invalid type: string \"not_a_struct\", expected struct Bar"
        );
        // Does not pass, but should
        assert_eq!(
            res.to_string(),
            "invalid type: string \"not_a_struct\", expected struct AnotherName!"
        );
    }

[Mingun]

This could be expected behavior. At least in one place there is a clear indication, that this was intended -- the rust_name is explicitly distinguished from the type_name:

serde/serde_derive/src/de.rs

Lines 1441 to 1445 in 05a5b7e

	let rust_name = params.type_name();
	let expecting = format!("adjacently tagged enum {}", rust_name);
	let expecting = cattrs.expecting().unwrap_or(&expecting);
	let type_name = cattrs.name().deserialize_name();
	let deny_unknown_fields = cattrs.deny_unknown_fields();

type_name is used in strings that passed to Deserializer::deserialize_struct, etc., rust_name is used in expecting messages. Should we unify that?

[dtolnay]

I think let's keep this behavior. In cases where just a type name isn't meaningful enough, one can use something like serde(expecting = "a map of proxy configs") to fill in the user-facing message.

invalid type: string "not_a_struct", expected a map of proxy configs