https://github.com/serde-rs/serde/issues/1545

.gitignore

/target
**/*.rs.bk

Cargo.lock

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Cargo.toml

[package]
name = "serde-issue-1545"
version = "0.1.0"
authors = ["Pascal Hertleif <pascal@technocreatives.com>"]
edition = "2018"

[[bin]]
name = "serde-issue-1545"
path = "main.rs"

[[test]]
name = "test_string"
path = "test_string.rs"

[[test]]
name = "test_status_code"
path = "test_status_code.rs"

[[test]]
name = "test_reference_enum"
path = "test_reference_enum.rs"

[dependencies]
serde = { version = "1.0.93", features = ["derive"] }
serde_yaml = "0.8.9"
unindent = "0.1.3"

main.rs

fn main() {}

status_code.rs

use serde::{Deserialize, Deserializer, de::{self, Unexpected, Visitor}};
use std::fmt;

#[derive(Debug, PartialEq, Eq, PartialOrd, Ord)]
pub enum StatusCode {
    Code(u16),
    Range(u16),
}

impl<'de> Deserialize<'de> for StatusCode {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: Deserializer<'de>,
    {
        struct StatusCodeVisitor;

        impl<'de> Visitor<'de> for StatusCodeVisitor {
            type Value = StatusCode;

            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
                formatter.write_str("A number between 100 and 999 (as string or integer) or a string that matches `\\dXX`")
            }

            fn visit_i64<E>(self, value: i64) -> Result<Self::Value, E>
            where
                E: de::Error,
            {
                if value < 100 && value > 100 {
                    return Err(E::invalid_value(
                        Unexpected::Signed(value),
                        &"range 100..1000",
                    ));
                }
                Ok(StatusCode::Code(value as u16))
            }

            fn visit_u64<E>(self, value: u64) -> Result<Self::Value, E>
            where
                E: de::Error,
            {
                if value >= 100 && value < 1000 {
                    Ok(StatusCode::Code(value as u16))
                } else {
                    Err(E::invalid_value(Unexpected::Unsigned(value), &self))
                }
            }

            fn visit_str<E>(self, value: &str) -> Result<Self::Value, E>
            where
                E: de::Error,
            {
                if value.len() != 3 {
                    return Err(E::invalid_value(Unexpected::Str(value), &"length 3"));
                }

                if let Ok(number) = value.parse::<i64>() {
                    return self.visit_i64(number);
                }

                if !value.is_ascii() {
                    return Err(E::invalid_value(
                        Unexpected::Str(value),
                        &"ascii, format `\\dXX`",
                    ));
                }

                let v = value.as_bytes().to_ascii_uppercase();

                match [v[0], v[1], v[2]] {
                    [n, b'X', b'X'] if n.is_ascii_digit() => {
                        Ok(StatusCode::Range((n - b'0') as u16))
                    }
                    _ => Err(E::invalid_value(Unexpected::Str(value), &"format `\\dXX`")),
                }
            }
        }

        deserializer.deserialize_any(StatusCodeVisitor)
    }
}

test_cases.rs

use unindent::unindent;

#[test]
fn string_key() {
    let item: Item = serde_yaml::from_str(&unindent(
        r#"
        responses:
            "200":
                description: All is well
        "#,
    ))
    .unwrap();

    println!("{:?}", item);
}

#[test]
fn int_key() {
    let item: Item = serde_yaml::from_str(&unindent(
        "
        responses:
            200:
                description: All is well
        ",
    ))
    .unwrap();

    println!("{:?}", item);
}

#[test]
fn mixed_keys() {
    let item: Item = serde_yaml::from_str(&unindent(
        r#"
        responses:
            200:
                description: All is well
            "404":
                description: All is well
        "#,
    ))
    .unwrap();

    println!("{:?}", item);
}

#[test]
fn default_key() {
    let item: Item = serde_yaml::from_str(&unindent(
        "
        responses:
            default:
                description: All is well
        ",
    ))
    .unwrap();

    println!("{:?}", item);
}

test_reference_enum.rs

#![allow(unused)]

use std::collections::BTreeMap;

mod status_code;
use status_code::StatusCode;

#[derive(serde::Deserialize, Clone, Debug, PartialEq)]
#[serde(untagged)]
pub enum ReferenceOr<T> {
    Reference {
        #[serde(rename = "$ref")]
        reference: String
    },
    Item(T),
}

#[derive(Debug, serde::Deserialize)]
struct Item {
    responses: ReferenceOr<Responses>,
}

#[derive(Debug, serde::Deserialize)]
struct Responses {
    default: Option<ReferenceOr<Unimportant>>,
    #[serde(flatten)]
    #[serde(default)]
    values: BTreeMap<StatusCode, Unimportant>,
}

#[derive(Debug, serde::Deserialize)]
struct Unimportant {
    description: String,
}

include!("test_cases.rs");

test_status_code.rs

#![allow(unused)]

mod status_code;
use status_code::StatusCode;

use std::collections::BTreeMap;

#[derive(Debug, serde::Deserialize)]
struct Item {
    responses: Responses,
}

#[derive(Debug, serde::Deserialize)]
struct Responses {
    default: Option<Unimportant>,
    #[serde(flatten)]
    #[serde(default)]
    values: BTreeMap<StatusCode, Unimportant>,
}

#[derive(Debug, serde::Deserialize)]
struct Unimportant {
    description: String,
}

include!("test_cases.rs");

test_string.rs

#![allow(unused)]

use std::collections::BTreeMap;

#[derive(Debug, serde::Deserialize)]
struct Item {
    responses: Responses,
}

#[derive(Debug, serde::Deserialize)]
struct Responses {
    default: Option<Unimportant>,
    #[serde(flatten)]
    #[serde(default)]
    values: BTreeMap<String, Unimportant>,
}

#[derive(Debug, serde::Deserialize)]
struct Unimportant {
    description: String,
}

include!("test_cases.rs");