serde_with/
flatten_maybe.rs

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1/// Support deserializing from flattened and non-flattened representation
2///
3/// When working with different serialization formats, sometimes it is more idiomatic to flatten
4/// fields, while other formats prefer nesting. Using `#[serde(flatten)]` only the flattened form
5/// is supported.
6///
7/// This helper creates a function, which support deserializing from either the flattened or the
8/// nested form. It gives an error, when both forms are provided. The `flatten` attribute is
9/// required on the field such that the helper works. The serialization format will always be
10/// flattened.
11///
12/// # Examples
13///
14/// ```rust
15/// # use serde::Deserialize;
16/// #
17/// // Setup the types
18/// #[derive(Deserialize, Debug)]
19/// struct S {
20///     #[serde(flatten, deserialize_with = "deserialize_t")]
21///     t: T,
22/// }
23///
24/// #[derive(Deserialize, Debug)]
25/// struct T {
26///     i: i32,
27/// }
28///
29/// // The macro creates custom deserialization code.
30/// // You need to specify a function name and the field name of the flattened field.
31/// serde_with::flattened_maybe!(deserialize_t, "t");
32///
33/// # fn main() {
34/// // Supports both flattened
35/// let j = r#" {"i":1} "#;
36/// assert!(serde_json::from_str::<S>(j).is_ok());
37/// # // Ensure the t field is not dead code
38/// # assert_eq!(serde_json::from_str::<S>(j).unwrap().t.i, 1);
39///
40/// // and non-flattened versions.
41/// let j = r#" {"t":{"i":1}} "#;
42/// assert!(serde_json::from_str::<S>(j).is_ok());
43///
44/// // Ensure that the value is given
45/// let j = r#" {} "#;
46/// assert!(serde_json::from_str::<S>(j).is_err());
47///
48/// // and only occurs once, not multiple times.
49/// let j = r#" {"i":1,"t":{"i":1}} "#;
50/// assert!(serde_json::from_str::<S>(j).is_err());
51/// # }
52/// ```
53#[macro_export]
54macro_rules! flattened_maybe {
55    ($fn:ident, $field:tt) => {
56        fn $fn<'de, T, D>(deserializer: D) -> $crate::__private__::Result<T, D::Error>
57        where
58            T: $crate::serde::Deserialize<'de>,
59            D: $crate::serde::Deserializer<'de>,
60        {
61            use $crate::{
62                __private__::{
63                    Option::{self, None, Some},
64                    Result::{self, Err, Ok},
65                },
66                serde,
67            };
68
69            #[derive($crate::serde_derive::Deserialize)]
70            #[serde(crate = "serde")]
71            pub struct Both<T> {
72                #[serde(flatten)]
73                flat: Option<T>,
74                #[serde(rename = $field)]
75                not_flat: Option<T>,
76            }
77
78            let both: Both<T> = $crate::serde::Deserialize::deserialize(deserializer)?;
79            match (both.flat, both.not_flat) {
80                (Some(t), None) | (None, Some(t)) => Ok(t),
81                (None, None) => Err($crate::serde::de::Error::missing_field($field)),
82                (Some(_), Some(_)) => Err($crate::serde::de::Error::custom(concat!(
83                    "`",
84                    $field,
85                    "` is both flattened and not"
86                ))),
87            }
88        }
89    };
90}
serde_with/flatten_maybe.rs

serde_with/
flatten_maybe.rs
