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Implement OneOrMany for std::collections::HashSet #925

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4 changes: 4 additions & 0 deletions serde_with/CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.

## [Unreleased]

### Added

* Support `OneOrMany` with `HashSet`

## [3.17.0] - 2026-02-24

### Added
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39 changes: 39 additions & 0 deletions serde_with/src/de/impls.rs
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Expand Up @@ -1771,6 +1771,45 @@ where
}
}

#[cfg(all(feature = "alloc", feature = "std"))]
impl<'de, T, TAs, FORMAT, S> DeserializeAs<'de, std::collections::HashSet<T, S>>
for OneOrMany<TAs, FORMAT>
where
T: Eq + std::hash::Hash,
S: BuildHasher + Default,
TAs: DeserializeAs<'de, T>,
FORMAT: Format,
{
fn deserialize_as<D>(deserializer: D) -> Result<std::collections::HashSet<T, S>, D::Error>
where
D: Deserializer<'de>,
{
let is_hr = deserializer.is_human_readable();
let content: content::de::Content<'de> = Deserialize::deserialize(deserializer)?;

let one_err: D::Error = match <DeserializeAsWrap<T, TAs>>::deserialize(
content::de::ContentRefDeserializer::new(&content, is_hr),
) {
Ok(one) => {
let mut hashset = std::collections::HashSet::default();
hashset.insert(one.into_inner());
return Ok(hashset);
}
Err(err) => err,
};
let many_err: D::Error =
match <DeserializeAsWrap<HashSet<T, S>, HashSet<TAs, S>>>::deserialize(
content::de::ContentDeserializer::new(content, is_hr),
) {
Ok(many) => return Ok(many.into_inner()),
Err(err) => err,
};
Err(DeError::custom(format_args!(
"OneOrMany could not deserialize any variant:\n One: {one_err}\n Many: {many_err}"
)))
}
}

#[cfg(feature = "alloc")]
impl<'de, T, TAs1> DeserializeAs<'de, T> for PickFirst<(TAs1,)>
where
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2 changes: 1 addition & 1 deletion serde_with/src/schemars_0_8.rs
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Expand Up @@ -632,7 +632,7 @@ where
let properties = &mut object.object().properties;
for schema in one_of {
if let Some(object) = schema.into_object().object {
properties.extend(object.properties.into_iter());
properties.extend(object.properties);
}
}

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44 changes: 42 additions & 2 deletions serde_with/src/ser/impls.rs
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Expand Up @@ -945,7 +945,7 @@ where
S: Serializer,
{
match source.len() {
1 => SerializeAsWrap::<T, U>::new(source.iter().next().expect("Cannot be empty"))
1 => SerializeAsWrap::<T, U>::new(source.first().expect("Cannot be empty"))
.serialize(serializer),
_ => SerializeAsWrap::<Vec<T>, Vec<U>>::new(source).serialize(serializer),
}
Expand Down Expand Up @@ -976,7 +976,7 @@ where
S: Serializer,
{
match source.len() {
1 => SerializeAsWrap::<T, TAs>::new(source.iter().next().expect("Cannot be empty"))
1 => SerializeAsWrap::<T, TAs>::new(source.first().expect("Cannot be empty"))
.serialize(serializer),
_ => SerializeAsWrap::<&[T], &[TAs]>::new(&source.as_slice()).serialize(serializer),
}
Expand All @@ -997,6 +997,46 @@ where
}
}

#[cfg(all(feature = "alloc", feature = "std"))]
impl<T, U, S> SerializeAs<std::collections::HashSet<T, S>> for OneOrMany<U, formats::PreferOne>
where
T: Eq + core::hash::Hash,
U: SerializeAs<T>,
{
fn serialize_as<Ser>(
source: &std::collections::HashSet<T, S>,
serializer: Ser,
) -> Result<Ser::Ok, Ser::Error>
where
Ser: Serializer,
{
match source.len() {
1 => SerializeAsWrap::<T, U>::new(source.iter().next().expect("Cannot be empty")).serialize(serializer),
_ => SerializeAsWrap::<std::collections::HashSet<T, S>, std::collections::HashSet<U, S>>::new(source).serialize(serializer),
}
}
}

#[cfg(all(feature = "alloc", feature = "std"))]
impl<T, U, S> SerializeAs<std::collections::HashSet<T, S>> for OneOrMany<U, formats::PreferMany>
where
T: Eq + core::hash::Hash,
U: SerializeAs<T>,
{
fn serialize_as<Ser>(
source: &std::collections::HashSet<T, S>,
serializer: Ser,
) -> Result<Ser::Ok, Ser::Error>
where
Ser: Serializer,
{
SerializeAsWrap::<std::collections::HashSet<T, S>, std::collections::HashSet<U, S>>::new(
source,
)
.serialize(serializer)
}
}

#[cfg(feature = "alloc")]
impl<T, TAs1> SerializeAs<T> for PickFirst<(TAs1,)>
where
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70 changes: 64 additions & 6 deletions serde_with/tests/serde_as/lib.rs
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Expand Up @@ -35,7 +35,7 @@ use serde_with::{
NoneAsEmptyString, OneOrMany, Same, Seq, StringWithSeparator,
};
use std::{
collections::HashMap,
collections::{HashMap, HashSet},
sync::{Mutex, RwLock},
};

Expand Down Expand Up @@ -1183,11 +1183,11 @@ fn test_one_or_many_prefer_one() {
is_equal(
S1Vec(vec![1, 2, 3]),
expect![[r#"
[
1,
2,
3
]"#]],
[
1,
2,
3
]"#]],
);
check_deserialization(S1Vec(vec![1]), r#"1"#);
check_deserialization(S1Vec(vec![1]), r#"[1]"#);
Expand Down Expand Up @@ -1323,6 +1323,64 @@ fn test_one_or_many_prefer_many() {
);
}

#[test]
fn test_one_or_many_hashset_prefer_one() {
#[serde_as]
#[derive(Debug, Serialize, Deserialize, PartialEq)]
struct S1(#[serde_as(as = "OneOrMany<_>")] HashSet<u32>);

is_equal(S1(HashSet::new()), expect![[r#"[]"#]]);
is_equal(S1(HashSet::from([1])), expect![[r#"1"#]]);
check_deserialization(S1(HashSet::from([1])), r#"1"#);
check_deserialization(S1(HashSet::from([1])), r#"[1]"#);
check_deserialization(S1(HashSet::from([1, 2, 3])), r#"[1, 2, 3]"#);
check_deserialization(S1(HashSet::from([1, 2, 3])), r#"[3, 2, 1]"#);
check_error_deserialization::<S1>(
r#""xx""#,
expect![[r#"
OneOrMany could not deserialize any variant:
One: invalid type: string "xx", expected u32
Many: invalid type: string "xx", expected a sequence"#]],
);

#[serde_as]
#[derive(Debug, Serialize, Deserialize, PartialEq)]
struct S2(#[serde_as(as = "OneOrMany<DisplayFromStr>")] HashSet<u32>);

is_equal(S2(HashSet::from([1])), expect![[r#""1""#]]);
check_deserialization(S2(HashSet::from([1])), r#""1""#);
check_deserialization(S2(HashSet::from([1])), r#"["1"]"#);
check_deserialization(S2(HashSet::from([1, 2, 3])), r#"["1", "2", "3"]"#);
check_error_deserialization::<S2>(
r#"{}"#,
expect![[r#"
OneOrMany could not deserialize any variant:
One: invalid type: map, expected a string
Many: invalid type: map, expected a sequence"#]],
);
}

#[test]
fn test_one_or_many_hashset_prefer_many() {
use serde_with::formats::PreferMany;

#[serde_as]
#[derive(Debug, Serialize, Deserialize, PartialEq)]
struct S1(#[serde_as(as = "OneOrMany<_, PreferMany>")] HashSet<u32>);

is_equal(S1(HashSet::new()), expect![[r#"[]"#]]);
is_equal(
S1(HashSet::from([1])),
expect![[r#"
[
1
]"#]],
);
check_deserialization(S1(HashSet::from([1])), r#"1"#);
check_deserialization(S1(HashSet::from([1])), r#"[1]"#);
check_deserialization(S1(HashSet::from([1, 2, 3])), r#"[1, 2, 3]"#);
}

/// Test that Cow borrows from the input
#[test]
fn test_borrow_cow_str() {
Expand Down