Simplify serde_as handling around Options

serde_with/CHANGELOG.md

@@ -7,6 +7,23 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+### Changed
+
+* Make `#[serde_as]` behave more intuitive on `Option<T>` fields.
+
+    The `#[serde_as]` macro now detects if a `#[serde_as(as = "Option<S>")]` is used on a field of type `Option<T>` and applies `#[serde(default)]` to the field.
+    This restores the ability to deserialize with missing fields and fixes a common annoyance (#183, #185, #311, #417).
+    This is a breaking change, since now deserialization will pass where it did not before and this might be undesired.
+
+    The `Option` field and transformation are detected by directly matching on the type name.
+    These variants are detected as `Option`.
+    * `Option`
+    * `std::option::Option`, with or without leading `::`
+    * `core::option::Option`, with or without leading `::`
+
+    If an existing `default` attribute is detected, the attribute is not applied again.
+    This behavior can be supressed by using `#[serde_as(no_default)]` or `#[serde_as(as = "Option<S>", no_default)]`.
+
 ## [1.14.0] - 2022-05-29
 
 ### Added

serde_with/tests/serde_as/serde_as_macro.rs

@@ -189,3 +189,119 @@ fn test_serde_as_macro_multiple_field_attributes() {
         }"#]],
     );
 }
+
+/// Ensure that `serde_as` applies `default` if both the field and the conversion are option.
+#[test]
+fn test_default_on_option() {
+    #[serde_as]
+    #[derive(Debug, Eq, PartialEq, Serialize, Deserialize)]
+    struct Data {
+        #[serde_as(as = "Option<DisplayFromStr>")]
+        a: Option<u32>,
+    }
+
+    is_equal(
+        Data { a: None },
+        expect![[r#"
+          {
+            "a": null
+          }"#]],
+    );
+    is_equal(
+        Data { a: Some(123) },
+        expect![[r#"
+          {
+            "a": "123"
+          }"#]],
+    );
+    check_deserialization(Data { a: None }, "{}");
+
+    #[serde_as]
+    #[derive(Debug, Eq, PartialEq, Serialize, Deserialize)]
+    struct DataNoDefault {
+        #[serde_as(as = "Option<DisplayFromStr>", no_default)]
+        a: Option<u32>,
+    }
+
+    is_equal(
+        DataNoDefault { a: None },
+        expect![[r#"
+          {
+            "a": null
+          }"#]],
+    );
+    is_equal(
+        DataNoDefault { a: Some(123) },
+        expect![[r#"
+          {
+            "a": "123"
+          }"#]],
+    );
+    check_error_deserialization::<DataNoDefault>(
+        "{}",
+        expect!["missing field `a` at line 1 column 2"],
+    );
+
+    fn default_555() -> Option<u32> {
+        Some(555)
+    }
+
+    #[serde_as]
+    #[derive(Debug, Eq, PartialEq, Serialize, Deserialize)]
+    struct DataExplicitDefault {
+        #[serde_as(as = "Option<DisplayFromStr>")]
+        #[serde(default = "default_555")]
+        a: Option<u32>,
+    }
+
+    is_equal(
+        DataExplicitDefault { a: None },
+        expect![[r#"
+          {
+            "a": null
+          }"#]],
+    );
+    is_equal(
+        DataExplicitDefault { a: Some(123) },
+        expect![[r#"
+          {
+            "a": "123"
+          }"#]],
+    );
+    check_deserialization(DataExplicitDefault { a: Some(555) }, "{}");
+
+    #[serde_as]
+    #[derive(Debug, Eq, PartialEq, Serialize, Deserialize)]
+    struct DataString {
+        #[serde_as(as = "NoneAsEmptyString")]
+        a: Option<String>,
+    }
+
+    is_equal(
+        DataString { a: None },
+        expect![[r#"
+            {
+              "a": ""
+            }"#]],
+    );
+    is_equal(
+        DataString {
+            a: Some("123".to_string()),
+        },
+        expect![[r#"
+          {
+            "a": "123"
+          }"#]],
+    );
+    check_deserialization(DataString { a: None }, r#"{"a": ""}"#);
+    check_deserialization(
+        DataString {
+            a: Some("555".to_string()),
+        },
+        r#"{"a": "555"}"#,
+    );
+    check_error_deserialization::<DataString>(
+        "{}",
+        expect!["missing field `a` at line 1 column 2"],
+    );
+}

serde_with_macros/CHANGELOG.md

@@ -7,9 +7,26 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+### Changed
+
+* Make `#[serde_as]` behave more intuitive on `Option<T>` fields.
+
+    The `#[serde_as]` macro now detects if a `#[serde_as(as = "Option<S>")]` is used on a field of type `Option<T>` and applies `#[serde(default)]` to the field.
+    This restores the ability to deserialize with missing fields and fixes a common annoyance (#183, #185, #311, #417).
+    This is a breaking change, since now deserialization will pass where it did not before and this might be undesired.
+
+    The `Option` field and transformation are detected by directly matching on the type name.
+    These variants are detected as `Option`.
+    * `Option`
+    * `std::option::Option`, with or without leading `::`
+    * `core::option::Option`, with or without leading `::`
+
+    If an existing `default` attribute is detected, the attribute is not applied again.
+    This behavior can be supressed by using `#[serde_as(no_default)]` or `#[serde_as(as = "Option<S>", no_default)]`.
+
 ### Fixed
 
-* Make the documentation clearer by stating that the `#[serde_as]` and `#[skip_serializing_none]` attributes must always be places before `#[derive]`.
+* Make the documentation clearer by stating that the `#[serde_as]` and `#[skip_serializing_none]` attributes must always be placed before `#[derive]`.
 
 ## [1.5.2] - 2022-04-07