[rust] fix: discriminated-union variants drop every child-specific field

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/RustClientCodegen.java

@@ -331,6 +331,42 @@ public CodegenModel fromModel(String name, Schema model) {
         return mdl;
     }
 
+    @Override
+    public Map<String, ModelsMap> postProcessAllModels(Map<String, ModelsMap> objs) {
+        objs = super.postProcessAllModels(objs);
+
+        for (ModelsMap modelsMap : objs.values()) {
+            for (ModelMap modelMap : modelsMap.getModels()) {
+                CodegenModel cm = modelMap.getModel();
+                CodegenDiscriminator discriminator = cm.discriminator;
+                if (discriminator == null || discriminator.getMappedModels() == null) {
+                    continue;
+                }
+                // a mapping that names the base itself leaves no struct to wrap, and an enum-typed tag would be
+                // written twice (the child's copy keeps its default): keep the inline variants
+                if (discriminator.getMappedModels().stream().anyMatch(m -> cm.name.equals(m.getSchemaName()))
+                        || cm.allVars.stream().anyMatch(v -> discriminator.getPropertyBaseName().equals(v.baseName) && v.getIsEnumOrRef())) {
+                    discriminator.getVendorExtensions().put("x-rust-inline-variants", true);
+                    continue;
+                }
+                // a mapped child's discriminator doubles as the union's serde tag, which is consumed before the
+                // child deserializes: mark it so the template defaults it and skips it while unset
+                for (CodegenDiscriminator.MappedModel mapped : discriminator.getMappedModels()) {
+                    if (mapped.getModel() == null) {
+                        continue;
+                    }
+                    for (CodegenProperty var : mapped.getModel().vars) {
+                        if (discriminator.getPropertyBaseName().equals(var.baseName)) {
+                            var.isDiscriminator = true;
+                        }
+                    }
+                }
+            }
+        }
+
+        return objs;
+    }
+
     @Override
     public ModelsMap postProcessModels(ModelsMap objs) {
         for (ModelMap model : objs.getModels()) {

modules/openapi-generator/src/main/resources/rust/model.mustache

@@ -84,6 +84,11 @@ pub enum {{{classname}}} {
     {{^oneOf}}
     {{#mappedModels}}
     #[serde(rename="{{mappingName}}")]
+    {{^vendorExtensions.x-rust-inline-variants}}
+    {{!-- newtype variant: the child's own fields survive; named by modelName (unique per mapping), wraps the real classname --}}
+    {{{modelName}}}({{^avoidBoxedModels}}Box<{{/avoidBoxedModels}}models::{{#model}}{{{classname}}}{{/model}}{{^model}}{{{modelName}}}{{/model}}{{^avoidBoxedModels}}>{{/avoidBoxedModels}}),
+    {{/vendorExtensions.x-rust-inline-variants}}
+    {{#vendorExtensions.x-rust-inline-variants}}
     {{{modelName}}} {
     {{#vars}}
         {{#description}}
@@ -93,6 +98,7 @@ pub enum {{{classname}}} {
         {{{name}}}: {{#required}}{{#isNullable}}Option<{{/isNullable}}{{/required}}{{^required}}Option<{{/required}}{{#isEnum}}{{{enumName}}}{{/isEnum}}{{^isEnum}}{{#isModel}}{{^avoidBoxedModels}}Box<{{/avoidBoxedModels}}{{{dataType}}}{{^avoidBoxedModels}}>{{/avoidBoxedModels}}{{/isModel}}{{^isModel}}{{{dataType}}}{{/isModel}}{{/isEnum}}{{#required}}{{#isNullable}}>{{/isNullable}}{{/required}}{{^required}}>{{/required}},
     {{/vars}}
     },
+    {{/vendorExtensions.x-rust-inline-variants}}
     {{/mappedModels}}
     {{/oneOf}}
     {{^oneOf.isEmpty}}
@@ -110,11 +116,11 @@ pub enum {{{classname}}} {
 
 impl Default for {{classname}} {
     fn default() -> Self {
-        {{^oneOf}}{{#mappedModels}}{{#-first}}Self::{{modelName}} {
+        {{^oneOf}}{{#mappedModels}}{{#-first}}{{^vendorExtensions.x-rust-inline-variants}}Self::{{modelName}}(Default::default()){{/vendorExtensions.x-rust-inline-variants}}{{#vendorExtensions.x-rust-inline-variants}}Self::{{modelName}} {
         {{#vars}}
             {{{name}}}: Default::default(),
         {{/vars}}
-        }{{/-first}}{{/mappedModels}}
+        }{{/vendorExtensions.x-rust-inline-variants}}{{/-first}}{{/mappedModels}}
         {{/oneOf}}{{^oneOf.isEmpty}}{{#composedSchemas.oneOf}}{{#-first}}Self::{{{name}}}(Default::default()){{/-first}}{{/composedSchemas.oneOf}}{{/oneOf.isEmpty}}
     }
 }
@@ -133,7 +139,8 @@ pub struct {{{classname}}} {
     {{#isByteArray}}
     {{#vendorExtensions.isMandatory}}#[serde_as(as = "serde_with::base64::Base64")]{{/vendorExtensions.isMandatory}}{{^vendorExtensions.isMandatory}}#[serde_as(as = "{{^serdeAsDoubleOption}}Option{{/serdeAsDoubleOption}}{{#serdeAsDoubleOption}}super::DoubleOption{{/serdeAsDoubleOption}}<serde_with::base64::Base64>")]{{/vendorExtensions.isMandatory}}
     {{/isByteArray}}
-    #[serde(rename = "{{{baseName}}}"{{^required}}{{#isNullable}}, default{{^isByteArray}}, with = "::serde_with::rust::double_option"{{/isByteArray}}{{/isNullable}}{{/required}}{{^required}}, skip_serializing_if = "Option::is_none"{{/required}}{{#required}}{{#isNullable}}, deserialize_with = "Option::deserialize"{{/isNullable}}{{/required}})]
+    {{!-- a mapped child's discriminator is the union's consumed serde tag: default it, skip it while unset --}}
+    #[serde(rename = "{{{baseName}}}"{{#isDiscriminator}}{{#required}}, default{{#isNullable}}, skip_serializing_if = "Option::is_none"{{/isNullable}}{{^isNullable}}{{#isString}}{{^isEnum}}, skip_serializing_if = "String::is_empty"{{/isEnum}}{{/isString}}{{/isNullable}}{{/required}}{{/isDiscriminator}}{{^required}}{{#isNullable}}, default{{^isByteArray}}, with = "::serde_with::rust::double_option"{{/isByteArray}}{{/isNullable}}{{/required}}{{^required}}, skip_serializing_if = "Option::is_none"{{/required}}{{#required}}{{#isNullable}}{{^isDiscriminator}}, deserialize_with = "Option::deserialize"{{/isDiscriminator}}{{/isNullable}}{{/required}})]
     pub {{{name}}}: {{!
     ### Option Start
     }}{{#isNullable}}Option<{{/isNullable}}{{^required}}Option<{{/required}}{{!

modules/openapi-generator/src/test/java/org/openapitools/codegen/rust/RustClientCodegenTest.java

@@ -298,6 +298,49 @@ public void testMultipleArrayTypesEnum() throws IOException {
         TestUtils.assertFileContains(outputPath, enumSpec);
     }
 
+    @Test
+    public void testDiscriminatedUnionKeepsChildFields() throws IOException {
+        Path target = Files.createTempDirectory("test");
+        target.toFile().deleteOnExit();
+        final CodegenConfigurator configurator = new CodegenConfigurator()
+                .setGeneratorName("rust")
+                .setInputSpec("src/test/resources/3_0/rust/discriminated-union.yaml")
+                .setSkipOverwrite(false)
+                .setOutputDir(target.toAbsolutePath().toString().replace("\\", "/"));
+        new DefaultGenerator().opts(configurator.toClientOptInput()).generate();
+
+        // newtype variants, so the child's own fields survive
+        Path unionPath = Path.of(target.toString(), "/src/models/api_error.rs");
+        TestUtils.assertFileContains(unionPath, "#[serde(tag = \"type\")]");
+        TestUtils.assertFileContains(unionPath, "ObjectExists(Box<models::ObjectExists>),");
+        TestUtils.assertFileContains(unionPath, "ValidationError(Box<models::ValidationError>),");
+        TestUtils.assertFileContains(unionPath, "Self::ObjectExists(Default::default())");
+        TestUtils.assertFileNotContains(unionPath, "ObjectExists {");
+
+        // the consumed tag key defaults and is skipped while unset; standalone field and new() unchanged
+        Path childPath = Path.of(target.toString(), "/src/models/object_exists.rs");
+        TestUtils.assertFileContains(childPath,
+                "#[serde(rename = \"type\", default, skip_serializing_if = \"String::is_empty\")]",
+                "pub identifier: String,",
+                "pub fn new(r#type: String, message: String, identifier: String) -> ObjectExists {");
+        TestUtils.assertFileContains(Path.of(target.toString(), "/src/models/alpha.rs"),
+                "#[serde(rename = \"kind\", default, skip_serializing_if = \"Option::is_none\")]");
+        // an enum-typed tag would be written twice, the child's copy keeping its default: inline variants, children untouched
+        TestUtils.assertFileContains(Path.of(target.toString(), "/src/models/pet.rs"),
+                "#[serde(rename=\"Cat\")]\n    Cat {", "#[serde(rename=\"Dog\")]\n    Dog {");
+        TestUtils.assertFileNotContains(Path.of(target.toString(), "/src/models/pet.rs"), "Box<models::Cat>");
+        TestUtils.assertFileContains(Path.of(target.toString(), "/src/models/cat.rs"), "#[serde(rename = \"petType\")]\n    pub pet_type: PetType,");
+        TestUtils.assertFileContains(Path.of(target.toString(), "/src/models/shape.rs"), "#[serde(rename=\"circle\")]\n    Circle {");
+        TestUtils.assertFileContains(Path.of(target.toString(), "/src/models/circle.rs"), "#[serde(rename = \"kind\")]\n    pub kind: models::ShapeKind,");
+
+        // a mapping that names the base itself leaves no struct to wrap (E0275): inline variants, children untouched
+        TestUtils.assertFileContains(Path.of(target.toString(), "/src/models/creature.rs"),
+                "#[serde(rename=\"Creature\")]\n    Creature {", "#[serde(rename=\"Bird\")]\n    Bird {");
+        TestUtils.assertFileNotContains(Path.of(target.toString(), "/src/models/creature.rs"), "Box<models::Creature>");
+        TestUtils.assertFileContains(Path.of(target.toString(), "/src/models/creature.rs"), "#[serde(tag = \"kind\")]");
+        TestUtils.assertFileContains(Path.of(target.toString(), "/src/models/bird.rs"), "#[serde(rename = \"kind\")]\n    pub kind: String,");
+    }
+
     @Test
     public void testIntegerPropertyEnum() throws IOException {
         Path target = Files.createTempDirectory("test");

modules/openapi-generator/src/test/resources/3_0/rust/discriminated-union.yaml

@@ -0,0 +1,143 @@
+openapi: 3.0.3
+info:
+  title: discriminated union
+  version: 1.0.0
+paths:
+  /errors:
+    get:
+      operationId: getError
+      responses:
+        '200':
+          description: ok
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/ApiError'
+components:
+  schemas:
+    ApiError:
+      type: object
+      required:
+        - type
+        - message
+      properties:
+        type:
+          type: string
+        message:
+          type: string
+      discriminator:
+        propertyName: type
+        mapping:
+          ObjectExists: '#/components/schemas/ObjectExists'
+          ValidationError: '#/components/schemas/ValidationError'
+    ObjectExists:
+      allOf:
+        - $ref: '#/components/schemas/ApiError'
+        - type: object
+          required:
+            - identifier
+          properties:
+            identifier:
+              type: string
+            objectType:
+              type: string
+    ValidationError:
+      allOf:
+        - $ref: '#/components/schemas/ApiError'
+        - type: object
+          properties:
+            field:
+              type: string
+    # nullable discriminator: String::is_empty would not compile against it
+    NullableTagged:
+      type: object
+      required:
+        - kind
+      properties:
+        kind:
+          type: string
+          nullable: true
+        label:
+          type: string
+      discriminator:
+        propertyName: kind
+        mapping:
+          Alpha: '#/components/schemas/Alpha'
+    Alpha:
+      allOf:
+        - $ref: '#/components/schemas/NullableTagged'
+        - type: object
+          properties:
+            alphaOnly:
+              type: string
+    # enum-typed discriminators, inline and $ref: the union keeps the inline variants
+    Pet:
+      type: object
+      required:
+        - petType
+      properties:
+        petType:
+          type: string
+          enum: [Cat, Dog]
+      discriminator:
+        propertyName: petType
+        mapping:
+          Cat: '#/components/schemas/Cat'
+          Dog: '#/components/schemas/Dog'
+    Cat:
+      allOf:
+        - $ref: '#/components/schemas/Pet'
+        - type: object
+          properties:
+            lives:
+              type: integer
+    Dog:
+      allOf:
+        - $ref: '#/components/schemas/Pet'
+        - type: object
+          properties:
+            bark:
+              type: boolean
+    ShapeKind:
+      type: string
+      enum: [circle]
+    Shape:
+      type: object
+      required:
+        - kind
+      properties:
+        kind:
+          $ref: '#/components/schemas/ShapeKind'
+      discriminator:
+        propertyName: kind
+        mapping:
+          circle: '#/components/schemas/Circle'
+    Circle:
+      allOf:
+        - $ref: '#/components/schemas/Shape'
+        - type: object
+          properties:
+            radius:
+              type: number
+    # the mapping names the base itself: no struct to wrap, so the union keeps the inline variants
+    Creature:
+      type: object
+      required:
+        - kind
+      properties:
+        kind:
+          type: string
+        name:
+          type: string
+      discriminator:
+        propertyName: kind
+        mapping:
+          Creature: '#/components/schemas/Creature'
+          Bird: '#/components/schemas/Bird'
+    Bird:
+      allOf:
+        - $ref: '#/components/schemas/Creature'
+        - type: object
+          properties:
+            wingspan:
+              type: number

samples/client/others/rust/hyper/oneOf/src/models/bar.rs

@@ -25,7 +25,7 @@ pub struct Bar {
     #[serde(rename = "@baseType", skip_serializing_if = "Option::is_none")]
     pub at_base_type: Option<String>,
     /// When sub-classing, this defines the sub-class Extensible name
-    #[serde(rename = "@type")]
+    #[serde(rename = "@type", default, skip_serializing_if = "String::is_empty")]
     pub at_type: String,
     #[serde(rename = "barPropA", skip_serializing_if = "Option::is_none")]
     pub bar_prop_a: Option<String>,

samples/client/others/rust/hyper/oneOf/src/models/bar_create.rs

@@ -26,7 +26,7 @@ pub struct BarCreate {
     #[serde(rename = "@baseType", skip_serializing_if = "Option::is_none")]
     pub at_base_type: Option<String>,
     /// When sub-classing, this defines the sub-class Extensible name
-    #[serde(rename = "@type")]
+    #[serde(rename = "@type", default, skip_serializing_if = "String::is_empty")]
     pub at_type: String,
     #[serde(rename = "barPropA", skip_serializing_if = "Option::is_none")]
     pub bar_prop_a: Option<String>,

samples/client/others/rust/hyper/oneOf/src/models/bar_ref.rs

@@ -26,7 +26,7 @@ pub struct BarRef {
     #[serde(rename = "@baseType", skip_serializing_if = "Option::is_none")]
     pub at_base_type: Option<String>,
     /// When sub-classing, this defines the sub-class Extensible name
-    #[serde(rename = "@type")]
+    #[serde(rename = "@type", default, skip_serializing_if = "String::is_empty")]
     pub at_type: String,
     /// Name of the related entity.
     #[serde(rename = "name", skip_serializing_if = "Option::is_none")]