Fix nullable date deserialization for OpenAPI v3 schemas

.github/workflows/dotnetcore.yml

@@ -17,11 +17,28 @@ jobs:
     runs-on: ${{ matrix.os }}
 
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v4
       - name: Setup .NET 10.0 SDK
         uses: actions/setup-dotnet@v4
         with:
           dotnet-version: "10.0.x"
+      - name: Cache NuGet packages
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.nuget/packages
+            ~/.local/share/NuGet
+            %LOCALAPPDATA%\NuGet\v3-cache
+          key: ${{ runner.os }}-nuget-${{ hashFiles('**/paket.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-nuget-
+      - name: Cache .paket directory
+        uses: actions/cache@v4
+        with:
+          path: .paket
+          key: ${{ runner.os }}-paket-${{ hashFiles('**/paket.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-paket-
       - name: Install local tools
         run: dotnet tool restore
       - name: Paket Restore

src/SwaggerProvider.DesignTime/v3/DefinitionCompiler.fs

@@ -268,6 +268,12 @@ type DefinitionCompiler(schema: OpenApiDocument, provideNullable) as this =
                     | true -> getReq schemaObj
                     |> Set.ofSeq
 
+                // Helper to check if a schema has the Null type flag (OpenAPI 3.0 nullable)
+                let isSchemaNullable(schema: IOpenApiSchema) =
+                    not(isNull schema)
+                    && schema.Type.HasValue
+                    && schema.Type.Value.HasFlag(JsonSchemaType.Null)
+
                 // Generate fields and properties
                 let members =
                     let generateProperty = generateProperty(UniqueNameGenerator())
@@ -279,7 +285,13 @@ type DefinitionCompiler(schema: OpenApiDocument, provideNullable) as this =
                         if String.IsNullOrEmpty propName then
                             failwithf $"Property cannot be created with empty name. TypeName:%A{tyName}; SchemaObj:%A{schemaObj}"
 
-                        let isRequired = schemaObjRequired.Contains propName
+                        // Check if the property is nullable (OpenAPI 3.0 nullable becomes Null type flag in 3.1)
+                        let isNullable = isSchemaNullable propSchema
+
+                        // A property is "required" for type generation if it's in the required list AND not nullable.
+                        // Nullable properties must be wrapped as Option<T>/Nullable<T> to represent null values,
+                        // even if they're in the required list (required + nullable means must be present but can be null).
+                        let isRequired = schemaObjRequired.Contains propName && not isNullable
 
                         let pTy =
                             compileBySchema ns (ns.ReserveUniqueName tyName (nicePascalName propName)) propSchema isRequired ns.RegisterType false
@@ -303,14 +315,17 @@ type DefinitionCompiler(schema: OpenApiDocument, provideNullable) as this =
                 let ctorParams, fields =
                     let required, optional =
                         List.zip (List.ofSeq schemaObjProperties) members
-                        |> List.partition(fun (x, _) -> schemaObjRequired.Contains x.Key)
+                        |> List.partition(fun (x, _) ->
+                            let isNullable = isSchemaNullable x.Value
+                            schemaObjRequired.Contains x.Key && not isNullable)
 
                     required @ optional
                     |> List.map(fun (x, (f, p)) ->
                         let paramName = niceCamelName p.Name
+                        let isNullable = isSchemaNullable x.Value
 
                         let prParam =
-                            if schemaObjRequired.Contains x.Key then
+                            if schemaObjRequired.Contains x.Key && not isNullable then
                                 ProvidedParameter(paramName, f.FieldType)
                             else
                                 let paramDefaultValue = this.GetDefaultValue f.FieldType

tests/SwaggerProvider.ProviderTests/Schemas/v3/nullable-date.yaml

@@ -0,0 +1,31 @@
+openapi: 3.0.0
+info:
+  title: Nullable Date Test API
+  version: 1.0.0
+paths:
+  /test:
+    get:
+      operationId: getTest
+      responses:
+        '200':
+          description: Success
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/PersonDto'
+components:
+  schemas:
+    PersonDto:
+      type: object
+      required:
+        - id
+        - name
+      properties:
+        id:
+          type: string
+        name:
+          type: string
+        birthDate:
+          type: string
+          format: date
+          nullable: true

tests/SwaggerProvider.ProviderTests/SwaggerProvider.ProviderTests.fsproj

@@ -26,6 +26,7 @@
     <Compile Include="v3\Swagger.I0181.Tests.fs" />
     <Compile Include="v3\Swagger.I0219.Tests.fs" />
     <Compile Include="v3\Swagger.I0279.Tests.fs" />
+    <Compile Include="v3\Swagger.NullableDate.Tests.fs" />
     <Compile Include="v3\Swashbuckle.ReturnControllers.Tests.fs" />
     <Compile Include="v3\Swashbuckle.ReturnTextControllers.Tests.fs" />
     <Compile Include="v3\Swashbuckle.UpdateControllers.Tests.fs" />

tests/SwaggerProvider.ProviderTests/v3/Swagger.NullableDate.Tests.fs

@@ -0,0 +1,86 @@
+module Swagger.NullableDate.Tests
+
+open SwaggerProvider
+open Xunit
+open FsUnitTyped
+open System.Text.Json
+open System.Text.Json.Serialization
+
+[<Literal>]
+let Schema = __SOURCE_DIRECTORY__ + "/../Schemas/v3/nullable-date.yaml"
+
+type TestApi = OpenApiClientProvider<Schema>
+
+[<Fact>]
+let ``PersonDto should have nullable birthDate property``() =
+    let personType = typeof<TestApi.PersonDto>
+    let birthDateProp = personType.GetProperty("BirthDate")
+    birthDateProp |> shouldNotEqual null
+
+    // The property should be Option<DateTimeOffset> (default) or Nullable<DateTimeOffset> (with PreferNullable=true)
+    let propType = birthDateProp.PropertyType
+    propType.IsGenericType |> shouldEqual true
+
+    let genericTypeDef = propType.GetGenericTypeDefinition()
+
+    let hasNullableWrapper =
+        genericTypeDef = typedefof<Option<_>>
+        || genericTypeDef = typedefof<System.Nullable<_>>
+
+    hasNullableWrapper |> shouldEqual true
+
+[<Fact>]
+let ``PersonDto can deserialize JSON with null birthDate using type provider deserialization``() =
+    // This JSON is from the issue - a person with null birthDate
+    let jsonWithNullBirthDate =
+        """{
+    "id": "04a38328-4202-44ef-9f2b-ee85b1cd1a48",
+    "name": "Test",
+    "birthDate": null
+}"""
+
+    // Use the same deserialization code as the type provider (System.Text.Json with JsonFSharpConverter)
+    let options = JsonSerializerOptions()
+    options.Converters.Add(JsonFSharpConverter())
+
+    // Deserialize - this should not throw
+    let person =
+        JsonSerializer.Deserialize<TestApi.PersonDto>(jsonWithNullBirthDate, options)
+
+    // Verify the properties
+    person.Id |> shouldEqual "04a38328-4202-44ef-9f2b-ee85b1cd1a48"
+    person.Name |> shouldEqual "Test"
+    person.BirthDate |> shouldEqual None
+
+[<Fact>]
+let ``PersonDto can deserialize JSON with valid birthDate using type provider deserialization``() =
+    // Test with a valid date value
+    let jsonWithValidBirthDate =
+        """{
+    "id": "test-id-123",
+    "name": "John Doe",
+    "birthDate": "1990-05-15"
+}"""
+
+    // Use the same deserialization code as the type provider
+    let options = JsonSerializerOptions()
+    options.Converters.Add(JsonFSharpConverter())
+
+    // Deserialize
+    let person =
+        JsonSerializer.Deserialize<TestApi.PersonDto>(jsonWithValidBirthDate, options)
+
+    // Verify the properties
+    person.Id |> shouldEqual "test-id-123"
+    person.Name |> shouldEqual "John Doe"
+
+    // BirthDate should be Some value
+    person.BirthDate |> shouldNotEqual None
+
+    match person.BirthDate with
+    | Some date ->
+        // Verify the date is correct (1990-05-15)
+        date.Year |> shouldEqual 1990
+        date.Month |> shouldEqual 5
+        date.Day |> shouldEqual 15
+    | None -> failwith "Expected Some date but got None"