[Repo Assist] feat: add WrapNullableStrings static parameter to OpenApiClientProvider

src/SwaggerProvider.DesignTime/Provider.OpenApiClient.fs

@@ -49,7 +49,8 @@ type public OpenApiClientTypeProvider(cfg: TypeProviderConfig) as this =
               ProvidedStaticParameter("PreferNullable", typeof<bool>, false)
               ProvidedStaticParameter("PreferAsync", typeof<bool>, false)
               ProvidedStaticParameter("SsrfProtection", typeof<bool>, true)
-              ProvidedStaticParameter("IgnoreParseErrors", typeof<bool>, false) ]
+              ProvidedStaticParameter("IgnoreParseErrors", typeof<bool>, false)
+              ProvidedStaticParameter("WrapNullableStrings", typeof<bool>, false) ]
 
         t.AddXmlDoc
             """<summary>Statically typed OpenAPI provider.</summary>
@@ -59,7 +60,8 @@ type public OpenApiClientTypeProvider(cfg: TypeProviderConfig) as this =
                <param name='PreferNullable'>Provide `Nullable<_>` for not required properties, instead of `Option<_>`. Defaults value `false`.</param>
                <param name='PreferAsync'>Generate async actions of type `Async<'T>` instead of `Task<'T>`. Defaults value `false`.</param>
                <param name='SsrfProtection'>Enable SSRF protection (blocks HTTP and localhost). Set to false for development/testing. Default value `true`.</param>
-               <param name='IgnoreParseErrors'>Continue generating the provider even when the OpenAPI parser reports validation errors (e.g. vendor extensions or non-strictly-compliant schemas). Warnings are printed to stderr. Default value `false`.</param>"""
+               <param name='IgnoreParseErrors'>Continue generating the provider even when the OpenAPI parser reports validation errors (e.g. vendor extensions or non-strictly-compliant schemas). Warnings are printed to stderr. Default value `false`.</param>
+               <param name='WrapNullableStrings'>Wrap optional/nullable string fields as `Option&lt;string&gt;` instead of plain `string`. Matches the treatment of other optional types. Default value `false`.</param>"""
 
         t.DefineStaticParameters(
             staticParams,
@@ -71,6 +73,7 @@ type public OpenApiClientTypeProvider(cfg: TypeProviderConfig) as this =
                 let preferAsync = unbox<bool> args.[4]
                 let ssrfProtection = unbox<bool> args.[5]
                 let ignoreParseErrors = unbox<bool> args.[6]
+                let wrapNullableStrings = unbox<bool> args.[7]
 
                 // Cache key includes cfg.RuntimeAssembly, cfg.ResolutionFolder, and cfg.SystemRuntimeAssemblyVersion
                 // to differentiate between different TFM builds (same approach as FSharp.Data)
@@ -83,6 +86,7 @@ type public OpenApiClientTypeProvider(cfg: TypeProviderConfig) as this =
                      preferAsync,
                      ssrfProtection,
                      ignoreParseErrors,
+                     wrapNullableStrings,
                      cfg.RuntimeAssembly,
                      cfg.ResolutionFolder,
                      cfg.SystemRuntimeAssemblyVersion)
@@ -119,7 +123,9 @@ type public OpenApiClientTypeProvider(cfg: TypeProviderConfig) as this =
                             |> Seq.toList
 
                         let useDateOnly = cfg.SystemRuntimeAssemblyVersion.Major >= 6
-                        let defCompiler = DefinitionCompiler(schema, preferNullable, useDateOnly)
+
+                        let defCompiler =
+                            DefinitionCompiler(schema, preferNullable, useDateOnly, wrapNullableStrings)
 
                         let opCompiler =
                             OperationCompiler(schema, defCompiler, ignoreControllerPrefix, ignoreOperationId, preferAsync)

src/SwaggerProvider.DesignTime/v3/DefinitionCompiler.fs

@@ -165,7 +165,9 @@ and NamespaceAbstraction(name: string) =
                 Some ty)
 
 /// Object for compiling definitions.
-type DefinitionCompiler(schema: OpenApiDocument, provideNullable, useDateOnly: bool) as this =
+type DefinitionCompiler(schema: OpenApiDocument, provideNullable, useDateOnly: bool, ?wrapNullableStrings: bool) as this =
+    let wrapNullableStrings = defaultArg wrapNullableStrings false
+
     let pathToSchema =
         let dict = Collections.Generic.Dictionary<string, IOpenApiSchema>()
 
@@ -538,6 +540,8 @@ type DefinitionCompiler(schema: OpenApiDocument, provideNullable, useDateOnly: b
                     typedefof<Option<obj>>
 
             ProvidedTypeBuilder.MakeGenericType(baseGenTy, [ tyType ])
+        else if wrapNullableStrings && tyType = typeof<string> then
+            ProvidedTypeBuilder.MakeGenericType(typedefof<Option<obj>>, [ tyType ])
         else
             tyType
 

tests/SwaggerProvider.Tests/v3/Schema.TestHelpers.fs

@@ -67,3 +67,52 @@ components:
             propYaml
 
     compileSchemaAndGetValueType schemaStr
+
+/// Compile a minimal v3 schema using the given DefinitionCompiler options.
+let compilePropertyTypeWith (propYaml: string) (required: bool) (provideNullable: bool) (wrapNullableStrings: bool) : Type =
+    let requiredBlock =
+        if required then
+            "      required:\n        - Value\n"
+        else
+            ""
+
+    let schemaStr =
+        sprintf
+            """openapi: "3.0.0"
+info:
+  title: TypeMappingTest
+  version: "1.0.0"
+paths: {}
+components:
+  schemas:
+    TestType:
+      type: object
+%s      properties:
+        Value:
+%s"""
+            requiredBlock
+            propYaml
+
+    let settings = OpenApiReaderSettings()
+    settings.AddYamlReader()
+
+    let readResult =
+        Microsoft.OpenApi.OpenApiDocument.Parse(schemaStr, settings = settings)
+
+    let schema =
+        match readResult.Document with
+        | null -> failwith "Failed to parse OpenAPI schema: Document is null."
+        | doc -> doc
+
+    let defCompiler =
+        DefinitionCompiler(schema, provideNullable, false, wrapNullableStrings)
+
+    let opCompiler = OperationCompiler(schema, defCompiler, true, false, true)
+    opCompiler.CompileProvidedClients(defCompiler.Namespace)
+
+    let types = defCompiler.Namespace.GetProvidedTypes()
+    let testType = types |> List.find(fun t -> t.Name = "TestType")
+
+    match testType.GetDeclaredProperty("Value") with
+    | null -> failwith "Property 'Value' not found on TestType"
+    | prop -> prop.PropertyType

tests/SwaggerProvider.Tests/v3/Schema.TypeMappingTests.fs

@@ -279,3 +279,33 @@ let ``optional allOf $ref to integer alias resolves to Option<int32>``() =
 let ``optional allOf $ref to int64 alias resolves to Option<int64>``() =
     let ty = compileAllOfRefType "      type: integer\n      format: int64\n" false
     ty |> shouldEqual typeof<int64 option>
+
+// ── WrapNullableStrings option ───────────────────────────────────────────────
+
+[<Fact>]
+let ``optional string without WrapNullableStrings maps to plain string``() =
+    let ty = compilePropertyType "          type: string\n" false
+    ty |> shouldEqual typeof<string>
+
+[<Fact>]
+let ``optional string with WrapNullableStrings maps to string option``() =
+    let ty = compilePropertyTypeWith "          type: string\n" false false true
+    ty |> shouldEqual typeof<string option>
+
+[<Fact>]
+let ``required string with WrapNullableStrings still maps to plain string``() =
+    let ty = compilePropertyTypeWith "          type: string\n" true false true
+    ty |> shouldEqual typeof<string>
+
+[<Fact>]
+let ``optional string date-time with WrapNullableStrings maps to DateTimeOffset option``() =
+    // Non-string reference types (DateTimeOffset is a value type) unaffected by WrapNullableStrings
+    let ty =
+        compilePropertyTypeWith "          type: string\n          format: date-time\n" false false true
+
+    ty |> shouldEqual typeof<DateTimeOffset option>
+
+[<Fact>]
+let ``optional integer with WrapNullableStrings still maps to int32 option``() =
+    let ty = compilePropertyTypeWith "          type: integer\n" false false true
+    ty |> shouldEqual typeof<int32 option>