[Repo Assist] fix: resolve oneOf/anyOf with single $ref to referenced type

src/SwaggerProvider.DesignTime/v3/DefinitionCompiler.fs

@@ -410,7 +410,7 @@ type DefinitionCompiler(schema: OpenApiDocument, provideNullable, useDateOnly: b
                 ty :> Type
 
         let resolvedType =
-            // If schemaObj.Type is missing, but allOf is present andallOf subschema has one element, use that
+            // If schemaObj.Type is missing, but allOf/oneOf/anyOf is present with one subschema, use that
             if
                 not schemaObj.Type.HasValue
                 && not(isNull schemaObj.AllOf)
@@ -422,6 +422,28 @@ type DefinitionCompiler(schema: OpenApiDocument, provideNullable, useDateOnly: b
                     Some firstAllOf.Type.Value
                 else
                     None
+            else if
+                not schemaObj.Type.HasValue
+                && not(isNull schemaObj.OneOf)
+                && schemaObj.OneOf.Count = 1
+            then
+                let firstOneOf = schemaObj.OneOf.[0]
+
+                if not(isNull firstOneOf) && firstOneOf.Type.HasValue then
+                    Some firstOneOf.Type.Value
+                else
+                    None
+            else if
+                not schemaObj.Type.HasValue
+                && not(isNull schemaObj.AnyOf)
+                && schemaObj.AnyOf.Count = 1
+            then
+                let firstAnyOf = schemaObj.AnyOf.[0]
+
+                if not(isNull firstAnyOf) && firstAnyOf.Type.HasValue then
+                    Some firstAnyOf.Type.Value
+                else
+                    None
             else if schemaObj.Type.HasValue then
                 Some schemaObj.Type.Value
             else
@@ -475,6 +497,28 @@ type DefinitionCompiler(schema: OpenApiDocument, provideNullable, useDateOnly: b
                     ns.ReleaseNameReservation tyName
                     compileByPath <| getFullPath schemaRef.Reference.Id
                 | _ -> compileNewObject()
+            // Handle oneOf with single reference (resolves to the referenced type)
+            | _ when
+                not(isNull schemaObj.OneOf)
+                && schemaObj.OneOf.Count = 1
+                && (schemaObj.Properties |> isNull || schemaObj.Properties.Count = 0)
+                ->
+                match schemaObj.OneOf.[0] with
+                | :? OpenApiSchemaReference as schemaRef when not(isNull schemaRef.Reference) ->
+                    ns.ReleaseNameReservation tyName
+                    compileByPath <| getFullPath schemaRef.Reference.Id
+                | _ -> compileNewObject()
+            // Handle anyOf with single reference (resolves to the referenced type)
+            | _ when
+                not(isNull schemaObj.AnyOf)
+                && schemaObj.AnyOf.Count = 1
+                && (schemaObj.Properties |> isNull || schemaObj.Properties.Count = 0)
+                ->
+                match schemaObj.AnyOf.[0] with
+                | :? OpenApiSchemaReference as schemaRef when not(isNull schemaRef.Reference) ->
+                    ns.ReleaseNameReservation tyName
+                    compileByPath <| getFullPath schemaRef.Reference.Id
+                | _ -> compileNewObject()
             | _ when
                 resolvedType.IsNone
                 || resolvedType = Some JsonSchemaType.Object

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

@@ -256,6 +256,100 @@ let ``allOf $ref to integer alias resolves to int32``() =
     let ty = compileAllOfRefType "      type: integer\n" true
     ty |> shouldEqual typeof<int32>
 
+// ── $ref to primitive-type alias (via oneOf wrapper) ─────────────────────────
+// oneOf: [$ref] with a single entry is semantically equivalent to a direct $ref.
+// Some code generators (e.g., NSwag, Kiota) emit this form.
+
+/// Compile a schema where `TestType.Value` uses `oneOf: [$ref]` to reference a component alias.
+let private compileOneOfRefType (aliasYaml: string) (required: bool) : Type =
+    let requiredBlock =
+        if required then
+            "      required:\n        - Value\n"
+        else
+            ""
+
+    let schemaStr =
+        sprintf
+            """openapi: "3.0.0"
+info:
+  title: OneOfRefAliasTest
+  version: "1.0.0"
+paths: {}
+components:
+  schemas:
+    AliasType:
+%s    TestType:
+      type: object
+%s      properties:
+        Value:
+          oneOf:
+            - $ref: '#/components/schemas/AliasType'
+"""
+            (aliasYaml.TrimEnd() + "\n")
+            requiredBlock
+
+    compileSchemaAndGetValueType schemaStr
+
+/// Compile a schema where `TestType.Value` uses `anyOf: [$ref]` to reference a component alias.
+let private compileAnyOfRefType (aliasYaml: string) (required: bool) : Type =
+    let requiredBlock =
+        if required then
+            "      required:\n        - Value\n"
+        else
+            ""
+
+    let schemaStr =
+        sprintf
+            """openapi: "3.0.0"
+info:
+  title: AnyOfRefAliasTest
+  version: "1.0.0"
+paths: {}
+components:
+  schemas:
+    AliasType:
+%s    TestType:
+      type: object
+%s      properties:
+        Value:
+          anyOf:
+            - $ref: '#/components/schemas/AliasType'
+"""
+            (aliasYaml.TrimEnd() + "\n")
+            requiredBlock
+
+    compileSchemaAndGetValueType schemaStr
+
+[<Fact>]
+let ``oneOf $ref to string alias resolves to string``() =
+    let ty = compileOneOfRefType "      type: string\n" true
+    ty |> shouldEqual typeof<string>
+
+[<Fact>]
+let ``oneOf $ref to integer alias resolves to int32``() =
+    let ty = compileOneOfRefType "      type: integer\n" true
+    ty |> shouldEqual typeof<int32>
+
+[<Fact>]
+let ``anyOf $ref to string alias resolves to string``() =
+    let ty = compileAnyOfRefType "      type: string\n" true
+    ty |> shouldEqual typeof<string>
+
+[<Fact>]
+let ``anyOf $ref to integer alias resolves to int32``() =
+    let ty = compileAnyOfRefType "      type: integer\n" true
+    ty |> shouldEqual typeof<int32>
+
+[<Fact>]
+let ``optional oneOf $ref to integer alias resolves to Option<int32>``() =
+    let ty = compileOneOfRefType "      type: integer\n" false
+    ty |> shouldEqual typeof<int32 option>
+
+[<Fact>]
+let ``optional anyOf $ref to integer alias resolves to Option<int32>``() =
+    let ty = compileAnyOfRefType "      type: integer\n" false
+    ty |> shouldEqual typeof<int32 option>
+
 // ── Optional $ref to primitive-type alias ─────────────────────────────────────
 // When a $ref/allOf alias property is non-required, value types must be wrapped
 // in Option<T> consistent with the behaviour of ordinary optional primitive properties.