[BUG][SWIFT6] unalias additionalProperties before building map type declaration

A nested map property whose additionalProperties is a $ref to an aliased
map schema (e.g. StringMap = type: object, additionalProperties: { type:
string }) resolved to `[String: Dictionary]` (no generic args, doesn't
compile in Swift 6) instead of `[String: [String: String]]`.

Wrap ModelUtils.getAdditionalProperties(p) with unaliasSchema(...) in
getTypeDeclaration so the alias resolves to the actual schema before
recursion.

Closes #23666

Author: winrid

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/Swift6ClientCodegen.java

@@ -753,7 +753,7 @@ public String getTypeDeclaration(Schema p) {
             Schema inner = ModelUtils.getSchemaItems(p);
             return ModelUtils.isSet(p) ? "Set<" + getTypeDeclaration(inner) + ">" : "[" + getTypeDeclaration(inner) + "]";
         } else if (ModelUtils.isMapSchema(p)) {
-            Schema inner = ModelUtils.getAdditionalProperties(p);
+            Schema inner = unaliasSchema(ModelUtils.getAdditionalProperties(p));
             return "[String: " + getItemsTypeDeclaration(inner) + "]";
         }
         return super.getTypeDeclaration(p);

modules/openapi-generator/src/test/java/org/openapitools/codegen/swift6/Swift6ClientCodegenModelTest.java

@@ -25,9 +25,12 @@
 import org.openapitools.codegen.DefaultCodegen;
 import org.openapitools.codegen.TestUtils;
 import org.openapitools.codegen.languages.Swift6ClientCodegen;
+import org.openapitools.codegen.utils.ModelUtils;
 import org.testng.Assert;
 import org.testng.annotations.Test;
 
+import java.util.Map;
+
 @SuppressWarnings("static-method")
 public class Swift6ClientCodegenModelTest {
 
@@ -163,4 +166,26 @@ public void useCustomDateTimeTest() {
         Assert.assertFalse(property7.isContainer);
     }
 
+    @Test(description = "nested map via $ref should resolve to [String: [String: String]], not [String: Dictionary]", enabled = true)
+    public void nestedMapRefTypeTest() {
+        final OpenAPI openAPI = TestUtils.parseFlattenSpec("src/test/resources/3_0/swift6_nested_map.yaml");
+        final Swift6ClientCodegen codegen = new Swift6ClientCodegen();
+        codegen.setOpenAPI(openAPI);
+        codegen.processOpts();
+
+        Map<String, Schema> schemas = ModelUtils.getSchemas(openAPI);
+        Schema emailTemplateSchema = schemas.get("EmailTemplate");
+        Assert.assertNotNull(emailTemplateSchema, "EmailTemplate schema should exist");
+
+        final CodegenModel cm = codegen.fromModel("EmailTemplate", emailTemplateSchema);
+
+        CodegenProperty translationProp = cm.vars.stream()
+                .filter(p -> p.baseName.equals("translationOverridesByLocale"))
+                .findFirst().orElse(null);
+        Assert.assertNotNull(translationProp, "translationOverridesByLocale property should exist");
+        // Must be [String: [String: String]], NOT [String: Dictionary]
+        Assert.assertEquals(translationProp.dataType, "[String: [String: String]]",
+                "Nested map via $ref should resolve to [String: [String: String]]");
+    }
+
 }

modules/openapi-generator/src/test/resources/3_0/swift6_nested_map.yaml

@@ -0,0 +1,29 @@
+openapi: 3.0.0
+info:
+  title: Nested Map Type Test
+  version: 1.0.0
+paths: {}
+components:
+  schemas:
+    StringMap:
+      type: object
+      additionalProperties:
+        type: string
+      description: A map of string to string
+    EmailTemplate:
+      type: object
+      required:
+        - id
+        - ejs
+      properties:
+        id:
+          type: string
+        ejs:
+          type: string
+        translationOverridesByLocale:
+          $ref: '#/components/schemas/NestedStringMap'
+    NestedStringMap:
+      type: object
+      additionalProperties:
+        $ref: '#/components/schemas/StringMap'
+      description: A map of string to map of string to string