feat: generate .default() in OpenAPI for fields with default

Author: qwuide

docs/guide/representations/attributes/encode-decode.md

@@ -88,12 +88,20 @@ attribute :name, empty: true, writable: true
 
 The database stores `NULL` for missing values, but the frontend expects empty strings. `empty: true` handles the conversion.
 
-In the Zod export, `empty: true` produces `default('')` instead of `nullable()`:
+In exports, `empty: true` produces a default empty string instead of `nullable`:
 
 ```typescript
+// Zod
 name: z.string().default('')
 ```
 
+```yaml
+# OpenAPI
+name:
+  type: string
+  default: ''
+```
+
 ## Examples
 
 - [Value Transforms](/examples/value-transforms) — Transform values during serialization and handle nil/empty conversion

docs/guide/types/modifiers.md

@@ -121,7 +121,7 @@ interface Example {
 const ExampleSchema = z.object({
   title: z.string().min(1).max(255),
   count: z.number().int().min(0).optional(),
-  notes: z.string().nullable().optional(),
+  notes: z.string().nullable().default(null),
 });
 ```
 

lib/apiwork/export/open_api.rb

@@ -324,6 +324,12 @@ def map_field(param)
 
         schema[:format] = param.format.to_s if param.formattable? && param.format
 
+        if param.respond_to?(:default) && !param.default.nil?
+          schema[:default] = param.default
+        elsif param.optional? && param.nullable?
+          schema[:default] = nil
+        end
+
         apply_nullable(schema, param.nullable?)
       end
 

spec/apiwork/export/open_api_spec.rb

@@ -52,6 +52,9 @@
           string :old_field, deprecated: true
           string :email, format: :email
           integer :min_field, max: 100, min: 0
+          boolean :archived, default: false, optional: true
+          string :category, default: 'general', optional: true
+          string :memo, nullable: true, optional: true
         end
 
         object :receipt do
@@ -237,6 +240,26 @@
       end
     end
 
+    context 'with default values' do
+      it 'includes null default for nullable optional field' do
+        property = schemas['invoice'][:properties]['memo']
+
+        expect(property[:default]).to be_nil
+      end
+
+      it 'includes boolean default' do
+        property = schemas['invoice'][:properties]['archived']
+
+        expect(property[:default]).to be(false)
+      end
+
+      it 'includes string default' do
+        property = schemas['invoice'][:properties]['category']
+
+        expect(property[:default]).to eq('general')
+      end
+    end
+
     context 'with object types' do
       it 'generates properties and required fields' do
         invoice_schema = schemas['invoice']