Fix an empty array is turned into nullable object wrongly

lib/rspec/openapi/schema_builder.rb

@@ -125,7 +125,11 @@ def build_property(value, disposition: nil)
 
     case value
     when Array
-      property[:items] = build_property(value.first)
+      if value.empty?
+        property[:items] = {} # unknown
+      else
+        property[:items] = build_property(value.first)
+      end
     when Hash
       property[:properties] = {}.tap do |properties|
         value.each do |key, v|

spec/rails/app/controllers/images_controller.rb

@@ -4,4 +4,14 @@ def show
     QBoAAAAASUVORK5CYII='.unpack('m').first
     send_data png, type: 'image/png', disposition: 'inline'
   end
+
+  def index
+    list = [
+      {
+        'name': 'file.png',
+        'tags': [], # Keep this empty to check empty array is accepted
+      }
+    ]
+    render json: list
+  end
 end

spec/rails/config/routes.rb

@@ -3,7 +3,7 @@
 
   defaults format: 'json' do
     resources :tables, only: [:index, :show, :create, :update, :destroy]
-    resources :images, only: [:show]
+    resources :images, only: [:index, :show]
 
     get '/test_block' => ->(_env) { [200, { 'Content-Type' => 'text/plain' }, ['A TEST']] }
   end

spec/rails/doc/openapi.json

@@ -652,6 +652,47 @@
           }
         }
       }
+    },
+    "/images": {
+      "get": {
+        "summary": "index",
+        "tags": [
+          "Image"
+        ],
+        "responses": {
+          "200": {
+            "description": "can return an object with an attribute of empty array",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "type": "array",
+                  "items": {
+                    "type": "object",
+                    "properties": {
+                      "name": {
+                        "type": "string"
+                      },
+                      "tags": {
+                        "type": "array",
+                        "items": {
+                        }
+                      }
+                    }
+                  }
+                },
+                "example": [
+                  {
+                    "name": "file.png",
+                    "tags": [
+
+                    ]
+                  }
+                ]
+              }
+            }
+          }
+        }
+      }
     }
   }
 }

spec/rails/doc/openapi.yaml

@@ -93,7 +93,7 @@ paths:
                 database:
                   id: 2
                   name: production
-                null_sample:
+                null_sample: 
                 storage_size: 12.3
                 created_at: '2020-07-17T00:00:00+00:00'
                 updated_at: '2020-07-17T00:00:00+00:00'
@@ -169,7 +169,7 @@ paths:
                 database:
                   id: 2
                   name: production
-                null_sample:
+                null_sample: 
                 storage_size: 12.3
                 created_at: '2020-07-17T00:00:00+00:00'
                 updated_at: '2020-07-17T00:00:00+00:00'
@@ -222,7 +222,7 @@ paths:
                 database:
                   id: 2
                   name: production
-                null_sample:
+                null_sample: 
                 storage_size: 12.3
                 created_at: '2020-07-17T00:00:00+00:00'
                 updated_at: '2020-07-17T00:00:00+00:00'
@@ -314,7 +314,7 @@ paths:
                 database:
                   id: 2
                   name: production
-                null_sample:
+                null_sample: 
                 storage_size: 12.3
                 created_at: '2020-07-17T00:00:00+00:00'
                 updated_at: '2020-07-17T00:00:00+00:00'
@@ -366,7 +366,7 @@ paths:
                 database:
                   id: 2
                   name: production
-                null_sample:
+                null_sample: 
                 storage_size: 12.3
                 created_at: '2020-07-17T00:00:00+00:00'
                 updated_at: '2020-07-17T00:00:00+00:00'
@@ -426,3 +426,26 @@ paths:
               schema:
                 type: string
               example: AN ENGINE TEST
+  "/images":
+    get:
+      summary: index
+      tags:
+      - Image
+      responses:
+        '200':
+          description: can return an object with an attribute of empty array
+          content:
+            application/json:
+              schema:
+                type: array
+                items:
+                  type: object
+                  properties:
+                    name:
+                      type: string
+                    tags:
+                      type: array
+                      items: {}
+              example:
+              - name: file.png
+                tags: []

spec/requests/rails_spec.rb

@@ -116,6 +116,13 @@
       expect(response.status).to eq(200)
     end
   end
+
+  describe '#index' do
+    it 'can return an object with an attribute of empty array' do
+      get '/images'
+      expect(response.status).to eq(200)
+    end
+  end
 end
 
 RSpec.describe 'Extra routes', type: :request do