Fix schema gathering oversight (oapi-codegen#2219)

Response and RequestBodies need to include any additional types
into model generation. This is an ancient bug, from the very
first days of oapi-codegen.

Extend the issue-200 spec with inline objects containing
additionalProperties inside components/responses and
components/requestBodies. The test confirms the codegen produces
named types (Bar_Pagination, Bar_Metadata) for these inline schemas.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: mromaszewicz

internal/test/issues/issue-200/issue200.gen.go

@@ -35,6 +35,21 @@ func TestDuplicateTypeNamesCompile(t *testing.T) {
 	// RequestBody type: BarRequestBody (was "Bar" in components/requestBodies)
 	_ = BarRequestBody{Value: ptr(42)}
 
+	// Inline nested object with additionalProperties inside a response
+	// must produce a named AdditionalType (not get silently dropped).
+	_ = Bar_Pagination{
+		Page:                 ptr(1),
+		TotalPages:           ptr(10),
+		AdditionalProperties: map[string]string{"cursor": "abc"},
+	}
+
+	// Inline nested object with additionalProperties inside a requestBody
+	// must produce a named AdditionalType (not get silently dropped).
+	_ = Bar_Metadata{
+		Key:                  ptr("k"),
+		AdditionalProperties: map[string]string{"extra": "val"},
+	}
+
 	// Operation-derived types
 	_ = PostFooParams{Bar: &Bar{}}
 	_ = PostFooJSONBody{Value: ptr(99)}

internal/test/issues/issue-200/issue200_test.go

@@ -58,6 +58,13 @@ components:
             properties:
               value:
                 type: integer
+              metadata:
+                type: object
+                properties:
+                  key:
+                    type: string
+                additionalProperties:
+                  type: string
 
   responses:
     Bar:
@@ -78,3 +85,12 @@ components:
                 $ref: '#/components/schemas/BarParam'
               value4:
                 $ref: '#/components/schemas/BarParam2'
+              pagination:
+                type: object
+                properties:
+                  page:
+                    type: integer
+                  totalPages:
+                    type: integer
+                additionalProperties:
+                  type: string

internal/test/issues/issue-200/spec.yaml

@@ -714,6 +714,7 @@ func GenerateTypesForResponses(t *template.Template, responses openapi3.Response
 			}
 
 			types = append(types, typeDef)
+			types = append(types, goType.AdditionalTypes...)
 		}
 	}
 	return types, nil
@@ -762,6 +763,7 @@ func GenerateTypesForRequestBodies(t *template.Template, bodies map[string]*open
 				typeDef.TypeName = SchemaNameToTypeName(refType)
 			}
 			types = append(types, typeDef)
+			types = append(types, goType.AdditionalTypes...)
 		}
 	}
 	return types, nil