Problem statement

I run following command to generate swagger spec but it just prints 3 lines of yaml to swagger.yaml

command: swagger generate spec -o ./swagger.yaml

yaml output:
info: {}
paths: {}
swagger: "2.0"

comments added to main file:
// Package classification Petstore API.
//
// the purpose of this application is to provide an application
// that is using plain go code to define an API
//
// This should demonstrate all the possible comment annotations
// that are available to turn go code into a fully compliant swagger 2.0 spec
//
// Terms Of Service:
//
// there are no TOS at this moment, use at your own risk we take no responsibility
//
// Schemes: http, https
// Host: localhost
// BasePath: /v2
// Version: 0.0.1
// License: MIT http://opensource.org/licenses/MIT
// Contact: John Doejohn.doe@example.com http://john.doe.com
//
// Consumes:
// - application/json
// - application/xml
//
// Produces:
// - application/json
// - application/xml
//
// Security:
// - api_key:
//
// SecurityDefinitions:
// api_key:
// type: apiKey
// name: KEY
// in: header
// oauth2:
// type: oauth2
// authorizationUrl: /oauth2/auth
// tokenUrl: /oauth2/token
// in: header
// scopes:
// bar: foo
// flow: accessCode
//
// Extensions:
// x-meta-value: value
// x-meta-array:
// - value1
// - value2
// x-meta-array-obj:
// - name: obj
// value: field
//
// swagger:meta

Environment

swagger version: v0.30.2
go version: 1.19.1
OS: macOS monterey 12.6