https://medium.com/@datvt9312/bb6aba1586ac

launch.json

{
    "version": "0.2.0",
    "configurations": [
      {
        "name": "Development",
        "request": "launch",
        "type": "dart",
        "program": "lib/main_development.dart",
        "args": [
          "--flavor",
          "development"
        ]
      },
      {
        "name": "Staging",
        "request": "launch",
        "type": "dart",
        "program": "lib/main_staging.dart",
        "args": [
          "--flavor",
          "staging"
        ]
      },
      {
        "name": "Production",
        "request": "launch",
        "type": "dart",
        "program": "lib/main_production.dart",
        "args": [
          "--flavor",
          "production"
        ]
      }
    ]
  }