• I am on the latest Poetry version.

• I have searched the issues of this repo and believe that this is not a duplicate.

• If an exception occurs when executing a command, I executed it again in debug mode (-vvv option).

• OS version and name:
  DISTRIB_ID=Ubuntu
  DISTRIB_RELEASE=20.04

• Poetry version: Poetry version 1.0.10

• Link of a Gist with the contents of your pyproject.toml file: https://gist.github.com/ycd/2311f6e9a48cb7e1e8811c87247dc3a6

Issue

When adding a new dependency with poetry add example[extra1, extra2] it tries to override existing [build-system] and breaks it.

[build-system]
requires = ["poetry>=0.12"]
build-backend = "poetry.masonry.api"

Also streamable link: https://streamable.com/xwvej8