Force locking a specific version without adjusting constraints in pyproject.toml

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

Feature Request

I have pyproject.toml and poetry.lock files and I'd like to be able to update the poetry.lock file so it uses a specific version of package without having to set or update an explicit constraint in the pyproject.toml file.

For example, I have the following in my pyproject.toml:

[tool.poetry.dependencies]
torch = "^1.3"

I want to update my poetry.lock file to use torch 1.5.0 but still use the ^1.3 constraint. While I can certainly run poetry update --lock torch, this will install the latest constraint compatible version of torch which would be 1.6.0.

The way I think about this is that I want to be able to set an additional constraint that would further limit which torch (and associated packages) would be considered during the poetry update --lock torch call.

Context

I'm building a docker image where I already have torch pinned at a certain version. When I install the poetry dependencies, the poetry.lock file needs to have a corresponding version as to not download torch again at a different version.

If I can run a command such as poetry update --lock torch==1.6.0 prior to poetry install, then I can easily make torch version specific images.

I also want to specify torch in the pyproject.toml file because it is a dependency of the project itself, which can be used as a package in other projects. Stating that torch is a dependency in some documentation instead of an explicit dependency isn't a great solution.

Start with the pyproject.toml and poetry.lock workflow described in the issue, then trace the poetry update --lock command and its package-version handling. Determine how an additional version constraint should interact with the existing ^1.3 constraint and related packages; done means the lock file selects the requested compatible version without changing pyproject.toml.