Poetry install and update resolve versions differently when requirements aren't pinned

• 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: Debian running in WSL2
• Poetry version: 1.1.0b2
• Link of a Gist with the contents of your pyproject.toml file: https://gist.github.com/iserko/ae0b5240bdb6af0a63264f834a3b4bee

Issue

Using the pyproject.toml I can run poetry install (log) and get the latest dbt installed (at the time that’s 0.17.2), but then when I run poetry update (log) it downgrades dbt and updates requests.

The workaround for this is to pin dbt to dbt = "^0.17.2", however I was surprised to see poetry just downgrade.

[radoering]

From #6470:

I would expect the code paths to be equivalent and poetry update to basically be a fancy poetry lock && poetry install, though I acknowledge that’s probably naive.

For those who are interested:

poetry lock ignores an existing lock file and creates a new lock file from scratch. poetry update takes a whitelist of packages to update. That’s why it’s more like a poetry lock --no-update except for the whitelisted packages. It considers an existing lock file and tries not to update packages that are not on the whitelist. If you don’t pass any names to poetry update all locked packages are on the whitelist, but the lockfile is still taken into consideration which can result in a different resolution order.

I drafted #6477 to make poetry update more determistic and similar to poetry lock.

[JacobHayes]

There’s a reproducible example in https://github.com/python-poetry/poetry/issues/6470, as of today at least.