Is there a better way to explain this change? I read it multiple times, but I still have no idea about what the change is.

There is certainly always room for improvement but I don't know how to explain it better. A warning becomes an error. In other words, the command will fail with return code unequal zero. If you have never seen the mentioned warning, it is probably irrelevant to you.

I believe everyone using poetry saw the warning multiple times 🙂 I'm not sure why, but I thought that "upgrade" comes with other changes, and the text was missing them. After rereading it, it feels clearer now. Let me share my other confusions, and the jury can decide if they need any updates:

• I'm missing how the --no-update parameter is relevant. I checked the PR and the discussions but couldn't find any reference. The only thing I saw was "Run poetry lock [--no-update] to fix it. on an unedited line, which I believe makes better sense, emphasizing that it's just an optional parameter.
• This happened if dependencies were changed in the pyproject.toml without running This only covers a portion of the relevant cases shared by people on the PR. My understanding is the issue and the solution is more about the hash from the lock file not matching the relevant fields of the pyproject.toml file than which file was edited by whom or for which purpose.

Also, thanks to confusion at the time, I did a terrible job explaining myself in the first comment. I hope it's more clear now.

I rephrased the paragraph also considering the changed wording from python-poetry/poetry#8962. I hope it is clearer now. I still believe that changing something from warning to error can be called an upgrade but I am open to better wording. 😄