I'm a little confused with composer.lock used in an application with a repository.

I saw many people saying that we should not .gitignore composer.lock from the repository.

If I update my libraries in my dev environment, I will have a new composer.lock but I will not be able to update them into production, will I ?

Won't it generate conflicts on this file ?

If you update your libs, you want to commit the lockfile too. It basically states that your project is locked to those specific versions of the libs you are using.

If you commit your changes, and someone pulls your code and updates the dependencies, the lockfile should be unmodified. If it is modified, it means that you have a new version of something.

Having it in the repository assures you that each developer is using the same versions.