postupdate script

[Blacksmoke16]

Currently the postinstall script is ran for both install and update. I propose to only run postinstall on install and introduce a postupdate script to only run on update.

Use case would be preventing something you only need to run once on install from running every time a shard is updated.

[straight-shoota]

I don't think that makes much sense. If the behaviour of install changes between versions, you would need to reflect that in an update script. And that can be highly complex when switching forth and back between versions or concurrent branches. Going from one version to another is not always linear.

IMO it's just easier to have a single script that makes sure the final state is what the shard expects. This gives you all the power to do whatever necessary. You should strive for idempotency, not for separate instructions.

[Blacksmoke16]

I was more so thinking of this for like private shards used within a closed-source project. I.e. that may run internal build processes, such as creating rabbitMQ queues for example; things that should happen once on an env when installing the app. Then there are things that should happen when updating a dependency, like writing parameter files based on the current env.

Currently there isn't really a nice way to handle this within Crystal/shards itself.

EDIT: On a related note, it would be nice if it supported an array of commands that it should run:

postinstall:
  - cmd 1
  - cmd 2
  - ..

[jhass]

So you think to have your install script be idempotent, that is examining the current environment and only doing necessary changes, is too much to ask?

[ysbaddaden]

From the point of view of Shards, there are no updates, only installs. The only update is to build a new lockfile of shards that will be installed. When installing, if the folder exists it's deleted then the shard is installed and the postinstall script is eventually run (when all shards have been installed).

I think the postinstall script must be idempotent. Whatever if the shard was previously installed, whatever version of it was previously installed. You can never assume a previous state.

My worry with a postupdate script is that we either dont prevent postinstall to run, making postupdate pointless, or require every shard to also have a postupdate... that is identical to postinstall, which is just as pointless :-(

[ysbaddaden]

I believe that's the whole reason only the postinstall script was added. We only ever install a shard, and whatever the previous version did, it must be usually redone ror the new version, and it doesn't hurt (e.g. build a binary, install some script to the dependent project, ...). If it does hurt, then the script must check whether something was done or not before doing it.