Config migrator

[GideonBear]

There should be a config migration tool built into Topgrade that users can use to (while not preserving comments) migrate their config to v18.

Lots of config options will be removed in favour of flags/args, which we can migrate them to.

This tool:

• Will be built into Topgrade (topgrade migrate-config)
• Will be removed after a while
• Will make a backup of the old config file
• Does not need to preserve comments

We will want to test this with many different user's configs before releasing.

[jy549883]

I suggest preserving comments is some instances. I am thinking in the pre-, post-, and commands section specifically. But this applies to the disable and pre_sudo variables and installer customization like git.

More generally, comments that were present in the previous version can be replaced with the new comments, but any custom comments should be preserved.

I use those! Helps me keep track of why I made the changes and situations change requiring me to adapt accordingly.

I also suggest commenting out any active commands that do not apply anymore with a surrounding unique comment stating why the update commented them out.

So, basically I vote to not do an upgrade to the config fault. Instead just put a version number comment at the top and if it is not present or is incompatible fault out with a message that there is an incompatible configuration file with instructions how to fix or a link to a page giving instructions on how to fix. I would say most users are savvy enough to fix this problem themselves with a little instruction and notice.

[GideonBear]

To be clear, the intention was never to automatically migrate config files; but to add a topgrade migrate-config command (and a message to run that when you run topgrade v18 for the first time).

The v18 config file will be sufficiently differently structured that I don't think it's worth the effort to try to preserve comments. I think it's better to generate a config file that retains the same behavior, and let the user copy over comments themselves.