Mechanisms to persist information (Re: Option to not automatically customize-save-variable `package-selected-packages')

["Clément Pit--Claudel" <clement.pit@gmail.com>]

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On 02/18/2016 11:49 AM, Eli Zaretskii wrote:
> This seems to be a general complaint about package.el using Custom to
> save the data about installed packages.  I see no arguments as to why
> it's wrong to use Custom for that.  After all, Custom is our standard
> way of saving customizations, so it could be argued that having a
> single mechanism through which to control where they are saved is
> better than inventing a separate mechanism just for package.el.

One thing that I would find convenient as a package developer is a notion of package-local storage. Right now, if I (as a package developer) want to persist information between Emacs sessions, I can either:

* Save the customization through Custom
* Create my own file in user-emacs-directory

The first one is unsuitable for persisted information that shouldn't be presented to the user (for example, if my package collects statistics, I don't want to change the custom file constantly and add large amounts of data to it). The second one in not uniform across packages, and forces me to invent my own storage format (some packages store a lisp form, other store a series of command that are just executed upon loading the file (viper, history), others use json or csv-like formats (as was suggested for package.el)).

In both cases, removing a package won't remove the storage that it uses (either in Custom or in separate files in .emacs.d). This is especially problematic when trying out packages: I launch a package to try it out, it initializes its backing store (often with a file, sometimes with an entry in custom-set-variables), then I remove it (if I don't like it), and yet the backing store is not removed. Take viper as an example (though viper is bundled with Emacs right now): launching it and allowing it to persist its settings creates a file ~/.emacs.d/viper.

It would be nice to have a uniform way to persist package-specific information; ideally one that would collaborate with package.el, so that removing a package would remove its stored state. One would need to figure out how to handle settings persisted through custom as well, but a simple key-value store that plays well with package.el would be a great start.

Clément.


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