Support for deferred installation

[raxod502]

First cut at :defer-install keyword

This new keyword, if provided along with a non-nil value, causes the action
of :ensure to be deferred until "necessary". Package installation can be
triggered by the user calling the new interactive function
`use-package-install-deferred-package', or by the feature declared by the
`use-package' form being required. This latter behavior seems to be the
simplest way to make sure that package installation actually takes place
when it needs to, but it requires that an advice be added to `require',
which may be considered overly intrusive. (Also, it's generally considered
bad practice for functions in Emacs to put advice on other functions in
Emacs.) Thus it may make sense to add an option or function to explicitly
enable this behavior, if there does not turn out to be a better way to
accomplish deferred installation.

Documentation has not been updated to reflect :defer-install yet.

Considering how to address #409. I think that this is not the right
approach to take (esp. because autoloads are handled in the C code and
therefore do not respect the advice on require), but I thought I
would post my progress so far. I think I have an idea about how to
proceed.

NB: The text of this message is severely obsolete. I completely changed the implementation; in particular, there are no advices placed on require!

[raxod502]

It works! Here is a short demo: https://youtu.be/az5C1nd3fh0. (In case you are wondering about the text that is printed when I install the package, that is from my package manager—but this should work with package.el too.)

Usage looks like this:

(use-package swift-mode
  :defer-install t
  :mode "\\.swift\\'")

In theory, specifying :defer-install t should "just work", in that all entry points to loading the package normally created by use-package will now prompt the user to install the package before requiring the feature.

I'll be testing this in my own config. Comments and suggestions would be appreciated!

[raxod502]

I've realized that the confirmation prompt needs to be moved out of the use-package logic and into to the package-manager-specific :ensure function, since otherwise there is no way to only prompt the user if the package is not installed.

I'm currently working on this.

[raxod502]

It appears to be at least mostly working! I have integrated deferred installation with my config, and out of 52 packages only 25 are installed on initial Emacs launch.

[raxod502]

Wow, how did I base this branch on a four-week-old commit? I've fixed the merge conflicts.

[drot]

After this merge the :after keyword stopped working, if I have something like this:

(use-package info+
  :ensure t
  :after info)

info+ doesn't get loaded anymore.

[raxod502]

That's not good—:defer-install should not affect behavior at all unless you explicitly include it in the use-package form. Let me see if I can reproduce the issue.

[raxod502]

@drot Should be fixed now, it was a silly quoting error.

[raxod502]

Can you please add use-package-always-defer-install as use-package-always-defer for this feature?

This would be trivial to add via `use-package-defaults`. One thing to note though, is that autoloads are no longer automatically accessible when the package is yet to be installed (because obviously if the source code isn't on your hard drive, there's no way to tell what autoloaded commands the package provides). Same for `auto-mode-alist`, etc. So you have to set these by hand (using `:commands`, `:mode`, etc.) if you want to use deferred installation.

[blaenk]

Just found out about this through the commit log and I think it's pretty cool! Thanks for taking the initiative to implement it!

I was wondering if there's a way to have something like use-package-always-ensure, or some way to have behavior as "always assume :ensure t unless :ensure is explicitly present in a use-package form which specifies otherwise (e.g. nil or a package name), and beyond that assume :defer-install t so that the package is only installed if it's needed because e.g. it was required, unless the use-package form explicitly has :defer-install nil or something."

So I guess said another way, assume :defer-install t unless it's overridden in the use-package declaration, and otherwise assume :ensure t in a similar manner (as already covered by use-package-always-ensure).

I was reading through the diff's elisp doc strings but couldn't figure out if this was already possible. If not, is it even possible? Or aside from that, is there a reason why that would be inadvisable?

[raxod502]

@blaenk This is a trivial change so I made a pull request, see #443. One thing to note is that :defer-install t does nothing unless :ensure t is also given (or, of course, use-package-always-ensure is non-nil).

[TrunovS]

@raxod502 It seems that change removed from master now. Is deferred install now possible in another way?

[raxod502]

No, there's no way to achieve this behavior. If the feature were to be reimplemented, it should be done at the package-manager level, in my opinion. The ideal place would be straight.el, where there is already a mechanism for saving autoloads persistently (sort of) and it would be easy to extend the existing code to generate deferred-installation stubs for all entry points to the package, not just the ones mentioned in use-package: a better solution.