Re: Suggestion: convert dispatchers to use transient

[João Pedro de Amorim Paula]

On 04 February 2022 08:30, Tim Cross <theophilusx@gmail.com> wrote:

> I'm assuming it is, but I have to admit I'm still not 100% clear on
> how Emacs handles the situation where you use a library that is both
> built-in and available in ELPA. Does Emacs use the latest version
> available or does it use the built-in version until you explicitly
> select the ELPA versions?

Welp, I happened to ponder the same question after trying to implement a
function to install packages that are not installed already (I'm not
using any helper configuration such as use-package, which would already
handle this). From what I gathered empirically, it appears that if
something is built-in, Emacs' package.el won't try to install -- it
checks with package-installed-p on any call to package-install, which
checks if the package is built-in with package-built-in-p as a fallback
on cond --, but you can force installation from the archives by passing
a package description object (defined as package-desc on package.el)
instead of a symbol

    (let ((pkg-desc (assq 'org package-archive-contents)))
      (package-install pkg-desc))

and Emacs seems to be loading the newest version when it is a dependency
of something else. Though I'm not really sure, as most of the packages I
have from ELPA have the same version as the ones built-in on Emacs
28.0.91. I'll try and install Emacs 27 to check this out.

In the mean time, I guess this would be a good opportunity to share a
couple of functions I have with the purpose of installing packages.

    (defun pkg-description (package)
      "Return the description for PACKAGE.
    If PACKAGE is installed, the will be present on `package-alist',
    otherwise look for it in `package-archive-contents'."
      (or (cadr (assoc package package-alist))
          (cadr (assoc package package-archive-contents))))

    (defun pkg-ensure-archive (package)
      "Install PACKAGE from the archives, if not already installed."
      (when-let ((pkg-desc (pkg-description package)))
        (unless (package-installed-p pkg-desc)
          (package-install-from-archive pkg-desc))))

    (defun require-package (package &optional force)
      "Ensure that PACKAGE is installed.
    If FORCE is non-nil, force installation regardless if PACKAGE is
    built-in or not.

    First, use `package-installed-p' to check if PACKAGE was
    installed via the Emacs package manager, otherwise, try to
    `require' PACKAGE; this ensures that we don't require PACKAGE if
    it was installed using the package manager. If both of those
    fail, run `package-refresh-contents' and install PACKAGE."
      (unless (and (not force)
                   (or (package-installed-p package)
                       (require package nil 'no-error)))
        (unless (assoc package package-archive-contents)
          (package-refresh-contents))
        (if force
            (pkg-ensure-archive package)
          (package-install package))))

On the last one, the main function that I use, if FORCE is non-nil it
will download and install the package from the archives even if it is
built-in.

Best regards,

-- 
João Pedro de Amorim Paula
IT undergraduate at Universidade Federal do Rio Grande do Norte (UFRN)