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Re: feature/package-vc has been merged

From: Eli Zaretskii
Subject: Re: feature/package-vc has been merged
Date: Sat, 05 Nov 2022 19:22:33 +0200

> From: Philip Kaludercic <philipk@posteo.net>
> Cc: monnier@iro.umontreal.ca,  rms@gnu.org,  emacs-devel@gnu.org
> Date: Sat, 05 Nov 2022 16:43:45 +0000
> >> (defcustom package-vc-repository-store
> >>   (expand-file-name "emacs/vc-packages" (xdg-data-home))
> >>   "Directory used by `package-vc--unpack' to store repositories."
> >
> > The doc string of a user option should not reference an internal
> > function, it should reference user-visible features.  Would it be
> > correct to say that this directory is used by package-vc to store
> > repositories of packages it fetches and/or installs?
> You are right, I forgot about this when renaming package-vc-unpack to
> package-vc--unpack.  How about
>   "Directory used to store clone repositories.  
> This directory is only used for packages with a special `:lisp-dir'
> entry in their package specification (for details on package
> specifications see `package-vc-selected-packages').  Repositories for
> packages like these are cloned into the directory specified here, and
> their `:lisp-dir' is then linked back into the user elpa directory."

Instead of "specified here", please use "specified by this variable".
And I don't think I understand what the "their `:lisp-dir' is then
linked back into the user elpa directory" part wants to say.

I also have a more general question: you say this "is only used for
packages with a special `:lisp-dir' entry", and that begs the
question: where will we clone a package that doesn't have the
:lisp-dir entry?

> >> (defcustom package-vc-selected-packages '()
> >>   "List of packages that must be installed.
> >> Each member of the list is of the form (NAME . SPEC), where NAME
> >> is a symbol designating the package and SPEC is one of:
> >> 
> >> - nil, if any package version can be installed;
> >> - a version string, if that specific revision is to be installed;
> >> - a property list of the form described in
> >>   `package-vc-archive-spec-alist', giving a package
> >>   specification.
> >
> > There's no variable package-vc-archive-spec-alist.  Did you mean
> > package-vc--archive-spec-alist instead?  In that case, I think the
> > format of that list should be spelled out in this doc string, as the
> > referenced variable is an internal one.
> You are right (same mistake as before), the documentation for package
> specifications should be moved from the internal variable to either
> 'package-vc-selected-packages' or some other place.  It might not be bad
> to document it in package.texi either?  Or would that be too Lisp-y for
> the Emacs manual?

It's okay to have this in package.texi, but perhaps with fewer
details.  Users should customize such complex variables via Custom

> >> This user option differs from `package-selected-packages' in that
> >> it is meant to be specified manually.  You can also use the
> >> function `package-vc-selected-packages' to apply the changes."
> >
> > The function package-vc-selected-packages mentioned in the last
> > sentence doesn't seem to exist.  Also, what does it mean "to apply the
> > changes" -- apply the changes to what?
> It was supposed to be `package-vc-ensure-packages'.  How about
> rephrasing that last sentence into "By calling the function
> `package-vc-selected-packages", the packages specified in this list can
> also be installed.

Just avoid the passive voice:

  If you want to also install the packages in this list, use

> >> (defvar package-vc--archive-spec-alist nil
> >>   "List of package specifications for each archive.
> >> The list maps each package name, as a string, to a plist.
> >> Valid keys include
> >> 
> >>         `:url' (string)
> >
> > The "Valid keys" part is "out of the blue" here.  Keys of what?  If
> > that's a reference to the "plist" part preceding it, then we aren't
> > talking about a plist, we are talking about keyword/value pairs,
> > right?
> Yes, these are plist keys.  Should we say something like "Valid keys for
> these plists include:".

I would say explicitly "plist of key/value pairs".

> >>   "Extract the commit of a development package PKG."
> >
> > This doc string doesn't seem to match what the function does.
> I was confused at first, as I was assuming you were talking about
> `package-vc-commit', but it appears I accidentally copied the docstring
> into `package-vc--version'.  A better documentation string here would be
>      "Return the version number for the source package PKG."

That's fine.

> >> (defun package-vc--build-documentation (pkg-desc file)
> >>   "Build documentation FILE for PKG-DESC."
> >>   (let ((pkg-dir (package-desc-dir pkg-desc)))
> >>     (when (string-match-p "\\.org\\'" file)
> >>       (require 'ox)
> >>       (require 'ox-texinfo)
> >>       (with-temp-buffer
> >>         (insert-file-contents file)
> >>         (setq file (make-temp-file "ox-texinfo-"))
> >>         (org-export-to-file 'texinfo file)))
> >>     (call-process "install-info" nil nil nil
> >>                   file pkg-dir)))
> >
> > I'm confused by this function.  Does org-export-to-file produce a
> > .texi file or an Info file?  In any case, the semantics is confusing:
> > if FILE has the .org extension, the function installs a file whose
> > name is not FILE, otherwise the function installs FILE.  This seems to
> > conflate source and destination files in a confusing way.
> I can expand the documentation here.
> "file" is the input, either a .texi or an .org file.

If FILE is input, then saying "Build documentation FILE" is
misleading: there's no need to build FILE, it already exists.  You
should say something like

  Build documentation for package PKG-DESC from documentation source in FILE.

> If it is an .org file, we want to convert it to .texi first (which
> is what the (when ...)  block does), and write the output into a
> temporary file.  The temporary file is used as an input to
> install-info, that builds the .info file.

Ah, so there's a problem here, I think.  install-info doesn't produce
Info files, it only installs existing Info files and updates the DIR
files with the entries of the installed Info files.  So the step of
producing Info files from Texinfo is missing here.

> >> (defun package-vc-update (pkg-desc)
> >>   "Attempt to update the package PKG-DESC."
> >>   ;; HACK: To run `package-vc--unpack-1' after checking out the new
> >>   ;; revision, we insert a hook into `vc-post-command-functions', and
> >>   ;; remove it right after it ran.  To avoid running the hook multiple
> >>   ;; times or even for the wrong repository (as `vc-pull' is often
> >>   ;; asynchronous), we extract the relevant arguments using a pseudo
> >>   ;; filter for `vc-filter-command-function', executed only for the
> >>   ;; side effect, and store them in the lexical scope.  When the hook
> >>   ;; is run, we check if the arguments are the same (`eq') as the ones
> >>   ;; previously extracted, and only in that case will be call
> >>   ;; `package-vc--unpack-1'.  Ugh...
> >
> > Shouldn't this use unwind-protect, to make sure the hacked
> > post-command-hook doesn't leak out?
> The issue is that vc-pull *can be* asynchronous, so wrapping it in a
> `unwind-protect' would un-modify the hook too soon.  But you are right
> that if vc-pull were to fail, the hook would remain inside of
> `vc-post-command-functions' for too long.
> As I said in that comment
>    "If there is a better way to do this, it should be done."

If you can use unwind-protect at least in the synchronous case, it
would be better, I think.

And if the async pull could take a long time, I think it's a problem
to have the additional entry in the post-command-hook for all that

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