bug#60418: [PATCH] Add :vc keyword to use-package

[Philip Kaludercic]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Philip Kaludercic <philipk@posteo.net>
>> Cc: Eli Zaretskii <eliz@gnu.org>,  60418@debbugs.gnu.org,
>>   felician.nemeth@gmail.com,  stefankangas@gmail.com
>> Date: Fri, 05 May 2023 05:04:59 +0000
>> 
>> Tony Zorman <soliditsallgood@mailbox.org> writes:
>> 
>> > You're right, but I don't think I'm using them as synonyms. There is a
>> > big difference between
>> >
>> >     (package-vc-install "foo")
>> >
>> > which installs the latest "commit" (or revision, which I'm actually
>> > using as a synonym to commit) of a package, and
>> >
>> >     (package-vc-install "foo" :last-release)
>> >
>> > which installs the latest "release". A release, as defined by
>> > package-vc.el seems to be 'the latest revision that bumps the "Version"
>> > tag.' It is queried in the package-vc--release-rev function, and
>> > actually retrieved in vc-retrieve-tag. The "Version" tag is, I think,
>> > just the "Version: XXX" string that's specified in the top comment of
>> > the main elisp file of the respective repository.
>> 
>> How about we just say "the commit of the latest release"?
>
> When package-vc-install is used, what is "the latest release"? isn't
> that the HEAD of the default branch?  IOW, what about packages that
> make no releases at all?

No, the commit of the latest release is interpreted the same way as
elpa-admin.el does, namely the last revision that modified the "Version"
header.  If no such commit can be found, then a message is printed out
and the installation continues under the assumption that the package is
using a rolling-release model.

>> >> All I know is that when I've read the documentation you wrote, I asked
>> >> myself "what is meant by 'release' here?"  I found the answer when you
>> >> later wrote "last commit".
>> >>
>> >> Are you talking about commits?  More generally, what kind of "release
>> >> IDs" does :rev accept as its valid value?
>> >
>> > The :rev keyword accepts the same as REV of package-vc-install, which is
>> > either
>> >
>> >   - nil, signaling that the latest commit should be installed,
>> >
>> >   - :last-release, signaling that the last release should be installed,
>> >     or
>> >
>> >   - a "version string" appropriate for the respective version control
>> >     system, specifying that version (e.g., a specific commit hash).
>> 
>> All correct.
>> 
>> >> I understand that the same confusion could exist elsewhere, but that
>> >> doesn't mean we should proliferate it or even live with what we have.
>> >> We should instead clarify this in every place where we use this
>> >> terminology.
>> >>
>> >> So let's figure out what are these "releases", and then let's examine
>> >> the existing and the new documentation and see if we need to get our
>> >> terminology right there.
>> >
>> > I totally agree, and I think the fact that "release" means "when has the
>> > release version as specified in the main .el file changed" should be
>> > documented somewhere (if it is I didn't see it). Sorry that this has
>> > caused so much confusion.
>> 
>> Are there any other places where we can fix this confusion?
>
> I guess the documentation of package-vc-install shares these issues?

How does this sound like to you:

diff --git a/lisp/emacs-lisp/package-vc.el b/lisp/emacs-lisp/package-vc.el
index 8f62e7d65f3..b28e33b3b89 100644
--- a/lisp/emacs-lisp/package-vc.el
+++ b/lisp/emacs-lisp/package-vc.el
@@ -747,11 +747,14 @@ package-vc-install
 symbol whose name is the package name, and the URL for the
 package will be taken from the package's metadata.
 
-By default, this function installs the last version of the package
-available from its repository, but if REV is given and non-nil, it
-specifies the revision to install.  If REV has the special value
-`:last-release' (interactively, the prefix argument), that stands
-for the last released version of the package.
+By default, this function installs the last revision of the
+package available from its repository, but if REV is given and
+non-nil, it specifies the revision to install.  If REV has the
+special value `:last-release' (interactively, the prefix
+argument), an attempt is made to find the revision of the latest
+release.  This is done by looking up the last revision that
+modified the \"Version\" header, as described in the Info
+node `(elisp) Library Headers'.
 
 Optional argument BACKEND specifies the VC backend to use for cloning
 the package's repository; this is only possible if NAME-OR-URL is a URL,

I can apply this or any variation thereof to emacs-29.