feature/package+vc eaafc10f67: Add support for :release-rev in 'package-vc-archive-spec-alist'

[Philip Kaludercic]

branch: feature/package+vc
commit eaafc10f673960e1cb971ed0cddd6e366daa9b1d
Author: Philip Kaludercic <philipk@posteo.net>
Commit: Philip Kaludercic <philipk@posteo.net>

    Add support for :release-rev in 'package-vc-archive-spec-alist'
    
    * lisp/emacs-lisp/package-vc.el (package-vc-archive-spec-alist):
    Update docstring.
    (package-vc-install): Use :release-rev if invoked with a prefix argument.
---
 lisp/emacs-lisp/package-vc.el | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/lisp/emacs-lisp/package-vc.el b/lisp/emacs-lisp/package-vc.el
index 5dc9086eae..8e4f2819db 100644
--- a/lisp/emacs-lisp/package-vc.el
+++ b/lisp/emacs-lisp/package-vc.el
@@ -136,6 +136,12 @@ The main file of the project, relevant to gather package
 metadata.  If not given, the assumed default is the package named
 with \".el\" concatenated to the end.
 
+        `:release-rev' (string)
+
+A revision string indicating the revision used for the current
+release in the package archive.  If missing or nil, no release
+was made.
+
 All other values are ignored.")
 
 (defun package-vc-desc->spec (pkg-desc &optional name)
@@ -414,7 +420,9 @@ guess the name of the package using `file-name-base'.  This 
can
 be overridden by manually passing the optional NAME.  Otherwise
 NAME-OR-URL is taken to be a package name, and the package
 metadata will be consulted for the URL.  An explicit revision can
-be requested using REV."
+be requested using REV.  If the command is invoked with a prefix
+argument, the revision used for the last release in the package
+archive is used."
   (interactive
    (progn
      ;; Initialize the package system to get the list of package
@@ -424,7 +432,12 @@ be requested using REV."
             (input (completing-read
                     "Fetch package source (name or URL): " packages))
             (name (file-name-base input)))
-       (list input (intern (string-remove-prefix "emacs-" name))))))
+       (list input (intern (string-remove-prefix "emacs-" name))
+             (and current-prefix-arg
+                  (or (package-vc-query-spec
+                       (cadr (assoc input package-archive-contents #'string=))
+                       :release-rev)
+                      (user-error "No release revision was found")))))))
   (package--archives-initialize)
   (cond
    ((and-let* ((stringp name-or-url)