bug#54747: 28.1.50; package.el - Better error message if newer Emacs is required

[Rudolf Schlatte <rudi@constantly.at>]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> Daniel Mendler <mail@daniel-mendler.de> writes:
>
>>> I forgot to mention the current error message. The message is for example:
>>> 
>>> "package emacs-27.1 unavailable"
>>> 
>>> See https://github.com/minad/vertico/issues/217 for the original bug
>>> report when a user tried to install a package from GNU ELPA on Emacs 26,
>>> while the package requires Emacs 27.
>>
>> On the other hand, `list-packages` refuses to mark the package as
>> installable. So maybe nothing needs to be done here? In any case it is a
>> very minor issue. You can probably judge better if people stumbled
>> before over this error message. Otherwise feel free to close the issue!
>
> I think it makes sense to make this error message better -- people may
> be calling `package-install' explicitly.
>
> It'd be easier to debug this if I had a recipe for reproduction, though.
> Do you have one handy?

I think I can reproduce this via `package-install-from-buffer', with the
buffer containing the following (the error message is "Package
'emacs-30.1' is unavailable"):



;;; package-try.el --- reproducing bug #54747 -*- lexical-binding: t; -*-

;; Author: Rudi Schlatte <rudi@constantly.at>
;; Version: 1.0
;; Package-Requires: ((emacs "30.1"))
;; Keywords: bugs

;; This program is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, version 3.

;; This program is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with this program.  If not, see <http://www.gnu.org/licenses/>.

;;; Commentary:

;; Open this file, then install via `package-install-from-buffer'

(provide 'package-try)
;;; package-try.el ends here