bug#48137: 27.2; `package-install-file' fails when loading a package file with DOS line endings

[Ioannis Kappas <ioannis.kappas@gmail.com>]

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There is an issue with `package-install-file' that fails with the
following error when trying to install a file written with DOS line
endings:

error: Package lacks a "Version" or "Package-Version" header

(This is more apparent on MS-Windows which writes files with DOS line
endings by default)

To reproduce, create a minimal package file with Emacs on MS-Windows
and write it to disk as package-install-file-test-win.el:

;;; package-install-file-test-win.el --- test issue

;; Version: 0.1

(provide 'package-install-file-test-win)

;;; package-install-file-test-win.el ends here


Then M-x package-install-file RET package-install-file-test-win.el RET

and it should produce the error.

The above succeeds on GNU/Linux and installs the dummy package as
expected.

I have attached an ert test to do the same. The test fail on windows
and succeeds on Linux.

You can run it from command line as:

: emacs -Q --batch -l ert -l ./issue-package-install-file-test.el -f
ert-run-tests-batch

The cause appears to be that 'package can't handle package files
encoded with DOS line endings. Analysis to follow.

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;;; -*- lexical-binding: t; -*-
(require 'ert)

(defconst test/package ";;; package-install-file-test-win.el --- test issue 

;; Version: 0.1

(defun package-install-file-test-win/5 () 5)

(provide 'package-install-file-test-win)

;;; package-install-file-test-win.el ends here
"
  "Minimal test package file")

(ert-deftest package-install-file ()
  "Test that package install file works on a minimal package file
written to disk by Emacs."
  (message ":system %s :version %s" system-configuration emacs-version)

  (let* ((temp-dir (make-temp-file "package-install-file-test-win" t))
         (package-path (expand-file-name
                        "package-install-file-test-win.el"
                        temp-dir)))
    ;; write file in the default encoding
    (with-temp-buffer
      (insert test/package)
      (write-region (point-min) (point-max) package-path))
    (message ":package-file-created-at %s" package-path)

    ;; report on file encoding
    (with-temp-buffer
      (insert-file-contents package-path)
      (let* ((contents (buffer-string)))
        (message ":package-file-coding-system %s" buffer-file-coding-system)))

    ;; install package
    (package-install-file package-path)
    (delete-directory temp-dir t)

    
    ;; call dummy function
    (require 'package-install-file-test-win)
    (should (equal 5 (package-install-file-test-win/5)))

    ;; remove package
    (package-delete (cadr (assq 'package-install-file-test-win package-alist)))))