Problems with Emacs-26

[angelog0]

With Emacs-26 on Windows (MSYS2/MinGW) I find the following issue reproducible with the init.el file below. Starting Emacs prints:

Warning (initialization): An error occurred while loading ‘c:/Users/utente/AppData/Roaming/.emacs.d/init.el’:

File is missing: Cannot open load file, No such file or directory, tabbar-ruler

To ensure normal operation, you should investigate and remove the
cause of the error in your initialization file.  Start Emacs with
the ‘--debug-init’ option to view a complete error backtrace.

Obviously I have installed tabbar-ruler..

Using the debug option (runemacs.exe --debug-init), it prints:

Debugger entered--Lisp error: (file-missing "Cannot open load file" "No such file or directory" "tabbar-ruler")
  require(tabbar-ruler)
  eval-buffer(#<buffer  *load*> nil "c:/Users/utente/AppData/Roaming/.emacs.d/init.el" nil t)  ; Reading at buffer position 196
  load-with-code-conversion("c:/Users/utente/AppData/Roaming/.emacs.d/init.el" "c:/Users/utente/AppData/Roaming/.emacs.d/init.el" t t)
  load("c:/Users/utente/AppData/Roaming/.emacs.d/init" t t)
  #f(compiled-function () #<bytecode 0x1000be22d>)()
  command-line()
  normal-top-level()

Notice that THE SAME init.el files works just fine with Emacs-27 from master!

Notice also that if I comment out the custom section from the init.el file then it works in Emacs-26 too but the custom section is added automatically by Emacs!

Now the minimal init.el with which I can reproduce the issue!

$ cat init.el
(when (>= emacs-major-version 24)
  (require 'package)
  (add-to-list
   'package-archives
   '("melpa" . "http://melpa.org/packages/")
   t)
  ;;(package-initialize)
  )

(require 'tabbar-ruler)

(custom-set-variables
 ;; custom-set-variables was added by Custom.
 ;; If you edit it by hand, you could mess it up, so be careful.
 ;; Your init file should contain only one such instance.
 ;; If there is more than one, they won't work right.
 '(package-selected-packages (quote (tabbar-ruler))))
(custom-set-faces
 ;; custom-set-faces was added by Custom.
 ;; If you edit it by hand, you could mess it up, so be careful.
 ;; Your init file should contain only one such instance.
 ;; If there is more than one, they won't work right.
 )

[mattfidler]

tabbar-ruler works just fine for me in emacs 26 using windows. Perhaps you byte compiled the lisp files under emacs 27. I have had problems with this in the past.

[angelog0]

@mattfidler, I found this issue with a fresh Emacs 26 installation on a fresh machine on which never used Emacs 27