bug#13814: 24.3.50; Dynamic variables shadowing prevent defvar

[Jorgen Schaefer <forcer@forcix.cx>]

When a file is autoloaded, defvar will fail to define locally-set,
dynamic variabls, resulting in such variables not being defined at all,
even after their local binding ends.

Situation:

(let ((some-var-that-influences-behavior t))
  (some-function-that-autoloads-a-library))

If the library which is autoloaded by
`some-function-that-autoloads-a-library' defines
`some-var-that-influences-behavior' using defvar or defcustom, the
variable is never bound globally because defvar thinks it's already
defined.

I would expect defvar to notice that the variable is bound only
locally/temporarily and define a global binding anyhow.

Reproduction:

Put this file, bug-lib.el, somewhere in `load-path':

-----8<----- bug-lib.el -----8<----- 

(defvar bug-variable t
  "This variable is not defined when autoloaded.")

(defun bug-variable-value ()
  bug-variable)

----->8----- ---------- ----->8-----

Then execute the following lines:

(autoload 'bug-variable-value "bug-lib.el")

(let ((bug-variable nil))
  (bug-variable-value))

=> nil

(bug-variable-value)

=> Error, `bug-variable' is not defined.


Regards,
        -- Jorgen


In GNU Emacs 24.3.50.1 (x86_64-unknown-linux-gnu)
Bzr revision: 111608 schwab@linux-m68k.org-20130126151309-wk3nb8t4xitw94lh
Configured using:
 `configure --without-x --with-x-toolkit=no'