bug#12766: read-from-minibuffer does not preserve current-buffer

[martin rudalics <rudalics@gmx.at>]

 >>> % src/emacs -Q --eval "(setq initial-frame-alist '((minibuffer . nil)))"
 >>> M-: (with-temp-buffer (list (read-string "toto: ") (current-buffer))) RET
 >> Two changes I made could be involved:
 >> (1) `select-window' now always makes the window's buffer current.
 >> (2) read_minibuf now calls set_window_buffer instead of
 >>     Fset_window_buffer.
 >
 > I think (1) is more likely to be the problem.

Verified (sloppily).

 > Could you check
 > read_minibuf to see which unwind is supposed to reset the
 > current buffer?

IIUC read_minibuf doesn't care about restoring the current buffer.

 > Maybe that code worked by accident (.e.g relying on the fact that
 > select-window didn't set current-buffer in that corner case) and the
 > right fix is simply to explicitly save&restore current buffer.

FWIW the problem already happens when choose_minibuf_frame calls
Fset_frame_selected_window.  The patch below seems to fix it.

martin, completely lost in the labyrinth of read_minibuf


*** src/minibuf.c	2012-10-11 16:23:37 +0000
--- src/minibuf.c	2012-10-30 18:25:26 +0000
***************
*** 472,477 ****
--- 472,479 ----

     /* Choose the minibuffer window and frame, and take action on them.  */

+   record_unwind_protect (Fset_buffer, Fcurrent_buffer ());
+
     choose_minibuf_frame ();

     record_unwind_protect (choose_minibuf_frame_1, Qnil);