Fix incompleteness in the implementation of minibuffer-follows-selected-frame

In particular, add a new value to the variable, and fix several bugs apparent
with the implementation up till now.

* doc/emacs/mini.texi (Basic Minibuffer): Add a description of the new
non-nil, non-t value of minibuffer-follows-selected-frame.

* doc/emacs/trouble.texi (Quitting): Add a description of how C-g handles
recursive minibuffers when typed in one which isn't the most nested.

* doc/lispref/minibuf.texi (Intro to Minibuffers): Add an @dfn for "active
minibuffer".
(Minibuffer Commands): Document that exit-minibuffer throws an error when not
invoked from the innermost Minibuffer.
(Recursive Mini): Amend the description of the visibility of outer level
minibuffers.
(Minibuffer Misc): In the description of the minibuffer hooks, replace "the
minibuffer" with "a minibuffer".

* etc/NEWS (Entry announcing minibuffer-follows-selected-frame): Add a
description of the new non-nil, non-t value.

* lisp/cus-start.el (top level): make the customize entry for
minibuffer-follows-selected-frame a choice between three entries.

* lisp/minibuffer.el (exit-minibuffer): throw an error when we're not in the
most nested minibuffer.
(top level): Bind C-g to abort-minibuffers in minibuffer-local-map.

* lisp/window.el (window-deletable-p): return the symbol `frame' when (amongst
other things) minibuffer-follows-selected-frame is t.

* src/eval.c (internal_catch): Add a mechanism to (throw 'exit t) repeatedly
when the throw currently being processed doesn't terminate the current
minibuffer.

* src/lisp.h (this_minibuffer_depth): New extern declaration
(minibuf_level): extern declaration moved here from window.h.

* src/minibuf.c (minibuffer_follows_frame, minibuf_stays_put)
(minibuf_moves_frame_when_opened): New and amended functions to query the
value of minibuffer-follows-selected-frame.
(choose_minibuf_frame): check (minibuf > 1) in place of (minibufer > 0) at a
particular place.  At another place, check that an alleged frame is so and is
live.  Before selecting a non-miniwindow on a different frame, ensure it
really is a different frame.
(move_minibuffer_onto_frame): Stack up all recursive minibuffers on the target
frame.  Check the minibuf_window isn't in the old frame before setting that
frame's miniwindow to an inactive minibuffer.
(Finnermost_minibuffer_p, Fabort_minibuffers): New primitives.
(this_minibuffer_depth): New function.
(read_minibuf): Record the calling frame in a variable, and switch back to it
after the recursive edit has terminated normally, using
select-frame-set-input-focus.  Stack up all the recursive minibuffers on the
miniwindow where a new minibuffer is being opened.  After the recursive edit,
switch the selected window away from the expired minibuffer's window.
(nth_minibuffer): New function.
(minibuffer-follows-selected-frame): Change from a DEFVAR_BOOL to a
DEFVAR_LISP.

* src/window.c (decode_next_window_args): Set *minibuf to w's mini-window's
content when that content is a minibuffer.

* src/window.h (minibuf_level) Declaration moved from here to lisp.h.

1 files changed, 7 insertions, 6 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 1a1f76d1281..a7a872d9791 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -102,12 +102,13 @@ effect should be negligible in the vast majority of cases anyway.
 By default, when you switch to another frame, an active minibuffer now
 moves to the newly selected frame.  Nevertheless, the effect of what
 you type in the minibuffer happens in the frame where the minibuffer
-was first activated, even if it moved to another frame.  An
-alternative behavior is available by customizing
-'minibuffer-follows-selected-frame' to nil.  Here, the minibuffer
-stays in the frame where you first opened it, and you must switch back
-to this frame to continue or abort its command.  The old, somewhat
-unsystematic behavior, which mixed these two is no longer available.
+was first activated.  An alternative behavior is available by
+customizing 'minibuffer-follows-selected-frame' to nil.  Here, the
+minibuffer stays in the frame where you first opened it, and you must
+switch back to this frame to continue or abort its command.  The old
+behavior, which mixed these two, can be approximated by customizing
+'minibuffer-follows-selected-frame' to a value which is neither nil
+nor t.
 
 +++
 ** New system for displaying documentation for groups of functions.