Undo in region after markers in undo history relocated

* simple.el (primitive-undo): Only process marker adjustments
validated against their corresponding (TEXT . POS).  Issue warning
for lone marker adjustments in undo history.  (Bug#16818)
(undo-make-selective-list): Add marker adjustments to selective
undo list based on whether their corresponding (TEXT . POS) is in
the region.  Remove variable adjusted-markers, which was unused
and only non nil during undo-make-selective-list.
(undo-elt-in-region): Return nil when passed a marker adjustment
and explain in function doc.

Have (MARKER . ADJUSTMENT) undo records always be immediately
after their corresponding (TEXT . POS) record in undo list.
(Bug#16818)
* lisp.h (record-delete): New arg record_markers.
(record_marker_adjustment): No longer needed outside undo.c.
* insdel.c (adjust_markers_for_delete): Move calculation of marker
adjustments to undo.c's record_marker_adjustments.  Note that
fileio.c's decide_coding_unwind is another caller to
adjust_markers_for_delete.  Because it has undo list bound to t,
it does not rely on adjust_markers_for_delete to record marker
adjustments.
(del_range_2): Swap call to record_delete and
adjust_markers_for_delete so as undo marker adjustments are
recorded before current deletion's adjustments, as before.
(adjust_after_replace):
(replace_range): Pass value for new record_markers arg to
delete_record.
* undo.c (record_marker_adjustment): Renamed to
record_marker_adjustments and made static.
(record_delete): Check record_markers arg and call
record_marker_adjustments.
(record_change): Pass value for new record_markers arg to
delete_record.
(record_point): at_boundary calculation no longer needs to account
for marker adjustments.

* undo-tests.el (undo-test-marker-adjustment-nominal):
(undo-test-region-t-marker): New tests of marker adjustments.
(undo-test-marker-adjustment-moved):
(undo-test-region-mark-adjustment): New tests to demonstrate
bug#16818, which fail without the fix.

* markers.texi (Moving Marker Positions): The 2014-03-02 doc
change mentioning undo's inability to handle relocated markers no
longer applies.  See bug#16818.
* text.texi (Undo): Expand documentation of (TEXT . POS) and
(MARKER . ADJUSTMENT) undo elements.

3 files changed, 18 insertions, 9 deletions

diff --git a/doc/lispref/ChangeLog b/doc/lispref/ChangeLog
index 1e57d4f0db2..3dfc0dffd76 100644
--- a/doc/lispref/ChangeLog
+++ b/doc/lispref/ChangeLog
@@ -1,3 +1,11 @@
+2014-03-24  Barry O'Reilly  <gundaetiapo@gmail.com>
+
+        * markers.texi (Moving Marker Positions): The 2014-03-02 doc
+        change mentioning undo's inability to handle relocated markers no
+        longer applies.  See bug#16818.
+        * text.texi (Undo): Expand documentation of (TEXT . POS) and
+        (MARKER . ADJUSTMENT) undo elements.
+
 2014-03-22  Glenn Morris  <rgm@gnu.org>
 
         * commands.texi (Defining Commands): List interactive-only values.
diff --git a/doc/lispref/markers.texi b/doc/lispref/markers.texi
index 19386d638fe..51b87ab1e5b 100644
--- a/doc/lispref/markers.texi
+++ b/doc/lispref/markers.texi
@@ -344,12 +344,10 @@ specify the insertion type, create them with insertion type
 @section Moving Marker Positions
 
   This section describes how to change the position of an existing
-marker.  When you do this, be sure you know how the marker is used
-outside of your program.  For example, moving a marker to an unrelated
-new position can cause undo to later adjust the marker incorrectly.
-Often when you wish to relocate a marker to an unrelated position, it
-is preferable to make a new marker and set the prior one to point
-nowhere.
+marker.  When you do this, be sure you know whether the marker is used
+outside of your program, and, if so, what effects will result from
+moving it---otherwise, confusing things may happen in other parts of
+Emacs.
 
 @defun set-marker marker position &optional buffer
 This function moves @var{marker} to @var{position}
diff --git a/doc/lispref/text.texi b/doc/lispref/text.texi
index f8a3e873449..7c5603fd645 100644
--- a/doc/lispref/text.texi
+++ b/doc/lispref/text.texi
@@ -1270,7 +1270,8 @@ This kind of element indicates how to reinsert text that was deleted.
 The deleted text itself is the string @var{text}.  The place to
 reinsert it is @code{(abs @var{position})}.  If @var{position} is
 positive, point was at the beginning of the deleted text, otherwise it
-was at the end.
+was at the end.  Zero or more (@var{marker} . @var{adjustment})
+elements follow immediately after this element.
 
 @item (t . @var{time-flag})
 This kind of element indicates that an unmodified buffer became
@@ -1296,8 +1297,10 @@ Here's how you might undo the change:
 @item (@var{marker} . @var{adjustment})
 This kind of element records the fact that the marker @var{marker} was
 relocated due to deletion of surrounding text, and that it moved
-@var{adjustment} character positions.  Undoing this element moves
-@var{marker} @minus{} @var{adjustment} characters.
+@var{adjustment} character positions.  If the marker's location is
+consistent with the (@var{text} . @var{position}) element preceding it
+in the undo list, then undoing this element moves @var{marker}
+@minus{} @var{adjustment} characters.
 
 @item (apply @var{funname} . @var{args})
 This is an extensible undo item, which is undone by calling