vi/v_undo.c

   1 /*-
   2  * Copyright (c) 1992, 1993, 1994
   3  *      The Regents of the University of California.  All rights reserved.
   4  * Copyright (c) 1992, 1993, 1994, 1995, 1996
   5  *      Keith Bostic.  All rights reserved.
   6  *
   7  * See the LICENSE file for redistribution information.
   8  */
   9
  10 #include "config.h"
  11
  12 #ifndef lint
  13 static const char sccsid[] = "$Id: v_undo.c,v 10.6 2001/06/25 15:19:36 skimo Exp $ (Berkeley) $Date: 2001/06/25 15:19:36 $";
  14 #endif /* not lint */
  15
  16 #include <sys/types.h>
  17 #include <sys/queue.h>
  18 #include <sys/time.h>
  19
  20 #include <bitstring.h>
  21 #include <errno.h>
  22 #include <limits.h>
  23 #include <stdio.h>
  24 #include <stdlib.h>
  25 #include <string.h>
  26
  27 #include "../common/common.h"
  28 #include "vi.h"
  29
  30 /*
  31  * v_Undo -- U
  32  *      Undo changes to this line.
  33  *
  34  * PUBLIC: int v_Undo __P((SCR *, VICMD *));
  35  */
  36 int
  37 v_Undo(SCR *sp, VICMD *vp)
  38 {
  39         /*
  40          * Historically, U reset the cursor to the first column in the line
  41          * (not the first non-blank).  This seems a bit non-intuitive, but,
  42          * considering that we may have undone multiple changes, anything
  43          * else (including the cursor position stored in the logging records)
  44          * is going to appear random.
  45          */
  46         vp->m_final.cno = 0;
  47
  48         /*
  49          * !!!
  50          * Set up the flags so that an immediately subsequent 'u' will roll
  51          * forward, instead of backward.  In historic vi, a 'u' following a
  52          * 'U' redid all of the changes to the line.  Given that the user has
  53          * explicitly discarded those changes by entering 'U', it seems likely
  54          * that the user wants something between the original and end forms of
  55          * the line, so starting to replay the changes seems the best way to
  56          * get to there.
  57          */
  58         F_SET(sp->ep, F_UNDO);
  59         sp->ep->lundo = BACKWARD;
  60
  61         return (log_setline(sp));
  62 }
  63
  64 /*
  65  * v_undo -- u
  66  *      Undo the last change.
  67  *
  68  * PUBLIC: int v_undo __P((SCR *, VICMD *));
  69  */
  70 int
  71 v_undo(SCR *sp, VICMD *vp)
  72 {
  73         EXF *ep;
  74
  75         /* Set the command count. */
  76         VIP(sp)->u_ccnt = sp->ccnt;
  77
  78         /*
  79          * !!!
  80          * In historic vi, 'u' toggled between "undo" and "redo", i.e. 'u'
  81          * undid the last undo.  However, if there has been a change since
  82          * the last undo/redo, we always do an undo.  To make this work when
  83          * the user can undo multiple operations, we leave the old semantic
  84          * unchanged, but make '.' after a 'u' do another undo/redo operation.
  85          * This has two problems.
  86          *
  87          * The first is that 'u' didn't set '.' in historic vi.  So, if a
  88          * user made a change, realized it was in the wrong place, does a
  89          * 'u' to undo it, moves to the right place and then does '.', the
  90          * change was reapplied.  To make this work, we only apply the '.'
  91          * to the undo command if it's the command immediately following an
  92          * undo command.  See vi/vi.c:getcmd() for the details.
  93          *
  94          * The second is that the traditional way to view the numbered cut
  95          * buffers in vi was to enter the commands "1pu.u.u.u. which will
  96          * no longer work because the '.' immediately follows the 'u' command.
  97          * Since we provide a much better method of viewing buffers, and
  98          * nobody can think of a better way of adding in multiple undo, this
  99          * remains broken.
 100          *
 101          * !!!
 102          * There is change to historic practice for the final cursor position
 103          * in this implementation.  In historic vi, if an undo was isolated to
 104          * a single line, the cursor moved to the start of the change, and
 105          * then, subsequent 'u' commands would not move it again. (It has been
 106          * pointed out that users used multiple undo commands to get the cursor
 107          * to the start of the changed text.)  Nvi toggles between the cursor
 108          * position before and after the change was made.  One final issue is
 109          * that historic vi only did this if the user had not moved off of the
 110          * line before entering the undo command; otherwise, vi would move the
 111          * cursor to the most attractive position on the changed line.
 112          *
 113          * It would be difficult to match historic practice in this area. You
 114          * not only have to know that the changes were isolated to one line,
 115          * but whether it was the first or second undo command as well.  And,
 116          * to completely match historic practice, we'd have to track users line
 117          * changes, too.  This isn't worth the effort.
 118          */
 119         ep = sp->ep;
 120         if (!F_ISSET(ep, F_UNDO)) {
 121                 F_SET(ep, F_UNDO);
 122                 ep->lundo = BACKWARD;
 123         } else if (!F_ISSET(vp, VC_ISDOT))
 124                 ep->lundo = ep->lundo == BACKWARD ? FORWARD : BACKWARD;
 125
 126         switch (ep->lundo) {
 127         case BACKWARD:
 128                 return (log_backward(sp, &vp->m_final));
 129         case FORWARD:
 130                 return (log_forward(sp, &vp->m_final));
 131         default:
 132                 abort();
 133         }
 134         /* NOTREACHED */
 135 }