contrib/nvi/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[] = "@(#)v_undo.c      10.5 (Berkeley) 3/6/96";
  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(sp, vp)
  38         SCR *sp;
  39         VICMD *vp;
  40 {
  41         /*
  42          * Historically, U reset the cursor to the first column in the line
  43          * (not the first non-blank).  This seems a bit non-intuitive, but,
  44          * considering that we may have undone multiple changes, anything
  45          * else (including the cursor position stored in the logging records)
  46          * is going to appear random.
  47          */
  48         vp->m_final.cno = 0;
  49
  50         /*
  51          * !!!
  52          * Set up the flags so that an immediately subsequent 'u' will roll
  53          * forward, instead of backward.  In historic vi, a 'u' following a
  54          * 'U' redid all of the changes to the line.  Given that the user has
  55          * explicitly discarded those changes by entering 'U', it seems likely
  56          * that the user wants something between the original and end forms of
  57          * the line, so starting to replay the changes seems the best way to
  58          * get to there.
  59          */
  60         F_SET(sp->ep, F_UNDO);
  61         sp->ep->lundo = BACKWARD;
  62
  63         return (log_setline(sp));
  64 }
  65
  66 /*
  67  * v_undo -- u
  68  *      Undo the last change.
  69  *
  70  * PUBLIC: int v_undo __P((SCR *, VICMD *));
  71  */
  72 int
  73 v_undo(sp, vp)
  74         SCR *sp;
  75         VICMD *vp;
  76 {
  77         EXF *ep;
  78
  79         /* Set the command count. */
  80         VIP(sp)->u_ccnt = sp->ccnt;
  81
  82         /*
  83          * !!!
  84          * In historic vi, 'u' toggled between "undo" and "redo", i.e. 'u'
  85          * undid the last undo.  However, if there has been a change since
  86          * the last undo/redo, we always do an undo.  To make this work when
  87          * the user can undo multiple operations, we leave the old semantic
  88          * unchanged, but make '.' after a 'u' do another undo/redo operation.
  89          * This has two problems.
  90          *
  91          * The first is that 'u' didn't set '.' in historic vi.  So, if a
  92          * user made a change, realized it was in the wrong place, does a
  93          * 'u' to undo it, moves to the right place and then does '.', the
  94          * change was reapplied.  To make this work, we only apply the '.'
  95          * to the undo command if it's the command immediately following an
  96          * undo command.  See vi/vi.c:getcmd() for the details.
  97          *
  98          * The second is that the traditional way to view the numbered cut
  99          * buffers in vi was to enter the commands "1pu.u.u.u. which will
 100          * no longer work because the '.' immediately follows the 'u' command.
 101          * Since we provide a much better method of viewing buffers, and
 102          * nobody can think of a better way of adding in multiple undo, this
 103          * remains broken.
 104          *
 105          * !!!
 106          * There is change to historic practice for the final cursor position
 107          * in this implementation.  In historic vi, if an undo was isolated to
 108          * a single line, the cursor moved to the start of the change, and
 109          * then, subsequent 'u' commands would not move it again. (It has been
 110          * pointed out that users used multiple undo commands to get the cursor
 111          * to the start of the changed text.)  Nvi toggles between the cursor
 112          * position before and after the change was made.  One final issue is
 113          * that historic vi only did this if the user had not moved off of the
 114          * line before entering the undo command; otherwise, vi would move the
 115          * cursor to the most attractive position on the changed line.
 116          *
 117          * It would be difficult to match historic practice in this area. You
 118          * not only have to know that the changes were isolated to one line,
 119          * but whether it was the first or second undo command as well.  And,
 120          * to completely match historic practice, we'd have to track users line
 121          * changes, too.  This isn't worth the effort.
 122          */
 123         ep = sp->ep;
 124         if (!F_ISSET(ep, F_UNDO)) {
 125                 F_SET(ep, F_UNDO);
 126                 ep->lundo = BACKWARD;
 127         } else if (!F_ISSET(vp, VC_ISDOT))
 128                 ep->lundo = ep->lundo == BACKWARD ? FORWARD : BACKWARD;
 129
 130         switch (ep->lundo) {
 131         case BACKWARD:
 132                 return (log_backward(sp, &vp->m_final));
 133         case FORWARD:
 134                 return (log_forward(sp, &vp->m_final));
 135         default:
 136                 abort();
 137         }
 138         /* NOTREACHED */
 139 }