[src/trunk]: src/lib/libedit The libedit implementation of history_get() also...

[christos <christos%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/fd78e72277de
branches:  trunk
changeset: 345140:fd78e72277de
user:      christos <christos%NetBSD.org@localhost>
date:      Mon May 09 21:25:11 2016 +0000

description:
The libedit implementation of history_get() also differs from the GNU
implementation:  libedit goes to the entry with the given number
stored in the HistEvent structure, while GNU subtracts history_base,
then advances that many entries from the oldest one.  If entries were
removed in between, GNU advances further than libedit.

The call sequence H_CURR, H_DELDATA, H_CURR, H_NEXT_EVDATA looks
weird, as if part of that must somehow be redundant.  But actually,
the user interface is so counter-intuitive that every single step
is really required.

 - The first H_CURR is needed to be able to go back after an error.
 - The H_DELDATA is needed to move the cursor.  Even though it takes
   a pointer to ev, that structure is not filled in when the call
   succeeds.  H_DELDATA only moves the cursor, it doesn't tell us
   the new event number.
 - Consequently, the second H_CURR is required to get ev.num filled
   in.  But it doesn't return the data because ev has no field for
   that.
 - So even though the cursor is already positioned correctly,
   H_NEXT_EVDATA is needed as the final step merely to get the data.

(Ingo Schwarze)

diffstat:

 lib/libedit/readline.c |  30 +++++++++++++++++++++---------
 1 files changed, 21 insertions(+), 9 deletions(-)

diffs (63 lines):

diff -r bb33d218469d -r fd78e72277de lib/libedit/readline.c
--- a/lib/libedit/readline.c    Mon May 09 21:03:10 2016 +0000
+++ b/lib/libedit/readline.c    Mon May 09 21:25:11 2016 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: readline.c,v 1.130 2016/05/08 20:15:00 christos Exp $  */
+/*     $NetBSD: readline.c,v 1.131 2016/05/09 21:25:11 christos Exp $  */
 
 /*-
  * Copyright (c) 1997 The NetBSD Foundation, Inc.
@@ -31,7 +31,7 @@
 
 #include "config.h"
 #if !defined(lint) && !defined(SCCSID)
-__RCSID("$NetBSD: readline.c,v 1.130 2016/05/08 20:15:00 christos Exp $");
+__RCSID("$NetBSD: readline.c,v 1.131 2016/05/09 21:25:11 christos Exp $");
 #endif /* not lint && not SCCSID */
 
 #include <sys/types.h>
@@ -1400,25 +1400,37 @@
        if (h == NULL || e == NULL)
                rl_initialize();
 
+       if (num < history_base)
+               return NULL;
+
        /* save current position */
        if (history(h, &ev, H_CURR) != 0)
                return NULL;
        curr_num = ev.num;
 
-       /* start from the oldest */
-       if (history(h, &ev, H_LAST) != 0)
-               return NULL;    /* error */
+       /*
+        * use H_DELDATA to set to nth history (without delete) by passing
+        * (void **)-1  -- as in history_set_pos
+        */
+       if (history(h, &ev, H_DELDATA, num - history_base, (void **)-1) != 0)
+               goto out;
 
-       /* look forwards for event matching specified offset */
-       if (history(h, &ev, H_NEXT_EVDATA, num, &she.data))
-               return NULL;
-
+       /* get current entry */
+       if (history(h, &ev, H_CURR) != 0)
+               goto out;
+       if (history(h, &ev, H_NEXT_EVDATA, ev.num, &she.data) != 0)
+               goto out;
        she.line = ev.str;
 
        /* restore pointer to where it was */
        (void)history(h, &ev, H_SET, curr_num);
 
        return &she;
+
+out:
+       /* restore pointer to where it was */
+       (void)history(h, &ev, H_SET, curr_num);
+       return NULL;
 }