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eggerteggert
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zic now supports links to links
* NEWS, backward, zic.8: Mention this. * zic.c (make_links): New function, which supports links to later links. In this function, improve quality of warnings about links to links. (main): Use it.
1 parent d04a4b3 commit 4878b64

4 files changed

Lines changed: 126 additions & 20 deletions

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‎NEWS‎

Lines changed: 14 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -5,6 +5,7 @@ Unreleased, experimental changes
55
Briefly:
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Move links to 'backward'.
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In vanguard form, GMT is now a Zone and Etc/GMT a link.
8+
zic now supports links to links.
89
Simplify four Ontario zones into one.
910
Fix a Y2438 bug when reading TZif data.
1011

@@ -28,6 +29,19 @@ Unreleased, experimental changes
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Changes to code
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32+
zic now supports links to links regardless of input line order.
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For example, if Australia/Sydney is a Zone, the lines
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Link Australia/Canberra Australia/ACT
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Link Australia/Sydney Australia/Canberra
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now work correctly, even though the shell commands
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ln Australia/Canberra Australia/ACT
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ln Australia/Sydney Australia/Canberra
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would fail because the first command attempts to use a link
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Australia/Canberra that does not exist until after the second
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command is executed. Previously, zic had unspecified behavior if
42+
a Link line's target was another link, and zic often misbehaved if
43+
a Link line's target was a later Link line.
44+
3145
Fix line number in zic's diagnostic for a link to a link.
3246

3347
Fix a bug that caused localtime to mishandle timestamps starting

‎backward‎

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -17,9 +17,9 @@
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# backward compatibility link. Each section is sorted by link name.
1818

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# A "#= TARGET1" comment labels each link inserted only because some
20-
# .zi parsers mishandle links to links. The comment says what the
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# target would be if these parsers were fixed so that data could
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# contain links to links. For example, the line
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# .zi parsers (including tzcode through 2022e) mishandle links to links.
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# The comment says what the target would be if these parsers were fixed
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# so that data could contain links to links. For example, the line
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# "Link Australia/Sydney Australia/ACT #= Australia/Canberra" would be
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# "Link Australia/Canberra Australia/ACT" were it not that data lines
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# refrain from linking to links like Australia/Canberra, which means

‎zic.8‎

Lines changed: 25 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -190,7 +190,10 @@ the named file rather than in the standard location.
190190
Be more verbose, and complain about the following situations:
191191
.RS
192192
.PP
193-
The input specifies a link to a link.
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The input specifies a link to a link,
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something not supported by some older parsers, including
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.B zic
196+
itself through release 2022e.
194197
.PP
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A year that appears in a data file is outside the range
196199
of representable years.
@@ -691,19 +694,37 @@ The
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.B TARGET
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field should appear as the
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.B NAME
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field in some zone line.
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field in some zone line or as the
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.B LINK-NAME
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field in some link line.
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The
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.B LINK-NAME
697702
field is used as an alternative name for that zone;
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it has the same syntax as a zone line's
699704
.B NAME
700705
field.
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Links can chain together, although the behavior is unspecified if a
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chain of one or more links does not terminate in a Zone name.
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A link line can appear before the line that defines the link target.
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For example:
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.sp
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.ne 3
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.nf
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.in +2m
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.ta \w'Zone\0\0'u +\w'Greenwich\0\0'u
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Link Greenwich G_M_T
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Link Etc/GMT Greenwich
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Zone Etc/GMT\0\00\0\0\*-\0\0GMT
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.sp
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.in
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.fi
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The two links are chained together, and G_M_T, Greenwich, and Etc/GMT
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all name the same zone.
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.PP
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Except for continuation lines,
703725
lines may appear in any order in the input.
704726
However, the behavior is unspecified if multiple zone or link lines
705-
define the same name, or if the source of one link line is the target
706-
of another.
727+
define the same name.
707728
.PP
708729
The file that describes leap seconds can have leap lines and an
709730
expiration line.

‎zic.c‎

Lines changed: 84 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -678,6 +678,89 @@ bsearch_linkcmp(void const *key, void const *b)
678678
return strcmp(key, m->l_linkname);
679679
}
680680

681+
/* Make the links specified by the Link lines. */
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static void
683+
make_links(void)
684+
{
685+
ptrdiff_t i, j, nalinks;
686+
qsort(links, nlinks, sizeof *links, qsort_linkcmp);
687+
688+
/* Ignore each link superseded by a later link with the same name. */
689+
j = 0;
690+
for (i = 0; i < nlinks; i++) {
691+
while (i + 1 < nlinks
692+
&& strcmp(links[i].l_linkname, links[i + 1].l_linkname) == 0)
693+
i++;
694+
links[j++] = links[i];
695+
}
696+
nlinks = j;
697+
698+
/* Walk through the link array making links. However,
699+
if a link's target has not been made yet, append a copy to the
700+
end of the array. The end of the array will gradually fill
701+
up with a small sorted subsequence of not-yet-made links.
702+
nalinks counts all the links in the array, including copies.
703+
When we reach the copied subsequence, it may still contain
704+
a link to a not-yet-made link, so the process repeats.
705+
At any given point in time, the link array consists of the
706+
following subregions, where 0 <= i <= j <= nalinks and
707+
0 <= nlinks <= nalinks:
708+
709+
0 .. (i - 1):
710+
links that either have been made, or have been copied to a
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later point point in the array (this later point can be in
712+
any of the three subregions)
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i .. (j - 1):
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not-yet-made links for this pass
715+
j .. (nalinks - 1):
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not-yet-made links that this pass has skipped because
717+
they were links to not-yet-made links
718+
719+
The first subregion might not be sorted if nlinks < i;
720+
the other two subregions are sorted. This algorithm does
721+
not alter entries 0 .. (nlinks - 1), which remain sorted.
722+
723+
If there are L links, this algorithm is O(C*L*log(L)) where
724+
C is the length of the longest link chain. Usually C is
725+
short (e.g., 3) though its worst-case value is L. */
726+
727+
j = nalinks = nlinks;
728+
729+
for (i = 0; i < nalinks; i++) {
730+
struct link *l;
731+
732+
eat(links[i].l_filenum, links[i].l_linenum);
733+
734+
/* If this pass examined all its links, start the next pass. */
735+
if (i == j)
736+
j = nalinks;
737+
738+
/* Make this link unless its target has not been made yet. */
739+
l = bsearch(links[i].l_target, &links[i + 1], j - (i + 1),
740+
sizeof *links, bsearch_linkcmp);
741+
if (!l)
742+
l = bsearch(links[i].l_target, &links[j], nalinks - j,
743+
sizeof *links, bsearch_linkcmp);
744+
if (!l)
745+
dolink(links[i].l_target, links[i].l_linkname, false);
746+
else {
747+
/* The link target has not been made yet; copy the link to the end. */
748+
links = growalloc (links, sizeof *links, nalinks, &nlinks_alloc);
749+
links[nalinks++] = links[i];
750+
}
751+
752+
if (noise && i < nlinks) {
753+
if (l)
754+
warning(_("link %s targeting link %s mishandled by pre-2023 zic"),
755+
links[i].l_linkname, links[i].l_target);
756+
else if (bsearch(links[i].l_target, links, nlinks, sizeof *links,
757+
bsearch_linkcmp))
758+
warning(_("link %s targeting link %s"),
759+
links[i].l_linkname, links[i].l_target);
760+
}
761+
}
762+
}
763+
681764
/* Simple signal handling: just set a flag that is checked
682765
periodically outside critical sections. To set up the handler,
683766
prefer sigaction if available to close a signal race. */
@@ -992,19 +1075,7 @@ _("%s: invalid time range: %s\n"),
9921075
continue;
9931076
outzone(&zones[i], j - i);
9941077
}
995-
/*
996-
** Make links.
997-
*/
998-
if (noise)
999-
qsort(links, nlinks, sizeof *links, qsort_linkcmp);
1000-
for (i = 0; i < nlinks; ++i) {
1001-
eat(links[i].l_filenum, links[i].l_linenum);
1002-
dolink(links[i].l_target, links[i].l_linkname, false);
1003-
if (noise
1004-
&& bsearch(links[i].l_target, links, nlinks, sizeof *links,
1005-
bsearch_linkcmp))
1006-
warning(_("link to link"));
1007-
}
1078+
make_links();
10081079
if (lcltime != NULL) {
10091080
eat(COMMAND_LINE_FILENUM, 1);
10101081
dolink(lcltime, tzdefault, true);

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