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Fix contrib/ltree's subpath() with negative offset.

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subpath(ltree,offset,len) now correctly errors when given an offset
less than -n, where n is the number of labels in the given ltree.
There was a duplicate block of code that allowed an offset as low
as -2n.  The documentation says no such thing, so this must have
been a copy-and-paste error in the original ltree patch.

While here, avoid redundant calculation of "end" and write
LTREE_MAX_LEVELS rather than its hard-coded value.

Author: Marcus Gartner <m.a.gartner@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CAAUGV_SvBO9gWYbaejb9nhe-mS9FkNP4QADNTdM3wdRhvLobwA@mail.gmail.com
This commit is contained in:
Tom Lane
2025-11-01 13:25:42 -04:00
parent 2648eab377
commit ff8aba65d4
3 changed files with 6 additions and 11 deletions
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2
contrib/ltree/expected/ltree.out
View File

@@ -128,6 +128,8 @@ SELECT subpath('Top.Child1.Child2',1);
Child1.Child2
(1 row)
SELECT subpath('Top.Child1.Child2',-4); -- error
ERROR: invalid positions
SELECT index('1.2.3.4.5.6','1.2');
index
-------

14
contrib/ltree/ltree_op.c
View File

@@ -316,23 +316,15 @@ subpath(PG_FUNCTION_ARGS)
int32 end;
ltree *res;
end = start + len;
if (start < 0)
{
start = t->numlevel + start;
end = start + len;
}
if (start < 0)
{ /* start > t->numlevel */
start = t->numlevel + start;
end = start + len;
}
if (len < 0)
end = t->numlevel + len;
else if (len == 0)
end = (fcinfo->nargs == 3) ? start : 0xffff;
end = (fcinfo->nargs == 3) ? start : LTREE_MAX_LEVELS;
else
end = start + len;
res = inner_subltree(t, start, end);

1
contrib/ltree/sql/ltree.sql
View File

@@ -34,6 +34,7 @@ SELECT subpath('Top.Child1.Child2',0,0);
SELECT subpath('Top.Child1.Child2',1,0);
SELECT subpath('Top.Child1.Child2',0);
SELECT subpath('Top.Child1.Child2',1);
SELECT subpath('Top.Child1.Child2',-4); -- error
SELECT index('1.2.3.4.5.6','1.2');