Fix incorrect search for "x?" style matches in creviterdissect().

When the number of allowed iterations is limited (either a "?" quantifier
or a bound expression), the last sub-match has to reach to the end of the
target string.  The previous coding here first tried the shortest possible
match (one character, usually) and then gave up and back-tracked if that
didn't work, typically leading to failure to match overall, as shown in
bug #11478 from Christoph Berg.  The minimum change to fix that would be to
not decrement k before "goto backtrack"; but that would be a pretty stupid
solution, because we'd laboriously try each possible sub-match length
before finally discovering that only ending at the end can work.  Instead,
force the sub-match endpoint limit up to the end for even the first
shortest() call if we cannot have any more sub-matches after this one.

Bug introduced in my rewrite that added the iterdissect logic, commit
173e29aa5d.  The shortest-first search code
was too closely modeled on the longest-first code, which hasn't got this
issue since it tries a match reaching to the end to start with anyway.
Back-patch to all affected branches.
This commit is contained in:
Tom Lane 2014-09-23 20:25:31 -04:00
parent a564307373
commit 3694b4d7e1
3 changed files with 16 additions and 0 deletions

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@ -1190,6 +1190,10 @@ creviterdissect(struct vars * v,
(k >= min_matches || min_matches - k < end - limit)) (k >= min_matches || min_matches - k < end - limit))
limit++; limit++;
/* if this is the last allowed sub-match, it must reach to the end */
if (k >= max_matches)
limit = end;
/* try to find an endpoint for the k'th sub-match */ /* try to find an endpoint for the k'th sub-match */
endpts[k] = shortest(v, d, endpts[k - 1], limit, end, endpts[k] = shortest(v, d, endpts[k - 1], limit, end,
(chr **) NULL, (int *) NULL); (chr **) NULL, (int *) NULL);

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@ -188,3 +188,11 @@ select regexp_matches('Programmer', '(\w)(.*?\1)', 'g');
{m,m} {m,m}
(2 rows) (2 rows)
-- Test for proper matching of non-greedy iteration (bug #11478)
select regexp_matches('foo/bar/baz',
'^([^/]+?)(?:/([^/]+?))(?:/([^/]+?))?$', '');
regexp_matches
----------------
{foo,bar,baz}
(1 row)

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@ -46,3 +46,7 @@ select 'a' ~ '((((((a+|)+|)+|)+|)+|)+|)';
-- https://core.tcl.tk/tcl/tktview/6585b21ca8fa6f3678d442b97241fdd43dba2ec0 -- https://core.tcl.tk/tcl/tktview/6585b21ca8fa6f3678d442b97241fdd43dba2ec0
select 'Programmer' ~ '(\w).*?\1' as t; select 'Programmer' ~ '(\w).*?\1' as t;
select regexp_matches('Programmer', '(\w)(.*?\1)', 'g'); select regexp_matches('Programmer', '(\w)(.*?\1)', 'g');
-- Test for proper matching of non-greedy iteration (bug #11478)
select regexp_matches('foo/bar/baz',
'^([^/]+?)(?:/([^/]+?))(?:/([^/]+?))?$', '');