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Fix regexport.c to behave sanely with lookaround constraints.

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regexport.c thought it could just ignore LACON arcs, but the correct
behavior is to treat them as satisfiable while consuming zero input
(rather reminiscently of commit 9f1e642d5).  Otherwise, the emitted
simplified-NFA representation may contain no paths leading from initial
to final state, which unsurprisingly confuses pg_trgm, as seen in
bug #14623 from Jeff Janes.

Since regexport's output representation has no concept of an arc that
consumes zero input, recurse internally to find the next normal arc(s)
after any LACON transitions.  We'd be forced into changing that
representation if a LACON could be the last arc reaching the final
state, but fortunately the regex library never builds NFAs with such
a configuration, so there always is a next normal arc.

Back-patch to 9.3 where this logic was introduced.

Discussion: https://postgr.es/m/20170413180503.25948.94871@wrigleys.postgresql.org
This commit is contained in:
Tom Lane
2017-04-13 17:18:35 -04:00
parent ff9398052d
commit 5be58cc89a
3 changed files with 82 additions and 25 deletions
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12
contrib/pg_trgm/expected/pg_trgm.out
View File

@ -3676,6 +3676,12 @@ select * from test2 where t ~ ' z foo';
z foo bar
(1 row)
select * from test2 where t ~ 'qua(?!foo)';
t
-------
quark
(1 row)
drop index test2_idx_gin;
create index test2_idx_gist on test2 using gist (t gist_trgm_ops);
set enable_seqscan=off;
@ -3856,3 +3862,9 @@ select * from test2 where t ~ ' z foo';
z foo bar
(1 row)
select * from test2 where t ~ 'qua(?!foo)';
t
-------
quark
(1 row)

3
contrib/pg_trgm/sql/pg_trgm.sql
View File

@ -81,7 +81,9 @@ select * from test2 where t ~ 'z foo bar';
select * from test2 where t ~ ' z foo bar';
select * from test2 where t ~ ' z foo bar';
select * from test2 where t ~ ' z foo';
select * from test2 where t ~ 'qua(?!foo)';
drop index test2_idx_gin;
create index test2_idx_gist on test2 using gist (t gist_trgm_ops);
set enable_seqscan=off;
explain (costs off)
@ -116,3 +118,4 @@ select * from test2 where t ~ 'z foo bar';
select * from test2 where t ~ ' z foo bar';
select * from test2 where t ~ ' z foo bar';
select * from test2 where t ~ ' z foo';
select * from test2 where t ~ 'qua(?!foo)';