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Fix lquery's NOT handling, and add ability to quantify non-'*' items.

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The existing implementation of the ltree ~ lquery match operator is
sufficiently complex and undocumented that it's hard to tell exactly
what it does.  But one thing it clearly gets wrong is the combination
of NOT symbols (!) and '*' symbols.  A pattern such as '*.!foo.*'
should, by any ordinary understanding of regular expression behavior,
match any ltree that has at least one label that's not "foo".  As best
we can tell by experimentation, what it's actually matching is any
ltree in which *no* label is "foo".  That's surprising, and not at all
what the documentation says.

Now, that's arguably a useful behavior, so if we rewrite to fix the
bug we should provide some other way to get it.  To do so, add the
ability to attach lquery quantifiers to non-'*' items as well as '*'s.
Then the pattern '!foo{,}' expresses "any ltree in which no label is
foo".  For backwards compatibility, the default quantifier for non-'*'
items has to be "{1}", although the default for '*' items is '{,}'.
I wouldn't have done it like that in a green field, but it's not
totally horrible.

Armed with that, rewrite checkCond() from scratch.  Treating '*' and
non-'*' items alike makes it simpler, not more complicated, so that
the function actually gets a lot shorter than it was.

Filip Rembiałkowski, Tom Lane, Nikita Glukhov, per a very
ancient bug report from M. Palm

Discussion: https://postgr.es/m/CAP_rww=waX2Oo6q+MbMSiZ9ktdj6eaJj0cQzNu=Ry2cCDij5fw@mail.gmail.com
This commit is contained in:
Tom Lane
2020-03-31 11:14:30 -04:00
parent e07e2a40bd
commit 70dc4c509b
6 changed files with 266 additions and 264 deletions
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11
contrib/ltree/ltree.h
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@ -65,14 +65,20 @@ typedef struct
/*
* In an lquery_level, "flag" contains the union of the variants' flags
* along with possible LQL_xxx flags; so those bit sets can't overlap.
*
* "low" and "high" are nominally the minimum and maximum number of matches.
* However, for backwards compatibility with pre-v13 on-disk lqueries,
* non-'*' levels (those with numvar > 0) only have valid low/high if the
* LQL_COUNT flag is set; otherwise those fields are zero, but the behavior
* is as if they were both 1.
*/
typedef struct
{
uint16 totallen; /* total length of this level, in bytes */
uint16 flag; /* see LQL_xxx and LVAR_xxx flags */
uint16 numvar; /* number of variants; 0 means '*' */
uint16 low; /* minimum repeat count for '*' */
uint16 high; /* maximum repeat count for '*' */
uint16 low; /* minimum repeat count */
uint16 high; /* maximum repeat count */
/* Array of maxalign'd lquery_variant structs follows: */
char variants[FLEXIBLE_ARRAY_MEMBER];
} lquery_level;
@ -82,6 +88,7 @@ typedef struct
#define LQL_FIRST(x) ( (lquery_variant*)( ((char*)(x))+LQL_HDRSIZE ) )
#define LQL_NOT 0x10 /* level has '!' (NOT) prefix */
#define LQL_COUNT 0x20 /* level is non-'*' and has repeat counts */
#ifdef LOWER_NODE
#define FLG_CANLOOKSIGN(x) ( ( (x) & ( LQL_NOT | LVAR_ANYEND | LVAR_SUBLEXEME ) ) == 0 )