Collations with nondeterministic comparison

This adds a flag "deterministic" to collations.  If that is false,
such a collation disables various optimizations that assume that
strings are equal only if they are byte-wise equal.  That then allows
use cases such as case-insensitive or accent-insensitive comparisons
or handling of strings with different Unicode normal forms.

This functionality is only supported with the ICU provider.  At least
glibc doesn't appear to have any locales that work in a
nondeterministic way, so it's not worth supporting this for the libc
provider.

The term "deterministic comparison" in this context is from Unicode
Technical Standard #10
(https://unicode.org/reports/tr10/#Deterministic_Comparison).

This patch makes changes in three areas:

- CREATE COLLATION DDL changes and system catalog changes to support
  this new flag.

- Many executor nodes and auxiliary code are extended to track
  collations.  Previously, this code would just throw away collation
  information, because the eventually-called user-defined functions
  didn't use it since they only cared about equality, which didn't
  need collation information.

- String data type functions that do equality comparisons and hashing
  are changed to take the (non-)deterministic flag into account.  For
  comparison, this just means skipping various shortcuts and tie
  breakers that use byte-wise comparison.  For hashing, we first need
  to convert the input string to a canonical "sort key" using the ICU
  analogue of strxfrm().

Reviewed-by: Daniel Verite <daniel@manitou-mail.org>
Reviewed-by: Peter Geoghegan <pg@bowt.ie>
Discussion: https://www.postgresql.org/message-id/flat/1ccc668f-4cbc-0bef-af67-450b47cdfee7@2ndquadrant.com

1 files changed, 21 insertions, 6 deletions

diff --git a/src/backend/utils/adt/like.c b/src/backend/utils/adt/like.c
index 853c9c01e92..704e5720cf5 100644
--- a/src/backend/utils/adt/like.c
+++ b/src/backend/utils/adt/like.c
@@ -45,7 +45,7 @@ static int UTF8_MatchText(const char *t, int tlen, const char *p, int plen,
 static int SB_IMatchText(const char *t, int tlen, const char *p, int plen,
 			  pg_locale_t locale, bool locale_is_c);
 
-static int	GenericMatchText(const char *s, int slen, const char *p, int plen);
+static int	GenericMatchText(const char *s, int slen, const char *p, int plen, Oid collation);
 static int	Generic_Text_IC_like(text *str, text *pat, Oid collation);
 
 /*--------------------
@@ -148,8 +148,18 @@ SB_lower_char(unsigned char c, pg_locale_t locale, bool locale_is_c)
 
 /* Generic for all cases not requiring inline case-folding */
 static inline int
-GenericMatchText(const char *s, int slen, const char *p, int plen)
+GenericMatchText(const char *s, int slen, const char *p, int plen, Oid collation)
 {
+	if (collation && !lc_ctype_is_c(collation) && collation != DEFAULT_COLLATION_OID)
+	{
+		pg_locale_t		locale = pg_newlocale_from_collation(collation);
+
+		if (locale && !locale->deterministic)
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("nondeterministic collations are not supported for LIKE")));
+	}
+
 	if (pg_database_encoding_max_length() == 1)
 		return SB_MatchText(s, slen, p, plen, 0, true);
 	else if (GetDatabaseEncoding() == PG_UTF8)
@@ -184,6 +194,11 @@ Generic_Text_IC_like(text *str, text *pat, Oid collation)
 					 errhint("Use the COLLATE clause to set the collation explicitly.")));
 		}
 		locale = pg_newlocale_from_collation(collation);
+
+		if (locale && !locale->deterministic)
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("nondeterministic collations are not supported for ILIKE")));
 	}
 
 	/*
@@ -240,7 +255,7 @@ namelike(PG_FUNCTION_ARGS)
 	p = VARDATA_ANY(pat);
 	plen = VARSIZE_ANY_EXHDR(pat);
 
-	result = (GenericMatchText(s, slen, p, plen) == LIKE_TRUE);
+	result = (GenericMatchText(s, slen, p, plen, PG_GET_COLLATION()) == LIKE_TRUE);
 
 	PG_RETURN_BOOL(result);
 }
@@ -261,7 +276,7 @@ namenlike(PG_FUNCTION_ARGS)
 	p = VARDATA_ANY(pat);
 	plen = VARSIZE_ANY_EXHDR(pat);
 
-	result = (GenericMatchText(s, slen, p, plen) != LIKE_TRUE);
+	result = (GenericMatchText(s, slen, p, plen, PG_GET_COLLATION()) != LIKE_TRUE);
 
 	PG_RETURN_BOOL(result);
 }
@@ -282,7 +297,7 @@ textlike(PG_FUNCTION_ARGS)
 	p = VARDATA_ANY(pat);
 	plen = VARSIZE_ANY_EXHDR(pat);
 
-	result = (GenericMatchText(s, slen, p, plen) == LIKE_TRUE);
+	result = (GenericMatchText(s, slen, p, plen, PG_GET_COLLATION()) == LIKE_TRUE);
 
 	PG_RETURN_BOOL(result);
 }
@@ -303,7 +318,7 @@ textnlike(PG_FUNCTION_ARGS)
 	p = VARDATA_ANY(pat);
 	plen = VARSIZE_ANY_EXHDR(pat);
 
-	result = (GenericMatchText(s, slen, p, plen) != LIKE_TRUE);
+	result = (GenericMatchText(s, slen, p, plen, PG_GET_COLLATION()) != LIKE_TRUE);
 
 	PG_RETURN_BOOL(result);
 }