Fix issues around strictness of SIMILAR TO.

As a result of some long-ago quick hacks, the SIMILAR TO operator
and the corresponding flavor of substring() interpreted "ESCAPE NULL"
as selecting the default escape character '\'.  This is both
surprising and not per spec: the standard is clear that these
functions should return NULL for NULL input.

Additionally, because of inconsistency of the strictness markings
of 3-argument substring() and similar_escape(), the planner could not
inline the SQL definition of substring(), resulting in a substantial
performance penalty compared to the underlying POSIX substring()
function.

The simplest fix for this would be to change the strictness marking
of similar_escape(), but if we do that we risk breaking existing views
that depend on that function.  Hence, leave similar_escape() as-is
as a compatibility function, and instead invent a new function
similar_to_escape() that comes in two strict variants.

There are a couple of other behaviors in this area that are also
not per spec, but they are documented and seem generally at least
as sane as the spec's definition, so leave them alone.  But improve
the documentation to describe them fully.

Patch by me; thanks to Álvaro Herrera and Andrew Gierth for review
and discussion.

Discussion: https://postgr.es/m/14047.1557708214@sss.pgh.pa.us

2 files changed, 11 insertions, 6 deletions

diff --git a/src/include/catalog/catversion.h b/src/include/catalog/catversion.h
index 80def7d4014..00cc71dcd12 100644
--- a/src/include/catalog/catversion.h
+++ b/src/include/catalog/catversion.h
@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	201908012
+#define CATALOG_VERSION_NO	201909071
 
 #endif
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index cf1f4093513..e6645f139ce 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -3346,9 +3346,15 @@
   proname => 'repeat', prorettype => 'text', proargtypes => 'text int4',
   prosrc => 'repeat' },
 
-{ oid => '1623', descr => 'convert SQL99 regexp pattern to POSIX style',
+{ oid => '1623', descr => 'convert SQL regexp pattern to POSIX style',
   proname => 'similar_escape', proisstrict => 'f', prorettype => 'text',
   proargtypes => 'text text', prosrc => 'similar_escape' },
+{ oid => '1986', descr => 'convert SQL regexp pattern to POSIX style',
+  proname => 'similar_to_escape', prorettype => 'text',
+  proargtypes => 'text text', prosrc => 'similar_to_escape_2' },
+{ oid => '1987', descr => 'convert SQL regexp pattern to POSIX style',
+  proname => 'similar_to_escape', prorettype => 'text', proargtypes => 'text',
+  prosrc => 'similar_to_escape_1' },
 
 { oid => '1624',
   proname => 'mul_d_interval', prorettype => 'interval',
@@ -5771,10 +5777,10 @@
 { oid => '2073', descr => 'extract text matching regular expression',
   proname => 'substring', prorettype => 'text', proargtypes => 'text text',
   prosrc => 'textregexsubstr' },
-{ oid => '2074', descr => 'extract text matching SQL99 regular expression',
+{ oid => '2074', descr => 'extract text matching SQL regular expression',
   proname => 'substring', prolang => 'sql', prorettype => 'text',
   proargtypes => 'text text text',
-  prosrc => 'select pg_catalog.substring($1, pg_catalog.similar_escape($2, $3))' },
+  prosrc => 'select pg_catalog.substring($1, pg_catalog.similar_to_escape($2, $3))' },
 
 { oid => '2075', descr => 'convert int8 to bitstring',
   proname => 'bit', prorettype => 'bit', proargtypes => 'int8 int4',
@@ -10554,8 +10560,7 @@
   proparallel => 'r', prorettype => 'void', proargtypes => '',
   prosrc => 'pg_replication_origin_xact_reset' },
 
-{ oid => '6012',
-  descr => 'advance replication origin to specific location',
+{ oid => '6012', descr => 'advance replication origin to specific location',
   proname => 'pg_replication_origin_advance', provolatile => 'v',
   proparallel => 'u', prorettype => 'void', proargtypes => 'text pg_lsn',
   prosrc => 'pg_replication_origin_advance' },