Add new OID alias type regdatabase.

This provides a convenient way to look up a database's OID.  For
example, the query

    SELECT * FROM pg_shdepend
    WHERE dbid = (SELECT oid FROM pg_database
                  WHERE datname = current_database());

can now be simplified to

    SELECT * FROM pg_shdepend
    WHERE dbid = current_database()::regdatabase;

Like the regrole type, regdatabase has cluster-wide scope, so we
disallow regdatabase constants from appearing in stored
expressions.

Bumps catversion.

Author: Ian Lawrence Barwick <barwick@gmail.com>
Reviewed-by: Greg Sabino Mullane <htamfids@gmail.com>
Reviewed-by: Jian He <jian.universality@gmail.com>
Reviewed-by: Fabrízio de Royes Mello <fabriziomello@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/aBpjJhyHpM2LYcG0%40nathan

4 files changed, 37 insertions, 1 deletions

diff --git a/src/include/catalog/catversion.h b/src/include/catalog/catversion.h
index 479629825f5..ff9ffd9d474 100644
--- a/src/include/catalog/catversion.h
+++ b/src/include/catalog/catversion.h
@@ -57,6 +57,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	202506291
+#define CATALOG_VERSION_NO	202506301
 
 #endif
diff --git a/src/include/catalog/pg_cast.dat b/src/include/catalog/pg_cast.dat
index ab46be606f0..fbfd669587f 100644
--- a/src/include/catalog/pg_cast.dat
+++ b/src/include/catalog/pg_cast.dat
@@ -281,6 +281,20 @@
   castcontext => 'a', castmethod => 'f' },
 { castsource => 'regnamespace', casttarget => 'int4', castfunc => '0',
   castcontext => 'a', castmethod => 'b' },
+{ castsource => 'oid', casttarget => 'regdatabase', castfunc => '0',
+  castcontext => 'i', castmethod => 'b' },
+{ castsource => 'regdatabase', casttarget => 'oid', castfunc => '0',
+  castcontext => 'i', castmethod => 'b' },
+{ castsource => 'int8', casttarget => 'regdatabase', castfunc => 'oid',
+  castcontext => 'i', castmethod => 'f' },
+{ castsource => 'int2', casttarget => 'regdatabase', castfunc => 'int4(int2)',
+  castcontext => 'i', castmethod => 'f' },
+{ castsource => 'int4', casttarget => 'regdatabase', castfunc => '0',
+  castcontext => 'i', castmethod => 'b' },
+{ castsource => 'regdatabase', casttarget => 'int8', castfunc => 'int8(oid)',
+  castcontext => 'a', castmethod => 'f' },
+{ castsource => 'regdatabase', casttarget => 'int4', castfunc => '0',
+  castcontext => 'a', castmethod => 'b' },
 
 # String category
 { castsource => 'text', casttarget => 'bpchar', castfunc => '0',
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index fb4f7f50350..d4650947c63 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -7455,6 +7455,17 @@
   prorettype => 'regnamespace', proargtypes => 'text',
   prosrc => 'to_regnamespace' },
 
+{ oid => '8321', descr => 'I/O',
+  proname => 'regdatabasein', provolatile => 's', prorettype => 'regdatabase',
+  proargtypes => 'cstring', prosrc => 'regdatabasein' },
+{ oid => '8322', descr => 'I/O',
+  proname => 'regdatabaseout', provolatile => 's', prorettype => 'cstring',
+  proargtypes => 'regdatabase', prosrc => 'regdatabaseout' },
+{ oid => '8323', descr => 'convert database name to regdatabase',
+  proname => 'to_regdatabase', provolatile => 's',
+  prorettype => 'regdatabase', proargtypes => 'text',
+  prosrc => 'to_regdatabase' },
+
 { oid => '6210', descr => 'test whether string is valid input for data type',
   proname => 'pg_input_is_valid', provolatile => 's', prorettype => 'bool',
   proargtypes => 'text text', prosrc => 'pg_input_is_valid' },
@@ -8313,6 +8324,12 @@
 { oid => '4088', descr => 'I/O',
   proname => 'regnamespacesend', prorettype => 'bytea',
   proargtypes => 'regnamespace', prosrc => 'regnamespacesend' },
+{ oid => '8324', descr => 'I/O',
+  proname => 'regdatabaserecv', prorettype => 'regdatabase',
+  proargtypes => 'internal', prosrc => 'regdatabaserecv' },
+{ oid => '8325', descr => 'I/O',
+  proname => 'regdatabasesend', prorettype => 'bytea',
+  proargtypes => 'regdatabase', prosrc => 'regdatabasesend' },
 { oid => '2456', descr => 'I/O',
   proname => 'bit_recv', prorettype => 'bit',
   proargtypes => 'internal oid int4', prosrc => 'bit_recv' },
diff --git a/src/include/catalog/pg_type.dat b/src/include/catalog/pg_type.dat
index 6dca77e0a22..29e4ffffc98 100644
--- a/src/include/catalog/pg_type.dat
+++ b/src/include/catalog/pg_type.dat
@@ -399,6 +399,11 @@
   typinput => 'regnamespacein', typoutput => 'regnamespaceout',
   typreceive => 'regnamespacerecv', typsend => 'regnamespacesend',
   typalign => 'i' },
+{ oid => '8326', array_type_oid => '8327', descr => 'registered database',
+  typname => 'regdatabase', typlen => '4', typbyval => 't', typcategory => 'N',
+  typinput => 'regdatabasein', typoutput => 'regdatabaseout',
+  typreceive => 'regdatabaserecv', typsend => 'regdatabasesend',
+  typalign => 'i' },
 
 # uuid
 { oid => '2950', array_type_oid => '2951', descr => 'UUID',