[Alvaro Herrera <alvherre@2ndquadrant.com>]

I extracted from the latest multirange patch a bit that creates a new
routine CastCreate() in src/backend/catalog/pg_cast.c.  It contains the
catalog-accessing bits to create a new cast.  It seems harmless, so I
thought I'd apply it to get rid of a couple of hunks in the large patch.

(I also threw in a move of get_cast_oid from functioncmds.c to
lsyscache.c, which seems its natural place; at first I thought to put it
in catalog/pg_cast.c but really it's not a great place IMO.  This
function was invented out of whole cloth in commit fd1843ff8979.  I also
contemplated the move of CreateCast and DropCastById from functioncmds.c
to some new place, but creating a new commands/castcmds.c seemed a bit
excessive, so I left them in their current locations.)

-- 
Álvaro Herrera                            39°49'30"S 73°17'W
"The problem with the future is that it keeps turning into the present"
(Hobbes)

Attachments:

  [text/x-diff] pg_cast.patch (11.8K, ../20200309210003.GA19992@alvherre.pgsql/2-pg_cast.patch)
  download | inline diff:
commit 928aa3fa75a2f244dfb3ac08c4b4d166e426f9cf
Author:     Alvaro Herrera <alvherre@alvh.no-ip.org>
AuthorDate: Mon Mar 9 17:19:50 2020 -0300
CommitDate: Mon Mar 9 17:59:30 2020 -0300

    add pg_cast.c for CastCreate()

diff --git a/src/backend/catalog/Makefile b/src/backend/catalog/Makefile
index f8f0b4841c..9499bb33e5 100644
--- a/src/backend/catalog/Makefile
+++ b/src/backend/catalog/Makefile
@@ -25,6 +25,7 @@ OBJS = \
 	objectaddress.o \
 	partition.o \
 	pg_aggregate.o \
+	pg_cast.o \
 	pg_collation.o \
 	pg_constraint.o \
 	pg_conversion.o \
diff --git a/src/backend/catalog/pg_cast.c b/src/backend/catalog/pg_cast.c
new file mode 100644
index 0000000000..19f410337d
--- /dev/null
+++ b/src/backend/catalog/pg_cast.c
@@ -0,0 +1,116 @@
+/*-------------------------------------------------------------------------
+ *
+ * pg_cast.c
+ *	  routines to support manipulation of the pg_cast relation
+ *
+ * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/catalog/pg_cast.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/htup_details.h"
+#include "access/table.h"
+#include "catalog/catalog.h"
+#include "catalog/dependency.h"
+#include "catalog/indexing.h"
+#include "catalog/objectaccess.h"
+#include "catalog/pg_cast.h"
+#include "catalog/pg_proc.h"
+#include "catalog/pg_type.h"
+#include "utils/builtins.h"
+#include "utils/rel.h"
+#include "utils/syscache.h"
+
+/*
+ * ----------------------------------------------------------------
+ *		CastCreate
+ * ----------------------------------------------------------------
+ */
+ObjectAddress
+CastCreate(Oid sourcetypeid, Oid targettypeid, Oid funcid, char castcontext,
+		   char castmethod, DependencyType behavior)
+{
+	Relation		relation;
+	HeapTuple		tuple;
+	Oid				castid;
+	Datum			values[Natts_pg_cast];
+	bool			nulls[Natts_pg_cast];
+	ObjectAddress	myself,
+					referenced;
+
+	relation = table_open(CastRelationId, RowExclusiveLock);
+
+	/*
+	 * Check for duplicate.  This is just to give a friendly error message,
+	 * the unique index would catch it anyway (so no need to sweat about race
+	 * conditions).
+	 */
+	tuple = SearchSysCache2(CASTSOURCETARGET,
+							ObjectIdGetDatum(sourcetypeid),
+							ObjectIdGetDatum(targettypeid));
+	if (HeapTupleIsValid(tuple))
+		ereport(ERROR,
+				(errcode(ERRCODE_DUPLICATE_OBJECT),
+				 errmsg("cast from type %s to type %s already exists",
+						format_type_be(sourcetypeid),
+						format_type_be(targettypeid))));
+
+	/* ready to go */
+	castid = GetNewOidWithIndex(relation, CastOidIndexId, Anum_pg_cast_oid);
+	values[Anum_pg_cast_oid - 1] = ObjectIdGetDatum(castid);
+	values[Anum_pg_cast_castsource - 1] = ObjectIdGetDatum(sourcetypeid);
+	values[Anum_pg_cast_casttarget - 1] = ObjectIdGetDatum(targettypeid);
+	values[Anum_pg_cast_castfunc - 1] = ObjectIdGetDatum(funcid);
+	values[Anum_pg_cast_castcontext - 1] = CharGetDatum(castcontext);
+	values[Anum_pg_cast_castmethod - 1] = CharGetDatum(castmethod);
+
+	MemSet(nulls, false, sizeof(nulls));
+
+	tuple = heap_form_tuple(RelationGetDescr(relation), values, nulls);
+
+	CatalogTupleInsert(relation, tuple);
+
+	/* make dependency entries */
+	myself.classId = CastRelationId;
+	myself.objectId = castid;
+	myself.objectSubId = 0;
+
+	/* dependency on source type */
+	referenced.classId = TypeRelationId;
+	referenced.objectId = sourcetypeid;
+	referenced.objectSubId = 0;
+	recordDependencyOn(&myself, &referenced, behavior);
+
+	/* dependency on target type */
+	referenced.classId = TypeRelationId;
+	referenced.objectId = targettypeid;
+	referenced.objectSubId = 0;
+	recordDependencyOn(&myself, &referenced, behavior);
+
+	/* dependency on function */
+	if (OidIsValid(funcid))
+	{
+		referenced.classId = ProcedureRelationId;
+		referenced.objectId = funcid;
+		referenced.objectSubId = 0;
+		recordDependencyOn(&myself, &referenced, behavior);
+	}
+
+	/* dependency on extension */
+	recordDependencyOnCurrentExtension(&myself, false);
+
+	/* Post creation hook for new cast */
+	InvokeObjectPostCreateHook(CastRelationId, castid, 0);
+
+	heap_freetuple(tuple);
+
+	table_close(relation, RowExclusiveLock);
+
+	return myself;
+}
diff --git a/src/backend/commands/functioncmds.c b/src/backend/commands/functioncmds.c
index 43a23c69af..5eac55aaca 100644
--- a/src/backend/commands/functioncmds.c
+++ b/src/backend/commands/functioncmds.c
@@ -1411,17 +1411,12 @@ CreateCast(CreateCastStmt *stmt)
 	char		sourcetyptype;
 	char		targettyptype;
 	Oid			funcid;
-	Oid			castid;
 	int			nargs;
 	char		castcontext;
 	char		castmethod;
-	Relation	relation;
 	HeapTuple	tuple;
-	Datum		values[Natts_pg_cast];
-	bool		nulls[Natts_pg_cast];
-	ObjectAddress myself,
-				referenced;
 	AclResult	aclresult;
+	ObjectAddress	myself;
 
 	sourcetypeid = typenameTypeId(NULL, stmt->sourcetype);
 	targettypeid = typenameTypeId(NULL, stmt->targettype);
@@ -1645,100 +1640,11 @@ CreateCast(CreateCastStmt *stmt)
 			break;
 	}
 
-	relation = table_open(CastRelationId, RowExclusiveLock);
-
-	/*
-	 * Check for duplicate.  This is just to give a friendly error message,
-	 * the unique index would catch it anyway (so no need to sweat about race
-	 * conditions).
-	 */
-	tuple = SearchSysCache2(CASTSOURCETARGET,
-							ObjectIdGetDatum(sourcetypeid),
-							ObjectIdGetDatum(targettypeid));
-	if (HeapTupleIsValid(tuple))
-		ereport(ERROR,
-				(errcode(ERRCODE_DUPLICATE_OBJECT),
-				 errmsg("cast from type %s to type %s already exists",
-						format_type_be(sourcetypeid),
-						format_type_be(targettypeid))));
-
-	/* ready to go */
-	castid = GetNewOidWithIndex(relation, CastOidIndexId, Anum_pg_cast_oid);
-	values[Anum_pg_cast_oid - 1] = ObjectIdGetDatum(castid);
-	values[Anum_pg_cast_castsource - 1] = ObjectIdGetDatum(sourcetypeid);
-	values[Anum_pg_cast_casttarget - 1] = ObjectIdGetDatum(targettypeid);
-	values[Anum_pg_cast_castfunc - 1] = ObjectIdGetDatum(funcid);
-	values[Anum_pg_cast_castcontext - 1] = CharGetDatum(castcontext);
-	values[Anum_pg_cast_castmethod - 1] = CharGetDatum(castmethod);
-
-	MemSet(nulls, false, sizeof(nulls));
-
-	tuple = heap_form_tuple(RelationGetDescr(relation), values, nulls);
-
-	CatalogTupleInsert(relation, tuple);
-
-	/* make dependency entries */
-	myself.classId = CastRelationId;
-	myself.objectId = castid;
-	myself.objectSubId = 0;
-
-	/* dependency on source type */
-	referenced.classId = TypeRelationId;
-	referenced.objectId = sourcetypeid;
-	referenced.objectSubId = 0;
-	recordDependencyOn(&myself, &referenced, DEPENDENCY_NORMAL);
-
-	/* dependency on target type */
-	referenced.classId = TypeRelationId;
-	referenced.objectId = targettypeid;
-	referenced.objectSubId = 0;
-	recordDependencyOn(&myself, &referenced, DEPENDENCY_NORMAL);
-
-	/* dependency on function */
-	if (OidIsValid(funcid))
-	{
-		referenced.classId = ProcedureRelationId;
-		referenced.objectId = funcid;
-		referenced.objectSubId = 0;
-		recordDependencyOn(&myself, &referenced, DEPENDENCY_NORMAL);
-	}
-
-	/* dependency on extension */
-	recordDependencyOnCurrentExtension(&myself, false);
-
-	/* Post creation hook for new cast */
-	InvokeObjectPostCreateHook(CastRelationId, castid, 0);
-
-	heap_freetuple(tuple);
-
-	table_close(relation, RowExclusiveLock);
-
+	myself = CastCreate(sourcetypeid, targettypeid, funcid, castcontext,
+						castmethod, DEPENDENCY_NORMAL);
 	return myself;
 }
 
-/*
- * get_cast_oid - given two type OIDs, look up a cast OID
- *
- * If missing_ok is false, throw an error if the cast is not found.  If
- * true, just return InvalidOid.
- */
-Oid
-get_cast_oid(Oid sourcetypeid, Oid targettypeid, bool missing_ok)
-{
-	Oid			oid;
-
-	oid = GetSysCacheOid2(CASTSOURCETARGET, Anum_pg_cast_oid,
-						  ObjectIdGetDatum(sourcetypeid),
-						  ObjectIdGetDatum(targettypeid));
-	if (!OidIsValid(oid) && !missing_ok)
-		ereport(ERROR,
-				(errcode(ERRCODE_UNDEFINED_OBJECT),
-				 errmsg("cast from type %s to type %s does not exist",
-						format_type_be(sourcetypeid),
-						format_type_be(targettypeid))));
-	return oid;
-}
-
 void
 DropCastById(Oid castOid)
 {
diff --git a/src/backend/commands/typecmds.c b/src/backend/commands/typecmds.c
index b088ca848d..8891b1d564 100644
--- a/src/backend/commands/typecmds.c
+++ b/src/backend/commands/typecmds.c
@@ -42,6 +42,7 @@
 #include "catalog/objectaccess.h"
 #include "catalog/pg_am.h"
 #include "catalog/pg_authid.h"
+#include "catalog/pg_cast.h"
 #include "catalog/pg_collation.h"
 #include "catalog/pg_constraint.h"
 #include "catalog/pg_depend.h"
diff --git a/src/backend/utils/cache/lsyscache.c b/src/backend/utils/cache/lsyscache.c
index 3da90cb72a..1955b846c2 100644
--- a/src/backend/utils/cache/lsyscache.c
+++ b/src/backend/utils/cache/lsyscache.c
@@ -23,6 +23,7 @@
 #include "catalog/pg_am.h"
 #include "catalog/pg_amop.h"
 #include "catalog/pg_amproc.h"
+#include "catalog/pg_cast.h"
 #include "catalog/pg_collation.h"
 #include "catalog/pg_constraint.h"
 #include "catalog/pg_language.h"
@@ -908,6 +909,31 @@ get_atttypetypmodcoll(Oid relid, AttrNumber attnum,
 	ReleaseSysCache(tp);
 }
 
+/*				---------- PG_CAST CACHE ----------					 */
+
+/*
+ * get_cast_oid - given two type OIDs, look up a cast OID
+ *
+ * If missing_ok is false, throw an error if the cast is not found.  If
+ * true, just return InvalidOid.
+ */
+Oid
+get_cast_oid(Oid sourcetypeid, Oid targettypeid, bool missing_ok)
+{
+	Oid			oid;
+
+	oid = GetSysCacheOid2(CASTSOURCETARGET, Anum_pg_cast_oid,
+						  ObjectIdGetDatum(sourcetypeid),
+						  ObjectIdGetDatum(targettypeid));
+	if (!OidIsValid(oid) && !missing_ok)
+		ereport(ERROR,
+				(errcode(ERRCODE_UNDEFINED_OBJECT),
+				 errmsg("cast from type %s to type %s does not exist",
+						format_type_be(sourcetypeid),
+						format_type_be(targettypeid))));
+	return oid;
+}
+
 /*				---------- COLLATION CACHE ----------					 */
 
 /*
diff --git a/src/include/catalog/pg_cast.h b/src/include/catalog/pg_cast.h
index 1b81b52df6..2620ff40f0 100644
--- a/src/include/catalog/pg_cast.h
+++ b/src/include/catalog/pg_cast.h
@@ -20,6 +20,7 @@
 #ifndef PG_CAST_H
 #define PG_CAST_H
 
+#include "catalog/dependency.h"
 #include "catalog/genbki.h"
 #include "catalog/pg_cast_d.h"
 
@@ -87,4 +88,12 @@ typedef enum CoercionMethod
 
 #endif							/* EXPOSE_TO_CLIENT_CODE */
 
+
+extern ObjectAddress CastCreate(Oid sourcetypeid,
+								Oid targettypeid,
+								Oid funcid,
+								char castcontext,
+								char castmethod,
+								DependencyType behavior);
+
 #endif							/* PG_CAST_H */
diff --git a/src/include/commands/defrem.h b/src/include/commands/defrem.h
index 5cd6975a22..cdb752243f 100644
--- a/src/include/commands/defrem.h
+++ b/src/include/commands/defrem.h
@@ -64,7 +64,6 @@ extern void IsThereFunctionInNamespace(const char *proname, int pronargs,
 extern void ExecuteDoStmt(DoStmt *stmt, bool atomic);
 extern void ExecuteCallStmt(CallStmt *stmt, ParamListInfo params, bool atomic, DestReceiver *dest);
 extern TupleDesc CallStmtResultDesc(CallStmt *stmt);
-extern Oid	get_cast_oid(Oid sourcetypeid, Oid targettypeid, bool missing_ok);
 extern Oid	get_transform_oid(Oid type_id, Oid lang_id, bool missing_ok);
 extern void interpret_function_parameter_list(ParseState *pstate,
 											  List *parameters,
diff --git a/src/include/utils/lsyscache.h b/src/include/utils/lsyscache.h
index f132d39458..52d4c77260 100644
--- a/src/include/utils/lsyscache.h
+++ b/src/include/utils/lsyscache.h
@@ -90,6 +90,7 @@ extern char get_attgenerated(Oid relid, AttrNumber attnum);
 extern Oid	get_atttype(Oid relid, AttrNumber attnum);
 extern void get_atttypetypmodcoll(Oid relid, AttrNumber attnum,
 								  Oid *typid, int32 *typmod, Oid *collid);
+extern Oid	get_cast_oid(Oid sourcetypeid, Oid targettypeid, bool missing_ok);
 extern char *get_collation_name(Oid colloid);
 extern bool get_collation_isdeterministic(Oid colloid);
 extern char *get_constraint_name(Oid conoid);