Avoid an unnecessary syscache lookup in parse_coerce.c.

All the other fields of the constant are being extracted from the syscache
entry we already have, so handle collation similarly.  (There don't seem
to be any other uses for the new function at the moment.)

src/backend/parser/parse_coerce.c

@@ -219,7 +219,7 @@ coerce_type(ParseState *pstate, Node *node,
 
 		newcon->consttype = baseTypeId;
 		newcon->consttypmod = inputTypeMod;
-		newcon->constcollid = get_typcollation(newcon->consttype);
+		newcon->constcollid = typeTypeCollation(targetType);
 		newcon->constlen = typeLen(targetType);
 		newcon->constbyval = typeByVal(targetType);
 		newcon->constisnull = con->constisnull;

src/backend/parser/parse_type.c

@@ -528,7 +528,7 @@ typeLen(Type t)
 	return typ->typlen;
 }
 
-/* given type (as type struct), return the value of its 'byval' attribute.*/
+/* given type (as type struct), return its 'byval' attribute */
 bool
 typeByVal(Type t)
 {
@@ -538,7 +538,7 @@ typeByVal(Type t)
 	return typ->typbyval;
 }
 
-/* given type (as type struct), return the name of type */
+/* given type (as type struct), return the type's name */
 char *
 typeTypeName(Type t)
 {
@@ -549,16 +549,26 @@ typeTypeName(Type t)
 	return pstrdup(NameStr(typ->typname));
 }
 
+/* given type (as type struct), return its 'typrelid' attribute */
 Oid
 typeTypeRelid(Type typ)
 {
 	Form_pg_type typtup;
 
 	typtup = (Form_pg_type) GETSTRUCT(typ);
-
 	return typtup->typrelid;
 }
 
+/* given type (as type struct), return its 'typcollation' attribute */
+Oid
+typeTypeCollation(Type typ)
+{
+	Form_pg_type typtup;
+
+	typtup = (Form_pg_type) GETSTRUCT(typ);
+	return typtup->typcollation;
+}
+
 /*
  * Given a type structure and a string, returns the internal representation
  * of that string.	The "string" can be NULL to perform conversion of a NULL

src/include/parser/parse_type.h

@@ -40,6 +40,7 @@ extern int16 typeLen(Type t);
 extern bool typeByVal(Type t);
 extern char *typeTypeName(Type t);
 extern Oid	typeTypeRelid(Type typ);
+extern Oid	typeTypeCollation(Type typ);
 extern Datum stringTypeDatum(Type tp, char *string, int32 atttypmod);
 
 extern Oid	typeidTypeRelid(Oid type_id);