Allow ALTER TYPE to update an existing type's typsubscript value.

This is essential if we'd like to allow existing extension data types
to support subscripting in future, since dropping and recreating the
type isn't a practical thing for an extension upgrade script, and
direct manipulation of pg_type isn't a great answer either.

There was some discussion about also allowing alteration of typelem,
but it's less clear whether that's a good idea or not, so for now
I forebore.

Discussion: https://postgr.es/m/3724341.1607551174@sss.pgh.pa.us

doc/src/sgml/ref/alter_type.sgml

@@ -194,6 +194,14 @@ ALTER TYPE <replaceable class="parameter">name</replaceable> SET ( <replaceable
          requires superuser privilege.
         </para>
        </listitem>
+       <listitem>
+        <para>
+         <literal>SUBSCRIPT</literal> can be set to the name of a type-specific
+         subscripting handler function, or <literal>NONE</literal> to remove
+         the type's subscripting handler function.  Using this option
+         requires superuser privilege.
+        </para>
+       </listitem>
        <listitem>
         <para>
          <literal>STORAGE</literal><indexterm>

src/backend/commands/typecmds.c

@@ -94,6 +94,7 @@ typedef struct
 	bool		updateTypmodin;
 	bool		updateTypmodout;
 	bool		updateAnalyze;
+	bool		updateSubscript;
 	/* New values for relevant attributes */
 	char		storage;
 	Oid			receiveOid;
@@ -101,6 +102,7 @@ typedef struct
 	Oid			typmodinOid;
 	Oid			typmodoutOid;
 	Oid			analyzeOid;
+	Oid			subscriptOid;
 } AlterTypeRecurseParams;
 
 /* Potentially set by pg_upgrade_support functions */
@@ -3885,6 +3887,18 @@ AlterType(AlterTypeStmt *stmt)
 			/* Replacing an analyze function requires superuser. */
 			requireSuper = true;
 		}
+		else if (strcmp(defel->defname, "subscript") == 0)
+		{
+			if (defel->arg != NULL)
+				atparams.subscriptOid =
+					findTypeSubscriptingFunction(defGetQualifiedName(defel),
+												 typeOid);
+			else
+				atparams.subscriptOid = InvalidOid; /* NONE, remove function */
+			atparams.updateSubscript = true;
+			/* Replacing a subscript function requires superuser. */
+			requireSuper = true;
+		}
 
 		/*
 		 * The rest of the options that CREATE accepts cannot be changed.
@@ -4042,6 +4056,11 @@ AlterTypeRecurse(Oid typeOid, bool isImplicitArray,
 		replaces[Anum_pg_type_typanalyze - 1] = true;
 		values[Anum_pg_type_typanalyze - 1] = ObjectIdGetDatum(atparams->analyzeOid);
 	}
+	if (atparams->updateSubscript)
+	{
+		replaces[Anum_pg_type_typsubscript - 1] = true;
+		values[Anum_pg_type_typsubscript - 1] = ObjectIdGetDatum(atparams->subscriptOid);
+	}
 
 	newtup = heap_modify_tuple(tup, RelationGetDescr(catalog),
 							   values, nulls, replaces);
@@ -4098,6 +4117,7 @@ AlterTypeRecurse(Oid typeOid, bool isImplicitArray,
 	atparams->updateReceive = false;	/* domains use F_DOMAIN_RECV */
 	atparams->updateTypmodin = false;	/* domains don't have typmods */
 	atparams->updateTypmodout = false;
+	atparams->updateSubscript = false;	/* domains don't have subscriptors */
 
 	/* Skip the scan if nothing remains to be done */
 	if (!(atparams->updateStorage ||

src/test/regress/expected/create_type.out

@@ -260,38 +260,40 @@ ALTER TYPE myvarchar SET (
     receive = myvarcharrecv,
     typmod_in = varchartypmodin,
     typmod_out = varchartypmodout,
-    analyze = array_typanalyze  -- bogus, but it doesn't matter
+    -- these are bogus, but it's safe as long as we don't use the type:
+    analyze = ts_typanalyze,
+    subscript = raw_array_subscript_handler
 );
 SELECT typinput, typoutput, typreceive, typsend, typmodin, typmodout,
-       typanalyze, typstorage
+       typanalyze, typsubscript, typstorage
 FROM pg_type WHERE typname = 'myvarchar';
-  typinput   |  typoutput   |  typreceive   |    typsend    |    typmodin     |    typmodout     |    typanalyze    | typstorage 
--------------+--------------+---------------+---------------+-----------------+------------------+------------------+------------
- myvarcharin | myvarcharout | myvarcharrecv | myvarcharsend | varchartypmodin | varchartypmodout | array_typanalyze | x
+  typinput   |  typoutput   |  typreceive   |    typsend    |    typmodin     |    typmodout     |  typanalyze   |        typsubscript         | typstorage 
+-------------+--------------+---------------+---------------+-----------------+------------------+---------------+-----------------------------+------------
+ myvarcharin | myvarcharout | myvarcharrecv | myvarcharsend | varchartypmodin | varchartypmodout | ts_typanalyze | raw_array_subscript_handler | x
 (1 row)
 
 SELECT typinput, typoutput, typreceive, typsend, typmodin, typmodout,
-       typanalyze, typstorage
+       typanalyze, typsubscript, typstorage
 FROM pg_type WHERE typname = '_myvarchar';
- typinput | typoutput | typreceive |  typsend   |    typmodin     |    typmodout     |    typanalyze    | typstorage 
-----------+-----------+------------+------------+-----------------+------------------+------------------+------------
- array_in | array_out | array_recv | array_send | varchartypmodin | varchartypmodout | array_typanalyze | x
+ typinput | typoutput | typreceive |  typsend   |    typmodin     |    typmodout     |    typanalyze    |      typsubscript       | typstorage 
+----------+-----------+------------+------------+-----------------+------------------+------------------+-------------------------+------------
+ array_in | array_out | array_recv | array_send | varchartypmodin | varchartypmodout | array_typanalyze | array_subscript_handler | x
 (1 row)
 
 SELECT typinput, typoutput, typreceive, typsend, typmodin, typmodout,
-       typanalyze, typstorage
+       typanalyze, typsubscript, typstorage
 FROM pg_type WHERE typname = 'myvarchardom';
- typinput  |  typoutput   | typreceive  |    typsend    | typmodin | typmodout |    typanalyze    | typstorage 
------------+--------------+-------------+---------------+----------+-----------+------------------+------------
- domain_in | myvarcharout | domain_recv | myvarcharsend | -        | -         | array_typanalyze | x
+ typinput  |  typoutput   | typreceive  |    typsend    | typmodin | typmodout |  typanalyze   | typsubscript | typstorage 
+-----------+--------------+-------------+---------------+----------+-----------+---------------+--------------+------------
+ domain_in | myvarcharout | domain_recv | myvarcharsend | -        | -         | ts_typanalyze | -            | x
 (1 row)
 
 SELECT typinput, typoutput, typreceive, typsend, typmodin, typmodout,
-       typanalyze, typstorage
+       typanalyze, typsubscript, typstorage
 FROM pg_type WHERE typname = '_myvarchardom';
- typinput | typoutput | typreceive |  typsend   | typmodin | typmodout |    typanalyze    | typstorage 
-----------+-----------+------------+------------+----------+-----------+------------------+------------
- array_in | array_out | array_recv | array_send | -        | -         | array_typanalyze | x
+ typinput | typoutput | typreceive |  typsend   | typmodin | typmodout |    typanalyze    |      typsubscript       | typstorage 
+----------+-----------+------------+------------+----------+-----------+------------------+-------------------------+------------
+ array_in | array_out | array_recv | array_send | -        | -         | array_typanalyze | array_subscript_handler | x
 (1 row)
 
 -- ensure dependencies are straight

src/test/regress/sql/create_type.sql

@@ -207,23 +207,25 @@ ALTER TYPE myvarchar SET (
     receive = myvarcharrecv,
     typmod_in = varchartypmodin,
     typmod_out = varchartypmodout,
-    analyze = array_typanalyze  -- bogus, but it doesn't matter
+    -- these are bogus, but it's safe as long as we don't use the type:
+    analyze = ts_typanalyze,
+    subscript = raw_array_subscript_handler
 );
 
 SELECT typinput, typoutput, typreceive, typsend, typmodin, typmodout,
-       typanalyze, typstorage
+       typanalyze, typsubscript, typstorage
 FROM pg_type WHERE typname = 'myvarchar';
 
 SELECT typinput, typoutput, typreceive, typsend, typmodin, typmodout,
-       typanalyze, typstorage
+       typanalyze, typsubscript, typstorage
 FROM pg_type WHERE typname = '_myvarchar';
 
 SELECT typinput, typoutput, typreceive, typsend, typmodin, typmodout,
-       typanalyze, typstorage
+       typanalyze, typsubscript, typstorage
 FROM pg_type WHERE typname = 'myvarchardom';
 
 SELECT typinput, typoutput, typreceive, typsend, typmodin, typmodout,
-       typanalyze, typstorage
+       typanalyze, typsubscript, typstorage
 FROM pg_type WHERE typname = '_myvarchardom';
 
 -- ensure dependencies are straight