Fixes in ALTER SUBSCRIPTION DROP PUBLICATION code

ALTER SUBSCRIPTION DROP PUBLICATION does not actually support
copy_data option, so remove it from tab completion.

Also, reword the error message that is thrown when all the
publications from a subscription are specified to be dropped.

Also, made few doc and cosmetic adjustments.

Author: Vignesh C <vignesh21@gmail.com>
Reviewed-by: Bharath Rupireddy <bharath.rupireddy@enterprisedb.com>
Reviewed-by: Japin Li <japinli@hotmail.com>
Discussion: https://www.postgresql.org/message-id/flat/CALDaNm21RwsDzs4xj14ApteAF7auyyomHNnp+NEL-sH8m-jMvQ@mail.gmail.com

doc/src/sgml/ref/alter_subscription.sgml

@@ -22,9 +22,9 @@ PostgreSQL documentation
  <refsynopsisdiv>
 <synopsis>
 ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> CONNECTION '<replaceable>conninfo</replaceable>'
-ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> SET PUBLICATION <replaceable class="parameter">publication_name</replaceable> [, ...] [ WITH ( <replaceable class="parameter">set_publication_option</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) ]
-ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> ADD PUBLICATION <replaceable class="parameter">publication_name</replaceable> [, ...] [ WITH ( <replaceable class="parameter">set_publication_option</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) ]
-ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> DROP PUBLICATION <replaceable class="parameter">publication_name</replaceable> [, ...] [ WITH ( <replaceable class="parameter">set_publication_option</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) ]
+ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> SET PUBLICATION <replaceable class="parameter">publication_name</replaceable> [, ...] [ WITH ( <replaceable class="parameter">publication_option</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) ]
+ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> ADD PUBLICATION <replaceable class="parameter">publication_name</replaceable> [, ...] [ WITH ( <replaceable class="parameter">publication_option</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) ]
+ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> DROP PUBLICATION <replaceable class="parameter">publication_name</replaceable> [, ...] [ WITH ( <replaceable class="parameter">publication_option</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) ]
 ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> REFRESH PUBLICATION [ WITH ( <replaceable class="parameter">refresh_option</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) ]
 ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> ENABLE
 ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> DISABLE
@@ -102,17 +102,17 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
      <para>
       Changes the list of subscribed publications.  <literal>SET</literal>
       replaces the entire list of publications with a new list,
-      <literal>ADD</literal> adds additional publications,
-      <literal>DROP</literal> removes publications from the list of
-      publications.  See <xref linkend="sql-createsubscription"/> for more
-      information.  By default, this command will also act like
+      <literal>ADD</literal> adds additional publications to the list of
+      publications, and <literal>DROP</literal> removes the publications from
+      the list of publications.  See <xref linkend="sql-createsubscription"/>
+      for more information.  By default, this command will also act like
       <literal>REFRESH PUBLICATION</literal>, except that in case of
       <literal>ADD</literal> or <literal>DROP</literal>, only the added or
       dropped publications are refreshed.
      </para>
 
      <para>
-      <replaceable>set_publication_option</replaceable> specifies additional
+      <replaceable>publication_option</replaceable> specifies additional
       options for this operation.  The supported options are:
 
       <variablelist>
@@ -129,7 +129,8 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       </variablelist>
 
       Additionally, refresh options as described
-      under <literal>REFRESH PUBLICATION</literal> may be specified.
+      under <literal>REFRESH PUBLICATION</literal> may be specified,
+      except in the case of <literal>DROP PUBLICATION</literal>.
      </para>
     </listitem>
    </varlistentry>

src/backend/commands/subscriptioncmds.c

@@ -953,8 +953,6 @@ AlterSubscription(AlterSubscriptionStmt *stmt, bool isTopLevel)
 				bool		refresh;
 				List	   *publist;
 
-				publist = merge_publications(sub->publications, stmt->publication, isadd, stmt->subname);
-
 				parse_subscription_options(stmt->options,
 										   NULL,	/* no "connect" */
 										   NULL, NULL,	/* no "enabled" */
@@ -967,6 +965,8 @@ AlterSubscription(AlterSubscriptionStmt *stmt, bool isTopLevel)
 										   NULL, NULL,	/* no "binary" */
 										   NULL, NULL); /* no "streaming" */
 
+				publist = merge_publications(sub->publications, stmt->publication, isadd, stmt->subname);
+
 				values[Anum_pg_subscription_subpublications - 1] =
 					publicationListToArray(publist);
 				replaces[Anum_pg_subscription_subpublications - 1] = true;
@@ -1676,7 +1676,7 @@ merge_publications(List *oldpublist, List *newpublist, bool addpub, const char *
 	if (!oldpublist)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
-				 errmsg("subscription must contain at least one publication")));
+				 errmsg("cannot drop all the publications from a subscription")));
 
 	return oldpublist;
 }

src/bin/psql/tab-complete.c

@@ -1675,10 +1675,14 @@ psql_completion(const char *text, int start, int end)
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) &&
 			 TailMatches("ADD|DROP|SET", "PUBLICATION", MatchAny))
 		COMPLETE_WITH("WITH (");
-	/* ALTER SUBSCRIPTION <name> ADD|DROP|SET PUBLICATION <name> WITH ( */
+	/* ALTER SUBSCRIPTION <name> ADD|SET PUBLICATION <name> WITH ( */
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) &&
-			 TailMatches("ADD|DROP|SET", "PUBLICATION", MatchAny, "WITH", "("))
+			 TailMatches("ADD|SET", "PUBLICATION", MatchAny, "WITH", "("))
 		COMPLETE_WITH("copy_data", "refresh");
+	/* ALTER SUBSCRIPTION <name> DROP PUBLICATION <name> WITH ( */
+	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) &&
+			 TailMatches("DROP", "PUBLICATION", MatchAny, "WITH", "("))
+		COMPLETE_WITH("refresh");
 
 	/* ALTER SCHEMA <name> */
 	else if (Matches("ALTER", "SCHEMA", MatchAny))

src/test/regress/expected/subscription.out

@@ -223,7 +223,7 @@ ALTER SUBSCRIPTION regress_testsub DROP PUBLICATION testpub1, testpub1 WITH (ref
 ERROR:  publication name "testpub1" used more than once
 -- fail - all publications are deleted
 ALTER SUBSCRIPTION regress_testsub DROP PUBLICATION testpub, testpub1, testpub2 WITH (refresh = false);
-ERROR:  subscription must contain at least one publication
+ERROR:  cannot drop all the publications from a subscription
 -- fail - publication does not exist in subscription
 ALTER SUBSCRIPTION regress_testsub DROP PUBLICATION testpub3 WITH (refresh = false);
 ERROR:  publication "testpub3" is not in subscription "regress_testsub"