Prevent duplicate RTEPermissionInfo for plain-inheritance parents

Currently, expand_single_inheritance_child() doesn't reset
perminfoindex in a plain-inheritance parent's child RTE, because
prior to 387f9ed0a0, the executor would use the first child RTE to
locate the parent's RTEPermissionInfo.  That in turn causes
add_rte_to_flat_rtable() to create an extra RTEPermissionInfo
belonging to the parent's child RTE with the same content as the one
belonging to the parent's original ("root") RTE.

In 387f9ed0a0, we changed things so that the executor can now use the
parent's "root" RTE for locating its RTEPermissionInfo instead of the
child RTE, so the latter's perminfoindex need not be set anymore, so
make it so.

Reported-by: Tom Lane
Discussion: https://postgr.es/m/839708.1698174464@sss.pgh.pa.us
Backpatch-through: 16

doc/src/sgml/ecpg.sgml

@@ -412,12 +412,6 @@ EXEC SQL DISCONNECT <optional><replaceable>connection</replaceable></optional>;
      </simpara>
     </listitem>
 
-    <listitem>
-     <simpara>
-      <literal>DEFAULT</literal>
-     </simpara>
-    </listitem>
-
     <listitem>
      <simpara>
       <literal>CURRENT</literal>
@@ -7128,7 +7122,6 @@ EXEC SQL DEALLOCATE DESCRIPTOR mydesc;
 <synopsis>
 DISCONNECT <replaceable class="parameter">connection_name</replaceable>
 DISCONNECT [ CURRENT ]
-DISCONNECT DEFAULT
 DISCONNECT ALL
 </synopsis>
    </refsynopsisdiv>
@@ -7169,15 +7162,6 @@ DISCONNECT ALL
       </listitem>
      </varlistentry>
 
-     <varlistentry id="ecpg-sql-disconnect-default">
-      <term><literal>DEFAULT</literal></term>
-      <listitem>
-       <para>
-        Close the default connection.
-       </para>
-      </listitem>
-     </varlistentry>
-
      <varlistentry id="ecpg-sql-disconnect-all">
       <term><literal>ALL</literal></term>
       <listitem>
@@ -7196,13 +7180,11 @@ DISCONNECT ALL
 int
 main(void)
 {
-    EXEC SQL CONNECT TO testdb AS DEFAULT USER testuser;
     EXEC SQL CONNECT TO testdb AS con1 USER testuser;
     EXEC SQL CONNECT TO testdb AS con2 USER testuser;
     EXEC SQL CONNECT TO testdb AS con3 USER testuser;
 
     EXEC SQL DISCONNECT CURRENT;  /* close con3          */
-    EXEC SQL DISCONNECT DEFAULT;  /* close DEFAULT       */
     EXEC SQL DISCONNECT ALL;      /* close con2 and con1 */
 
     return 0;
@@ -7770,11 +7752,11 @@ SET CONNECTION [ TO | = ] <replaceable class="parameter">connection_name</replac
       </listitem>
      </varlistentry>
 
-     <varlistentry id="ecpg-sql-set-connection-default">
+     <varlistentry id="ecpg-sql-set-connection-current">
-      <term><literal>DEFAULT</literal></term>
+      <term><literal>CURRENT</literal></term>
       <listitem>
        <para>
-        Set the connection to the default connection.
+        Set the connection to the current connection (thus, nothing happens).
        </para>
       </listitem>
      </varlistentry>

src/backend/optimizer/util/inherit.c

@@ -494,13 +494,8 @@ expand_single_inheritance_child(PlannerInfo *root, RangeTblEntry *parentrte,
 		childrte->inh = false;
 	childrte->securityQuals = NIL;
 
-	/*
+	/* No permission checking for child RTEs. */
-	 * No permission checking for the child RTE unless it's the parent
+	childrte->perminfoindex = 0;
-	 * relation in its child role, which only applies to traditional
-	 * inheritance.
-	 */
-	if (childOID != parentOID)
-		childrte->perminfoindex = 0;
 
 	/* Link not-yet-fully-filled child RTE into data structures */
 	parse->rtable = lappend(parse->rtable, childrte);