Implement an "S" option for psql's \dn command.

\dn without "S" now hides all pg_XXX schemas as well as information_schema.
Thus, in a bare database you'll only see "public".  ("public" is considered
a user schema, not a system schema, mainly because it's droppable.)
Per discussion back in late September.

doc/src/sgml/ref/psql-ref.sgml

@@ -1232,16 +1232,17 @@ testdb=>
 
 
       <varlistentry>
-        <term><literal>\dn[+] [ <link linkend="APP-PSQL-patterns"><replaceable class="parameter">pattern</replaceable></link> ]</literal></term>
+        <term><literal>\dn[S+] [ <link linkend="APP-PSQL-patterns"><replaceable class="parameter">pattern</replaceable></link> ]</literal></term>
 
         <listitem>
         <para>
         Lists schemas (namespaces). If <replaceable
         class="parameter">pattern</replaceable>
         is specified, only schemas whose names match the pattern are listed.
-        Non-local temporary schemas are suppressed.  If <literal>+</literal>
-        is appended to the command name, each object is listed with its associated
-        permissions and description, if any.
+        By default, only user-created objects are shown; supply a
+        pattern or the <literal>S</literal> modifier to include system objects.
+        If <literal>+</literal> is appended to the command name, each object
+        is listed with its associated permissions and description, if any.
         </para>
         </listitem>
       </varlistentry>

src/bin/psql/command.c

@@ -417,7 +417,7 @@ exec_command(const char *cmd,
 				success = do_lo_list();
 				break;
 			case 'n':
-				success = listSchemas(pattern, show_verbose);
+				success = listSchemas(pattern, show_verbose, show_system);
 				break;
 			case 'o':
 				success = describeOperators(pattern, show_system);

src/bin/psql/describe.c

@@ -2697,7 +2697,7 @@ listCasts(const char *pattern)
  * Describes schemas (namespaces)
  */
 bool
-listSchemas(const char *pattern, bool verbose)
+listSchemas(const char *pattern, bool verbose, bool showSystem)
 {
 	PQExpBufferData buf;
 	PGresult   *res;
@@ -2720,11 +2720,14 @@ listSchemas(const char *pattern, bool verbose)
 	}
 
 	appendPQExpBuffer(&buf,
-					  "\nFROM pg_catalog.pg_namespace n\n"
-					  "WHERE	(n.nspname !~ '^pg_temp_' OR\n"
-		   "		 n.nspname = (pg_catalog.current_schemas(true))[1])\n");		/* temp schema is first */
+					  "\nFROM pg_catalog.pg_namespace n\n");
 
-	processSQLNamePattern(pset.db, &buf, pattern, true, false,
+	if (!showSystem && !pattern)
+		appendPQExpBuffer(&buf,
+						  "WHERE n.nspname !~ '^pg_' AND n.nspname <> 'information_schema'\n");
+
+	processSQLNamePattern(pset.db, &buf, pattern,
+						  !showSystem && !pattern, false,
 						  NULL, "n.nspname", NULL,
 						  NULL);
 

src/bin/psql/describe.h

@@ -70,7 +70,7 @@ extern bool listConversions(const char *pattern, bool showSystem);
 extern bool listCasts(const char *pattern);
 
 /* \dn */
-extern bool listSchemas(const char *pattern, bool verbose);
+extern bool listSchemas(const char *pattern, bool verbose, bool showSystem);
 
 /* \dew */
 extern bool listForeignDataWrappers(const char *pattern, bool verbose);