Author:     Noah Misch <noah@leadboat.com>
Commit:     Noah Misch <noah@leadboat.com>

    Dump COMMENT ON SCHEMA public.
    
    As we do for other attributes of the public schema, omit the COMMENT
    command when its payload would match what initdb had installed.  For
    dumps that do carry this new COMMENT command, non-superusers restoring
    them are likely to get an error.
    
    Reviewed by FIXME.
    
    Discussion: https://postgr.es/m/ab48a34c-60f6-e388-502a-3e5fe46a2dae@postgresfriends.org

diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index e8ea385..0a3f40d 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -1565,15 +1565,12 @@ selectDumpableNamespace(NamespaceInfo *nsinfo, Archive *fout)
 	{
 		/*
 		 * The public schema is a strange beast that sits in a sort of
-		 * no-mans-land between being a system object and a user object.  We
-		 * don't want to dump creation or comment commands for it, because
-		 * that complicates matters for non-superuser use of pg_dump.  But we
-		 * should dump any ownership changes, security labels, and ACL
-		 * changes, and of course we should dump contained objects.  pg_dump
-		 * ties ownership to DUMP_COMPONENT_DEFINITION.  Hence, unless the
-		 * owner is the default, dump a "definition" bearing just a comment.
+		 * no-mans-land between being a system object and a user object.
+		 * CREATE SCHEMA would fail, so its DUMP_COMPONENT_DEFINITION is just
+		 * a comment and an indication of ownership.  If the owner is the
+		 * default, that DUMP_COMPONENT_DEFINITION is superfluous.
 		 */
-		nsinfo->dobj.dump = DUMP_COMPONENT_ALL & ~DUMP_COMPONENT_COMMENT;
+		nsinfo->dobj.dump = DUMP_COMPONENT_ALL;
 		if (nsinfo->nspowner == BOOTSTRAP_SUPERUSERID)
 			nsinfo->dobj.dump &= ~DUMP_COMPONENT_DEFINITION;
 		nsinfo->dobj.dump_contains = DUMP_COMPONENT_ALL;
@@ -9914,6 +9911,28 @@ dumpComment(Archive *fout, const char *type, const char *name,
 		ncomments--;
 	}
 
+	/*
+	 * Skip dumping the initdb-provided public schema comment, which would
+	 * complicate matters for non-superuser use of pg_dump.  When the DBA has
+	 * removed initdb's comment, replicate that.
+	 */
+	if (strcmp(type, "SCHEMA") == 0 && strcmp(name, "public") == 0)
+	{
+		static CommentItem empty_comment = {.descr = ""};
+
+		if (ncomments == 0)
+		{
+			comments = &empty_comment;
+			ncomments = 1;
+		}
+		else if (strcmp(comments->descr, (fout->remoteVersion >= 80300 ?
+										  "standard public schema" :
+										  "Standard public schema")) == 0)
+		{
+			ncomments = 0;
+		}
+	}
+
 	/* If a comment exists, build COMMENT ON statement */
 	if (ncomments > 0)
 	{
diff --git a/src/bin/pg_dump/t/002_pg_dump.pl b/src/bin/pg_dump/t/002_pg_dump.pl
index 392da3b..4693292 100644
--- a/src/bin/pg_dump/t/002_pg_dump.pl
+++ b/src/bin/pg_dump/t/002_pg_dump.pl
@@ -968,9 +968,19 @@ my %tests = (
 
 	'COMMENT ON SCHEMA public' => {
 		regexp => qr/^COMMENT ON SCHEMA public IS .+;/m,
+		# regress_public_owner emits this, due to create_sql of next test
+		like => {
+			pg_dumpall_dbprivs => 1,
+			pg_dumpall_exclude => 1,
+		},
+	},
 
-		# this shouldn't ever get emitted
-		like => {},
+	'COMMENT ON SCHEMA public IS NULL' => {
+		database     => 'regress_public_owner',
+		create_order => 100,
+		create_sql   => 'COMMENT ON SCHEMA public IS NULL;',
+		regexp       => qr/^COMMENT ON SCHEMA public IS '';/m,
+		like         => { defaults_public_owner => 1 },
 	},
 
 	'COMMENT ON TABLE dump_test.test_table' => {
diff --git a/src/include/catalog/pg_namespace.dat b/src/include/catalog/pg_namespace.dat
index 2ed136b..988f1c4 100644
--- a/src/include/catalog/pg_namespace.dat
+++ b/src/include/catalog/pg_namespace.dat
@@ -18,6 +18,7 @@
 { oid => '99', oid_symbol => 'PG_TOAST_NAMESPACE',
   descr => 'reserved schema for TOAST tables',
   nspname => 'pg_toast', nspacl => '_null_' },
+# update dumpComment() if changing this descr
 { oid => '2200', oid_symbol => 'PG_PUBLIC_NAMESPACE',
   descr => 'standard public schema',
   nspname => 'public', nspacl => '_null_' },