Do not require 'public' to exist for pg_dump -c

Commit 330b84d8 didn't contemplate the case where the public schema
has been dropped and introduced a query which fails when there is no
public schema into pg_dump (when used with -c).

Adjust the query used by pg_dump to handle the case where the public
schema doesn't exist and add tests to check that such a case no longer
fails.

Back-patch the specific fix to 9.6, as the prior commit was.

Adding tests for this case involved adding support to the pg_dump
TAP tests to work with multiple databases, which, while not a large
change, is a bit much to back-patch, so that's only done in master.

Addresses bug #14650
Discussion: https://www.postgresql.org/message-id/20170512181801.1795.47483%40wrigleys.postgresql.org

src/bin/pg_dump/pg_dump.c

@@ -4135,9 +4135,14 @@ getNamespaces(Archive *fout, int *numNamespaces)
 		 * essentially a no-op because the new public schema won't have an
 		 * entry in pg_init_privs anyway, as the entry will be removed when
 		 * the public schema is dropped.
+		 *
+		 * Further, we have to handle the case where the public schema does
+		 * not exist at all.
 		 */
 		if (dopt->outputClean)
-			appendPQExpBuffer(query, " AND pip.objoid <> 'public'::regnamespace");
+			appendPQExpBuffer(query, " AND pip.objoid <> "
+									 "coalesce((select oid from pg_namespace "
+									 "where nspname = 'public'),0)");
 
 		appendPQExpBuffer(query, ") ");
 

src/bin/pg_dump/t/002_pg_dump.pl

@@ -97,6 +97,23 @@ my %pgdump_runs = (
 			'pg_dump', '--no-sync',
 			'-f',      "$tempdir/defaults.sql",
 			'postgres', ], },
+	defaults_no_public => {
+		database => 'regress_pg_dump_test',
+		dump_cmd => [
+			'pg_dump',
+			'--no-sync',
+			'-f',
+			"$tempdir/defaults_no_public.sql",
+			'regress_pg_dump_test', ], },
+	defaults_no_public_clean => {
+		database => 'regress_pg_dump_test',
+		dump_cmd => [
+			'pg_dump',
+			'--no-sync',
+			'-c',
+			'-f',
+			"$tempdir/defaults_no_public_clean.sql",
+			'regress_pg_dump_test', ], },
 
 	# Do not use --no-sync to give test coverage for data sync.
 	defaults_custom_format => {
@@ -4524,6 +4541,35 @@ qr/CREATE TRANSFORM FOR integer LANGUAGE sql \(FROM SQL WITH FUNCTION pg_catalog
 			pg_dumpall_globals_clean => 1,
 			test_schema_plus_blobs   => 1, }, },
 
+	'CREATE SCHEMA public' => {
+		all_runs     => 1,
+		catch_all    => 'CREATE ... commands',
+		regexp       => qr/^CREATE SCHEMA public;/m,
+		like         => {
+			clean                   => 1,
+			clean_if_exists         => 1, },
+		unlike => {
+			binary_upgrade           => 1,
+			createdb                 => 1,
+			defaults                 => 1,
+			exclude_test_table       => 1,
+			exclude_test_table_data  => 1,
+			no_blobs                 => 1,
+			no_privs                 => 1,
+			no_owner                 => 1,
+			only_dump_test_schema    => 1,
+			pg_dumpall_dbprivs       => 1,
+			schema_only              => 1,
+			section_pre_data         => 1,
+			test_schema_plus_blobs   => 1,
+			with_oids                => 1,
+			exclude_dump_test_schema => 1,
+			only_dump_test_table     => 1,
+			pg_dumpall_globals       => 1,
+			pg_dumpall_globals_clean => 1,
+			role                     => 1,
+			section_post_data        => 1, }, },
+
 	'CREATE SCHEMA dump_test' => {
 		all_runs     => 1,
 		catch_all    => 'CREATE ... commands',
@@ -5219,6 +5265,34 @@ qr/CREATE TRANSFORM FOR integer LANGUAGE sql \(FROM SQL WITH FUNCTION pg_catalog
 			data_only      => 1,
 			section_data   => 1, }, },
 
+	'DROP SCHEMA public (for testing without public schema)' => {
+		all_runs  => 1,
+		database => 'regress_pg_dump_test',
+		create_order => 100,
+		create_sql => 'DROP SCHEMA public;',
+		regexp    => qr/^DROP SCHEMA public;/m,
+		like      => { },
+		unlike    => { defaults_no_public => 1,
+		               defaults_no_public_clean => 1, } },
+
+	'DROP SCHEMA public' => {
+		all_runs  => 1,
+		catch_all => 'DROP ... commands',
+		regexp    => qr/^DROP SCHEMA public;/m,
+		like         => { clean => 1 },
+		unlike => {
+			clean_if_exists         => 1,
+			pg_dumpall_globals_clean => 1, }, },
+
+	'DROP SCHEMA IF EXISTS public' => {
+		all_runs  => 1,
+		catch_all => 'DROP ... commands',
+		regexp    => qr/^DROP SCHEMA IF EXISTS public;/m,
+		like         => { clean_if_exists => 1 },
+		unlike => {
+			clean => 1,
+			pg_dumpall_globals_clean => 1, }, },
+
 	'DROP EXTENSION plpgsql' => {
 		all_runs  => 1,
 		catch_all => 'DROP ... commands',
@@ -6433,6 +6507,9 @@ if ($collation_check_stderr !~ /ERROR: /)
 	$collation_support = 1;
 }
 
+# Create a second database for certain tests to work against
+$node->psql('postgres','create database regress_pg_dump_test;');
+
 # Start with number of command_fails_like()*2 tests below (each
 # command_fails_like is actually 2 tests)
 my $num_tests = 12;
@@ -6440,6 +6517,11 @@ my $num_tests = 12;
 foreach my $run (sort keys %pgdump_runs)
 {
 	my $test_key = $run;
+	my $run_db = 'postgres';
+
+	if (defined($pgdump_runs{$run}->{database})) {
+		$run_db = $pgdump_runs{$run}->{database};
+	}
 
 	# Each run of pg_dump is a test itself
 	$num_tests++;
@@ -6458,6 +6540,19 @@ foreach my $run (sort keys %pgdump_runs)
 	# Then count all the tests run against each run
 	foreach my $test (sort keys %tests)
 	{
+		# postgres is the default database, if it isn't overridden
+		my $test_db = 'postgres';
+
+		# Specific tests can override the database to use
+		if (defined($tests{$test}->{database})) {
+			$test_db = $tests{$test}->{database};
+		}
+
+		# The database to test against needs to match the database the run is
+		# for, so skip combinations where they don't match up.
+		if ($run_db ne $test_db) {
+			next;
+		}
 
 		# Skip any collation-related commands if there is no collation support
 		if (!$collation_support && defined($tests{$test}->{collation}))
@@ -6507,7 +6602,7 @@ plan tests => $num_tests;
 # Set up schemas, tables, etc, to be dumped.
 
 # Build up the create statements
-my $create_sql = '';
+my %create_sql = ();
 
 foreach my $test (
 	sort {
@@ -6529,6 +6624,12 @@ foreach my $test (
 		}
 	} keys %tests)
 {
+	my $test_db = 'postgres';
+
+	if (defined($tests{$test}->{database})) {
+		$test_db = $tests{$test}->{database};
+	}
+
 	if ($tests{$test}->{create_sql})
 	{
 
@@ -6539,12 +6640,15 @@ foreach my $test (
 		}
 
 		# Add terminating semicolon
-		$create_sql .= $tests{$test}->{create_sql} . ";";
+		$create_sql{$test_db} .= $tests{$test}->{create_sql} . ";";
 	}
 }
 
 # Send the combined set of commands to psql
-$node->safe_psql('postgres', $create_sql);
+foreach my $db (sort keys %create_sql)
+{
+	$node->safe_psql($db, $create_sql{$db});
+}
 
 #########################################
 # Test connecting to a non-existent database