Fix pg_rewind with in-place tablespaces when source is remote

libpq_source.c would consider any result returned by
pg_tablespace_location() as a symlink, resulting in run-time errors like
that:
pg_rewind: error: file "pg_tblspc/NN" is of different type in source and target

In-place tablespaces are directories located in pg_tblspc/, returned as
relative paths instead of absolute paths, so rely on that to make the
difference with a normal tablespace and an in-place one.  If the path is
relative, the tablespace is handled as a directory.  If the path is
absolute, consider it as a symlink.

In-place tablespaces are only intended for development purposes, so like
363e8f9 no backpatch is done.  A test is added in pg_rewind with an
in-place tablespace and some data in it.

Author: Rui Zhao, Michael Paquier
Discussion: https://postgr.es/m/2b79d2a8-b2d5-4bd7-a15b-31e485100980.xiyuan.zr@alibaba-inc.com

src/bin/pg_rewind/libpq_source.c

@@ -298,7 +298,16 @@ libpq_traverse_files(rewind_source *source, process_file_callback_t callback)
 		link_target = PQgetvalue(res, i, 3);
 
 		if (link_target[0])
+		{
+			/*
+			 * In-place tablespaces are directories located in pg_tblspc/ with
+			 * relative paths.
+			 */
+			if (is_absolute_path(link_target))
 				type = FILE_TYPE_SYMLINK;
+			else
+				type = FILE_TYPE_DIRECTORY;
+		}
 		else if (isdir)
 			type = FILE_TYPE_DIRECTORY;
 		else

src/bin/pg_rewind/t/001_basic.pl

@@ -18,6 +18,12 @@ sub run_test
 	RewindTest::setup_cluster($test_mode);
 	RewindTest::start_primary();
 
+	# Create an in-place tablespace with some data on it.
+	primary_psql("CREATE TABLESPACE space_test LOCATION ''");
+	primary_psql("CREATE TABLE space_tbl (d text) TABLESPACE space_test");
+	primary_psql(
+		"INSERT INTO space_tbl VALUES ('in primary, before promotion')");
+
 	# Create a test table and insert a row in primary.
 	primary_psql("CREATE TABLE tbl1 (d text)");
 	primary_psql("INSERT INTO tbl1 VALUES ('in primary')");
@@ -78,6 +84,13 @@ sub run_test
 		"insert into drop_tbl values ('in primary, after promotion')");
 	primary_psql("DROP TABLE drop_tbl");
 
+	# Insert some data in the in-place tablespace for the old primary and
+	# the standby.
+	primary_psql(
+		"INSERT INTO space_tbl VALUES ('in primary, after promotion')");
+	standby_psql(
+		"INSERT INTO space_tbl VALUES ('in standby, after promotion')");
+
 	# Before running pg_rewind, do a couple of extra tests with several
 	# option combinations.  As the code paths taken by those tests
 	# do not change for the "local" and "remote" modes, just run them
@@ -145,6 +158,13 @@ sub run_test
 
 	RewindTest::run_pg_rewind($test_mode);
 
+	check_query(
+		'SELECT * FROM space_tbl ORDER BY d',
+		qq(in primary, before promotion
+in standby, after promotion
+),
+		'table content');
+
 	check_query(
 		'SELECT * FROM tbl1',
 		qq(in primary

src/bin/pg_rewind/t/RewindTest.pm

@@ -131,6 +131,7 @@ sub setup_cluster
 	$node_primary->append_conf(
 		'postgresql.conf', qq(
 wal_keep_size = 320MB
+allow_in_place_tablespaces = on
 ));
 	return;
 }