Warn about tablespace creation in PGDATA

Also add warning to pg_upgrade

Report by Josh Berkus

src/backend/commands/tablespace.c

@@ -288,6 +288,12 @@ CreateTableSpace(CreateTableSpaceStmt *stmt)
 				 errmsg("tablespace location \"%s\" is too long",
 						location)));
 
+	/* Warn if the tablespace is in the data directory. */
+	if (path_is_prefix_of_path(DataDir, location))
+		ereport(WARNING,
+				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+				 errmsg("tablespace location should not be inside the data directory")));
+
 	/*
 	 * Disallow creation of tablespaces named "pg_xxx"; we reserve this
 	 * namespace for system purposes.

src/bin/pg_upgrade/check.c

@@ -508,6 +508,10 @@ create_script_for_old_cluster_deletion(char **deletion_script_file_name)
 		canonicalize_path(old_tablespace_dir);
 		if (path_is_prefix_of_path(old_cluster_pgdata, old_tablespace_dir))
 		{
+			/* reproduce warning from CREATE TABLESPACE that is in the log */
+			pg_log(PG_WARNING,
+				"\nWARNING:  user-defined tablespace locations should not be inside the data directory, e.g. %s\n", old_tablespace_dir);
+
 			/* Unlink file in case it is left over from a previous run. */
 			unlink(*deletion_script_file_name);
 			pg_free(*deletion_script_file_name);