PR 2117 - Only check the prefix is writable if installing and not a dry run.

source-builder/sb/setbuilder.py

@@ -367,6 +367,10 @@ def run():
         else:
             deps = None
         if not list_bset_cfg_files(opts, configs):
+            prefix = opts.defaults.expand('%{_prefix}')
+            if not opts.dry_run() and not opts.no_install() and \
+                    not path.ispathwritable(prefix):
+                raise error.general('prefix is not writable: %s' % (path.host(prefix)))
             for bset in opts.params():
                 b = buildset(bset, configs, opts)
                 b.build(deps)