do not delete yml metadata when raumel not installed

fdroidserver/metadata.py

@@ -27,6 +27,7 @@ import logging
 import textwrap
 import io
 import yaml
+import importlib
 from collections import OrderedDict
 
 import fdroidserver.common
@@ -1584,11 +1585,15 @@ def write_metadata(metadatapath, app):
         warn_or_exception(_('Cannot write "{path}", not an accepted format, use: {formats}')
                           .format(path=metadatapath, formats=', '.join(accepted)))
 
-    with open(metadatapath, 'w') as mf:
-        if ext == 'txt':
+    if ext == 'txt':
+        with open(metadatapath, 'w') as mf:
             return write_txt(mf, app)
-        elif ext == 'yml':
-            return write_yaml(mf, app)
+    elif ext == 'yml':
+        if importlib.util.find_spec('ruamel.yaml'):
+            with open(metadatapath, 'w') as mf:
+                return write_yaml(mf, app)
+        else:
+            raise FDroidException('ruamel.yaml not installed, can not write metadata.')
 
     warn_or_exception(_('Unknown metadata format: %s') % metadatapath)
 

tests/rewritemeta.TestCase

@@ -110,8 +110,8 @@ class RewriteMetaTest(unittest.TestCase):
             with open('metadata/a.txt', 'w') as f:
                 f.write('Auto Name:a')
 
-            def boom(mf, app):
-                raise FDroidException()
+            def boom(*args):
+                raise FDroidException(' '.join((str(x) for x in args)))
 
             with mock.patch('fdroidserver.metadata.write_yaml', boom):
                 with self.assertRaises(FDroidException):
@@ -128,10 +128,10 @@ class RewriteMetaTest(unittest.TestCase):
             with open('metadata/a.yml', 'w') as f:
                 f.write('AutoName: a')
 
-            def boom(mf, app):
-                raise FDroidException()
+            def boom(*args):
+                raise FDroidException(' '.join((str(x) for x in args)))
 
-            with mock.patch('fdroidserver.metadata.write_yaml', boom):
+            with mock.patch('importlib.util.find_spec', boom):
                 with self.assertRaises(FDroidException):
                     rewritemeta.main()