Merge pull request #2750 from evanunderscore/fix-filescompleter

Fix crash in FastFilesCompleter with no prefix

_pytest/_argcomplete.py

@@ -78,7 +78,8 @@ class FastFilesCompleter:
         completion = []
         globbed = []
         if '*' not in prefix and '?' not in prefix:
-            if prefix[-1] == os.path.sep:  # we are on unix, otherwise no bash
+            # we are on unix, otherwise no bash
+            if not prefix or prefix[-1] == os.path.sep:
                 globbed.extend(glob(prefix + '.*'))
             prefix += '*'
         globbed.extend(glob(prefix))
@@ -98,7 +99,7 @@ if os.environ.get('_ARGCOMPLETE'):
     filescompleter = FastFilesCompleter()
 
     def try_argcomplete(parser):
-        argcomplete.autocomplete(parser)
+        argcomplete.autocomplete(parser, always_complete_options=False)
 else:
     def try_argcomplete(parser):
         pass