Print inifile and rootdir when there's usage errors

CHANGELOG

@@ -1,6 +1,11 @@
 2.8.0.dev (compared to 2.7.X)
 -----------------------------
 
+- rootdir and inifile are now displayed during usage errors to help
+  users diagnose problems such as unexpected ini files which add
+  unknown options being picked up by pytest. Thanks to Pavel Savchenko for
+  bringing the problem to attention in #821 and Bruno Oliveira for the PR.
+
 - Summary bar now is colored yellow for warning
   situations such as: all tests either were skipped or xpass/xfailed,
   or no tests were run at all (this is a partial fix for issue500). 

_pytest/config.py

@@ -382,7 +382,11 @@ def import_plugin(self, modname):
 
 
 class Parser:
-    """ Parser for command line arguments and ini-file values.  """
+    """ Parser for command line arguments and ini-file values.
+
+    :ivar extra_info: dict of generic param -> value to display in case
+        there's an error processing the command line arguments.
+    """
 
     def __init__(self, usage=None, processopt=None):
         self._anonymous = OptionGroup("custom options", parser=self)
@@ -391,6 +395,7 @@ def __init__(self, usage=None, processopt=None):
         self._usage = usage
         self._inidict = {}
         self._ininames = []
+        self.extra_info = {}
 
     def processoption(self, option):
         if self._processopt:
@@ -444,7 +449,7 @@ def parse(self, args):
 
     def _getparser(self):
         from _pytest._argcomplete import filescompleter
-        optparser = MyOptionParser(self)
+        optparser = MyOptionParser(self, self.extra_info)
         groups = self._groups + [self._anonymous]
         for group in groups:
             if group.options:
@@ -669,19 +674,26 @@ def _addoption_instance(self, option, shortupper=False):
 
 
 class MyOptionParser(argparse.ArgumentParser):
-    def __init__(self, parser):
+    def __init__(self, parser, extra_info=None):
+        if not extra_info:
+            extra_info = {}
         self._parser = parser
         argparse.ArgumentParser.__init__(self, usage=parser._usage,
             add_help=False, formatter_class=DropShorterLongHelpFormatter)
+        # extra_info is a dict of (param -> value) to display if there's
+        # an usage error to provide more contextual information to the user
+        self.extra_info = extra_info
 
     def parse_args(self, args=None, namespace=None):
         """allow splitting of positional arguments"""
         args, argv = self.parse_known_args(args, namespace)
         if argv:
             for arg in argv:
                 if arg and arg[0] == '-':
-                    msg = argparse._('unrecognized arguments: %s')
-                    self.error(msg % ' '.join(argv))
+                    lines = ['unrecognized arguments: %s' % (' '.join(argv))]
+                    for k, v in sorted(self.extra_info.items()):
+                        lines.append('  %s: %s' % (k, v))
+                    self.error('\n'.join(lines))
             getattr(args, FILE_OR_DIR).extend(argv)
         return args
 
@@ -863,6 +875,8 @@ def _initini(self, args):
         parsed_args = self._parser.parse_known_args(args)
         r = determine_setup(parsed_args.inifilename, parsed_args.file_or_dir)
         self.rootdir, self.inifile, self.inicfg = r
+        self._parser.extra_info['rootdir'] = self.rootdir
+        self._parser.extra_info['inifile'] = self.inifile
         self.invocation_dir = py.path.local()
         self._parser.addini('addopts', 'extra command line options', 'args')
         self._parser.addini('minversion', 'minimally required pytest version')

testing/test_config.py

@@ -326,6 +326,19 @@ def pytest_cmdline_preparse(args):
         "*-h*",
     ])
 
+def test_invalid_options_show_extra_information(testdir):
+    """display extra information when pytest exits due to unrecognized
+    options in the command-line"""
+    testdir.makeini("""
+        [pytest]
+        addopts = --invalid-option
+    """)
+    result = testdir.runpytest()
+    result.stderr.fnmatch_lines([
+        "*error: unrecognized arguments: --invalid-option*",
+        "*  inifile: %s*" % testdir.tmpdir.join('tox.ini'),
+        "*  rootdir: %s*" % testdir.tmpdir,
+    ])
 
 @pytest.mark.skipif("sys.platform == 'win32'")
 def test_toolongargs_issue224(testdir):