Fix --help with required options

This works by adding an argparse Action that will raise an exception in
order to skip the rest of the argument parsing. This prevents argparse
from quitting due to missing required arguments, similar to the way that
the builtin argparse --help option is implemented by raising SystemExit.

Fixes: #1999

AUTHORS

@@ -144,6 +144,7 @@ Ross Lawley
 Russel Winder
 Ryan Wooden
 Samuele Pedroni
+Segev Finer
 Simon Gomizelj
 Skylar Downes
 Stefan Farmbauer

_pytest/config.py

@@ -71,6 +71,12 @@ class UsageError(Exception):
     """ error in pytest usage or invocation"""
 
 
+class PrintHelp(Exception):
+    """Raised when pytest should print it's help to skip the rest of the
+    argument parsing and validation."""
+    pass
+
+
 def filename_arg(path, optname):
     """ Argparse type validator for filename arguments.
 
@@ -1100,14 +1106,18 @@ class Config(object):
         self._preparse(args, addopts=addopts)
         # XXX deprecated hook:
         self.hook.pytest_cmdline_preparse(config=self, args=args)
-        args = self._parser.parse_setoption(args, self.option, namespace=self.option)
-        if not args:
-            cwd = os.getcwd()
-            if cwd == self.rootdir:
-                args = self.getini('testpaths')
+        self._parser.after_preparse = True
+        try:
+            args = self._parser.parse_setoption(args, self.option, namespace=self.option)
             if not args:
-                args = [cwd]
-        self.args = args
+                cwd = os.getcwd()
+                if cwd == self.rootdir:
+                    args = self.getini('testpaths')
+                if not args:
+                    args = [cwd]
+            self.args = args
+        except PrintHelp:
+            pass
 
     def addinivalue_line(self, name, line):
         """ add a line to an ini-file option. The option must have been

_pytest/helpconfig.py

@@ -3,13 +3,38 @@ from __future__ import absolute_import, division, print_function
 
 import py
 import pytest
+from _pytest.config import PrintHelp
 import os, sys
+from argparse import Action
+
+
+class HelpAction(Action):
+    def __init__(self,
+                 option_strings,
+                 dest=None,
+                 default=False,
+                 help=None):
+        super(HelpAction, self).__init__(
+            option_strings=option_strings,
+            dest=dest,
+            const=True,
+            default=default,
+            nargs=0,
+            help=help)
+
+    def __call__(self, parser, namespace, values, option_string=None):
+        setattr(namespace, self.dest, self.const)
+
+        # We should only skip the rest of the parsing after preparse is done
+        if getattr(parser._parser, 'after_preparse', False):
+            raise PrintHelp
+
 
 def pytest_addoption(parser):
     group = parser.getgroup('debugconfig')
     group.addoption('--version', action="store_true",
             help="display pytest lib version and import information.")
-    group._addoption("-h", "--help", action="store_true", dest="help",
+    group._addoption("-h", "--help", action=HelpAction, dest="help",
             help="show help message and configuration info")
     group._addoption('-p', action="append", dest="plugins", default = [],
                metavar="name",

changelog/1999.bugfix

@@ -0,0 +1,2 @@
+Required options added via ``pytest_addoption`` will no longer prevent
+using --help without passing them.

testing/test_conftest.py

@@ -449,3 +449,15 @@ def test_hook_proxy(testdir):
         '*test_foo4.py*',
         '*3 passed*',
     ])
+
+
+def test_required_option_help(testdir):
+    testdir.makeconftest("assert 0")
+    x = testdir.mkdir("x")
+    x.join("conftest.py").write(_pytest._code.Source("""
+        def pytest_addoption(parser):
+            parser.addoption("--xyz", action="store_true", required=True)
+    """))
+    result = testdir.runpytest("-h", x)
+    assert 'argument --xyz is required' not in result.stdout.str()
+    assert 'general:' in result.stdout.str()