# Source code for _pytest.assertion

    """
    support for presenting detailed information in failing assertions.
    """
    from __future__ import absolute_import, division, print_function
    import sys
    import six

    from _pytest.assertion import util
    from _pytest.assertion import rewrite
    from _pytest.assertion import truncate

    def pytest_addoption(parser):
        group = parser.getgroup("debugconfig")
        group.addoption('--assert',
                        action="store",
                        dest="assertmode",
                        choices=("rewrite", "plain",),
                        default="rewrite",
                        metavar="MODE",
                        help="""Control assertion debugging tools.  'plain'
                                performs no assertion debugging.  'rewrite'
                                (the default) rewrites assert statements in
                                test modules on import to provide assert
                                expression information.""")

    def register_assert_rewrite(*names):
        """Register one or more module names to be rewritten on import.

        This function will make sure that this module or all modules inside
        the package will get their assert statements rewritten.
        Thus you should make sure to call this before the module is
        actually imported, usually in your __init__.py if you are a plugin
        using a package.

        :raise TypeError: if the given module names are not strings.
        """
        for name in names:
            if not isinstance(name, str):
                msg = 'expected module names as *args, got {0} instead'
                raise TypeError(msg.format(repr(names)))
        for hook in sys.meta_path:
            if isinstance(hook, rewrite.AssertionRewritingHook):
                importhook = hook
                break
        else:
            importhook = DummyRewriteHook()
        importhook.mark_rewrite(*names)

    class DummyRewriteHook(object):
        """A no-op import hook for when rewriting is disabled."""

        def mark_rewrite(self, *names):
            pass

    class AssertionState:
        """State for the assertion plugin."""

        def __init__(self, config, mode):
            self.mode = mode
            self.trace = config.trace.root.get("assertion")
            self.hook = None

    def install_importhook(config):
        """Try to install the rewrite hook, raise SystemError if it fails."""
        # Jython has an AST bug that make the assertion rewriting hook malfunction.
        if (sys.platform.startswith('java')):
            raise SystemError('rewrite not supported')

        config._assertstate = AssertionState(config, 'rewrite')
        config._assertstate.hook = hook = rewrite.AssertionRewritingHook(config)
        sys.meta_path.insert(0, hook)
        config._assertstate.trace('installed rewrite import hook')

        def undo():
            hook = config._assertstate.hook
            if hook is not None and hook in sys.meta_path:
                sys.meta_path.remove(hook)

        config.add_cleanup(undo)
        return hook

    def pytest_collection(session):
        # this hook is only called when test modules are collected
        # so for example not in the master process of pytest-xdist
        # (which does not collect test modules)
        assertstate = getattr(session.config, '_assertstate', None)
        if assertstate:
            if assertstate.hook is not None:
                assertstate.hook.set_session(session)

    def pytest_runtest_setup(item):
        """Setup the pytest_assertrepr_compare hook

        The newinterpret and rewrite modules will use util._reprcompare if
        it exists to use custom reporting via the
        pytest_assertrepr_compare hook.  This sets up this custom
        comparison for the test.
        """
        def callbinrepr(op, left, right):
            """Call the pytest_assertrepr_compare hook and prepare the result

            This uses the first result from the hook and then ensures the
            following:
            * Overly verbose explanations are truncated unless configured otherwise
              (eg. if running in verbose mode).
            * Embedded newlines are escaped to help util.format_explanation()
              later.
            * If the rewrite mode is used embedded %-characters are replaced
              to protect later % formatting.

            The result can be formatted by util.format_explanation() for
            pretty printing.
            """
            hook_result = item.ihook.pytest_assertrepr_compare(
                config=item.config, op=op, left=left, right=right)
            for new_expl in hook_result:
                if new_expl:
                    new_expl = truncate.truncate_if_required(new_expl, item)
                    new_expl = [line.replace("\n", "\\n") for line in new_expl]
                    res = six.text_type("\n~").join(new_expl)
                    if item.config.getvalue("assertmode") == "rewrite":
                        res = res.replace("%", "%%")
                    return res
        util._reprcompare = callbinrepr

    def pytest_runtest_teardown(item):
        util._reprcompare = None

    def pytest_sessionfinish(session):
        assertstate = getattr(session.config, '_assertstate', None)
        if assertstate:
            if assertstate.hook is not None:
                assertstate.hook.set_session(None)

    # Expose this plugin's implementation for the pytest_assertrepr_compare hook
    pytest_assertrepr_compare = util.assertrepr_compare