def make_resolver(
        preparer,                            # type: RequirementPreparer
        finder,                              # type: PackageFinder
        options,                             # type: Values
        wheel_cache=None,                    # type: Optional[WheelCache]
        use_user_site=False,                 # type: bool
        ignore_installed=True,               # type: bool
        ignore_requires_python=False,        # type: bool
        force_reinstall=False,               # type: bool
        upgrade_strategy="to-satisfy-only",  # type: str
        use_pep517=None,                     # type: Optional[bool]
        py_version_info=None            # type: Optional[Tuple[int, ...]]
    ):
        # type: (...) -> BaseResolver
        """
        Create a Resolver instance for the given parameters.
        """
        make_install_req = partial(
            install_req_from_req_string,
            isolated=options.isolated_mode,
            use_pep517=use_pep517,
        )
        # The long import name and duplicated invocation is needed to convince
        # Mypy into correctly typechecking. Otherwise it would complain the
        # "Resolver" class being redefined.
        if 'resolver' in options.unstable_features:
            import pip._internal.resolution.resolvelib.resolver
            return pip._internal.resolution.resolvelib.resolver.Resolver(
                preparer=preparer,
                finder=finder,
                wheel_cache=wheel_cache,
                make_install_req=make_install_req,
                use_user_site=use_user_site,
                ignore_dependencies=options.ignore_dependencies,
                ignore_installed=ignore_installed,
                ignore_requires_python=ignore_requires_python,
                force_reinstall=force_reinstall,
                upgrade_strategy=upgrade_strategy,
                py_version_info=py_version_info,
            )
        import pip._internal.resolution.legacy.resolver
        return pip._internal.resolution.legacy.resolver.Resolver(
            preparer=preparer,
            finder=finder,
            wheel_cache=wheel_cache,
            make_install_req=make_install_req,
            use_user_site=use_user_site,
            ignore_dependencies=options.ignore_dependencies,
            ignore_installed=ignore_installed,
            ignore_requires_python=ignore_requires_python,
            force_reinstall=force_reinstall,
            upgrade_strategy=upgrade_strategy,
            py_version_info=py_version_info,
        )

        Create a Resolver instance for the given parameters.
        
product/gradle-plugin/src/main/python/pip/_internal/cli/req_command.py