Flip the switch on new resolver

.travis.yml

@@ -10,7 +10,6 @@ addons:
 stages:
 - primary
 - secondary
-- experimental
 
 jobs:
   include:
@@ -32,25 +31,6 @@ jobs:
     - env: GROUP=2
       python: pypy2.7-7.1.1
 
-    # Test experimental stuff that are not part of the standard pip usage.
-    # Helpful for developers working on them to see how they're doing.
-    - stage: experimental
-      env:
-      - GROUP=1
-      - NEW_RESOLVER=1
-    - env:
-      - GROUP=2
-      - NEW_RESOLVER=1
-    - env:
-      - GROUP=3
-      - NEW_RESOLVER=1
-
-  fast_finish: true
-  allow_failures:
-    - env:
-      - GROUP=3
-      - NEW_RESOLVER=1
-
 before_install: tools/travis/setup.sh
 install: travis_retry tools/travis/install.sh
 script: tools/travis/run.sh

news/9019.feature.rst

@@ -0,0 +1 @@
+Switch to the new dependency resolver by default.

setup.cfg

@@ -61,7 +61,6 @@ markers =
     mercurial: VCS: Mercurial
     git: VCS: git
     yaml: yaml based tests
-    fails_on_new_resolver: Does not yet work on the new resolver
 
 [coverage:run]
 branch = True

src/pip/_internal/cli/cmdoptions.py

@@ -905,7 +905,7 @@ def check_list_path_option(options):
     metavar='feature',
     action='append',
     default=[],
-    choices=[],
+    choices=['legacy-resolver'],
     help=(
         'Enable deprecated functionality, that will be removed in the future.'
     ),

src/pip/_internal/cli/req_command.py

@@ -9,6 +9,8 @@
 import os
 from functools import partial
 
+from pip._vendor.six import PY2
+
 from pip._internal.cli import cmdoptions
 from pip._internal.cli.base_command import Command
 from pip._internal.cli.command_context import CommandContextMixIn
@@ -195,7 +197,33 @@ def __init__(self, *args, **kw):
         self.cmd_opts.add_option(cmdoptions.no_clean())
 
     @staticmethod
+    def determine_resolver_variant(options):
+        # type: (Values) -> str
+        """Determines which resolver should be used, based on the given options."""
+        # We didn't want to change things for Python 2, since it's nearly done with
+        # and we're using performance improvements that only work on Python 3.
+        if PY2:
+            if '2020-resolver' in options.features_enabled:
+                return "2020-resolver"
+            else:
+                return "legacy"
+
+        # Warn about the options that are gonna be removed.
+        if '2020-resolver' in options.features_enabled:
+            logger.warning(
+                "--use-feature=2020-resolver no longer has any effect, "
+                "since it is now the default dependency resolver in pip. "
+                "This will become an error in pip 21.0."
+            )
+
+        if "legacy-resolver" in options.deprecated_features_enabled:
+            return "legacy"
+
+        return "2020-resolver"
+
+    @classmethod
     def make_requirement_preparer(
+        cls,
         temp_build_dir,           # type: TempDirectory
         options,                  # type: Values
         req_tracker,              # type: RequirementTracker
@@ -211,7 +239,8 @@ def make_requirement_preparer(
         temp_build_dir_path = temp_build_dir.path
         assert temp_build_dir_path is not None
 
-        if '2020-resolver' in options.features_enabled:
+        resolver_variant = cls.determine_resolver_variant(options)
+        if resolver_variant == "2020-resolver":
             lazy_wheel = 'fast-deps' in options.features_enabled
             if lazy_wheel:
                 logger.warning(
@@ -223,6 +252,10 @@ def make_requirement_preparer(
                 )
         else:
             lazy_wheel = False
+            if 'fast-deps' in options.features_enabled:
+                logger.warning(
+                    'fast-deps has no effect when used with the legacy resolver.'
+                )
 
         return RequirementPreparer(
             build_dir=temp_build_dir_path,
@@ -238,8 +271,9 @@ def make_requirement_preparer(
             lazy_wheel=lazy_wheel,
         )
 
-    @staticmethod
+    @classmethod
     def make_resolver(
+        cls,
         preparer,                            # type: RequirementPreparer
         finder,                              # type: PackageFinder
         options,                             # type: Values
@@ -250,7 +284,7 @@ def make_resolver(
         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, ...]]
+        py_version_info=None,                # type: Optional[Tuple[int, ...]]
     ):
         # type: (...) -> BaseResolver
         """
@@ -261,10 +295,11 @@ def make_resolver(
             isolated=options.isolated_mode,
             use_pep517=use_pep517,
         )
+        resolver_variant = cls.determine_resolver_variant(options)
         # 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 '2020-resolver' in options.features_enabled:
+        if resolver_variant == "2020-resolver":
             import pip._internal.resolution.resolvelib.resolver
 
             return pip._internal.resolution.resolvelib.resolver.Resolver(

src/pip/_internal/commands/install.py

@@ -427,7 +427,7 @@ def run(self, options, args):
             if conflicts is not None:
                 self._warn_about_conflicts(
                     conflicts,
-                    new_resolver='2020-resolver' in options.features_enabled,
+                    resolver_variant=self.determine_resolver_variant(options),
                 )
 
             installed_desc = ' '.join(items)
@@ -520,14 +520,14 @@ def _determine_conflicts(self, to_install):
             )
             return None
 
-    def _warn_about_conflicts(self, conflict_details, new_resolver):
-        # type: (ConflictDetails, bool) -> None
+    def _warn_about_conflicts(self, conflict_details, resolver_variant):
+        # type: (ConflictDetails, str) -> None
         package_set, (missing, conflicting) = conflict_details
         if not missing and not conflicting:
             return
 
         parts = []  # type: List[str]
-        if not new_resolver:
+        if resolver_variant == "legacy":
             parts.append(
                 "After October 2020 you may experience errors when installing "
                 "or updating packages. This is because pip will change the "

tests/conftest.py

@@ -39,16 +39,11 @@ def pytest_addoption(parser):
         help="keep temporary test directories",
     )
     parser.addoption(
-        "--new-resolver",
-        action="store_true",
-        default=False,
-        help="use new resolver in tests",
-    )
-    parser.addoption(
-        "--new-resolver-runtests",
-        action="store_true",
-        default=False,
-        help="run the skipped tests for the new resolver",
+        "--resolver",
+        action="store",
+        default="2020-resolver",
+        choices=["2020-resolver", "legacy"],
+        help="use given resolver in tests",
     )
     parser.addoption(
         "--use-venv",
@@ -68,12 +63,6 @@ def pytest_collection_modifyitems(config, items):
             if item.get_closest_marker('network') is not None:
                 item.add_marker(pytest.mark.flaky(reruns=3, reruns_delay=2))
 
-        if (item.get_closest_marker('fails_on_new_resolver') and
-                config.getoption("--new-resolver") and
-                not config.getoption("--new-resolver-runtests")):
-            item.add_marker(pytest.mark.skip(
-                'This test does not work with the new resolver'))
-
         if six.PY3:
             if (item.get_closest_marker('incompatible_with_test_venv') and
                     config.getoption("--use-venv")):
@@ -103,17 +92,32 @@ def pytest_collection_modifyitems(config, items):
 
 
 @pytest.fixture(scope="session", autouse=True)
-def use_new_resolver(request):
-    """Set environment variable to make pip default to the new resolver.
+def resolver_variant(request):
+    """Set environment variable to make pip default to the correct resolver.
     """
-    new_resolver = request.config.getoption("--new-resolver")
+    resolver = request.config.getoption("--resolver")
+
+    # Handle the environment variables for this test.
     features = set(os.environ.get("PIP_USE_FEATURE", "").split())
-    if new_resolver:
-        features.add("2020-resolver")
+    deprecated_features = set(os.environ.get("PIP_USE_DEPRECATED", "").split())
+
+    if six.PY3:
+        if resolver == "legacy":
+            deprecated_features.add("legacy-resolver")
+        else:
+            deprecated_features.discard("legacy-resolver")
     else:
-        features.discard("2020-resolver")
-    with patch.dict(os.environ, {"PIP_USE_FEATURE": " ".join(features)}):
-        yield new_resolver
+        if resolver == "2020-resolver":
+            features.add("2020-resolver")
+        else:
+            features.discard("2020-resolver")
+
+    env = {
+        "PIP_USE_FEATURE": " ".join(features),
+        "PIP_USE_DEPRECATED": " ".join(deprecated_features),
+    }
+    with patch.dict(os.environ, env):
+        yield resolver
 
 
 @pytest.fixture(scope='session')

tests/functional/test_install.py

@@ -407,7 +407,7 @@ def test_vcs_url_urlquote_normalization(script, tmpdir):
     )
 
 
-@pytest.mark.parametrize("resolver", ["", "--use-feature=2020-resolver"])
+@pytest.mark.parametrize("resolver", ["", "--use-deprecated=legacy-resolver"])
 def test_basic_install_from_local_directory(
     script, data, resolver, with_wheel
 ):
@@ -538,7 +538,7 @@ def assert_re_match(pattern, text):
 
 
 @pytest.mark.network
-@pytest.mark.fails_on_new_resolver
+@pytest.mark.skip("Fails on new resolver")
 def test_hashed_install_failure_later_flag(script, tmpdir):
     with requirements_file(
         "blessings==1.0\n"
@@ -941,7 +941,7 @@ def test_install_nonlocal_compatible_wheel(script, data):
 def test_install_nonlocal_compatible_wheel_path(
     script,
     data,
-    use_new_resolver
+    resolver_variant,
 ):
     target_dir = script.scratch_path / 'target'
 
@@ -952,9 +952,9 @@ def test_install_nonlocal_compatible_wheel_path(
         '--no-index',
         '--only-binary=:all:',
         Path(data.packages) / 'simplewheel-2.0-py3-fakeabi-fakeplat.whl',
-        expect_error=use_new_resolver
+        expect_error=(resolver_variant == "2020-resolver"),
     )
-    if use_new_resolver:
+    if resolver_variant == "2020-resolver":
         assert result.returncode == ERROR
     else:
         assert result.returncode == SUCCESS
@@ -1456,7 +1456,7 @@ def test_install_no_binary_disables_cached_wheels(script, data, with_wheel):
     assert "Running setup.py install for upper" in str(res), str(res)
 
 
-def test_install_editable_with_wrong_egg_name(script, use_new_resolver):
+def test_install_editable_with_wrong_egg_name(script, resolver_variant):
     script.scratch_path.joinpath("pkga").mkdir()
     pkga_path = script.scratch_path / 'pkga'
     pkga_path.joinpath("setup.py").write_text(textwrap.dedent("""
@@ -1467,12 +1467,12 @@ def test_install_editable_with_wrong_egg_name(script, use_new_resolver):
     result = script.pip(
         'install', '--editable',
         'file://{pkga_path}#egg=pkgb'.format(**locals()),
-        expect_error=use_new_resolver,
+        expect_error=(resolver_variant == "2020-resolver"),
     )
     assert ("Generating metadata for package pkgb produced metadata "
             "for project name pkga. Fix your #egg=pkgb "
             "fragments.") in result.stderr
-    if use_new_resolver:
+    if resolver_variant == "2020-resolver":
         assert "has different name in metadata" in result.stderr, str(result)
     else:
         assert "Successfully installed pkga" in str(result), str(result)
@@ -1505,7 +1505,7 @@ def test_double_install(script):
     assert msg not in result.stderr
 
 
-def test_double_install_fail(script, use_new_resolver):
+def test_double_install_fail(script, resolver_variant):
     """
     Test double install failing with two different version requirements
     """
@@ -1514,9 +1514,9 @@ def test_double_install_fail(script, use_new_resolver):
         'pip==7.*',
         'pip==7.1.2',
         # The new resolver is perfectly capable of handling this
-        expect_error=(not use_new_resolver)
+        expect_error=(resolver_variant == "legacy"),
     )
-    if not use_new_resolver:
+    if resolver_variant == "legacy":
         msg = ("Double requirement given: pip==7.1.2 (already in pip==7.*, "
                "name='pip')")
         assert msg in result.stderr
@@ -1770,11 +1770,11 @@ def test_user_config_accepted(script):
 )
 @pytest.mark.parametrize("use_module", [True, False])
 def test_install_pip_does_not_modify_pip_when_satisfied(
-        script, install_args, expected_message, use_module, use_new_resolver):
+        script, install_args, expected_message, use_module, resolver_variant):
     """
     Test it doesn't upgrade the pip if it already satisfies the requirement.
     """
-    variation = "satisfied" if use_new_resolver else "up-to-date"
+    variation = "satisfied" if resolver_variant else "up-to-date"
     expected_message = expected_message.format(variation)
     result = script.pip_install_local(
         'pip', *install_args, use_module=use_module
@@ -1837,6 +1837,7 @@ def test_install_yanked_file_and_print_warning(script, data):
     assert 'Successfully installed simple-3.0\n' in result.stdout, str(result)
 
 
+@skip_if_python2
 @pytest.mark.parametrize("install_args", [
     (),
     ("--trusted-host", "localhost"),

tests/functional/test_install_config.py

@@ -5,6 +5,7 @@
 
 import pytest
 
+from tests.lib import skip_if_python2
 from tests.lib.server import (
     authorization_response,
     file_response,
@@ -129,6 +130,7 @@ def test_command_line_appends_correctly(script, data):
     ), 'stdout: {}'.format(result.stdout)
 
 
+@skip_if_python2
 def test_config_file_override_stack(
     script, virtualenv, mock_server, shared_data
 ):
@@ -247,6 +249,7 @@ def test_prompt_for_authentication(script, data, cert_factory):
            result.stdout, str(result)
 
 
+@skip_if_python2
 def test_do_not_prompt_for_authentication(script, data, cert_factory):
     """Test behaviour if --no-input option is given while installing
     from a index url requiring authentication