Add '--ignore-constraint' option

Constraint files are often shared across an organization. When
developing a package included in such a constraint file, it is not
possible to install the package with constraints since the constraint on
the package prevents us installing a development version.

    ❯ cd my-amazing-package
    ❯ cat constraints.txt
    my-amazing-package==1.2.3
    Jinja2==3.1.2
    iso8601==1.1.0
    msgpack==1.0.4
    ❯ pip install -c constraints.txt .
    Processing /dev/my-amazing-package
      Preparing metadata (setup.py) ... done
    ERROR: Cannot install my-amazing-package 1.2.4.dev1 (from /dev/my-amazing-package) because these package versions have conflicting dependencies.

    The conflict is caused by:
        The user requested my-amazing-package 1.2.4.dev1 (from /dev/my-amazing-package)
        The user requested (constraint) my-amazing-package===1.2.4.dev1

    To fix this you could try to:
    1. loosen the range of package versions you've specified
    2. remove package versions to allow pip attempt to solve the dependency conflict

    ERROR: ResolutionImpossible: for help visit https://pip.pypa.io/en/latest/topics/dependency-resolution/#dealing-with-dependency-conflicts

Resolve this by allowing users to opt out of individual constraints to
the 'install', 'wheel', and 'download' subcommands. This is rather
manual but it's expected that tools like tox could automatically
generate a value for this option when invoking 'pip install' command.

   ❯ pip install -c constraints.txt --ignore-constraint my-amazing-package .
   ❯ pip wheel -c constraints.txt --ignore-constraint my-amazing-package .
   ❯ pip download -c constraints.txt --ignore-constraint my-amazing-package .

This is only added for the '2020-resolver' resolver, not the
'legacy-resolver' resolver, given the latter is deprecated for removal.

Signed-off-by: Stephen Finucane <stephenfin@redhat.com>
Fixes: pypa#7839

news/7839.feature.rst

@@ -0,0 +1,3 @@
+Add the ``--ignore-constraint`` option to ``pip install``, ``pip download``
+and ``pip wheel`` commands to ignore an individual constraint from a
+constraints file.

src/pip/_internal/cli/cmdoptions.py

@@ -394,6 +394,19 @@ def constraints() -> Option:
     )
 
 
+def ignored_constraints() -> Option:
+    return Option(
+        "--ignore-constraint",
+        dest="ignored_constraints",
+        action="append",
+        default=[],
+        metavar="package",
+        help="Ignore constraints for given package. This is commonly used "
+        "during development of a package when using a common constraints "
+        "file. This option be used multiple times.",
+    )
+
+
 def requirements() -> Option:
     return Option(
         "-r",

src/pip/_internal/cli/req_command.py

@@ -363,10 +363,13 @@ def make_resolver(
                 ignore_requires_python=ignore_requires_python,
                 force_reinstall=force_reinstall,
                 upgrade_strategy=upgrade_strategy,
+                ignored_constraints=options.ignored_constraints,
                 py_version_info=py_version_info,
             )
         import pip._internal.resolution.legacy.resolver
 
+        # we intentionally don't pass ignored_constraints to this since the
+        # resolver is deprecated
         return pip._internal.resolution.legacy.resolver.Resolver(
             preparer=preparer,
             finder=finder,

src/pip/_internal/commands/download.py

@@ -40,6 +40,7 @@ class DownloadCommand(RequirementCommand):
 
     def add_options(self) -> None:
         self.cmd_opts.add_option(cmdoptions.constraints())
+        self.cmd_opts.add_option(cmdoptions.ignored_constraints())
         self.cmd_opts.add_option(cmdoptions.requirements())
         self.cmd_opts.add_option(cmdoptions.no_deps())
         self.cmd_opts.add_option(cmdoptions.global_options())

src/pip/_internal/commands/install.py

@@ -94,6 +94,7 @@ class InstallCommand(RequirementCommand):
     def add_options(self) -> None:
         self.cmd_opts.add_option(cmdoptions.requirements())
         self.cmd_opts.add_option(cmdoptions.constraints())
+        self.cmd_opts.add_option(cmdoptions.ignored_constraints())
         self.cmd_opts.add_option(cmdoptions.no_deps())
         self.cmd_opts.add_option(cmdoptions.pre())
 

src/pip/_internal/commands/wheel.py

@@ -64,6 +64,7 @@ def add_options(self) -> None:
         self.cmd_opts.add_option(cmdoptions.no_use_pep517())
         self.cmd_opts.add_option(cmdoptions.check_build_deps())
         self.cmd_opts.add_option(cmdoptions.constraints())
+        self.cmd_opts.add_option(cmdoptions.ignored_constraints())
         self.cmd_opts.add_option(cmdoptions.editable())
         self.cmd_opts.add_option(cmdoptions.requirements())
         self.cmd_opts.add_option(cmdoptions.src())

src/pip/_internal/resolution/resolvelib/provider.py

@@ -84,6 +84,8 @@ class PipProvider(_ProviderBase):
     :params upgrade_strategy: The user-specified upgrade strategy.
     :params user_requested: A set of canonicalized package names that the user
         supplied for pip to install/upgrade.
+    :params ignored_constraints: A list of canonicalized package names that the
+        user has asked us to ignore constraints for.
     """
 
     def __init__(
@@ -93,12 +95,14 @@ def __init__(
         ignore_dependencies: bool,
         upgrade_strategy: str,
         user_requested: Dict[str, int],
+        ignored_constraints: Sequence[str],
     ) -> None:
         self._factory = factory
         self._constraints = constraints
         self._ignore_dependencies = ignore_dependencies
         self._upgrade_strategy = upgrade_strategy
         self._user_requested = user_requested
+        self._ignored_constraints = ignored_constraints
         self._known_depths: Dict[str, float] = collections.defaultdict(lambda: math.inf)
 
     def identify(self, requirement_or_candidate: Union[Requirement, Candidate]) -> str:
@@ -216,11 +220,15 @@ def _eligible_for_upgrade(identifier: str) -> bool:
                 return user_order is not None
             return False
 
-        constraint = _get_with_identifier(
-            self._constraints,
-            identifier,
-            default=Constraint.empty(),
-        )
+        if identifier not in self._ignored_constraints:
+            constraint = _get_with_identifier(
+                self._constraints,
+                identifier,
+                default=Constraint.empty(),
+            )
+        else:
+            constraint = Constraint.empty()
+
         return self._factory.find_candidates(
             identifier=identifier,
             requirements=requirements,

src/pip/_internal/resolution/resolvelib/resolver.py

@@ -1,7 +1,7 @@
 import functools
 import logging
 import os
-from typing import TYPE_CHECKING, Dict, List, Optional, Set, Tuple, cast
+from typing import TYPE_CHECKING, Dict, List, Optional, Sequence, Set, Tuple, cast
 
 from pip._vendor.packaging.utils import canonicalize_name
 from pip._vendor.resolvelib import BaseReporter, ResolutionImpossible
@@ -47,6 +47,7 @@ def __init__(
         ignore_requires_python: bool,
         force_reinstall: bool,
         upgrade_strategy: str,
+        ignored_constraints: Sequence[str],
         py_version_info: Optional[Tuple[int, ...]] = None,
     ):
         super().__init__()
@@ -65,6 +66,7 @@ def __init__(
         )
         self.ignore_dependencies = ignore_dependencies
         self.upgrade_strategy = upgrade_strategy
+        self.ignored_constraints = ignored_constraints
         self._result: Optional[Result] = None
 
     def resolve(
@@ -77,6 +79,7 @@ def resolve(
             ignore_dependencies=self.ignore_dependencies,
             upgrade_strategy=self.upgrade_strategy,
             user_requested=collected.user_requested,
+            ignored_constraints=self.ignored_constraints,
         )
         if "PIP_RESOLVER_DEBUG" in os.environ:
             reporter: BaseReporter = PipDebuggingReporter()

tests/functional/test_new_resolver.py

@@ -679,6 +679,26 @@ def test_new_resolver_constraints(
     script.assert_not_installed("constraint_only")
 
 
+def test_new_resolver_constraint_ignored(script: PipTestEnvironment) -> None:
+    "We can ignore constraints. Useful when hacking on a constrained package."
+    create_basic_wheel_for_package(script, "pkg", "1.1.dev1")
+    constraints_file = script.scratch_path / "constraints.txt"
+    constraints_file.write_text("pkg==1.0")
+    script.pip(
+        "install",
+        "--no-cache-dir",
+        "--no-index",
+        "--find-links",
+        script.scratch_path,
+        "-c",
+        constraints_file,
+        "--ignore-constraint",
+        "pkg",
+        "pkg",
+    )
+    script.assert_installed(pkg="1.1.dev1")
+
+
 def test_new_resolver_constraint_no_specifier(script: PipTestEnvironment) -> None:
     "It's allowed (but useless...) for a constraint to have no specifier"
     create_basic_wheel_for_package(script, "pkg", "1.0")

tests/unit/resolution_resolvelib/conftest.py

@@ -75,4 +75,5 @@ def provider(factory: Factory) -> Iterator[PipProvider]:
         ignore_dependencies=False,
         upgrade_strategy="to-satisfy-only",
         user_requested={},
+        ignored_constraints=[],
     )

tests/unit/resolution_resolvelib/test_provider.py

@@ -36,6 +36,7 @@ def test_provider_known_depths(factory: Factory) -> None:
         ignore_dependencies=False,
         upgrade_strategy="to-satisfy-only",
         user_requested={root_requirement_name: 0},
+        ignored_constraints=[],
     )
 
     root_requirement_information = build_requirement_information(

tests/unit/resolution_resolvelib/test_resolver.py

@@ -29,6 +29,7 @@ def resolver(preparer: RequirementPreparer, finder: PackageFinder) -> Resolver:
         ignore_requires_python=False,
         force_reinstall=False,
         upgrade_strategy="to-satisfy-only",
+        ignored_constraints=[],
     )
     return resolver