Imply using new behavior when build constraints are provided without needing to use the build-constraint feature

Author: notatallshaw

docs/html/user_guide.rst

@@ -262,20 +262,16 @@ serve them in a centralized place.
 Build Constraints
 -----------------
 
-.. versionadded:: 25.2
-.. note::
-
-   Build constraints are currently an **experimental feature** and must be
-   enabled  using ``--use-feature=build-constraint``.
+.. versionadded:: 25.3
 
-Build constraints are a specialized type of constraints file that apply only
-to the build environment when building packages from source. Unlike regular
-constraints which affect the installed packages in your environment, build
+Build constraints are a type of constraints file that applies only to isolated
+build environments used for building packages from source. Unlike regular
+constraints, which affect the packages installed in your environment, build
 constraints only influence the versions of packages available during the
 build process.
 
-This is particularly useful when you need to constrain build dependencies
-(like ``setuptools``, ``cython``, etc.) without affecting the
+This is useful when you need to constrain build dependencies
+(such as ``setuptools``, ``cython``, etc.) without affecting the
 final installed environment.
 
 Use build constraints like so:
@@ -284,21 +280,21 @@ Use build constraints like so:
 
    .. code-block:: shell
 
-      python -m pip install --build-constraint build-constraints.txt --use-feature=build-constraint SomePackage
+      python -m pip install --build-constraint build-constraints.txt SomePackage
 
 .. tab:: Windows
 
    .. code-block:: shell
 
-      py -m pip install --build-constraint build-constraints.txt --use-feature=build-constraint SomePackage
+      py -m pip install --build-constraint build-constraints.txt SomePackage
 
 Example build constraints file (``build-constraints.txt``):
 
 .. code-block:: text
 
    # Constrain setuptools version during build
-   setuptools>=45.0.0,<60.0.0
-   # Pin Cython for packages that use it
+   setuptools>=45,<80
+   # Pin Cython for packages that use it to build
    cython==0.29.24
 
 

news/13534.feature.rst

@@ -1,4 +1,8 @@
-Add experimental build constraints support via ``--use-feature=build-constraint``.
-This allows constraining the versions of packages used during the build process
-(e.g., setuptools). Build constraints can be specified via ``PIP_BUILD_CONSTRAINT``
-environment variable or ``--build-constraint`` flag.
+Add support for build constraints via the ``--build-constraint`` option. This
+allows constraining the versions of packages used during the build process
+(e.g., setuptools).
+
+When using ``--build-constraint``, you can no longer pass constraints to
+isolated build environments via the ``PIP_CONSTRAINT`` environment variable.
+To opt in to this behavior without specifying any build constraints, use
+``--use-feature=build-constraint``.

src/pip/_internal/build_env.py

@@ -128,23 +128,29 @@ def _deprecation_constraint_check(self) -> None:
         if self._build_constraint_feature_enabled:
             return
 
+        if self._build_constraints:
+            return
+
         if not self._constraints:
             return
 
         if not os.environ.get("PIP_CONSTRAINT"):
             return
 
         pip_constraint_files = [
-            f.strip() for f in os.environ["PIP_CONSTRAINT"].split() if f.strip()
+            f for f in os.environ["PIP_CONSTRAINT"].split() if f.strip()
         ]
-        if pip_constraint_files and set(pip_constraint_files) == set(self._constraints):
+        if pip_constraint_files and pip_constraint_files == self._constraints:
             deprecated(
                 reason=(
                     "Setting PIP_CONSTRAINT will not affect "
                     "build constraints in the future,"
                 ),
                 replacement=(
-                    'PIP_BUILD_CONSTRAINT with PIP_USE_FEATURE="build-constraint"'
+                    "to specify build constraints use --build-constraint or "
+                    "PIP_BUILD_CONSTRAINT, to disable this warning without "
+                    "any build constraints set --use-feature=build-constraint or "
+                    'PIP_USE_FEATURE="build-constraint"'
                 ),
                 gone_in="26.2",
                 issue=None,
@@ -219,13 +225,17 @@ def install(
         # Handle build constraints
         extra_environ: ExtraEnviron = {}
         if self._build_constraint_feature_enabled:
+            args.extend(["--use-feature", "build-constraint"])
+
+        if self._build_constraints:
             # Build constraints must be passed as both constraints
-            # and build constraints to the subprocess
+            # and build constraints, so that nested builds receive
+            # build constraints
             for constraint_file in self._build_constraints:
                 args.extend(["--constraint", constraint_file])
                 args.extend(["--build-constraint", constraint_file])
-                args.extend(["--use-feature", "build-constraint"])
 
+        if self._build_constraint_feature_enabled and not self._build_constraints:
             # If there are no build constraints but the build constraint
             # process is enabled then we must ignore regular constraints
             if not self._build_constraints:

src/pip/_internal/cli/cmdoptions.py

@@ -107,11 +107,6 @@ def check_build_constraints(options: Values) -> None:
     :param options: The OptionParser options.
     """
     if hasattr(options, "build_constraints") and options.build_constraints:
-        if "build-constraint" not in options.features_enabled:
-            raise CommandError(
-                "To use --build-constraint, you must enable this feature with "
-                "--use-feature=build-constraint."
-            )
         if not options.build_isolation:
             raise CommandError(
                 "--build-constraint cannot be used with --no-build-isolation."
@@ -457,8 +452,7 @@ def build_constraint() -> Option:
         metavar="file",
         help=(
             "Constrain build dependencies using the given constraints file. "
-            "This option can be used multiple times. "
-            "Requires --use-feature=build-constraint."
+            "This option can be used multiple times."
         ),
     )
 

tests/functional/test_build_constraints.py

@@ -69,7 +69,6 @@ def _run_pip_install_with_build_constraints_no_feature_flag(
         "--build-constraint",
         str(constraints_file),
         str(project_dir),
-        expect_error=True,
     )
 
 
@@ -164,13 +163,14 @@ def test_build_constraints_file_not_found(
 def test_build_constraints_without_feature_flag(
     script: PipTestEnvironment, tmpdir: Path
 ) -> None:
-    """Test that --build-constraint requires the feature flag."""
+    """Test that --build-constraint automatically enables the feature."""
     project_dir = _create_simple_test_package(script=script, name="test_no_feature")
     constraints_file = _create_constraints_file(
         script=script, filename="constraints.txt", content="setuptools==45.0.0\n"
     )
     result = _run_pip_install_with_build_constraints_no_feature_flag(
         script=script, project_dir=project_dir, constraints_file=constraints_file
     )
-    assert result.returncode != 0
-    assert "build-constraint" in result.stderr.lower()
+    # Should succeed now that --build-constraint auto-enables the feature
+    assert result.returncode == 0
+    _assert_successful_installation(result=result, package_name="test_no_feature")

tests/unit/test_build_constraints.py

@@ -81,7 +81,10 @@ def test_deprecation_check_warning_shown(self) -> None:
             "Setting PIP_CONSTRAINT will not affect build constraints in the future"
             in message
         )
-        assert 'PIP_BUILD_CONSTRAINT with PIP_USE_FEATURE="build-constraint"' in message
+        assert (
+            "to specify build constraints use "
+            "--build-constraint or PIP_BUILD_CONSTRAINT" in message
+        )
 
     @mock.patch.dict(os.environ, {"PIP_CONSTRAINT": "constraint1.txt constraint2.txt"})
     def test_deprecation_check_multiple_constraints(self) -> None:
@@ -96,19 +99,6 @@ def test_deprecation_check_multiple_constraints(self) -> None:
         with pytest.warns(PipDeprecationWarning):
             installer._deprecation_constraint_check()
 
-    @mock.patch.dict(os.environ, {"PIP_CONSTRAINT": "constraint1.txt constraint2.txt"})
-    def test_deprecation_check_multiple_constraints_different_order(self) -> None:
-        """Test deprecation warning works when constraints are in different order."""
-        finder = make_test_finder()
-        installer = SubprocessBuildEnvironmentInstaller(
-            finder,
-            constraints=["constraint2.txt", "constraint1.txt"],
-            build_constraint_feature_enabled=False,
-        )
-
-        with pytest.warns(PipDeprecationWarning):
-            installer._deprecation_constraint_check()
-
     @mock.patch.dict(
         os.environ, {"PIP_CONSTRAINT": "constraint1.txt constraint2.txt extra.txt"}
     )