Make in-tree-build the default

Add an out-of-tree-build feature flag to ease the transition.

docs/html/cli/pip_install.rst

@@ -490,18 +490,20 @@ You can install local projects by specifying the project path to pip:
 
       py -m pip install path/to/SomeProject
 
-During regular installation, pip will copy the entire project directory to a
-temporary location and install from there. The exception is that pip will
-exclude .tox and .nox directories present in the top level of the project from
-being copied. This approach is the cause of several performance and correctness
-issues, so it is planned that pip 21.3 will change to install directly from the
-local project directory. Depending on the build backend used by the project,
-this may generate secondary build artifacts in the project directory, such as
-the ``.egg-info`` and ``build`` directories in the case of the setuptools
-backend.
+.. note::
 
-To opt in to the future behavior, specify the ``--use-feature=in-tree-build``
-option in pip's command line.
+   Depending on the build backend used by the project, this may generate
+   secondary build artifacts in the project directory, such as the
+   ``.egg-info`` and ``build`` directories in the case of the setuptools
+   backend.
+
+   Pip has a legacy behaviour that copies the entire project directory to a
+   temporary location and installs from there. This approach was the cause of
+   several performance and correctness issues, so it is now disabled by
+   default, and it is planned that pip 22.1 will remove it.
+
+   To opt in to the legacy behavior, specify the
+   ``--use-deprecated=out-of-tree-build`` option in pip's command line.
 
 
 .. _`editable-installs`:

news/10495.removal.rst

@@ -0,0 +1,3 @@
+In-tree builds are now the default. ``--use-feature=in-tree-build`` is now
+ignored. ``--use-deprecated=out-of-tree-build`` may be used temporarily to ease
+the transition.

src/pip/_internal/cli/cmdoptions.py

@@ -961,7 +961,7 @@ use_deprecated_feature: Callable[..., Option] = partial(
     metavar="feature",
     action="append",
     default=[],
-    choices=["legacy-resolver"],
+    choices=["legacy-resolver", "out-of-tree-build"],
     help=("Enable deprecated functionality, that will be removed in the future."),
 )
 

src/pip/_internal/cli/req_command.py

@@ -34,6 +34,7 @@ from pip._internal.req.req_install import InstallRequirement
 from pip._internal.req.req_tracker import RequirementTracker
 from pip._internal.resolution.base import BaseResolver
 from pip._internal.self_outdated_check import pip_self_version_check
+from pip._internal.utils.deprecation import deprecated
 from pip._internal.utils.temp_dir import (
     TempDirectory,
     TempDirectoryTypeRegistry,
@@ -260,6 +261,20 @@ class RequirementCommand(IndexGroupCommand):
                     "fast-deps has no effect when used with the legacy resolver."
                 )
 
+        in_tree_build = "out-of-tree-build" not in options.deprecated_features_enabled
+        if "in-tree-build" in options.features_enabled:
+            deprecated(
+                reason="In-tree builds are now the default.",
+                replacement="to remove the --use-feature=in-tree-build flag",
+                gone_in="22.1",
+            )
+        if "out-of-tree-build" in options.deprecated_features_enabled:
+            deprecated(
+                reason="Out-of-tree builds are deprecated.",
+                replacement=None,
+                gone_in="22.1",
+            )
+
         return RequirementPreparer(
             build_dir=temp_build_dir_path,
             src_dir=options.src_dir,
@@ -272,7 +287,7 @@ class RequirementCommand(IndexGroupCommand):
             require_hashes=options.require_hashes,
             use_user_site=use_user_site,
             lazy_wheel=lazy_wheel,
-            in_tree_build="in-tree-build" in options.features_enabled,
+            in_tree_build=in_tree_build,
         )
 
     @classmethod

src/pip/_internal/operations/prepare.py

@@ -35,7 +35,6 @@ from pip._internal.network.lazy_wheel import (
 from pip._internal.network.session import PipSession
 from pip._internal.req.req_install import InstallRequirement
 from pip._internal.req.req_tracker import RequirementTracker
-from pip._internal.utils.deprecation import deprecated
 from pip._internal.utils.filesystem import copy2_fixed
 from pip._internal.utils.hashes import Hashes, MissingHashes
 from pip._internal.utils.logging import indent_log
@@ -197,19 +196,9 @@ def unpack_url(
     #
     # As further cleanup, _copy_source_tree and accompanying tests can
     # be removed.
+    #
+    # TODO when use-deprecated=out-of-tree-build is removed
     if link.is_existing_dir():
-        deprecated(
-            reason=(
-                "pip copied the source tree into a temporary directory "
-                "before building it. This is changing so that packages "
-                "are built in-place "
-                'within the original source tree ("in-tree build").'
-            ),
-            replacement=None,
-            gone_in="21.3",
-            feature_flag="in-tree-build",
-            issue=7555,
-        )
         if os.path.isdir(location):
             rmtree(location)
         _copy_source_tree(link.file_path, location)

tests/functional/test_cli.py

@@ -36,7 +36,8 @@ def test_entrypoints_work(entrypoint, script):
         )
     )
 
-    script.pip("install", "-vvv", str(fake_pkg))
+    # expect_temp because pip install will generate fake_pkg.egg-info
+    script.pip("install", "-vvv", str(fake_pkg), expect_temp=True)
     result = script.pip("-V")
     result2 = script.run("fake_pip", "-V", allow_stderr_warning=True)
     assert result.stdout == result2.stdout

tests/functional/test_install.py

@@ -587,7 +587,12 @@ def test_install_from_local_directory_with_symlinks_to_directories(script, data)
     Test installing from a local directory containing symlinks to directories.
     """
     to_install = data.packages.joinpath("symlinks")
-    result = script.pip("install", to_install)
+    result = script.pip(
+        "install",
+        "--use-deprecated=out-of-tree-build",
+        to_install,
+        allow_stderr_warning=True,  # TODO: set to False when removing out-of-tree-build
+    )
     pkg_folder = script.site_packages / "symlinks"
     dist_info_folder = script.site_packages / "symlinks-0.1.dev0.dist-info"
     result.did_create(pkg_folder)
@@ -597,10 +602,10 @@ def test_install_from_local_directory_with_symlinks_to_directories(script, data)
 @pytest.mark.usefixtures("with_wheel")
 def test_install_from_local_directory_with_in_tree_build(script, data):
     """
-    Test installing from a local directory with --use-feature=in-tree-build.
+    Test installing from a local directory with default in tree build.
     """
     to_install = data.packages.joinpath("FSPkg")
-    args = ["install", "--use-feature=in-tree-build", to_install]
+    args = ["install", to_install]
 
     in_tree_build_dir = to_install / "build"
     assert not in_tree_build_dir.exists()
@@ -618,6 +623,8 @@ def test_install_from_local_directory_with_socket_file(script, data, tmpdir):
     """
     Test installing from a local directory containing a socket file.
     """
+    # TODO: remove this test when removing out-of-tree-build support,
+    # it is only meant to test the copy of socket files
     dist_info_folder = script.site_packages / "FSPkg-0.1.dev0.dist-info"
     package_folder = script.site_packages / "fspkg"
     to_copy = data.packages.joinpath("FSPkg")
@@ -628,7 +635,13 @@ def test_install_from_local_directory_with_socket_file(script, data, tmpdir):
     socket_file_path = os.path.join(to_install, "example")
     make_socket_file(socket_file_path)
 
-    result = script.pip("install", "--verbose", to_install)
+    result = script.pip(
+        "install",
+        "--use-deprecated=out-of-tree-build",
+        "--verbose",
+        to_install,
+        allow_stderr_warning=True,  # because of the out-of-tree deprecation warning
+    )
     result.did_create(package_folder)
     result.did_create(dist_info_folder)
     assert str(socket_file_path) in result.stderr

tests/functional/test_uninstall.py

@@ -12,6 +12,7 @@ from pip._internal.req.constructors import install_req_from_line
 from pip._internal.utils.misc import rmtree
 from tests.lib import assert_all_changes, create_test_package_with_setup, need_svn
 from tests.lib.local_repos import local_checkout, local_repo
+from tests.lib.path import Path
 
 
 @pytest.mark.network
@@ -279,7 +280,15 @@ def test_uninstall_console_scripts(script):
     result = script.pip("install", pkg_path)
     result.did_create(script.bin / "discover" + script.exe)
     result2 = script.pip("uninstall", "discover", "-y")
-    assert_all_changes(result, result2, [script.venv / "build", "cache"])
+    assert_all_changes(
+        result,
+        result2,
+        [
+            script.venv / "build",
+            "cache",
+            Path("scratch") / "discover" / "discover.egg-info",
+        ],
+    )
 
 
 def test_uninstall_console_scripts_uppercase_name(script):