pip download: make sure that --use-pep517 is propagated to the dependencies

news/9523.bugfix.rst

@@ -0,0 +1,3 @@
+Make the ``--use-pep517`` option of the ``download`` command apply not just
+to the requirements specified on the command line, but to their dependencies,
+as well.

src/pip/_internal/commands/download.py

@@ -122,6 +122,7 @@ def run(self, options: Values, args: List[str]) -> int:
             finder=finder,
             options=options,
             ignore_requires_python=options.ignore_requires_python,
+            use_pep517=options.use_pep517,
             py_version_info=options.python_version,
         )
 

tests/functional/test_download.py

@@ -9,7 +9,12 @@
 
 from pip._internal.cli.status_codes import ERROR
 from tests.conftest import MockServer, ScriptFactory
-from tests.lib import PipTestEnvironment, TestData, create_really_basic_wheel
+from tests.lib import (
+    PipTestEnvironment,
+    TestData,
+    create_basic_sdist_for_package,
+    create_really_basic_wheel,
+)
 from tests.lib.server import file_response
 
 
@@ -1166,3 +1171,46 @@ def test_download_editable(
     downloads = os.listdir(download_dir)
     assert len(downloads) == 1
     assert downloads[0].endswith(".zip")
+
+
+def test_download_use_pep517_propagation(
+    script: PipTestEnvironment, tmpdir: Path, common_wheels: Path
+) -> None:
+    """
+    Check that --use-pep517 applies not just to the requirements specified
+    on the command line, but to their dependencies too.
+    """
+
+    create_basic_sdist_for_package(script, "fake_proj", "1.0", depends=["fake_dep"])
+
+    # If --use-pep517 is in effect, then setup.py should be running in an isolated
+    # environment that doesn't have pip in it.
+    create_basic_sdist_for_package(
+        script,
+        "fake_dep",
+        "1.0",
+        setup_py_prelude=textwrap.dedent(
+            """\
+            try:
+                import pip
+            except ImportError:
+                pass
+            else:
+                raise Exception(f"not running in isolation")
+            """
+        ),
+    )
+
+    download_dir = tmpdir / "download_dir"
+    script.pip(
+        "download",
+        f"--dest={download_dir}",
+        "--no-index",
+        f"--find-links={common_wheels}",
+        f"--find-links={script.scratch_path}",
+        "--use-pep517",
+        "fake_proj",
+    )
+
+    downloads = os.listdir(download_dir)
+    assert len(downloads) == 2

tests/lib/__init__.py

@@ -1211,12 +1211,17 @@ def create_basic_sdist_for_package(
     *,
     fails_egg_info: bool = False,
     fails_bdist_wheel: bool = False,
+    depends: Optional[List[str]] = None,
+    setup_py_prelude: str = "",
 ) -> pathlib.Path:
     files = {
-        "setup.py": f"""\
+        "setup.py": textwrap.dedent(
+            """\
             import sys
             from setuptools import find_packages, setup
 
+            {setup_py_prelude}
+
             fails_bdist_wheel = {fails_bdist_wheel!r}
             fails_egg_info = {fails_egg_info!r}
 
@@ -1226,19 +1231,22 @@ def create_basic_sdist_for_package(
             if fails_bdist_wheel and "bdist_wheel" in sys.argv:
                 raise Exception("Simulated failure for building a wheel.")
 
-            setup(name={name!r}, version={version!r})
-        """,
+            setup(name={name!r}, version={version!r},
+                install_requires={depends!r})
+        """
+        ).format(
+            name=name,
+            version=version,
+            depends=depends or [],
+            setup_py_prelude=setup_py_prelude,
+            fails_bdist_wheel=fails_bdist_wheel,
+            fails_egg_info=fails_egg_info,
+        ),
     }
 
     # Some useful shorthands
     archive_name = f"{name}-{version}.tar.gz"
 
-    # Replace key-values with formatted values
-    for key, value in list(files.items()):
-        del files[key]
-        key = key.format(name=name)
-        files[key] = textwrap.dedent(value)
-
     # Add new files after formatting
     if extra_files:
         files.update(extra_files)