Support --use-pep517 and --no-use-pep517 inside requirements files.

news/6438.feature.rst

@@ -0,0 +1,2 @@
+Support using ``--use-pep517`` and ``--no-use-pep517`` inside requirements
+files for all packages installed.

src/pip/_internal/req/req_file.py

@@ -53,6 +53,8 @@
     cmdoptions.constraints,
     cmdoptions.requirements,
     cmdoptions.editable,
+    cmdoptions.use_pep517,
+    cmdoptions.no_use_pep517,
     cmdoptions.find_links,
     cmdoptions.no_binary,
     cmdoptions.only_binary,
@@ -239,6 +241,8 @@ def handle_option_line(
             options.features_enabled.extend(
                 f for f in opts.features_enabled if f not in options.features_enabled
             )
+        if opts.use_pep517 is not None:
+            options.use_pep517 = opts.use_pep517
 
     # set finder options
     if finder:

tests/unit/test_req_file.py

@@ -53,6 +53,7 @@ def options(session: PipSession) -> mock.Mock:
         index_url="default_url",
         format_control=FormatControl(set(), set()),
         features_enabled=[],
+        use_pep517=None,
     )
 
 
@@ -675,6 +676,40 @@ def get_file_content(
         assert result[0].name == req_name
         assert not result[0].constraint
 
+    @pytest.mark.parametrize(
+        "use_pep517_cmd_line, line, expected",
+        [
+            # Test passing use_pep517=None.
+            (None, "", None),
+            (None, "--use-pep517", True),
+            (None, "--no-use-pep517", False),
+            # Test passing use_pep517=True.
+            (True, "", True),
+            (True, "--use-pep517", True),
+            (True, "--no-use-pep517", False),
+            # Test passing use_pep517=False.
+            (False, "", False),
+            (False, "--use-pep517", True),
+            (False, "--no-use-pep517", False),
+        ],
+    )
+    def test_set_pep517_option_in_req_file(
+        self,
+        use_pep517_cmd_line: bool | None,
+        line: str,
+        expected: bool | None,
+        line_processor: LineProcessor,
+        options: mock.Mock,
+    ) -> None:
+        """
+        Test that using --use-pep517 or --no-use-pep517 in a requirements file
+        is both accepted and overrides the command line choices for that pep.
+        """
+        filename = "filename"
+        options.use_pep517 = use_pep517_cmd_line
+        line_processor(line, filename, 1, options=options)
+        assert options.use_pep517 == expected
+
 
 class TestBreakOptionsArgs:
     def test_no_args(self) -> None: