From af5f9fc3fb6fb433e937faa4a33ab310ce495073 Mon Sep 17 00:00:00 2001
From: Mark Final <mark.final@foundry.com>
Date: Thu, 26 Jun 2025 17:14:55 +0100
Subject: [PATCH 1/2] Support --use-pep517 and --no-use-pep517 inside
 requirements files.

---
 news/6438.feature.rst             |  2 ++
 src/pip/_internal/req/req_file.py |  4 ++++
 tests/unit/test_req_file.py       | 27 +++++++++++++++++++++++++++
 3 files changed, 33 insertions(+)
 create mode 100644 news/6438.feature.rst

diff --git a/news/6438.feature.rst b/news/6438.feature.rst
new file mode 100644
index 00000000000..dcc260cacd4
--- /dev/null
+++ b/news/6438.feature.rst
@@ -0,0 +1,2 @@
+Support using ``--use-pep517`` and ``--no-use-pep517`` inside requirements
+files for all packages installed.
diff --git a/src/pip/_internal/req/req_file.py b/src/pip/_internal/req/req_file.py
index 0aad0a36602..99fb8194c20 100644
--- a/src/pip/_internal/req/req_file.py
+++ b/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:
diff --git a/tests/unit/test_req_file.py b/tests/unit/test_req_file.py
index 248171c7b5c..3632926f7c5 100644
--- a/tests/unit/test_req_file.py
+++ b/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 +676,32 @@ 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, line, expected, 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:

From b05e7099729940c598de30b3ba7cb30cae29081d Mon Sep 17 00:00:00 2001
From: Mark Final <mark.final@foundry.com>
Date: Wed, 17 Sep 2025 19:47:23 +0100
Subject: [PATCH 2/2] Fixing black formatting and mypy missing annotations

---
 tests/unit/test_req_file.py | 42 ++++++++++++++++++++++---------------
 1 file changed, 25 insertions(+), 17 deletions(-)

diff --git a/tests/unit/test_req_file.py b/tests/unit/test_req_file.py
index 3632926f7c5..a2f9bb0b611 100644
--- a/tests/unit/test_req_file.py
+++ b/tests/unit/test_req_file.py
@@ -676,26 +676,34 @@ 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),
-    ])
+    @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, line, expected, line_processor: LineProcessor, options: mock.Mock
+        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.
+        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