From 8f620405e3b3aab543e17cf12b8abee9becb7fc9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Filipe=20La=C3=ADns?= <lains@riseup.net>
Date: Fri, 10 Mar 2023 10:55:49 +0000
Subject: [PATCH] Support passing the same key multiple times in
 --config-settings
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Signed-off-by: Filipe Laíns <lains@riseup.net>
---
 news/11681.feature.rst              |  4 ++++
 src/pip/_internal/cli/cmdoptions.py |  8 +++++++-
 tests/unit/test_pyproject_config.py | 15 ++++++++++++---
 3 files changed, 23 insertions(+), 4 deletions(-)
 create mode 100644 news/11681.feature.rst

diff --git a/news/11681.feature.rst b/news/11681.feature.rst
new file mode 100644
index 00000000000..a0d918b19f9
--- /dev/null
+++ b/news/11681.feature.rst
@@ -0,0 +1,4 @@
+The ``--config-settings``/``-C`` option now supports using the same key multiple
+times. When the same key is specified multiple times, all values are passed to
+the build backend as a list, as opposed to the previous behavior where pip would
+only pass the last value is the same key was used multiple times.
diff --git a/src/pip/_internal/cli/cmdoptions.py b/src/pip/_internal/cli/cmdoptions.py
index 6a33cf48dc5..d7d6df00981 100644
--- a/src/pip/_internal/cli/cmdoptions.py
+++ b/src/pip/_internal/cli/cmdoptions.py
@@ -811,7 +811,13 @@ def _handle_config_settings(
     if dest is None:
         dest = {}
         setattr(parser.values, option.dest, dest)
-    dest[key] = val
+    if key in dest:
+        if isinstance(dest[key], list):
+            dest[key].append(val)
+        else:
+            dest[key] = [dest[key], val]
+    else:
+        dest[key] = val
 
 
 config_settings: Callable[..., Option] = partial(
diff --git a/tests/unit/test_pyproject_config.py b/tests/unit/test_pyproject_config.py
index 9937f3880aa..c7e46956055 100644
--- a/tests/unit/test_pyproject_config.py
+++ b/tests/unit/test_pyproject_config.py
@@ -1,3 +1,5 @@
+from typing import Dict, List
+
 import pytest
 
 from pip._internal.commands import create_command
@@ -36,9 +38,16 @@ def test_set_config_empty_value() -> None:
     assert options.config_settings == {"x": ""}
 
 
-def test_replace_config_value() -> None:
+@pytest.mark.parametrize(
+    ("passed", "expected"),
+    [
+        (["x=hello", "x=world"], {"x": ["hello", "world"]}),
+        (["x=hello", "x=world", "x=other"], {"x": ["hello", "world", "other"]}),
+    ],
+)
+def test_multiple_config_values(passed: List[str], expected: Dict[str, str]) -> None:
     i = create_command("install")
     options, _ = i.parse_args(
-        ["xxx", "--config-settings", "x=hello", "--config-settings", "x=world"]
+        ["xxx", *(f"--config-settings={option}" for option in passed)]
     )
-    assert options.config_settings == {"x": "world"}
+    assert options.config_settings == expected