Accept multiple values for the same config settings

pyproject_wheel.py

@@ -13,6 +13,12 @@ def parse_config_settings_args(config_settings):
     new_config_settings = {}
     for arg in config_settings:
         key, _, value = arg.partition('=')
+        if key in new_config_settings:
+            if not isinstance(new_config_settings[key], list):
+                # convert the existing value to a list
+                new_config_settings[key] = [new_config_settings[key]]
+            new_config_settings[key].append(value)
+        else:
             new_config_settings[key] = value
     return new_config_settings
 
@@ -24,7 +30,10 @@ def get_config_settings_args(config_settings):
     """
     if not config_settings:
         return
-    for key, value in config_settings.items():
+    for key, values in config_settings.items():
+        if not isinstance(values, list):
+            values = [values]
+        for value in values:
             if value == '':
                 yield f'--config-settings={key}'
             else:

tests/config-settings-test.spec

@@ -27,7 +27,7 @@ cat <<'EOF' >pyproject.toml
 [build-system]
 build-backend = "config_settings_test_backend"
 backend-path = ["."]
-requires = ["flit-core"]
+requires = ["flit-core", "packaging", "pip"]
 
 [project]
 name = "config_settings"
@@ -37,12 +37,12 @@ EOF
 
 
 %generate_buildrequires
-%pyproject_buildrequires -C abc=123 -C xyz=456 -C--option-with-dashes=1
-%pyproject_buildrequires -C abc=123 -C xyz=456 -C--option-with-dashes=1 -w
+%pyproject_buildrequires -C abc=123 -C xyz=456 -C--option-with-dashes=1 -C--option-with-dashes=2
+%{!?el9:%pyproject_buildrequires -C abc=123 -C xyz=456 -C--option-with-dashes=1 -C--option-with-dashes=2 -w}
 
 
 %build
-%pyproject_wheel -C abc=123 -C xyz=456 -C--option-with-dashes=1
+%{!?el9:%pyproject_wheel -C abc=123 -C xyz=456 -C--option-with-dashes=1 -C--option-with-dashes=2}
 
 
 %changelog

tests/config_settings_test_backend.py

@@ -4,13 +4,22 @@ It is not compliant with PEP 517 and omits some required hooks.
 """
 
 from flit_core import buildapi
+from packaging.version import parse
+from pip import __version__ as pip_version
 
-EXPECTED_CONFIG_SETTINGS = {"abc": "123", "xyz": "456", "--option-with-dashes": "1"}
+EXPECTED_CONFIG_SETTINGS = [{"abc": "123", "xyz": "456", "--option-with-dashes": ["1", "2"]}]
+# Older pip did not accept multiple values,
+# but we might backport that later,
+# hence we accept it both ways with older pips
+if parse(pip_version) < parse("23.1"):
+    EXPECTED_CONFIG_SETTINGS.append(
+        EXPECTED_CONFIG_SETTINGS[0] | {"--option-with-dashes": "2"}
+    )
 
 
 def _verify_config_settings(config_settings):
     print(f"config_settings={config_settings}")
-    if config_settings != EXPECTED_CONFIG_SETTINGS:
+    if config_settings not in EXPECTED_CONFIG_SETTINGS:
         raise ValueError(
             f"{config_settings!r} does not match expected {EXPECTED_CONFIG_SETTINGS!r}"
         )