fix: pip config options were broken

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

cibuildwheel/linux.py

@@ -240,7 +240,9 @@ def build_in_container(
             container.call(["mkdir", "-p", built_wheel_dir])
 
             verbosity_flags = get_build_verbosity_extra_flags(build_options.build_verbosity)
-            extra_flags = split_config_settings(build_options.config_settings)
+            extra_flags = split_config_settings(
+                build_options.config_settings, plural=build_options.build_frontend == "pip"
+            )
 
             if build_options.build_frontend == "pip":
                 extra_flags += verbosity_flags

cibuildwheel/macos.py

@@ -374,7 +374,9 @@ def build(options: Options, tmp_path: Path) -> None:
                 built_wheel_dir.mkdir()
 
                 verbosity_flags = get_build_verbosity_extra_flags(build_options.build_verbosity)
-                extra_flags = split_config_settings(build_options.config_settings)
+                extra_flags = split_config_settings(
+                    build_options.config_settings, plural=build_options.build_frontend == "pip"
+                )
 
                 if build_options.build_frontend == "pip":
                     extra_flags += verbosity_flags

cibuildwheel/util.py

@@ -208,9 +208,10 @@ def get_build_verbosity_extra_flags(level: int) -> list[str]:
         return []
 
 
-def split_config_settings(config_settings: str) -> list[str]:
+def split_config_settings(config_settings: str, *, plural: bool) -> list[str]:
     config_settings_list = shlex.split(config_settings)
-    return [f"--config-setting={setting}" for setting in config_settings_list]
+    s = "s" if plural else ""
+    return [f"--config-setting{s}={setting}" for setting in config_settings_list]
 
 
 def read_python_configs(config: PlatformName) -> list[dict[str, str]]:

cibuildwheel/windows.py

@@ -411,7 +411,9 @@ def build(options: Options, tmp_path: Path) -> None:
                 built_wheel_dir.mkdir()
 
                 verbosity_flags = get_build_verbosity_extra_flags(build_options.build_verbosity)
-                extra_flags = split_config_settings(build_options.config_settings)
+                extra_flags = split_config_settings(
+                    build_options.config_settings, plural=build_options.build_frontend == "pip"
+                )
 
                 if build_options.build_frontend == "pip":
                     extra_flags += verbosity_flags

unit_test/main_tests/main_options_test.py

@@ -283,12 +283,18 @@ def test_config_settings(platform_specific, platform, intercepted_build_args, mo
 
     assert build_options.config_settings == config_settings
 
-    assert split_config_settings(config_settings) == [
+    assert split_config_settings(config_settings, plural=False) == [
         "--config-setting=setting=value",
         "--config-setting=setting=value2",
         "--config-setting=other=something else",
     ]
 
+    assert split_config_settings(config_settings, plural=True) == [
+        "--config-settings=setting=value",
+        "--config-settings=setting=value2",
+        "--config-settings=other=something else",
+    ]
+
 
 @pytest.mark.parametrize(
     "selector",