Set the defualt build_frontend to be "default" (which is still "pip")

Instead of using pip as the default, set it to default. This way
each platform can choose independently what to do as the default
behavior.

This is intended as part of adding Pyodide support. Pyodide cannot
use pip as the build frontend. It always uses a modified pypa/build.
So if the build_frontend is explicitly set to pip we want to raise
an error. But if it's unset, then we should be able to tell and just
do what we want.

cibuildwheel/linux.py

@@ -16,6 +16,7 @@
 from .util import (
     AlreadyBuiltWheelError,
     BuildSelector,
+    build_frontend_or_default,
     NonPlatformWheelError,
     find_compatible_wheel,
     get_build_verbosity_extra_flags,
@@ -143,6 +144,7 @@ def build_in_container(
     container_package_dir: PurePath,
 ) -> None:
     container_output_dir = PurePosixPath("/output")
+    build_frontend = build_frontend_or_default(options.build_frontend, "pip")
 
     check_all_python_exist(platform_configs=platform_configs, container=container)
 
@@ -242,10 +244,10 @@ def build_in_container(
 
             verbosity_flags = get_build_verbosity_extra_flags(build_options.build_verbosity)
             extra_flags = split_config_settings(
-                build_options.config_settings, build_options.build_frontend
+                build_options.config_settings, build_frontend
             )
 
-            if build_options.build_frontend == "pip":
+            if build_frontend == "pip":
                 extra_flags += verbosity_flags
                 container.call(
                     [
@@ -260,7 +262,7 @@ def build_in_container(
                     ],
                     env=env,
                 )
-            elif build_options.build_frontend == "build":
+            elif build_frontend == "build":
                 verbosity_setting = " ".join(verbosity_flags)
                 extra_flags += (f"--config-setting={verbosity_setting}",)
                 container.call(
@@ -276,7 +278,7 @@ def build_in_container(
                     env=env,
                 )
             else:
-                assert_never(build_options.build_frontend)
+                assert_never(build_frontend)
 
             built_wheel = container.glob(built_wheel_dir, "*.whl")[0]
 

cibuildwheel/macos.py

@@ -25,6 +25,7 @@
     AlreadyBuiltWheelError,
     BuildFrontend,
     BuildSelector,
+    build_frontend_or_default,
     NonPlatformWheelError,
     call,
     detect_ci_provider,
@@ -311,6 +312,9 @@ def build(options: Options, tmp_path: Path) -> None:
         options.globals.build_selector, options.globals.architectures
     )
 
+    build_frontend = build_frontend_or_default(options.build_frontend, "pip")
+
+
     if not python_configurations:
         return
 
@@ -353,7 +357,7 @@ def build(options: Options, tmp_path: Path) -> None:
                 config,
                 dependency_constraint_flags,
                 build_options.environment,
-                build_options.build_frontend,
+                build_frontend,
             )
 
             compatible_wheel = find_compatible_wheel(built_wheels, config.identifier)
@@ -376,10 +380,10 @@ def build(options: Options, tmp_path: Path) -> None:
 
                 verbosity_flags = get_build_verbosity_extra_flags(build_options.build_verbosity)
                 extra_flags = split_config_settings(
-                    build_options.config_settings, build_options.build_frontend
+                    build_options.config_settings, build_frontend
                 )
 
-                if build_options.build_frontend == "pip":
+                if build_frontend == "pip":
                     extra_flags += verbosity_flags
                     # Path.resolve() is needed. Without it pip wheel may try to fetch package from pypi.org
                     # see https://github.com/pypa/cibuildwheel/pull/369
@@ -394,7 +398,7 @@ def build(options: Options, tmp_path: Path) -> None:
                         *extra_flags,
                         env=env,
                     )
-                elif build_options.build_frontend == "build":
+                elif build_frontend == "build":
                     verbosity_setting = " ".join(verbosity_flags)
                     extra_flags += (f"--config-setting={verbosity_setting}",)
                     build_env = env.copy()
@@ -417,7 +421,7 @@ def build(options: Options, tmp_path: Path) -> None:
                         env=build_env,
                     )
                 else:
-                    assert_never(build_options.build_frontend)
+                    assert_never(build_frontend)
 
                 built_wheel = next(built_wheel_dir.glob("*.whl"))
 

cibuildwheel/options.py

@@ -94,7 +94,7 @@ class BuildOptions:
     test_requires: list[str]
     test_extras: str
     build_verbosity: int
-    build_frontend: BuildFrontend
+    build_frontend: BuildFrontend | Literal["default"]
     config_settings: str
 
     @property
@@ -499,11 +499,13 @@ def build_options(self, identifier: str | None) -> BuildOptions:
             test_extras = self.reader.get("test-extras", sep=",")
             build_verbosity_str = self.reader.get("build-verbosity")
 
-            build_frontend: BuildFrontend
+            build_frontend: BuildFrontend | Literal["default"]
             if build_frontend_str == "build":
                 build_frontend = "build"
             elif build_frontend_str == "pip":
                 build_frontend = "pip"
+            elif build_frontend_str == "default":
+                build_frontend = "default"
             else:
                 msg = f"cibuildwheel: Unrecognised build frontend {build_frontend_str!r}, only 'pip' and 'build' are supported"
                 print(msg, file=sys.stderr)

cibuildwheel/resources/defaults.toml

@@ -4,7 +4,7 @@ skip = ""
 test-skip = ""
 
 archs = ["auto"]
-build-frontend = "pip"
+build-frontend = "default"
 config-settings = {}
 dependency-versions = "pinned"
 environment = {}

cibuildwheel/util.py

@@ -71,6 +71,11 @@
 
 BuildFrontend = Literal["pip", "build"]
 
+def build_frontend_or_default(setting: BuildFrontend | Literal["default"], default: BuildFrontend) -> BuildFrontend:
+    if setting == "default":
+        return default
+    return setting
+
 MANYLINUX_ARCHS: Final[tuple[str, ...]] = (
     "x86_64",
     "i686",

cibuildwheel/windows.py

@@ -26,6 +26,7 @@
     AlreadyBuiltWheelError,
     BuildFrontend,
     BuildSelector,
+    build_frontend_or_default,
     NonPlatformWheelError,
     call,
     download,
@@ -347,6 +348,7 @@ def build(options: Options, tmp_path: Path) -> None:
     python_configurations = get_python_configurations(
         options.globals.build_selector, options.globals.architectures
     )
+    build_frontend = build_frontend_or_default(options.build_frontend, "pip")
 
     if not python_configurations:
         return
@@ -387,7 +389,7 @@ def build(options: Options, tmp_path: Path) -> None:
                 config,
                 dependency_constraint_flags,
                 build_options.environment,
-                build_options.build_frontend,
+                build_frontend,
             )
 
             compatible_wheel = find_compatible_wheel(built_wheels, config.identifier)
@@ -413,10 +415,10 @@ def build(options: Options, tmp_path: Path) -> None:
 
                 verbosity_flags = get_build_verbosity_extra_flags(build_options.build_verbosity)
                 extra_flags = split_config_settings(
-                    build_options.config_settings, build_options.build_frontend
+                    build_options.config_settings, build_frontend
                 )
 
-                if build_options.build_frontend == "pip":
+                if build_frontend == "pip":
                     extra_flags += verbosity_flags
                     # Path.resolve() is needed. Without it pip wheel may try to fetch package from pypi.org
                     # see https://github.com/pypa/cibuildwheel/pull/369
@@ -431,7 +433,7 @@ def build(options: Options, tmp_path: Path) -> None:
                         *extra_flags,
                         env=env,
                     )
-                elif build_options.build_frontend == "build":
+                elif build_frontend == "build":
                     verbosity_setting = " ".join(verbosity_flags)
                     extra_flags += (f"--config-setting={verbosity_setting}",)
                     build_env = env.copy()
@@ -464,7 +466,7 @@ def build(options: Options, tmp_path: Path) -> None:
                             env=build_env,
                         )
                 else:
-                    assert_never(build_options.build_frontend)
+                    assert_never(build_frontend)
 
                 built_wheel = next(built_wheel_dir.glob("*.whl"))