Add some type safety to the container_engine option

cibuildwheel/docker_container.py

@@ -13,7 +13,9 @@ from typing import IO, Dict, List, Optional, Sequence, Type, cast
 
 from cibuildwheel.util import CIProvider, detect_ci_provider
 
-from .typing import PathOrStr, PopenBytes
+from .typing import Literal, PathOrStr, PopenBytes
+
+ContainerEngine = Literal["docker", "podman"]
 
 
 class DockerContainer:
@@ -54,7 +56,7 @@ class DockerContainer:
         docker_image: str,
         simulate_32_bit: bool = False,
         cwd: Optional[PathOrStr] = None,
-        container_engine: str = "docker",
+        container_engine: ContainerEngine = "docker",
     ):
         if not docker_image:
             raise ValueError("Must have a non-empty docker image to run.")
@@ -193,8 +195,6 @@ class DockerContainer:
         to_path.mkdir(parents=True, exist_ok=True)
 
         if self.container_engine == "podman":
-            # There is a bug in docker that prevents this simple implementation
-            # from working https://github.com/moby/moby/issues/38995
             subprocess.run(
                 [
                     self.container_engine,
@@ -206,6 +206,8 @@ class DockerContainer:
                 cwd=to_path,
             )
         elif self.container_engine == "docker":
+            # There is a bug in docker that prevents a simple 'cp' invocation
+            # from working https://github.com/moby/moby/issues/38995
             command = f"{self.container_engine} exec -i {self.name} tar -cC {shell_quote(from_path)} -f - . | tar -xf -"
             subprocess.run(
                 command,

cibuildwheel/options.py

@@ -16,6 +16,7 @@ from typing import (
     Set,
     Tuple,
     Union,
+    cast,
 )
 
 if sys.version_info >= (3, 11):
@@ -26,6 +27,7 @@ else:
 from packaging.specifiers import SpecifierSet
 
 from .architecture import Architecture
+from .docker_container import ContainerEngine
 from .environment import EnvironmentParseError, ParsedEnvironment, parse_environment
 from .projectfiles import get_requires_python_str
 from .typing import PLATFORMS, Literal, PlatformName, TypedDict
@@ -79,7 +81,7 @@ class BuildOptions(NamedTuple):
     test_extras: str
     build_verbosity: int
     build_frontend: BuildFrontend
-    container_engine: str
+    container_engine: ContainerEngine
 
     @property
     def package_dir(self) -> Path:
@@ -423,7 +425,14 @@ class Options:
             test_requires = self.reader.get("test-requires", sep=" ").split()
             test_extras = self.reader.get("test-extras", sep=",")
             build_verbosity_str = self.reader.get("build-verbosity")
-            container_engine = self.reader.get("container-engine")
+            container_engine_str = self.reader.get("container-engine")
+
+            if container_engine_str not in ["docker", "podman"]:
+                msg = f"cibuildwheel: Unrecognised container_engine '{container_engine_str}', only 'docker' and 'podman' are supported"
+                print(msg, file=sys.stderr)
+                sys.exit(2)
+
+            container_engine = cast(ContainerEngine, container_engine_str)
 
             build_frontend: BuildFrontend
             if build_frontend_str == "build":