fix: Don't error if no new wheels were built

cibuildwheel/macos.py

@@ -275,6 +275,9 @@ def build(options: Options, tmp_path: Path) -> None:
         options.globals.build_selector, options.globals.architectures
     )
 
+    if len(python_configurations) == 0:
+        return
+
     try:
         before_all_options_identifier = python_configurations[0].identifier
         before_all_options = options.build_options(before_all_options_identifier)

cibuildwheel/util.py

@@ -435,6 +435,10 @@ class FileReport(NamedTuple):
         FileReport(wheel.name, f"{(wheel.stat().st_size + 1023) // 1024:,d}")
         for wheel in final_contents - existing_contents
     ]
+
+    if len(new_contents) == 0:
+        return
+
     max_name_len = max(len(f.name) for f in new_contents)
     max_size_len = max(len(f.size) for f in new_contents)
     n = len(new_contents)

cibuildwheel/windows.py

@@ -234,6 +234,9 @@ def build(options: Options, tmp_path: Path) -> None:
         options.globals.build_selector, options.globals.architectures
     )
 
+    if len(python_configurations) == 0:
+        return
+
     try:
         before_all_options_identifier = python_configurations[0].identifier
         before_all_options = options.build_options(before_all_options_identifier)

test/test_0_basic.py

@@ -59,3 +59,19 @@ def test_build_identifiers(tmp_path):
     assert len(expected_wheels) == len(
         build_identifiers
     ), f"{expected_wheels} vs {build_identifiers}"
+
+
+def test_allow_empty(tmp_path):
+    project_dir = tmp_path / "project"
+    basic_project.generate(project_dir)
+
+    # Sanity check - --allow-empty should cause a no-op build to complete
+    # without error
+    actual_wheels = utils.cibuildwheel_run(
+        project_dir,
+        add_env={"CIBW_BUILD": "BUILD_NOTHING_AT_ALL"},
+        add_args=["--allow-empty"],
+    )
+
+    # check that nothing was built
+    assert len(actual_wheels) == 0

test/utils.py

@@ -44,7 +44,9 @@ def cibuildwheel_get_build_identifiers(project_path, env=None, *, prerelease_pyt
     return cmd_output.strip().split("\n")
 
 
-def cibuildwheel_run(project_path, package_dir=".", env=None, add_env=None, output_dir=None):
+def cibuildwheel_run(
+    project_path, package_dir=".", env=None, add_env=None, output_dir=None, add_args=None
+):
     """
     Runs cibuildwheel as a subprocess, building the project at project_path.
 
@@ -57,13 +59,17 @@ def cibuildwheel_run(project_path, package_dir=".", env=None, add_env=None, outp
     :param add_env: environment used to update env
     :param output_dir: directory where wheels are saved. If None, a temporary
     directory will be used for the duration of the command.
+    :param add_args: Additional command-line arguments to pass to cibuildwheel.
     :return: list of built wheels (file names).
     """
     if env is None:
         env = os.environ.copy()
         # If present in the host environment, remove the MACOSX_DEPLOYMENT_TARGET for consistency
         env.pop("MACOSX_DEPLOYMENT_TARGET", None)
 
+    if add_args is None:
+        add_args = []
+
     if add_env is not None:
         env.update(add_env)
 
@@ -77,6 +83,7 @@ def cibuildwheel_run(project_path, package_dir=".", env=None, add_env=None, outp
                 "--output-dir",
                 str(output_dir or tmp_output_dir),
                 str(package_dir),
+                *add_args,
             ],
             env=env,
             cwd=project_path,