feat: add CIBW_ALLOW_EMPTY environment variable (#1937)

Co-authored-by: Matthieu Darbois <mayeut@users.noreply.github.com>

Author: ConorMacBride

cibuildwheel/__main__.py

@@ -334,7 +334,7 @@ def build_in_directory(args: CommandLineArguments) -> None:
 
     if not identifiers:
         message = f"No build identifiers selected: {options.globals.build_selector}"
-        if args.allow_empty:
+        if options.globals.allow_empty:
             print(f"cibuildwheel: {message}", file=sys.stderr)
         else:
             raise errors.NothingToDoError(message)

cibuildwheel/options.py

@@ -75,6 +75,7 @@ class GlobalOptions:
     build_selector: BuildSelector
     test_selector: TestSelector
     architectures: set[Architecture]
+    allow_empty: bool
 
 
 @dataclasses.dataclass(frozen=True)
@@ -520,6 +521,8 @@ def globals(self) -> GlobalOptions:
             self.reader.get("free-threaded-support", env_plat=False, ignore_empty=True)
         )
 
+        allow_empty = args.allow_empty or strtobool(self.env.get("CIBW_ALLOW_EMPTY", "0"))
+
         prerelease_pythons = args.prerelease_pythons or strtobool(
             self.env.get("CIBW_PRERELEASE_PYTHONS", "0")
         )
@@ -557,6 +560,7 @@ def globals(self) -> GlobalOptions:
             build_selector=build_selector,
             test_selector=test_selector,
             architectures=architectures,
+            allow_empty=allow_empty,
         )
 
     def build_options(self, identifier: str | None) -> BuildOptions:

docs/options.md

@@ -621,6 +621,28 @@ This option can also be set using the [command-line option](#command-line) `--pr
     CIBW_PRERELEASE_PYTHONS: True
     ```
 
+### `CIBW_ALLOW_EMPTY` {: #allow-empty}
+> Suppress the error code if no wheels match the specified build identifiers
+
+When none of the specified build identifiers match any available versions,
+cibuildwheel will typically return error code 3, indicating that there are
+no wheels to build. Enabling this option will suppress this error, allowing
+the build process to complete without signaling an error.
+
+Default: Off (0). Error code 3 is returned when no builds are selected.
+
+This option can also be set using the [command-line option](#command-line)
+`--allow-empty`. This option is not available in the `pyproject.toml` config.
+
+#### Examples
+
+!!! tab examples "Environment variables"
+
+    ```yaml
+    # Prevent an error code if the build does not match any wheels
+    CIBW_ALLOW_EMPTY: True
+    ```
+
 ## Build customization
 
 ### `CIBW_BUILD_FRONTEND` {: #build-frontend}
@@ -1667,7 +1689,7 @@ cibuildwheel exits 0 on success, or >0 if an error occurs.
 Specific error codes are defined:
 
 - 2 means a configuration error
-- 3 means no builds are selected (and --allow-empty wasn't passed)
+- 3 means no builds are selected (and [`--allow-empty`](#allow-empty) wasn't passed)
 - 4 means you specified an option that has been deprecated.
 
 

test/test_0_basic.py

@@ -69,16 +69,24 @@ def test_build_identifiers(tmp_path):
     ), f"{expected_wheels} vs {build_identifiers}"
 
 
-def test_allow_empty(tmp_path):
+@pytest.mark.parametrize(
+    ("add_args", "env_allow_empty"),
+    [
+        (["--allow-empty"], {}),
+        (["--allow-empty"], {"CIBW_ALLOW_EMPTY": "0"}),
+        (None, {"CIBW_ALLOW_EMPTY": "1"}),
+    ],
+)
+def test_allow_empty(tmp_path, add_args, env_allow_empty):
     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"],
+        add_env={"CIBW_BUILD": "BUILD_NOTHING_AT_ALL", **env_allow_empty},
+        add_args=add_args,
     )
 
     # check that nothing was built