feat: support passenv (#914)

* feat: support passenv

* refactor: environment-pass and spaces

* docs: document environment pass

* Add unit test for passing through awkward env variable values

* Remove unused as_shell_commands method from environment

* Fix passthrough edge case by avoiding bash for passthrough assignments

* Fix mypy error in test

* Fix unit test

* Apply suggestions from code review

Co-authored-by: Joe Rickerby <joerick@mac.com>

unit_test/options_test.py

@@ -1,5 +1,7 @@
 import platform as platform_module
 
+import pytest
+
 from cibuildwheel.__main__ import get_build_identifiers
 from cibuildwheel.environment import parse_environment
 from cibuildwheel.options import Options, _get_pinned_docker_images
@@ -15,6 +17,8 @@ test-command = "pyproject"
 
 manylinux-x86_64-image = "manylinux1"
 
+environment-pass = ["EXAMPLE_ENV"]
+
 [tool.cibuildwheel.macos]
 test-requires = "else"
 
@@ -66,3 +70,47 @@ test_command: 'pyproject'
     assert local.manylinux_images is not None
     assert local.test_command == "pyproject-override"
     assert local.manylinux_images["x86_64"] == pinned_x86_64_docker_image["manylinux2014"]
+
+
+def test_passthrough(tmp_path, monkeypatch):
+    with tmp_path.joinpath("pyproject.toml").open("w") as f:
+        f.write(PYPROJECT_1)
+
+    args = get_default_command_line_arguments()
+    args.package_dir = str(tmp_path)
+
+    monkeypatch.setattr(platform_module, "machine", lambda: "x86_64")
+    monkeypatch.setenv("EXAMPLE_ENV", "ONE")
+
+    options = Options(platform="linux", command_line_arguments=args)
+
+    default_build_options = options.build_options(identifier=None)
+
+    assert default_build_options.environment.as_dictionary(prev_environment={}) == {
+        "FOO": "BAR",
+        "EXAMPLE_ENV": "ONE",
+    }
+
+
+@pytest.mark.parametrize(
+    "env_var_value",
+    [
+        "normal value",
+        '"value wrapped in quotes"',
+        "an unclosed single-quote: '",
+        'an unclosed double-quote: "',
+        "string\nwith\ncarriage\nreturns\n",
+        "a trailing backslash \\",
+    ],
+)
+def test_passthrough_evil(tmp_path, monkeypatch, env_var_value):
+    args = get_default_command_line_arguments()
+    args.package_dir = str(tmp_path)
+
+    monkeypatch.setattr(platform_module, "machine", lambda: "x86_64")
+    monkeypatch.setenv("CIBW_ENVIRONMENT_PASS_LINUX", "ENV_VAR")
+    options = Options(platform="linux", command_line_arguments=args)
+
+    monkeypatch.setenv("ENV_VAR", env_var_value)
+    parsed_environment = options.build_options(identifier=None).environment
+    assert parsed_environment.as_dictionary(prev_environment={}) == {"ENV_VAR": env_var_value}