fix(schema): default is fine for pyodide too (#2951)

unit_test/validate_schema_test.py

@@ -143,6 +143,65 @@ def test_overrides_invalid_inherit_value(validator: validate_pyproject.api.Valid
         validator(example)
 
 
+def test_pyodide_build_frontend(validator: validate_pyproject.api.Validator) -> None:
+    """
+    pyodide-build is accepted anywhere the frontend can be set, as an override
+    or a global value can apply to pyodide builds only.
+    """
+    example = tomllib.loads(
+        """
+        [tool.cibuildwheel]
+        build-frontend = "pyodide-build"
+
+        [tool.cibuildwheel.pyodide]
+        build-frontend = { name = "pyodide-build", args = ["--some-arg"] }
+
+        [[tool.cibuildwheel.overrides]]
+        select = "*pyodide*"
+        build-frontend = "pyodide-build; args: --some-arg"
+        """
+    )
+
+    assert validator(example) is not None
+
+
+@pytest.mark.parametrize("frontend", ['"uv"', '"build; args: --some-arg"', '{ name = "pip" }'])
+def test_pyodide_bad_build_frontend(
+    validator: validate_pyproject.api.Validator, frontend: str
+) -> None:
+    """
+    The pyodide table only accepts the pyodide-build frontend.
+    """
+    example = tomllib.loads(
+        f"""
+        [tool.cibuildwheel.pyodide]
+        build-frontend = {frontend}
+        """
+    )
+
+    with pytest.raises(validate_pyproject.error_reporting.ValidationError):
+        validator(example)
+
+
+@pytest.mark.parametrize("platform", ["linux", "macos", "windows", "ios", "android"])
+@pytest.mark.parametrize("frontend", ["pyodide-build", "pyodide-build; args: --some-arg"])
+def test_bad_pyodide_build_frontend(
+    validator: validate_pyproject.api.Validator, platform: str, frontend: str
+) -> None:
+    """
+    Only the pyodide table accepts the pyodide-build frontend.
+    """
+    example = tomllib.loads(
+        f"""
+        [tool.cibuildwheel.{platform}]
+        build-frontend = "{frontend}"
+        """
+    )
+
+    with pytest.raises(validate_pyproject.error_reporting.ValidationError):
+        validator(example)
+
+
 def test_docs_examples(validator: validate_pyproject.api.Validator) -> None:
     """
     Parse out all the configuration examples, build valid TOML out of them, and