forward args to subprocess by default, block explicit unsupported list

[dyollb]

MR Summary

Switched pytest-isolated to a blacklist model for CLI forwarding: options are now forwarded to child subprocesses by default, and only a small explicit set of truly incompatible options is blocked. This improves plugin and custom-option compatibility.

What changed

• Updated forwarding behavior to “allow by default” with explicit blocklist validation in config.py and orchestration adjustments in execution.py.
• Kept parent-only handling where appropriate (for options resolved before child execution), with compatibility checks integrated via grouping.py.
• Added/expanded regression coverage for custom options and key compatibility scenarios in test_options.py and test_execution_units.py.
• Documented the new compatibility taxonomy:
  • unsupported options
  • supported but parent-handled options
  • forwarded-by-default options
    in incompatible-options.md, plus a high-level note in README.md.

Related

• closes --setup-show flag doesn't display fixture information for @pytest.mark.isolated tests #47
• closes Custom CLI options lost when running @pytest.mark.isolated tests #48

[Copilot]

Pull request overview

This PR updates pytest-isolated’s subprocess CLI-argument handling to a forward-by-default (blacklist) model, adds early validation for explicitly incompatible options when isolation is active, and documents the option-compatibility behavior with expanded test coverage.

Changes:

• Switch argument forwarding to a blacklist approach so custom/third-party options are forwarded by default.
• Add early validation to raise UsageError when isolation is active alongside explicitly incompatible options (including via PYTEST_ADDOPTS).
• Add tests + documentation for option compatibility/forwarding behavior (including PYTEST_ADDOPTS, -p, --setup-show, and --import-mode).

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
tests/test_options.py	Adds integration tests for forwarding behavior, env var propagation, and several option compatibility scenarios.
tests/test_execution_units.py	Updates unit expectations for _build_forwarded_args to match forward-by-default behavior.
src/pytest_isolated/grouping.py	Adds early incompatible-option validation when isolation will be used.
src/pytest_isolated/execution.py	Reworks _build_forwarded_args for blacklist forwarding and adds --setup-show output re-emission.
src/pytest_isolated/config.py	Introduces _INCOMPATIBLE_OPTIONS and _validate_isolation_compatibility.
README.md	Documents the new compatibility model and links to a reference page.
docs/incompatible-options.md	New reference documentation describing blocked/parent-handled/forwarded options.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[pcrespov]

thx!