Better message if override violates Liskov substitution principle
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Description
Some users don't understand why mypy complains about incompatible overrides. We could add an extra note in cases where the argument type is narrower in an override or the return type is wider (or all incompatible overrides). The note could mention Liskov substitution principle and add a link to mypy documentation (add a new section to https://mypy.readthedocs.io/en/latest/common_issues.html perhaps). We can also mention that # type: ignore[override] can be used to silence this error.
#7992 is an example where this came up, but several users have been confused about this.
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by locating mypy's incompatible-override diagnostic handling and review the common issues documentation linked in the issue. Check issue #7992 for the motivating example. Done means the relevant override cases explain the Liskov substitution principle, link to the documentation, and mention the override type-ignore option, with tests covering the message.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- documentation, tooling
- Issue type
- Feature
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Active
- Clarity
- Mostly clear
- Newbie friendliness
- 68/100